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General Discussion => Advanced Concepts => Topic started by: john smith 19 on 04/14/2018 05:41 pm

Title: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/14/2018 05:41 pm
I wasn't sure if this should go in "Advance Concepts" or "Commercial" with the main SABRESkylon thread, but it's not meant to be a product and it' would certainly be advanced.  :)

REL have talked about the idea of a "Flight Test Vehicle" on a couple of occasions. Earlier ideas were for a scaled down Skylon, running LOX/Methane rockets while the current design, resembles the D-21 M3 reconnaissance  drone designed to launch off the back of a couple of modified SR71s in hte late 60's. then modified with a booster longer than the drone, was tested off a modified B52, before the whole project was cancelled.

However looking through the archives I located this.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000004765.pdf
and this.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990110312.pdf

Basically a late 90's plan to modify a couple of D-21 to demonstrate the "DRACO" Rock Based Combined Cycle engine some NASA centers were working on.  This system has multiple mode transitions in its flight trajectory and also featured a moving inlet spike to accommodate the speed changes.

In the process the second one discusses the D-21 in some detail, along with the LM Advanced Projects "Experimental Prototype" approach to cutting the development cost by about 1/3 (page 35 if you're interested).

Interestingly they reckoned you could  add a LOX tank between the fuel wing tanks and the engine duct, and they didn't think it would have thermal issues, although once you got above M3.5 the titanium skin and duct leading edge looked doubtful. Interestingly the issue around the LOX tank was not temperature related but pressurization. The D-21 was designed to operate its fuel tanks (there were 3, front, middle and back cross ways) at 1.5psi above the ambient pressure. Pressurizing the tanks to make the engine pressure fed was viewed as too dangerous.

On the upside the REL FTV is a clean sheet design with a thrust about 29x bigger than the D-21 ramjet. (Marquardt RJ43-MA-20S4) and recovery and reuse will be designed in from day one.

Beyond that we have a few data points.

The SABRE test engine is expected to have a thrust of 20 tonnes (44 000lbf) and according to the SEI study on the USAF TSTO design thrust needs to be at least 70% of GTOW, giving about 28500Kg of mass.

SABRE's T/W ratio is expected to be 14:1 so engine mass is say 1430Kg.
The D21 dry mass 5500lb vs fully loaded at 11200lb means it was 49% structure. It was stressed to withstand -2/+5g in both axial and directions normal to axial. So a lower peak acceleration should give a lighter structure.

28,500-1,430kg is a total mass of 27,070Kg. A 15% mass growth allowance means the maximum mass (structure and propellant) is 23,539Kg.

To put this in perspective 30tonnes is a small(ish) regional airliner or a large(ish) fighter aircraft.

My instinct is this layout is not a good fit to the issues around LH2 as a fuel, hence my interest in wheather it would be possible to make 2 engines and go with a "Mini Skylon" airframe.

Given the D-21 is going to be REL's FTV design to test inlet design and spike schedule what does that say about its capabilities?


My instinct is REL can go one of two ways on this.

A "bare bones" X-plane approach.
This is totally focused on flying SABRE through as much of its trajectory as possible and refining the inlet and spike performance to meet its goals. The vehicle structure is as simple as possible to do that.  Not intended to be anywhere close to deliver a substantial payload to orbit, or a 2nd stage to release.

A "Skylon risk retirement" approach.
This implements the FTV in technologies more like those planned for Skylon. IE a truss framework with appropriate levels of MLI and the SiC reinforced ceramic skin fabricated in corrugated panels.

Both options can help retire a number of operations features of a Skylon as well. EG fully automated fueling and de-fueling, although that would not be necessary for early tests. Likewise early tests could treat it as an RPV flown from a ground station, before moving to fully AGV status.

the big question would be what else  could it be used for ? What sort of things would 3rd parties like to test, and what sorts of instrumentation would they want to install to do so?

Title: Reaction engines Flight Test Vehicle speculation
Post by: Star One on 04/14/2018 06:56 pm
This will not be civilian related. BAE will make sure of that.

I donít know why you cling to this idea that initially at least this flight demonstrator is going to be anything other than a vehicle that services military requirements in all itís aspects. Especially as we now have three heavily military invested companies onboard. I donít even expect the demonstrator to fly anywhere than the US. Military hypersonic research is where the money is and probably the main reason Boeing & RR invested in REL.

Skylon is pretty certainly off the table for the foreseeable future.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/14/2018 10:08 pm
This will not be civilian related. BAE will make sure of that.
BAe have less than a 20% stake in the company.
Quote from: Star One
I donít know why you cling to this idea that initially at least this flight demonstrator is going to be anything other than a vehicle that services military requirements in all itís aspects.
Because a demonstrator is what it is.
It will not be capable of "Servicing military requirements" until it's demonstrated it can actually work, just as none of the SCRamjet research vehicles have done.

But mostly because
a)There are no sensible hypersonic military applications that stand up to close scrutiny.
The truth is if you want fast long range strike nothing beats an ICBM already. The problem is to design a cheap 1 warhead ICBM to do so. The trouble is (and military contractors understand this verywell) once you do so the "floor price" for an actual ICBM drops through the floor

b) I have a long standing interest in substantially dropping the cost of launch IE by 10x. There are lots of people who want "on demand" launch to LEO. Some are military, others are not.
Not a ticket to ride with a 1-2% failure rate (on mature systems). I mean an actual asset they control.
And a lot more people would pay for P2P with rather more "aircraft like" operations than BFR will ever achieve.
Quote from: Star One
Especially as we now have three heavily military invested companies onboard. I donít even expect the demonstrator to fly anywhere than the US. Military hypersonic research is where the money is and probably the main reason Boeing & RR invested in REL.
No, you have 1 (BAe), one (RR) that's got mixed military and civilian interests and the Boeing connection is an investment fund, not actually the Boeing aircraft company.

Note that word research.
Hence my question about what features would the FTV need to appeal to other groups who want to do basic research in what is (AFAIK) the first reusable M5+ vehicle in half a century.
The continuing inability to build a viable SCramjet suggests there is still quite a need for basic data collection in this area.
Quote from: Star One
Skylon is pretty certainly off the table for the foreseeable future.
As I noted there are quite a number of operational and structural features of Skylon that could be tested as part of the FTV programme.

Many of them have applications to whatever vehicle is ultimately used to house an operational SABRE engine.  Everyone of those tested by the FTV pushes Skylons TRL a notch further up the scale.
Title: Reaction engines Flight Test Vehicle speculation
Post by: Star One on 04/14/2018 11:34 pm
This will not be civilian related. BAE will make sure of that.
BAe have less than a 20% stake in the company.
Quote from: Star One
I donít know why you cling to this idea that initially at least this flight demonstrator is going to be anything other than a vehicle that services military requirements in all itís aspects.
Because a demonstrator is what it is.
It will not be capable of "Servicing military requirements" until it's demonstrated it can actually work, just as none of the SCRamjet research vehicles have done.

But mostly because
a)There are no sensible hypersonic military applications that stand up to close scrutiny.
The truth is if you want fast long range strike nothing beats an ICBM already. The problem is to design a cheap 1 warhead ICBM to do so. The trouble is (and military contractors understand this verywell) once you do so the "floor price" for an actual ICBM drops through the floor

b) I have a long standing interest in substantially dropping the cost of launch IE by 10x. There are lots of people who want "on demand" launch to LEO. Some are military, others are not.
Not a ticket to ride with a 1-2% failure rate (on mature systems). I mean an actual asset they control.
And a lot more people would pay for P2P with rather more "aircraft like" operations than BFR will ever achieve.
Quote from: Star One
Especially as we now have three heavily military invested companies onboard. I donít even expect the demonstrator to fly anywhere than the US. Military hypersonic research is where the money is and probably the main reason Boeing & RR invested in REL.
No, you have 1 (BAe), one (RR) that's got mixed military and civilian interests and the Boeing connection is an investment fund, not actually the Boeing aircraft company.

Note that word research.
Hence my question about what features would the FTV need to appeal to other groups who want to do basic research in what is (AFAIK) the first reusable M5+ vehicle in half a century.
The continuing inability to build a viable SCramjet suggests there is still quite a need for basic data collection in this area.
Quote from: Star One
Skylon is pretty certainly off the table for the foreseeable future.
As I noted there are quite a number of operational and structural features of Skylon that could be tested as part of the FTV programme.

Many of them have applications to whatever vehicle is ultimately used to house an operational SABRE engine.  Everyone of those tested by the FTV pushes Skylons TRL a notch further up the scale.

Every other discussion Iíve seen regarding this recent deal online, and other past developments leading up to this outside of this forum has been in terms of its military application.

BAE are the steering force now in this, their actual percentage is pretty irrelevant but itís big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isnít civilian.

Quote
BAEís investments also highlight the potential defence applications, such as weapons capable of flying at hypersonic speeds.

https://www.telegraph.co.uk/business/2018/04/12/reaction-engines-secures-boeing-rolls-royce-backing-hypersonic/

Outside of that thereís plenty of applications for the technology fully outside of the aviation field and I imagine theyíd be both easier and quicker to exploit than a space vehicle. After all a lot of investors these days are looking for the quick return or the shortest route to a return which this seems to offer here.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/15/2018 09:57 am
Every other discussion Iíve seen regarding this recent deal online, and other past developments leading up to this outside of this forum has been in terms of its military application.
Again this vehicle has no direct military applications.

I'd certainly agree that it could be used to gather the data to build a military vehicle. I'd also agree that many of the research groups who would like to use it are military funded.

You seem to be equating "Looks like a reconnaissance drone" with is a reconnaissance drone. IRL what you're talking about is about as sensible as sticking missiles on an X-15 (which is a plot device in a Stephen Baxter novel IIRC, but makes no real sense IRL).

Besides when was the last time you ever heard BAe spend their money on developing their own vehicle without an actual MoD or DoD requirements document or research budget?
Quote from: Star One
BAE are the steering force now in this, their actual percentage is pretty irrelevant but itís big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isnít civilian.
If it comes to a shareholder vote you'll find the difference is between "We would very much like and" and "This is what you will do" to REL management.  :(
Quote from: Star One
Quote
BAEís investments also highlight the potential defence applications, such as weapons capable of flying at hypersonic speeds.

https://www.telegraph.co.uk/business/2018/04/12/reaction-engines-secures-boeing-rolls-royce-backing-hypersonic/
And if they'd made floor cleaners they'd no doubt stress its application to floor cleaning. It's what they do.
Quote from: Star One
Outside of that thereís plenty of applications for the technology fully outside of the aviation field and I imagine theyíd be both easier and quicker to exploit than a space vehicle.
Which won't need a Flight Test Vehicle. So not really relevant to this topic.
Quote from: Star One
After all a lot of investors these days are looking for the quick return or the shortest route to a return which this seems to offer here.
The issue with REL is that it's not a get rich quick scheme.  It is (potentially) a get very rich scheme  (and lower the price of space access 10x).
This is a stage toward that process.

Could we discuss what this vehicle could do rather than why it would do it? I'd like to hear from people who have some idea what the outstanding questions in hypersonics are and what would be needed to resolve them if a reusable flight vehicle was available.
Title: Reaction engines Flight Test Vehicle speculation
Post by: Star One on 04/15/2018 12:17 pm
Every other discussion Iíve seen regarding this recent deal online, and other past developments leading up to this outside of this forum has been in terms of its military application.
Again this vehicle has no direct military applications.

I'd certainly agree that it could be used to gather the data to build a military vehicle. I'd also agree that many of the research groups who would like to use it are military funded.

You seem to be equating "Looks like a reconnaissance drone" with is a reconnaissance drone. IRL what you're talking about is about as sensible as sticking missiles on an X-15 (which is a plot device in a Stephen Baxter novel IIRC, but makes no real sense IRL).

Besides when was the last time you ever heard BAe spend their money on developing their own vehicle without an actual MoD or DoD requirements document or research budget?
Quote from: Star One
BAE are the steering force now in this, their actual percentage is pretty irrelevant but itís big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isnít civilian.
If it comes to a shareholder vote you'll find the difference is between "We would very much like and" and "This is what you will do" to REL management. 
Quote from: Star One
Quote
BAEís investments also highlight the potential defence applications, such as weapons capable of flying at hypersonic speeds.

https://www.telegraph.co.uk/business/2018/04/12/reaction-engines-secures-boeing-rolls-royce-backing-hypersonic/
And if they'd made floor cleaners they'd no doubt stress its application to floor cleaning. It's what they do.
Quote from: Star One
Outside of that thereís plenty of applications for the technology fully outside of the aviation field and I imagine theyíd be both easier and quicker to exploit than a space vehicle.
Which won't need a Flight Test Vehicle. So not really relevant to this topic.
Quote from: Star One
After all a lot of investors these days are looking for the quick return or the shortest route to a return which this seems to offer here.
The issue with REL is that it's not a get rich quick scheme.  It is (potentially) a get very rich scheme  (and lower the price of space access 10x).
This is a stage toward that process.

Could we discuss what this vehicle could do rather than why it would do it? I'd like to hear from people who have some idea what the outstanding questions in hypersonics are and what would be needed to resolve them if a reusable flight vehicle was available.

Anyway why did you feel the need to start a new thread on this when there is already a perfectly serviceable thread to discuss this. There is nothing in your OP that made it worthy of a separate thread. In fact it would quite easily have fitted in the main REL thread. Especially when any such demonstrator is still many years away and much could change before then.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Phillip Clark on 04/15/2018 10:00 pm
Has anyone considered asking Reaction Engines about this?   I am sure that alan Bond would tell, if he's able to.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/16/2018 07:20 am
Anyway why did you feel the need to start a new thread on this when there is already a perfectly serviceable thread to discuss this. There is nothing in your OP that made it worthy of a separate thread. In fact it would quite easily have fitted in the main REL thread. Especially when any such demonstrator is still many years away and much could change before then.
Perhaps you'd like to try putting an "IMHO" in that first sentence?

It's certainly advanced and there is a pretty wide range of options for REL to consider. while not a top priority some of the initial planning should be started now.

For instance the outline conversion report for turning the D-21 into a test bed for the DRACO engine said there is no low speed wind tunnel data for this shape, because it was never designed to land in the first place.

That's fine for a 1 shot expendable system but a problem if you want to get it back.

Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Star One on 04/16/2018 11:41 am
Anyway why did you feel the need to start a new thread on this when there is already a perfectly serviceable thread to discuss this. There is nothing in your OP that made it worthy of a separate thread. In fact it would quite easily have fitted in the main REL thread. Especially when any such demonstrator is still many years away and much could change before then.
Perhaps you'd like to try putting an "IMHO" in that first sentence?

It's certainly advanced and there is a pretty wide range of options for REL to consider. while not a top priority some of the initial planning should be started now.

For instance the outline conversion report for turning the D-21 into a test bed for the DRACO engine said there is no low speed wind tunnel data for this shape, because it was never designed to land in the first place.

That's fine for a 1 shot expendable system but a problem if you want to get it back.

Iíd thought post #7 probably suggests the best route to your OP.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/16/2018 07:25 pm

Iíd thought post #7 probably suggests the best route to your OP.
No.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Asteroza on 04/16/2018 11:11 pm
Even if you were considering the D-21 planform, the mentioned LOX saddle tank by itself wouldn't be enough right? You would need to also colocate a methane or hydrogen tank in the same barrel area (concentric barrels with shared wall?). If, like some artist impressions, there is a secondary engine, then having wet wing tanks for kerosene makes some sense, but you aren't putting cryogens in the wings. Since this would be a test vehicle, you might have drop tanks for added propellant during takeoff/climbout, assuming you don't airdrop from something (Stratolaunch's Roc?)
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/17/2018 07:11 am
Even if you were considering the D-21 planform, the mentioned LOX saddle tank by itself wouldn't be enough right? You would need to also colocate a methane or hydrogen tank in the same barrel area (concentric barrels with shared wall?). If, like some artist impressions, there is a secondary engine, then having wet wing tanks for kerosene makes some sense, but you aren't putting cryogens in the wings. Since this would be a test vehicle, you might have drop tanks for added propellant during takeoff/climbout, assuming you don't airdrop from something (Stratolaunch's Roc?)
This is where it gets tricky.  The 2nd file I linked to shows part of the actual D-21's internal structure. It's a series of frames running across the vehicle with a big hole punched through all of them. The original ramjet duct ran through the hole. The first, last and 2 middle frames ran right up to the duct. These were the original JP7 fuel tanks. NASA's planned DRACO installation would have put a (roughly elongated C section) tank in this gap and left the original tanks in place for JP7.

Note 2 things.
This is how Lockheed built it. REL have shown roughly the same shape. It's internal structure could (should?) be completely different.
DRACO's goal was to test up to M6 also but the feasibility study warned the D-21 was built out of Titanium and only really good up to M4, unless the skin was thicker and the leading edge TPS improved.

TBH I was pretty shocked when they planned to wrap the LOX tank around  the engine duct, given it's going to be a bit warm.  :) I can only presume that as long as it's not in actual contact  then the air (probably GN2 or GAr IRL) and some fibre insulation would be sufficient to keep it cool, given the LOX tank on the F9 booster seems to be protected by nothing much more than a thick coat of pain.  :o

But LH2 is not going to be so easy to deal with. AFAIK All LH2 proposals (including airliner designs from the mid 70's) wanted to keep it in one block, either in a big fuselage tank or a long fuselage "hump" running on top of the fuselage.
LH2 is not dense and it really needs volume.  The upside is this design is not pressure stabilized. It relies on the static strength of the materials. the D-21 DRACO conversion planned to run the LOX tank at about 1.5psi above the ambient pressure (which would not have been high at its launch altitude on a B52.

Moving to Methane helps the coldness issue a bit but then you lose LH2's great shc (4x that of water, which is excellent to begin with). OTOH REL plan on both cryogens to be sub cooled, which reduces burst issues due to heat leaks.

Basically monocoque construction does not work too well with temperature gradients this extreme. This is where you have to ask yourself "Do I really need minimum surface area cylinders or spheres inside the moldline, or could I go with a  low pressure more-or-less conformal tank with a layer of insulation between?"
BTW the SS301 used to make the Centaur tanks has 1/10 the thermal conductivity of Aluminium and very good weld properties.

For on orbit storage REL have done some work with a LH2 tank housing LO2 and LH2 for the on orbit RCS. The LHe vaporizes, cooling the internal LO2 and LH2 further, which is just what you want.  But LHe is an ever bigger PITA to keep cold on Earth.

Hmm. Perhaps separate LH2 tank inside LO2 tank either side of the duct? With internal partitions for CoG control.

This also raises the question of wheather they build it with the Skylon structural baseline of SiC reinforced Titanium trusses with SiC reinforced ceramic skins. It sounds exotic, but really, are there any options that are less exotic, that can handle the mass and thermal issues as well?

Incidentally the DRACO engine also uses an aerospike and the power to move it over the projected flight range was anticipated to peak at 5KVA, with average levels at 2.5KVA. That sounds a lot but was apparently expected to be within range of a ram air powered generator based APU.

It's also now clear from the presentation the engineers in charge of the test site that the test engine will not fly. It will generate the test data for that engine.

I was curious about this as once you've designed an engine the second copy of it is likely to be a lot less expensive, and something looking rather more Skylon like (whatever its made of internally) looks a simpler bet to solving the LH2 storage problem, along with various other fringe benefits (confirming the layout, aerodynamics, plume heating etc). That said whatever the FTV it will teach a lot of lessons about how to operate a HTOL reusable LO2/LH2 or Methane fueled vehicle.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: speedevil on 04/17/2018 12:21 pm
Incidentally the DRACO engine also uses an aerospike and the power to move it over the projected flight range was anticipated to peak at 5KVA, with average levels at 2.5KVA. That sounds a lot but was apparently expected to be within range of a ram air powered generator based APU.
Addressing only this part, 2.5KVA*10 minutes = a couple of kilos of batteries.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/17/2018 03:08 pm
Incidentally the DRACO engine also uses an aerospike and the power to move it over the projected flight range was anticipated to peak at 5KVA, with average levels at 2.5KVA. That sounds a lot but was apparently expected to be within range of a ram air powered generator based APU.
Addressing only this part, 2.5KVA*10 minutes = a couple of kilos of batteries.
Noted.
Batteries and a ram air driven generator were the planned power source for the DRACO conversion back in 1999. Obviously the battery tech has moved on a bit since then.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: RanulfC on 04/18/2018 12:38 am
JS19 wrote:
Quote
I wasn't sure if this should go in "Advance Concepts" or "Commercial" with the main SABRE/Skylon thread, but it's not meant to be a product and it' would certainly be advanced. :)

Works for me

Quote
REL have talked about the idea of a "Flight Test Vehicle" on a couple of occasions. Earlier ideas were for a scaled down Skylon, running LOX/Methane rockets while the current design, resembles the D-21 M3 reconnaissance drone designed to launch off the back of a couple of modified SR71s in the late 60's. then modified with a booster longer than the drone, was tested off a modified B52, before the whole project was cancelled.

I recall the rocket powered vehicles were actually more like aerodynamic test vehicles rather than an engine/cycle test vehicle which is what the current "FTV" seems to be aimed at. (Speaking of how about some links to past and present concepts, test goals, and other information?)

Nice find on the DRACO/D-21 having something to build on would help with the costing as even a subscale demonstrator is going to be expensive. (Despite what the cited studies actually "say" I'll note that they both include the verbiage "only vehicle designed to attain/maintain hypersonic speeds" which is wrong as the D-21 never came close to Mach-5 which is the actual boundary of "hypersonic" speed) I suppose the first question is what exactly are they trying to 'test'?

1) If they want to test the airframe design, (which I'm doubting as we've already seen the details differ from one company or group to another) then whatever is used will be designed around both the engines and the airframe and an integration of the two. Being's Boeing is onboard I highly doubt it will look like the Skylon we're used to from REL.

2) If they want to flight test the engine/cycle/system , (much more likely) then the airframe doesn't matter as much though the higher the testing speeds the more the design will want to "close" towards an approximation of "real" design. But initially you want to demonstrate a series of tests along a spectrum of speed if not to 'full' capability then at least to certain significant test points. For example such test points could include; Take off, climb, acceleration, ability to perform subsonic/transonic/supersonic and back transitions, accelerate to a 'maximum' speed, decelerate back through transonic and return to land, (or be recovered) and then do it all over again multiple times. (Note switching between air-breathing and pure rocket mode at various points will be a requirement so it will have to haul a LOX tank around as you suggest :) )

As noted in the reports the D21 doesn't have very good low speed handling qualities so it would probably need modification to the wings to provide such. You're also going to have to install landing and possibly take off gear.

If you are 'just' wanting to test the engine at various flight speeds then it might be better to pull a page from history and use a much simpler and more robust design type which while you'd have to 'build' can in fact be pretty straight forward AND cost effective. You can't really go wrong with something along the lines of the Lockheed X7 (https://en.wikipedia.org/wiki/Lockheed_X-7) ramjet test vehicle, which I will note CAN hit hypersonic speeds. (Late model drones topped out very near Mach-5 {and with a better engine could have done so) Given the SABRE T/W launch can be from a rail and landing kept 'simple' by keeping the parachute and "spike" from the original. Granted dimensions would have to be larger but it's certainly an option.

Lastly there is the "existing aircraft airframe" conversion option. Not that I can see a Learjet outfitted with a pair of 'mini-SABRE's' but conversions have been made of several supersonic aircraft by many nations with some of the US ones being "Q" series versions of the F-106, F4, and F-16 and of course there are 'sale' versions of the T-38, F-106, F-104 and others.

Finding and converting an Starfighter might be an good option as it's a bit bigger than the D-21 and if suitably braced you might be able to mount "mini-SABRE's" in place of the wingtip tanks and utilize the full capacity of the fuselage.

Of course having said all the above IF the various contractors can find someone to 'pay' for it most of them (Boeing, BAE, etc, frankly probably everyone BUT REL :) ) might prefer to 'build-from-scratch', especially if that 'customer' is a government. And while I DO agree the initial test vehicle won't have an obvious or "built-in" Military Operational Capability and disagree with Star One that there is any "obvious" bias towards having such in a "test" vehicle simple because who's interested and who's building it the fact is such a vehicle 'could' have a secondary purpose IF built to certain specifications. It's that last part that will be telling because I recall that the original (AF driven) specifications for the X-33 program were in fact quite interesting, especially given the launch and landing locations chosen for the program.

(Launch from Edwards AFB towards a facility in Utah, Speed in excess of Mach-12 and 'several hundred pounds' of "test instruments" in a long narrow bay... At the time it was noted by several people the 'test instrument bay' could hold a STAR solid motor and a microsatellite as 'payload' after all :) )

And while Star One is kind of obsessed with "hypersonic strike" missions the ACTUAL most likely mission is frankly as an advanced D-21 system for a reconnaissance drone. (Any 'weapon' has to be deployed from the inside of the vehicle mind you and THEN transition through a Mach-5+ shockwave AND still remain aimed at the target all of which is VERY difficult. And since it can't mass more than 2,000lbs at most it has to be highly accurate so obviously guided and everything has to be able to stand up to hypersonic speeds since that's when it's launched. As we've not developed any that work yet...) And for that you'd need specialized sensors, environmental conditioning equipment, (hypersonic speeds remember) power and others which will amount to something on the order of several hundred to maybe a thousand pounds. (Remember also you're flying at hypersonic speeds at almost 100,000ft so "OTS" sensor won't work) And then there's the 'range' question. The D-21 had a range of over 3,000 miles while modern UAV's have ranges from under 200 miles to over 14,000 miles but using LH2 or Liquid Methane there would be no opportunity for air-to-air refueling, (and transferring cryogenic fluids has been shown to have issue and that's before the operational problems with working with the stuff in bulk) and internal storage and insulation, (hypersonic again) issues abound for a smaller airframe.

Still the 'customer' has to be very upfront about such and willing to pay for it. Sensors, weapons bays, internal fuel storage will all have to specified UP FRONT so they can be included in the design as there won't be any way to 'retrofit' them once the vehicle is built. And all this has a very real possibility of not only the actual vehicle or engine not performing to specifications but that the 'added' requirements don't themselves cause the vehicle to fall short of requirements.

Since the main 'question' is (obviously) does the SABRE live up to expectations AND if so what are its actual performance metrics IN FLIGHT I have very high confidence that no one will be willing to pay for anything likely to be 'useful' till after all that data is in. Now something 'based' on the FTV could eventually be pitched but keep in mind there will be certain and strict requirements that have to be met along the way.

The most likely outcome is the FTV will be (as suggested by the "usual" aerospace contractors such as Boeing, BAE, etc) an expendable "test" vehicle on the line of the X-45/47 with each vehicle pushing the performance envelope along a series of 'goals' over the program. It's typical of such test programs today so it won't be either unexpected nor vastly difficult to pitch. On the other hand JS19 has a point that making it 'reusable' may in fact be both the better and 'simpler' option given the minimum size needed. But even a conversion of an existing airframe is going to be expensive and a 'scratch built' one probably out of the question. But you really DO want reusable despite the 'cost analysis' tending towards expendable since what you REALLY want to do is get data from the full spectrum of flight operations rather than just selected 'segments' which might induce errors or miss issues.

Star One wrote:
Quote
Every other discussion I've seen regarding this recent deal online, and other past developments leading up to this outside of this forum has been in terms of its military application.

Actually every time "hypersonics" is mentioned or written about the 'subject' turns to military applications which is different than what you're implying. Simply put, inserting "military applications" is a standard way to pad a subject that "might" actually have "military applications" whether the actual work being done IS directed towards that goal or not. Hypersonic flight has been specifically 'tied' to proposed "military applications" since the 1950s but actual versus assumed applications have been severely lacking and this is no different. SABRE, (which is the whole point of any test vehicle) is another, albeit rather better thought out, propulsion system that can possibly be used to push a vehicle to hypersonic speeds. Since it is possible for any vehicle to be used for 'military purposes', (and therefor used to pitch money from either the government or the military) such 'padding' is always inserted no matter if the actual application doesn't fit the suggested concept.

Let's take a look at the ACTUAL "military applications" of the SABRE engine:
1) It can be used to power a booster vehicle to launch expendable or reusable upper stages for vastly cheaper than current launch costs.

Now 'suggested' applications tend to be:
a) It can be used to power a bomber/fighter/recon aircraft flying at the edge of space and hypersonic, (Mach-6 to -10) speeds!

Actually no since a 'fighter' by definition needs a propulsion system that can allow it to do its job which is engage and destroy enemy aircraft and flying at 100,000ft and Mach-6 to Mach-10 you can't see, identify, lock-onto and engage a target with any reasonable chance of success. Similarly a 'bomber' needs to find, identify and engage its target which while not moving, (generally in fact the main 'purpose' of a hypersonic bomber is supposed to be the ability to reach a target area before a MOVING target can move outside its engagement area) and destroy it. Anyone that thinks that a platform moving as hypersonic speed at an altitude of 100,000ft plus can do this 'easily' is sadly out of touch with the reality of weapons technology. (Or trying to get money which pretty much covers the majority of sources for such suggestions) So that leaves the reconnaissance role which actually has possibilities as long as you ignore the rather obvious problems with a super-fast, super high altitude very "visible" (both to radar and basic IR sensors) target that while it might spot targets that would normally avoid predictable satellite passes or low and relatively slow "normal" aircraft is both vulnerable and restricted on what information it can gather. How can something flying so high and fast be 'vulnerable'? It is flying 'high' so again it's a LOT more visible than something flying very low and very slow so its chances of being spotted are vastly higher and unfortunately even 100,000ft is not 'low' enough to "hide" behind the curvature of the Earth as has often erroneously been suggested. Barring flying against someone with only the "Mark-One Eyeball" you WILL be spotted and tracked. You're also vulnerable in that neither the speed or altitude are immune from aggressive interception.

Further the SABRE cycle due to the inclusion of a rocket motor is vastly inferior for ANY hypersonic mission of any of the type given except launch vehicle when compared to vastly better cycles such as the Scimitar or other 'turbine' rather than 'rocket' based cycles. The 800-pound gorilla in the room everyone who focuses on 'military applications' for the SABRE is the fact it has ONE possible application and ONLY one: Launch Vehicle.

So therefor, (it should be quite obvious) if the FTV is planned to use SABRE cycle engines then it actually has one 'possible' application and most likely it will therefore be used to PROVE the SABRE cycle itself and not some way to 'sneak' a military drone into production.

Quote
BAE are the steering force now in this, their actual percentage is pretty irrelevant but it's big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isn't civilian.

Actually DARPA does in fact do a lot of projects that while they 'may' have military applications in the future can and have found civilian applications in more near term time frames. Self-driving vehicles is one good example as that started as a DARPA sponsored program but was rapidly embraced and improved upon by civilian agencies. Also while DARPA is sponsoring some of the work the actual main interest is from the Air Force Research Laboratory which is specifically tasked with 'long term' research and not procurement or operations. This is on purpose because the last time DARPA tried to 'shortcut' a research program it not only failed to get to flight testing it failed to reach the level of 50 year old research and development that the DARPA researchers didn't know had already been done! (RASCAL and MIPCC) AFRL was one of the agencies that pointed out the cost models for the program were significantly lacking in basic data while the proposed 'research' areas had already been done and the suggested 'vehicle' was in no way a 'research' or 'test' model but a clear 'operational' vehicle with which DARPA was attempting to bypass standard procurement and contracting procedures. (Which in fact they were doing)

Quote
https://www.telegraph.co.uk/business/2018/04/12/reaction-engines-secures-boeing-rolls-royce-backing-hypersonic/

Outside of that there's plenty of applications for the technology fully outside of the aviation field and I imagine they'd be both easier and quicker to exploit than a space vehicle. After all a lot of investors these days are looking for the quick return or the shortest route to a return which this seems to offer here.

Nice of you to point out another article that fully and totally misses the main 'point' of its own information in order to pad the word count with nonsensical and non-relevant subjects. Point of fact where in that article can you find ONE "application" for the SABRE OTHER than as a launch vehicle? That is after all the ONLY application that is suggested or implied by those quoted in the article. Supersonic and hypersonic flight is 'suggested' as something that can be 'derived' from the SABRE cycle in the future a number of times but any connection with the SABRE FTV is inferred and not explicit by anyone quoted in the article. Wonder why that is?

It's because the SABRE is not suitable for either supersonic or hypersonic "flight" and those being quoted are WELL aware of this fact. The engine that would power supersonic or hypersonic aircraft, (note not "spacecraft" which is what the SABRE is stated to be used for in the article) is the Scimitar which is optimized and designed for just such applications and does the job VASTLY better than the SABRE.

I think one thing that people seem to ignore is due to its nature SABRE powered vehicles simply can NOT fly from ANY 'standard' airport anywhere in the world. Not even 'lightly loaded' or 'partially fueled' and REL has pointed this out several times. It has nothing to do with runway length or loading or any of the other "operational" issue that have been discussed but directly due to the fact it uses a rocket engine in its design. It can't fly from an standard airport because it is impossible for it to meet the noise regulations of any standard airport. Period.
Scimitar CAN do so and is specifically designed to do so and meet ALL regulations and guidelines.

And lets discuss the applications outside the aviation industry which can be so lucrative...

Point of fact REL has a nice heat exchanger technology but as was pointed out back when they were trying to hype it, (and SABRE) up to get investment it is highly specialized and has few if any applications outside the ones REL has in mind. Granted if they exist you can be sure BAE will exploit them but really that has nothing to do with the thread. Still if you'd like to list them we can disassemble them again I suppose.

Phillip Clark wrote:
Quote
Has anyone considered asking Reaction Engines about this? I am sure that Alan Bond would tell, if he's able to.

And deprive ourselves of the possibly of vastly speculative and argumentative postings? What are you? Mad? I mean look how boring and mundane BFS turned out to be compared to our ideas and concepts, come on loosen up some :)

Some additional comments on the D21 design:
Note the LOX tank was wrapped around the 'duct' not the actual engine. Even at Mach-6 the heating wasn't going to be really 'bad' and there was insulation. But in any case, (Liquid Methane or LH2) is going to require a larger tankage and not be compatible with 'wet-wings' normally. (You have to admire the way they got 'away' with "wet-wings" cyro-LOX in the Star-Raker design though: http://www.alternatewars.com/SpaceRace/Star_Raker/Star_Raker.htm
https://motherboard.vice.com/en_us/article/ezvj4j/the-747-to-space-that-never-was
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790010900.pdf (page 73)

Having said that since you don't actually NEED to put propellant in the wings, and at hypersonic speeds "wings" aren't really needed there would be tendency to move towards a lifting fuselage body similar to the "waverider" and advanced aircraft we've been working on the last 50 years. Now with that as pointed out with the D-21 you DO need wings at lower speeds so unlike NASP and some of the more extreme designs you want good low speed landing wings. On the other hand if you don't assume that you have to squeeze every ounce of efficiency out of the propulsion, (Skylon doesn't, whereas most of the others DO and therefore the engines and fuselage are designed to synergistically support each other) then you can consider other options for engine placement. (I should note the ENTIRE fuselage is synergistically used so that the forward body helps compress and ingest the air while the after body helps align and expand the exhaust for more efficient operation)

Again this isn't 'lazy' on REL's part but it greatly simplifies the figures you need to play with since with the engines on the wingtips reduces some of the aerodynamic and weight-and-balance problems. (Of course you get a similar effect without the "engine-out" issues by putting the engine near the center of the airframe, again which is common on engine/body designs) I suppose the main question is how small can they make a SABRE engine?

Randy
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Star One on 04/18/2018 07:32 am
JS19 wrote:
Quote
I wasn't sure if this should go in "Advance Concepts" or "Commercial" with the main SABRE/Skylon thread, but it's not meant to be a product and it' would certainly be advanced. :)

Works for me

Quote
REL have talked about the idea of a "Flight Test Vehicle" on a couple of occasions. Earlier ideas were for a scaled down Skylon, running LOX/Methane rockets while the current design, resembles the D-21 M3 reconnaissance drone designed to launch off the back of a couple of modified SR71s in the late 60's. then modified with a booster longer than the drone, was tested off a modified B52, before the whole project was cancelled.

I recall the rocket powered vehicles were actually more like aerodynamic test vehicles rather than an engine/cycle test vehicle which is what the current "FTV" seems to be aimed at. (Speaking of how about some links to past and present concepts, test goals, and other information?)

Nice find on the DRACO/D-21 having something to build on would help with the costing as even a subscale demonstrator is going to be expensive. (Despite what the cited studies actually "say" I'll note that they both include the verbiage "only vehicle designed to attain/maintain hypersonic speeds" which is wrong as the D-21 never came close to Mach-5 which is the actual boundary of "hypersonic" speed) I suppose the first question is what exactly are they trying to 'test'?

1) If they want to test the airframe design, (which I'm doubting as we've already seen the details differ from one company or group to another) then whatever is used will be designed around both the engines and the airframe and an integration of the two. Being's Boeing is onboard I highly doubt it will look like the Skylon we're used to from REL.

2) If they want to flight test the engine/cycle/system , (much more likely) then the airframe doesn't matter as much though the higher the testing speeds the more the design will want to "close" towards an approximation of "real" design. But initially you want to demonstrate a series of tests along a spectrum of speed if not to 'full' capability then at least to certain significant test points. For example such test points could include; Take off, climb, acceleration, ability to perform subsonic/transonic/supersonic and back transitions, accelerate to a 'maximum' speed, decelerate back through transonic and return to land, (or be recovered) and then do it all over again multiple times. (Note switching between air-breathing and pure rocket mode at various points will be a requirement so it will have to haul a LOX tank around as you suggest :) )

As noted in the reports the D21 doesn't have very good low speed handling qualities so it would probably need modification to the wings to provide such. You're also going to have to install landing and possibly take off gear.

If you are 'just' wanting to test the engine at various flight speeds then it might be better to pull a page from history and use a much simpler and more robust design type which while you'd have to 'build' can in fact be pretty straight forward AND cost effective. You can't really go wrong with something along the lines of the Lockheed X7 (https://en.wikipedia.org/wiki/Lockheed_X-7) ramjet test vehicle, which I will note CAN hit hypersonic speeds. (Late model drones topped out very near Mach-5 {and with a better engine could have done so) Given the SABRE T/W launch can be from a rail and landing kept 'simple' by keeping the parachute and "spike" from the original. Granted dimensions would have to be larger but it's certainly an option.

Lastly there is the "existing aircraft airframe" conversion option. Not that I can see a Learjet outfitted with a pair of 'mini-SABRE's' but conversions have been made of several supersonic aircraft by many nations with some of the US ones being "Q" series versions of the F-106, F4, and F-16 and of course there are 'sale' versions of the T-38, F-106, F-104 and others.

Finding and converting an Starfighter might be an good option as it's a bit bigger than the D-21 and if suitably braced you might be able to mount "mini-SABRE's" in place of the wingtip tanks and utilize the full capacity of the fuselage.

Of course having said all the above IF the various contractors can find someone to 'pay' for it most of them (Boeing, BAE, etc, frankly probably everyone BUT REL :) ) might prefer to 'build-from-scratch', especially if that 'customer' is a government. And while I DO agree the initial test vehicle won't have an obvious or "built-in" Military Operational Capability and disagree with Star One that there is any "obvious" bias towards having such in a "test" vehicle simple because who's interested and who's building it the fact is such a vehicle 'could' have a secondary purpose IF built to certain specifications. It's that last part that will be telling because I recall that the original (AF driven) specifications for the X-33 program were in fact quite interesting, especially given the launch and landing locations chosen for the program.

(Launch from Edwards AFB towards a facility in Utah, Speed in excess of Mach-12 and 'several hundred pounds' of "test instruments" in a long narrow bay... At the time it was noted by several people the 'test instrument bay' could hold a STAR solid motor and a microsatellite as 'payload' after all :) )

And while Star One is kind of obsessed with "hypersonic strike" missions the ACTUAL most likely mission is frankly as an advanced D-21 system for a reconnaissance drone. (Any 'weapon' has to be deployed from the inside of the vehicle mind you and THEN transition through a Mach-5+ shockwave AND still remain aimed at the target all of which is VERY difficult. And since it can't mass more than 2,000lbs at most it has to be highly accurate so obviously guided and everything has to be able to stand up to hypersonic speeds since that's when it's launched. As we've not developed any that work yet...) And for that you'd need specialized sensors, environmental conditioning equipment, (hypersonic speeds remember) power and others which will amount to something on the order of several hundred to maybe a thousand pounds. (Remember also you're flying at hypersonic speeds at almost 100,000ft so "OTS" sensor won't work) And then there's the 'range' question. The D-21 had a range of over 3,000 miles while modern UAV's have ranges from under 200 miles to over 14,000 miles but using LH2 or Liquid Methane there would be no opportunity for air-to-air refueling, (and transferring cryogenic fluids has been shown to have issue and that's before the operational problems with working with the stuff in bulk) and internal storage and insulation, (hypersonic again) issues abound for a smaller airframe.

Still the 'customer' has to be very upfront about such and willing to pay for it. Sensors, weapons bays, internal fuel storage will all have to specified UP FRONT so they can be included in the design as there won't be any way to 'retrofit' them once the vehicle is built. And all this has a very real possibility of not only the actual vehicle or engine not performing to specifications but that the 'added' requirements don't themselves cause the vehicle to fall short of requirements.

Since the main 'question' is (obviously) does the SABRE live up to expectations AND if so what are its actual performance metrics IN FLIGHT I have very high confidence that no one will be willing to pay for anything likely to be 'useful' till after all that data is in. Now something 'based' on the FTV could eventually be pitched but keep in mind there will be certain and strict requirements that have to be met along the way.

The most likely outcome is the FTV will be (as suggested by the "usual" aerospace contractors such as Boeing, BAE, etc) an expendable "test" vehicle on the line of the X-45/47 with each vehicle pushing the performance envelope along a series of 'goals' over the program. It's typical of such test programs today so it won't be either unexpected nor vastly difficult to pitch. On the other hand JS19 has a point that making it 'reusable' may in fact be both the better and 'simpler' option given the minimum size needed. But even a conversion of an existing airframe is going to be expensive and a 'scratch built' one probably out of the question. But you really DO want reusable despite the 'cost analysis' tending towards expendable since what you REALLY want to do is get data from the full spectrum of flight operations rather than just selected 'segments' which might induce errors or miss issues.

Star One wrote:
Quote
Every other discussion I've seen regarding this recent deal online, and other past developments leading up to this outside of this forum has been in terms of its military application.

Actually every time "hypersonics" is mentioned or written about the 'subject' turns to military applications which is different than what you're implying. Simply put, inserting "military applications" is a standard way to pad a subject that "might" actually have "military applications" whether the actual work being done IS directed towards that goal or not. Hypersonic flight has been specifically 'tied' to proposed "military applications" since the 1950s but actual versus assumed applications have been severely lacking and this is no different. SABRE, (which is the whole point of any test vehicle) is another, albeit rather better thought out, propulsion system that can possibly be used to push a vehicle to hypersonic speeds. Since it is possible for any vehicle to be used for 'military purposes', (and therefor used to pitch money from either the government or the military) such 'padding' is always inserted no matter if the actual application doesn't fit the suggested concept.

Let's take a look at the ACTUAL "military applications" of the SABRE engine:
1) It can be used to power a booster vehicle to launch expendable or reusable upper stages for vastly cheaper than current launch costs.

Now 'suggested' applications tend to be:
a) It can be used to power a bomber/fighter/recon aircraft flying at the edge of space and hypersonic, (Mach-6 to -10) speeds!

Actually no since a 'fighter' by definition needs a propulsion system that can allow it to do its job which is engage and destroy enemy aircraft and flying at 100,000ft and Mach-6 to Mach-10 you can't see, identify, lock-onto and engage a target with any reasonable chance of success. Similarly a 'bomber' needs to find, identify and engage its target which while not moving, (generally in fact the main 'purpose' of a hypersonic bomber is supposed to be the ability to reach a target area before a MOVING target can move outside its engagement area) and destroy it. Anyone that thinks that a platform moving as hypersonic speed at an altitude of 100,000ft plus can do this 'easily' is sadly out of touch with the reality of weapons technology. (Or trying to get money which pretty much covers the majority of sources for such suggestions) So that leaves the reconnaissance role which actually has possibilities as long as you ignore the rather obvious problems with a super-fast, super high altitude very "visible" (both to radar and basic IR sensors) target that while it might spot targets that would normally avoid predictable satellite passes or low and relatively slow "normal" aircraft is both vulnerable and restricted on what information it can gather. How can something flying so high and fast be 'vulnerable'? It is flying 'high' so again it's a LOT more visible than something flying very low and very slow so its chances of being spotted are vastly higher and unfortunately even 100,000ft is not 'low' enough to "hide" behind the curvature of the Earth as has often erroneously been suggested. Barring flying against someone with only the "Mark-One Eyeball" you WILL be spotted and tracked. You're also vulnerable in that neither the speed or altitude are immune from aggressive interception.

Further the SABRE cycle due to the inclusion of a rocket motor is vastly inferior for ANY hypersonic mission of any of the type given except launch vehicle when compared to vastly better cycles such as the Scimitar or other 'turbine' rather than 'rocket' based cycles. The 800-pound gorilla in the room everyone who focuses on 'military applications' for the SABRE is the fact it has ONE possible application and ONLY one: Launch Vehicle.

So therefor, (it should be quite obvious) if the FTV is planned to use SABRE cycle engines then it actually has one 'possible' application and most likely it will therefore be used to PROVE the SABRE cycle itself and not some way to 'sneak' a military drone into production.

Quote
BAE are the steering force now in this, their actual percentage is pretty irrelevant but it's big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isn't civilian.

Actually DARPA does in fact do a lot of projects that while they 'may' have military applications in the future can and have found civilian applications in more near term time frames. Self-driving vehicles is one good example as that started as a DARPA sponsored program but was rapidly embraced and improved upon by civilian agencies. Also while DARPA is sponsoring some of the work the actual main interest is from the Air Force Research Laboratory which is specifically tasked with 'long term' research and not procurement or operations. This is on purpose because the last time DARPA tried to 'shortcut' a research program it not only failed to get to flight testing it failed to reach the level of 50 year old research and development that the DARPA researchers didn't know had already been done! (RASCAL and MIPCC) AFRL was one of the agencies that pointed out the cost models for the program were significantly lacking in basic data while the proposed 'research' areas had already been done and the suggested 'vehicle' was in no way a 'research' or 'test' model but a clear 'operational' vehicle with which DARPA was attempting to bypass standard procurement and contracting procedures. (Which in fact they were doing)

Quote
https://www.telegraph.co.uk/business/2018/04/12/reaction-engines-secures-boeing-rolls-royce-backing-hypersonic/

Outside of that there's plenty of applications for the technology fully outside of the aviation field and I imagine they'd be both easier and quicker to exploit than a space vehicle. After all a lot of investors these days are looking for the quick return or the shortest route to a return which this seems to offer here.

Nice of you to point out another article that fully and totally misses the main 'point' of its own information in order to pad the word count with nonsensical and non-relevant subjects. Point of fact where in that article can you find ONE "application" for the SABRE OTHER than as a launch vehicle? That is after all the ONLY application that is suggested or implied by those quoted in the article. Supersonic and hypersonic flight is 'suggested' as something that can be 'derived' from the SABRE cycle in the future a number of times but any connection with the SABRE FTV is inferred and not explicit by anyone quoted in the article. Wonder why that is?

It's because the SABRE is not suitable for either supersonic or hypersonic "flight" and those being quoted are WELL aware of this fact. The engine that would power supersonic or hypersonic aircraft, (note not "spacecraft" which is what the SABRE is stated to be used for in the article) is the Scimitar which is optimized and designed for just such applications and does the job VASTLY better than the SABRE.

I think one thing that people seem to ignore is due to its nature SABRE powered vehicles simply can NOT fly from ANY 'standard' airport anywhere in the world. Not even 'lightly loaded' or 'partially fueled' and REL has pointed this out several times. It has nothing to do with runway length or loading or any of the other "operational" issue that have been discussed but directly due to the fact it uses a rocket engine in its design. It can't fly from an standard airport because it is impossible for it to meet the noise regulations of any standard airport. Period.
Scimitar CAN do so and is specifically designed to do so and meet ALL regulations and guidelines.

And lets discuss the applications outside the aviation industry which can be so lucrative...

Point of fact REL has a nice heat exchanger technology but as was pointed out back when they were trying to hype it, (and SABRE) up to get investment it is highly specialized and has few if any applications outside the ones REL has in mind. Granted if they exist you can be sure BAE will exploit them but really that has nothing to do with the thread. Still if you'd like to list them we can disassemble them again I suppose.

Phillip Clark wrote:
Quote
Has anyone considered asking Reaction Engines about this? I am sure that Alan Bond would tell, if he's able to.

And deprive ourselves of the possibly of vastly speculative and argumentative postings? What are you? Mad? I mean look how boring and mundane BFS turned out to be compared to our ideas and concepts, come on loosen up some :)

Some additional comments on the D21 design:
Note the LOX tank was wrapped around the 'duct' not the actual engine. Even at Mach-6 the heating wasn't going to be really 'bad' and there was insulation. But in any case, (Liquid Methane or LH2) is going to require a larger tankage and not be compatible with 'wet-wings' normally. (You have to admire the way they got 'away' with "wet-wings" cyro-LOX in the Star-Raker design though: http://www.alternatewars.com/SpaceRace/Star_Raker/Star_Raker.htm
https://motherboard.vice.com/en_us/article/ezvj4j/the-747-to-space-that-never-was
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790010900.pdf (page 73)

Having said that since you don't actually NEED to put propellant in the wings, and at hypersonic speeds "wings" aren't really needed there would be tendency to move towards a lifting fuselage body similar to the "waverider" and advanced aircraft we've been working on the last 50 years. Now with that as pointed out with the D-21 you DO need wings at lower speeds so unlike NASP and some of the more extreme designs you want good low speed landing wings. On the other hand if you don't assume that you have to squeeze every ounce of efficiency out of the propulsion, (Skylon doesn't, whereas most of the others DO and therefore the engines and fuselage are designed to synergistically support each other) then you can consider other options for engine placement. (I should note the ENTIRE fuselage is synergistically used so that the forward body helps compress and ingest the air while the after body helps align and expand the exhaust for more efficient operation)

Again this isn't 'lazy' on REL's part but it greatly simplifies the figures you need to play with since with the engines on the wingtips reduces some of the aerodynamic and weight-and-balance problems. (Of course you get a similar effect without the "engine-out" issues by putting the engine near the center of the airframe, again which is common on engine/body designs) I suppose the main question is how small can they make a SABRE engine?

Randy

I suggest you read any history of DARPA before suggesting they do anything civilian, if they do itís accidental rather intentional.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/18/2018 08:36 am
I recall the rocket powered vehicles were actually more like aerodynamic test vehicles rather than an engine/cycle test vehicle which is what the current "FTV" seems to be aimed at. (Speaking of how about some links to past and present concepts, test goals, and other information?)
I think the key thing for the Methane rocket version was inlet development. The "Peace Jack" programme showed what a big difference you could get with a better (and bigger) inlet on a conventional turbojet.

Links? Hmm.  Only a few REL presentations mention the idea in any detail. They were also looking at a kind of sounding rocket using IIRC LO2/LNH3/LN2 to simulate the combustion and trajectory.
Quote from: RanulfC
Nice find on the DRACO/D-21 having something to build on would help with the costing as even a subscale demonstrator is going to be expensive. (Despite what the cited studies actually "say" I'll note that they both include the verbiage "only vehicle designed to attain/maintain hypersonic speeds" which is wrong as the D-21 never came close to Mach-5 which is the actual boundary of "hypersonic" speed) I suppose the first question is what exactly are they trying to 'test'?
Indeed.  I think the DRACO programme was relatively small scale and NASA had looked at doing LASRE on the back of one of their SR71's. Basically a D-21 was the closest thing they could get OTS. The study made no bones that M3 was OK, they were probably good to M4.5, but after that....
Quote from: RanulfC
1) If they want to test the airframe design, (which I'm doubting as we've already seen the details differ from one company or group to another) then whatever is used will be designed around both the engines and the airframe and an integration of the two. Being's Boeing is onboard I highly doubt it will look like the Skylon we're used to from REL.
I think people are making a lot of the Boeing involvement but this is the VC arm of Boeing. I'm not sure how much 2 way interaction happens between them and the actual aircraft building parts (either military or civilian). Of course as a potential customer it would good to get their input (provided  it can be done in a non ITAR contaminating way of course).
Quote from: RanulfC
2) If they want to flight test the engine/cycle/system , (much more likely) then the airframe doesn't matter as much though the higher the testing speeds the more the design will want to "close" towards an approximation of "real" design. But initially you want to demonstrate a series of tests along a spectrum of speed if not to 'full' capability then at least to certain significant test points. For example such test points could include; Take off, climb, acceleration, ability to perform subsonic/transonic/supersonic and back transitions, accelerate to a 'maximum' speed, decelerate back through transonic and return to land, (or be recovered) and then do it all over again multiple times. (Note switching between air-breathing and pure rocket mode at various points will be a requirement so it will have to haul a LOX tank around as you suggest :) )
Exactly. It's pretty clear that a lot of people simply won't believe a vehicle and engine can fly this trajectory until one does (although they seem to have no trouble believing a SCramjet will do whatever its promoters claim it will  :( ) Therefor that needs to be the key goal.
Quote from: RanulfC
As noted in the reports the D21 doesn't have very good low speed handling qualities so it would probably need modification to the wings to provide such. You're also going to have to install landing and possibly take off gear.
Actually they dug up the top aerodynamics guy at the time and he said they never tested the shape for low speed handling. No point. It's never going to land. TBH that's probably the case for any existing shape.
Looking at the D-21's internal structure what struck was how SR71 it was. Basically, take an SR71, chop off the wings past the engine nacelles (and the nacelles themselves), then core out the fuselage and stick the ramjet in there. No doubt it was considerably more subtle than that but that's the high level view I got.
Quote from: RanulfC
If you are 'just' wanting to test the engine at various flight speeds then it might be better to pull a page from history and use a much simpler and more robust design type which while you'd have to 'build' can in fact be pretty straight forward AND cost effective. You can't really go wrong with something along the lines of the Lockheed X7 (https://en.wikipedia.org/wiki/Lockheed_X-7) ramjet test vehicle, which I will note CAN hit hypersonic speeds. (Late model drones topped out very near Mach-5 {and with a better engine could have done so) Given the SABRE T/W launch can be from a rail and landing kept 'simple' by keeping the parachute and "spike" from the original. Granted dimensions would have to be larger but it's certainly an option.
Now this works better. When this Idea came up I was thinking more of the V-1 but with proven high Mach flight to go on...
My instinct is LH2 storage is going to be the big issue for any test design. A design that gives you a solid centre body to put an LH2 tank inside seems  easier.  Of course if you goal is to demonstrate "mad design skillz" then the LH2 wet wing is definitely the way to go. But there's a very fine line between mad skillz, and just plain mad.  :)
Quote from: RanulfC
Lastly there is the "existing aircraft airframe" conversion option. Not that I can see a Learjet outfitted with a pair of 'mini-SABRE's' but conversions have been made of several supersonic aircraft by many nations with some of the US ones being "Q" series versions of the F-106, F4, and F-16 and of course there are 'sale' versions of the T-38, F-106, F-104 and others.

Finding and converting an Starfighter might be an good option as it's a bit bigger than the D-21 and if suitably braced you might be able to mount "mini-SABRE's" in place of the wingtip tanks and utilize the full capacity of the fuselage.
IIRC HMX was involved with MIPCC and said they could get their hands on a couple of F106's, which had a pretty big weapons bay. They reckoned with upgraded leading edges it could  hit M5. Junking all that 1950's era SAGE computer hardware should've lightened it up considerably.

I think this is the issue with adapting existing designs. No existing design (except the X-15, X37b and Shuttle) were designed to fly above roughly M3.5.  True they wouldn't have to last long (for engine and trajectory test get up to the right altitude/speed, switch over and get stable combustion in rocket mode. 10s of seconds after transition?) but it's a gamble. And you'd probably need a pilot as well.
Quote from: RanulfC
Of course having said all the above IF the various contractors can find someone to 'pay' for it most of them (Boeing, BAE, etc, frankly probably everyone BUT REL :) ) might prefer to 'build-from-scratch', especially if that 'customer' is a government. And while I DO agree the initial test vehicle won't have an obvious or "built-in" Military Operational Capability and disagree with Star One that there is any "obvious" bias towards having such in a "test" vehicle simple because who's interested and who's building it the fact is such a vehicle 'could' have a secondary purpose IF built to certain specifications. It's that last part that will be telling because I recall that the original (AF driven) specifications for the X-33 program were in fact quite interesting, especially given the launch and landing locations chosen for the program.
Agreed.  But now you have 2 goals.
1) Build a vehicle that can test the engine/inlet over its planned Mach and altitude range
2) Design it as a pre-production prototype for an actual vehicle with a specific purpose.

One of the ways APD said they cut development costs by 1/3 was not to include support for things like repairability or maintainability.  The language is quite important. It's a demonstrator, not a prototype.
The X-33 programme should have taught people what happens when you make one vehicle do both. You end up with no vehicle and no improvement in your ability to design one, unless you count "Designing multi lobed conformal composite LH2 tanks is hard." Did it really need a $1.5Bn programme to "discover" this?

OTOH setting aside some resources in the design (details TBD in discussion with interested parties) would give a resource other groups could use as a "flying laboratory" once it'd proved SABRE can do what they claim it can do.
REL recovers some costs, the groups get access to the first reusable hypersonic test vehicle in 50 years. Everyone wins.

Quote from: RanulfC
(Launch from Edwards AFB towards a facility in Utah, Speed in excess of Mach-12 and 'several hundred pounds' of "test instruments" in a long narrow bay... At the time it was noted by several people the 'test instrument bay' could hold a STAR solid motor and a microsatellite as 'payload' after all :) )

And while Star One is kind of obsessed with "hypersonic strike" missions the ACTUAL most likely mission is frankly as an advanced D-21 system for a reconnaissance drone. (Any 'weapon' has to be deployed from the inside of the vehicle mind you and THEN transition through a Mach-5+ shockwave AND still remain aimed at the target all of which is VERY difficult. And since it can't mass more than 2,000lbs at most it has to be highly accurate so obviously guided and everything has to be able to stand up to hypersonic speeds since that's when it's launched. As we've not developed any that work yet...) And for that you'd need specialized sensors, environmental conditioning equipment, (hypersonic speeds remember) power and others which will amount to something on the order of several hundred to maybe a thousand pounds. (Remember also you're flying at hypersonic speeds at almost 100,000ft so "OTS" sensor won't work) And then there's the 'range' question. The D-21 had a range of over 3,000 miles while modern UAV's have ranges from under 200 miles to over 14,000 miles but using LH2 or Liquid Methane there would be no opportunity for air-to-air refueling, (and transferring cryogenic fluids has been shown to have issue and that's before the operational problems with working with the stuff in bulk) and internal storage and insulation, (hypersonic again) issues abound for a smaller airframe.
Of those the sensors thing might be got round by data transfer from reconnaissance satellites but that doesn't crack any of the other issues. 14 000 miles but at what speed? I know weather survey drones have been designed for at least 12-24 hour endurance but those things have propellers. The D-21 was not in flight refueled either and a 20tonne thrust engine (44 000lbf) would be quite a lot larger vehicle. Protecting any payload is going to be kind of tough (you know some of one of those propellants is going to a cooling package for the the equipment at some point). Making it deploy something in mid flight is going to be a royal PITA.

Quote from: RanulfC
Still the 'customer' has to be very upfront about such and willing to pay for it. Sensors, weapons bays, internal fuel storage will all have to specified UP FRONT so they can be included in the design as there won't be any way to 'retrofit' them once the vehicle is built. And all this has a very real possibility of not only the actual vehicle or engine not performing to specifications but that the 'added' requirements don't themselves cause the vehicle to fall short of requirements.
And it wouldn't be the first time that's happened either.  :(

The "demonstrator" becomes essentially a "prototype" and the costs go up 10x (or more)?
I really hope REL management don't go down this road.  :( It ties so much that is completely irrelevant to the engine/inlet demonstration.  Fly the engine over as much of the trajectory as possible. Show it works with the inlet design. Show it can do AB/rocket transition to stable combustion. All else is nice to have.

Quote from: RanulfC
Since the main 'question' is (obviously) does the SABRE live up to expectations AND if so what are its actual performance metrics IN FLIGHT I have very high confidence that no one will be willing to pay for anything likely to be 'useful' till after all that data is in. Now something 'based' on the FTV could eventually be pitched but keep in mind there will be certain and strict requirements that have to be met along the way.
I hope not, but aerospace contractors can be very persuasive when they have something that could (sort of) plausibly meet a long held desire. That's basically how NASP sank close to $3Bn. The PI told a really  good story. Which in the end was exactly what it turned out to be.  :(

Quote from: RanulfC
The most likely outcome is the FTV will be (as suggested by the "usual" aerospace contractors such as Boeing, BAE, etc) an expendable "test" vehicle on the line of the X-45/47 with each vehicle pushing the performance envelope along a series of 'goals' over the program. It's typical of such test programs today so it won't be either unexpected nor vastly difficult to pitch. On the other hand JS19 has a point that making it 'reusable' may in fact be both the better and 'simpler' option given the minimum size needed. But even a conversion of an existing airframe is going to be expensive and a 'scratch built' one probably out of the question. But you really DO want reusable despite the 'cost analysis' tending towards expendable since what you REALLY want to do is get data from the full spectrum of flight operations rather than just selected 'segments' which might induce errors or miss issues.
I wonder if anyone's counted up how many of those hypersonic programmes demonstrators there have been, along with
a)How many of them failed in flight with little or no data gathered?
b)How many of the programmes delivered all the data they promised by the end?

Expendability means everything on every flight is a one-shot deal. That sounds a great deal for the contractors, not so good for the customers.

One of SABRE's goals is T/W ratio of about 14:1, about 7x (or at least 3.5x)better than any SCramjets I'm aware of. How does that affect the reusability/expendabilty calculation?

I came across a NASA study (didn't copy it) that had a diagram of a M8 passenger aircraft (SCramjet naturally) and its temperatures. Most of it was 800-1000c with the nose at 2200c.
Now where can REL find a jobbing shop that does Titanium, superalloys or ceramics?

Quote from: RanulfC
Star One wrote:
Quote
Every other discussion I've seen regarding this recent deal online, and other past developments leading up to this outside of this forum has been in terms of its military application.

Actually every time "hypersonics" is mentioned or written about the 'subject' turns to military applications which is different than what you're implying. Simply put, inserting "military applications" is a standard way to pad a subject that "might" actually have "military applications" whether the actual work being done IS directed towards that goal or not. Hypersonic flight has been specifically 'tied' to proposed "military applications" since the 1950s but actual versus assumed applications have been severely lacking and this is no different. SABRE, (which is the whole point of any test vehicle) is another, albeit rather better thought out, propulsion system that can possibly be used to push a vehicle to hypersonic speeds. Since it is possible for any vehicle to be used for 'military purposes', (and therefor used to pitch money from either the government or the military) such 'padding' is always inserted no matter if the actual application doesn't fit the suggested concept.

Let's take a look at the ACTUAL "military applications" of the SABRE engine:
1) It can be used to power a booster vehicle to launch expendable or reusable upper stages for vastly cheaper than current launch costs.

Now 'suggested' applications tend to be:
a) It can be used to power a bomber/fighter/recon aircraft flying at the edge of space and hypersonic, (Mach-6 to -10) speeds!

Actually no since a 'fighter' by definition needs a propulsion system that can allow it to do its job which is engage and destroy enemy aircraft and flying at 100,000ft and Mach-6 to Mach-10 you can't see, identify, lock-onto and engage a target with any reasonable chance of success. Similarly a 'bomber' needs to find, identify and engage its target which while not moving, (generally in fact the main 'purpose' of a hypersonic bomber is supposed to be the ability to reach a target area before a MOVING target can move outside its engagement area) and destroy it. Anyone that thinks that a platform moving as hypersonic speed at an altitude of 100,000ft plus can do this 'easily' is sadly out of touch with the reality of weapons technology. (Or trying to get money which pretty much covers the majority of sources for such suggestions) So that leaves the reconnaissance role which actually has possibilities as long as you ignore the rather obvious problems with a super-fast, super high altitude very "visible" (both to radar and basic IR sensors) target that while it might spot targets that would normally avoid predictable satellite passes or low and relatively slow "normal" aircraft is both vulnerable and restricted on what information it can gather. How can something flying so high and fast be 'vulnerable'? It is flying 'high' so again it's a LOT more visible than something flying very low and very slow so its chances of being spotted are vastly higher and unfortunately even 100,000ft is not 'low' enough to "hide" behind the curvature of the Earth as has often erroneously been suggested. Barring flying against someone with only the "Mark-One Eyeball" you WILL be spotted and tracked. You're also vulnerable in that neither the speed or altitude are immune from aggressive interception.

Further the SABRE cycle due to the inclusion of a rocket motor is vastly inferior for ANY hypersonic mission of any of the type given except launch vehicle when compared to vastly better cycles such as the Scimitar or other 'turbine' rather than 'rocket' based cycles. The 800-pound gorilla in the room everyone who focuses on 'military applications' for the SABRE is the fact it has ONE possible application and ONLY one: Launch Vehicle.

So therefor, (it should be quite obvious) if the FTV is planned to use SABRE cycle engines then it actually has one 'possible' application and most likely it will therefore be used to PROVE the SABRE cycle itself and not some way to 'sneak' a military drone into production.
I do note that SABRE 4 lets you run air in the pre burner and has separate air breathing and rocket combustion chambers. In principle you can do air breathing flight exclusively, but I always thought Scimitar was more "tuned" to the air breathing role.
Quote from: RanulfC
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BAE are the steering force now in this, their actual percentage is pretty irrelevant but it's big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isn't civilian.

Actually DARPA does in fact do a lot of projects that while they 'may' have military applications in the future can and have found civilian applications in more near term time frames. Self-driving vehicles is one good example as that started as a DARPA sponsored program but was rapidly embraced and improved upon by civilian agencies. Also while DARPA is sponsoring some of the work the actual main interest is from the Air Force Research Laboratory which is specifically tasked with 'long term' research and not procurement or operations. This is on purpose because the last time DARPA tried to 'shortcut' a research program it not only failed to get to flight testing it failed to reach the level of 50 year old research and development that the DARPA researchers didn't know had already been done! (RASCAL and MIPCC) AFRL was one of the agencies that pointed out the cost models for the program were significantly lacking in basic data while the proposed 'research' areas had already been done and the suggested 'vehicle' was in no way a 'research' or 'test' model but a clear 'operational' vehicle with which DARPA was attempting to bypass standard procurement and contracting procedures. (Which in fact they were doing)
Good point. I'd never considered RASCAL from that PoV.
Quote from: RanulfC
Quote
https://www.telegraph.co.uk/business/2018/04/12/reaction-engines-secures-boeing-rolls-royce-backing-hypersonic/

Outside of that there's plenty of applications for the technology fully outside of the aviation field and I imagine they'd be both easier and quicker to exploit than a space vehicle. After all a lot of investors these days are looking for the quick return or the shortest route to a return which this seems to offer here.

Nice of you to point out another article that fully and totally misses the main 'point' of its own information in order to pad the word count with nonsensical and non-relevant subjects. Point of fact where in that article can you find ONE "application" for the SABRE OTHER than as a launch vehicle? That is after all the ONLY application that is suggested or implied by those quoted in the article. Supersonic and hypersonic flight is 'suggested' as something that can be 'derived' from the SABRE cycle in the future a number of times but any connection with the SABRE FTV is inferred and not explicit by anyone quoted in the article. Wonder why that is?

It's because the SABRE is not suitable for either supersonic or hypersonic "flight" and those being quoted are WELL aware of this fact. The engine that would power supersonic or hypersonic aircraft, (note not "spacecraft" which is what the SABRE is stated to be used for in the article) is the Scimitar which is optimized and designed for just such applications and does the job VASTLY better than the SABRE.

I think one thing that people seem to ignore is due to its nature SABRE powered vehicles simply can NOT fly from ANY 'standard' airport anywhere in the world. Not even 'lightly loaded' or 'partially fueled' and REL has pointed this out several times. It has nothing to do with runway length or loading or any of the other "operational" issue that have been discussed but directly due to the fact it uses a rocket engine in its design. It can't fly from an standard airport because it is impossible for it to meet the noise regulations of any standard airport. Period.
Scimitar CAN do so and is specifically designed to do so and meet ALL regulations and guidelines.
A lesson the developers of Concorde learned the hard way. Only air bases might tolerate it, and that's got to be doubtful. 

Quote from: RanulfC

And lets discuss the applications outside the aviation industry which can be so lucrative...

Point of fact REL has a nice heat exchanger technology but as was pointed out back when they were trying to hype it, (and SABRE) up to get investment it is highly specialized and has few if any applications outside the ones REL has in mind. Granted if they exist you can be sure BAE will exploit them but really that has nothing to do with the thread. Still if you'd like to list them we can disassemble them again I suppose.

Phillip Clark wrote:
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Has anyone considered asking Reaction Engines about this? I am sure that Alan Bond would tell, if he's able to.

And deprive ourselves of the possibly of vastly speculative and argumentative postings? What are you? Mad? I mean look how boring and mundane BFS turned out to be compared to our ideas and concepts, come on loosen up some :)

Ho, ho.   :)
Quote from: RanulfC
Some additional comments on the D21 design:
Note the LOX tank was wrapped around the 'duct' not the actual engine. Even at Mach-6 the heating wasn't going to be really 'bad' and there was insulation. But in any case, (Liquid Methane or LH2) is going to require a larger tankage and not be compatible with 'wet-wings' normally. (You have to admire the way they got 'away' with "wet-wings" cyro-LOX in the Star-Raker design though: http://www.alternatewars.com/SpaceRace/Star_Raker/Star_Raker.htm
https://motherboard.vice.com/en_us/article/ezvj4j/the-747-to-space-that-never-was
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790010900.pdf (page 73)
What a beast.  :o

Unfortunately that's the sort of vehicle that makes REL's claims and goals that much harder for skeptics to believe ("doubters" won't believe them anyway).  :(
Quote from: RanulfC
Having said that since you don't actually NEED to put propellant in the wings, and at hypersonic speeds "wings" aren't really needed there would be tendency to move towards a lifting fuselage body similar to the "waverider" and advanced aircraft we've been working on the last 50 years. Now with that as pointed out with the D-21 you DO need wings at lower speeds so unlike NASP and some of the more extreme designs you want good low speed landing wings. On the other hand if you don't assume that you have to squeeze every ounce of efficiency out of the propulsion, (Skylon doesn't, whereas most of the others DO and therefore the engines and fuselage are designed to synergistically support each other) then you can consider other options for engine placement. (I should note the ENTIRE fuselage is synergistically used so that the forward body helps compress and ingest the air while the after body helps align and expand the exhaust for more efficient operation)
As NASA noted, plume heating is one of the "known unknowns."
Yes, it would be nice to get a jump on scoping how serious an issue (is it an issue?) this is.
But for now just getting something into the air seems adequately ambitious enough to me.
Quote from: RanulfC
Again this isn't 'lazy' on REL's part but it greatly simplifies the figures you need to play with since with the engines on the wingtips reduces some of the aerodynamic and weight-and-balance problems. (Of course you get a similar effect without the "engine-out" issues by putting the engine near the center of the airframe, again which is common on engine/body designs) I suppose the main question is how small can they make a SABRE engine?
This being a UK project I think the question is "how small can they make a SABRE engine affordably?"  :)
The recording of the BIS meeting from the head of the TF1 test stand project said the test engine is basically a SABRE 4 engine but with "1 of everything."
previous posters on that thread mentioned that SABRE is roughly a 4 segment pre-cooler, dual LOX pump, dual LH2 pump engine.

So logically the test engine will be 1 pre cooler segment, 1 LOX, 1LH2 pump. The LH2 pump is from the Ariane programme, but REL remain coy about wheather it's from a Vulcain or a Vinci engine. The former is way too big for the test stand (and still too small for the full Skylon sized SABRE) and the latter is a little undersized, but probably has enough margin to cope.

The implication is you just need to make multiple copies of those parts to upscale to a full Skylon sized SABRE. The joker is the LHe circulator which they describe as OTS, so probably too heavy for flight.   There aren't too many uses for these outside of a)Air separation plants and b) Some high temperature nuclear reactors. By the end of the test programme I expect they will have a  much better idea of what the issues of building one in house will be to meet the Skylon weight budget.

Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 04/18/2018 03:15 pm
The X7 airframe is great to begin with: simple and straightforward to mount a test engine, optimized for top speed at M4+ (even with aerodynamics of 1950s).

X7B have dual engines below wigs, resembling subsequent operational BOMARC missile with the same Marquardt RJ43 ramjets. BOMARC is optimized for balance between speed, range, and climbing ability after ground launch.

Eventually came the D21 with a special version of RJ43 optimized for long range cruise. The reasons for D21 to have a SR71 style flat lifting body are basically range and radar stealth, not top speed.

Having LH2 tanks around the engine is seeking trouble for a test vehicle.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/18/2018 04:08 pm
The X7 airframe is great to begin with: simple and straightforward to mount a test engine, optimized for top speed at M4+ (even with aerodynamics of 1950s).
More importantly a place to put a big LH2 tank which is not a funny shape.
Quote from: Katana
X7B have dual engines below wigs, resembling subsequent operational BOMARC missile with the same Marquardt RJ43 ramjets. BOMARC is optimized for balance between speed, range, and climbing ability after ground launch.
No. Those are the booster rockets to get it to ramjet operating speed.
Quote from: Katana
Eventually came the D21 with a special version of RJ43 optimized for long range cruise. The reasons for D21 to have a SR71 style flat lifting body are basically range and radar stealth, not top speed.
True. Also the JP7 was fairly easy to store in any shape of tank.  LH2 is less forgiving.
Quote from: Katana
Having LH2 tanks around the engine is seeking trouble for a test vehicle.
It seems an awful lot of work for the ability to inherit what is at best only a partial aerodynamic database (especially if you want to reuse the vehicle).
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/20/2018 08:37 am
To give some idea of the sort of information people might want to get from a FTV this is a description of the 
X-5's telemetry setup. (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640009985.pdf)

It would be interesting to find out how many of the questions the X-15 collected data on are still relevant today. 

Obviously the FTV's goal is primarily to flight test the SABRE engine and its inlet, so I wouldn't expect it to have anything like the 590Kg (1300lb) allocated to flight test instrumentation the X-15 had. Most of this was prepared away from the aircraft and mounted onto an "elevator" pallet for installation into the instrument bay.

OTOH it is true that such hardware has become much smaller and lighter in the half century since the X-15 last flew. Although I'm not sure if a combined pressure and temperature sensor operating over the needed range exists. For this environment I think Low or High Temperature Cofired Ceramic would be a better technology than Silicon based MEMS. No one is going to be doing multi channel recording by deflecting light beams with mirrors onto film stock, when you can record onto a 32GB micro SD card today.

As for its construction one technique I'd not seen to help construct leading edges is the notion of prestressing  them, (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660020789.pdf)  although it never seems to have been tried in practice it looks like quite a good way to save mass, especially given that carbon fibre was still a lab curiosity when the report was written.

Other potential design features would be making the body as a Sears Haack shape for minimal drag (as Skylon does) and possibly use winglets to lower drag further (as they won't have to withstand full reentry).
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: RanulfC on 04/28/2018 08:43 pm
Katana wrote:
Quote
The X7 airframe is great to begin with: simple and straightforward to mount a test engine, optimized for top speed at M4+ (even with aerodynamics of 1950s).

I'd also point out it would give the fuselage construction scheme REL has suggested a chance to be used :) With the later design, (for example the last version produced the X-7A-3/XQ-5/AQM-60A) and updated materials it probably wouldn't be difficult to hit speeds above Mach-6. You'd need to protect

Quote
X7B have dual engines below wigs, resembling subsequent operational BOMARC missile with the same Marquardt RJ43 ramjets. BOMARC is optimized for balance between speed, range, and climbing ability after ground launch.

The X-7B was canceled before flight and was a 'standard' (single engine) configuration that was to test guidance and control (GnC) systems. You may be confusing the later X-7A-3 models which had two under-wing rocket boosters instead of the large tail booster to allow semi-internal carry on the B-29 mother ship. (See: http://www.designation-systems.net/dusrm/m-60.html)

Quote
Eventually came the D21 with a special version of RJ43 optimized for long range cruise. The reasons for D21 to have a SR71 style flat lifting body are basically range and radar stealth, not top speed.

Well stealth isn't an option for anything travelling above Mach-2 really :) But the others are correct as the much more recent RATTLRS airframe shows: http://www.designation-systems.net/dusrm/app4/rattlrs.html
Note it has even less 'wing' than the D-21 so probably not very helpful :)

Quote
Having LH2 tanks around the engine is seeking trouble for a test vehicle.

Keep in mind folks the tankage wraps around the inlet DUCT not the engine which is at the very back of the vehicle :)
Here's a picture of the engine removed from one drone for separate display:
http://roadrunnersinternationale.com/d-21_ramjet.html
Details: http://roadrunnersinternationale.com/d_21/d-21.html
Removal: http://roadrunnersinternationale.com/d_21/d-21_removal.html

It's actually about 'half' a standard RJ43 with a quite different centerbody, (white object in the photo's, which BTW includes magnesium and thorium making it slightly radioactive!) because it uses the D-21 inlet and ducting unlike the 'integral' inlet and fixed spike of the standard RJ43. Also unlike the standard RJ43 it incorperated a 'restartable' ignition system (using TEB the same as the SR-71 and the Falcon-9 rocket btw :) ) and a more sophsitcated fuel flow and operations controller due to using the D-21 inlet system.

And in general note the size comparision between the D-21 and the NASA F-104 and T-38.


Star One wrote:
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I suggest you read any history of DARPA before suggesting they do anything civilian, if they do it's accidental rather intentional.

I'm very well aware of the history and operations of DARPA and if you'd read what I wrote you would see I never said they "do" civilian work but that many projects have civilian as well as military applications and this is by design as part of DARPA's charter is to explore military AND civilian applications of advanced technology. Military work is of course the core priority but in order to perform that work DARPA has to contract through and work with civilian agencies and organizations and is encouraged to allow cross-pollination and expansion of non-classified projects with those same groups. The SABRE FTV is just such a case as it has limited military application, (space launch) and therefore is neither classified nor restricted and is being treated as such by DARPA and AFRL.

Again, SABRE brings very little to the 'table' for militayr missions OTHER than Space Launch so it's direct military value is only 'played-up' for funding purposes or by those who see any support by the military as being directly tied to the 'latest' weapons fad. Let me break it down again;

There are three basic areas where the military "needs" a very fast, high flying platform:
1 ) Space Launch
2) Reconisscene
3) Strike

The SABRE cycle has direct applicabiity to the first one since, (of course) it is the mission it is designed to perform. Hence military interest in the technology being demonstrated to a high level.

SABRE has some applicability to the second mission but very little compared to other forms of propulsion because it has a high operations cost and is not as efficient as more operationally flexible and cheaper systems that are already at a higher TRL. While more work on "deep-cooling" will probably be done with an eye to application the use of LH2 is operationally and economically far less atractive than other more workable propellants. While Liquid Methane is an option the miliitary frankly would prefer a much more operationally flexible and available propelant based on hydrocarbon. Now if large segments of the civilian aerospace industry move to establish and utilize crygenic fuels such as methane or hydrogen then of course the military will tap into that infrastrcuturre but they have experience that shows utilizing 'specialtiy' propellants even in small quanties and for specific missions is not cost effective and signifincalty increses operational costs and difficulties.

In addition, despite the hype over hypersonics, a high-supersonic or hypersonic platform is neither 'stealthy' nor invulnerable to interception. Much has been made about no one every 'hitting' (or coming close to) an SR-71 in flight. But to really understand this you need to understand that for the most part none of these 'attempts' were able to generate direct intercepts or even get very close to the aircraft in flight. The flights WERE closely tracked and the SR-71s never directly overflew the targets on most missions, getting most information by 'side' or oblique scans of the area. Those that did overfly targets were in areas where it was known in advancce that no possible aircraft or defenses encounted could be a threat.

Part of the reason for retiring the SR-71 is to many nations now have aircraft capable of reaching altituds where they could launch a missile* that would have a very high chance of sucessfully engaging a very fast, very high flying overflight or even a near-overflight. Vehicles at 100,000ft are vulnerable to current aircraft and missile combinations and given any decent air defense radar system a hypersonic platform above 80,000ft (where they have to operate due to aerodynamic heating) is going to be highly visible to even passive IR tracking systems let alone radar. (And just for an FYI effective 'stealth' coatings are incompatable with high speed flight)

*Something people who assume 'hypersonics-is-the-new-stealth' need to know is you have to fly HIGH to sustain hypersonic speed, and that makes you visible a long way off. Further a main reason that missiles were not effective at very high altitude was due to having aerodynamic control surfaces (fins) which were not effective in the thin air. Most intercept missiles today and in the future are moving to reducing or removing the control sufaces in favor of vectored thrust and/or thruster controls which allow much more radical manuevers than 'fins'. This also allows them to be HIGHLY more effective at extreme altitudes where the air is to thin for fins to work! The only way you get 'low reaction time' is to fly at hypersonic speeds at less than 1000 feet, (actually less than 500 feet works best) but think for just second on how dense the air is at that altitude and how tough your vehicle has to be to survive that environment. The PLUTO/SLAM 'only' did Mach-3 at less than 1000 ft and its shockwave was calculated, (and planned) to be a 'weapon' all by itself!

Finally we have the "strike" mission which entails the ability to locate, engage and destroy targets on the ground which has all the issues of "reconisncee" and adds the need to be able to deploy weapons at high speed and altitude. (And gets worse if your platform is itself supposed to be the 'weapon' and needs to engage the target at the surface) Now keep in mind the whole basis that advocates of hypersonic recon/strike vehicles have always based the concept on was NOT 'stealth' or the ability of the vehicle to arrive over the target without being detected. This is all 'new' hyperbole which conflates hypersonic speed as the 'new stealth' and is frankly unsupportable as well as unworkable. Hypersonic recon/strike as always about being able to cover 'more' area by the virtue of flying so high and fast that any 'located' (recon) target could not remove itself from the engegement area (strike) so mobile targets could be more easily engaged. Even so it was quite obvious that the platform would be both visible and engageable itself but at the time these systems were proposed, (from the late 50s through the mid-80s) engagment with existing defensive systems was 'assumed' to be difficult if not impossible. Similarly the only weapons 'assumed' to be deployed by these hypersonic systems that could be effectivly used were nuclear in nature because no weapon of the period could be effectivly guided to the target from a hypersonic platform.

While effectie guidance can be done now from off-platform resources, (GPS, and other systems such as local laser guidance etc) delivery by hypersonic platform still requires the 'target' be located and isolated which presents issue as noted above. Things get worse not better if the hypersonic platform IS the weapon because once it begins an attack run it LOSES the ability to track the target. While granting any target can't move very 'far' once the attack run begins without a nuclear warhead anything less than a direct hit is problematical since in most cases hypersonic weapons have smaller than average or no warhead and depend much more on actual physical impact. Why does the weapon lose the target? Because no sensor can 'see' through the rapidly increasing aerodynamic heating effect around the weapon. The only way to 'guide' such a weapon is again by some off-platform sensor and guidance system which is effectivly limited to what bandwidth you can push through the rear-end of the heating. (No GPS won't work because the target is MOBILE and can in fact 'move' sufficently from a position in the time it takes a Mach-6 projectile to get from 100,000ft to the surface to possibly generate a 'miss' from the original target point. GPS will put a weapon on a set of coordinates only which is why an 'active' targeting system is required)

Lastly there is the 'size' factor to be considered. Nothinig powered by LH2 is going to be 'small' and even Liquid Methane is still about twice the area of a hydrocarbon fueled vehicle. You can't 'launch' such a vehicle from any standard aircraft without it being externally carried and any aircraft that does carry it is going to be huge, subsonic and rather obvious to any defender.
Keep in mind the 'range' factor as well. Whereas hydrocarbon fueled vehicles such as the D-21 or RATTLRS have ranges of 600 to 3, 000 miles a similar sized LH2 or Methane powered vehicle will not. It could have several hundred miles or up to 500 miles if it uses some ballistic 'coasting' flight. And it is going to be as BIG as a manned fighter jet to get THAT much range. And don't forget it will also require high operations support due to the cryogenic propellant.

Final nail in the coffin? You don't NEED it, there are far more cost effective and capable propulsion systems for both 'recon' and 'strike' platforms the we KNOW work and work quite well. The main drawback over the years has been fixation on certain propulsion types (Scramjet) as the 'only' type that can do the mission when in fact "real-world" testing has shown that 'simple' subsonic combustion ramjets, (ALSAM) advanced turbojets, (RATTLRS) or even rockets (Falcon) have shown you don't need either Scramjets or the SABRE to get the job done. Deep-Cooling intake air for the purposes of allowing sustained hypersonic flight DO have some military applications in that it could allow a recon platform of sufficient size to be operated but the SABRE cycle isn't the one you want unless that platform is going into suborbital or orbital flight. It's simiply not the best soluton to the problems. But again you also don't NEED it as we've been studying hypersonic flight for decades and "propulsion" is the least of the issues and always has been.

There is a very good and obvious, (if one cares to look) why so many "Blackbird" follow-ons have never actually flown. It's the same reason no one bothers to field supersonic bombers in great numbers in that the "mission" is only one aspect of the overall operational environment and frankly the faster and higher you go the more limited it becomes because everyone can see you and see exactly where you're going.

Randy
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: RanulfC on 04/28/2018 08:50 pm
JS19 wrote:
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I think the key thing for the Methane rocket version was inlet development. The "Peace Jack" programme showed what a big difference you could get with a better (and bigger) inlet on a conventional turbojet.

And more sophisticated don't forget :) The intake design had a series of internal segments to help handle the changing airstream as it went along. IIRC the work also spawned a suggested version of the F4 that had variable intakes similar t that of the F-15 for the same reason.

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Links? Hmm. Only a few REL presentations mention the idea in any detail. They were also looking at a kind of sounding rocket using IIRC LO2/LNH3/LN2 to simulate the combustion and trajectory.

I was hoping for some 'new' and possibly more detailed information but ah well :)

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I think people are making a lot of the Boeing involvement but this is the VC arm of Boeing. I'm not sure how much 2 way interaction happens between them and the actual aircraft building parts (either military or civilian). Of course as a potential customer it would good to get their input (provided it can be done in a non ITAR contaminating way of course).

We tend to make a lot about Boeing because they are clearly an "airframe" manufacturer whereas BAE isn't as 'big' a name at this time. Mostly Boeing "VC" arm is there to invest in "interesting" technology that Boeing wants to keep abreast of but not enough to take on internal spending and effort. On the other hand if this propulsion system tests out then they will have a 'foot' in the door as it were. IIRC Airbus was considering a similar effort but I don't recall if they actually put anything into it. Yet...

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Exactly. It's pretty clear that a lot of people simply won't believe a vehicle and engine can fly this trajectory until one does (although they seem to have no trouble believing a SCramjet will do whatever its promoters claim it will :( ) Therefor that needs to be the key goal.

Given how much Scramjet hasn't yet lived up to the hype... And then there's the significant inertia of the concept of 'air-breathing' rocket engines that don't 'need' to have the air turned to a liquid first. Granted the information was THERE even in the late 50s but the 'institutional thinking' was stuck on LACE despite the subcontractors noting it wasn't true. (Then again consider the 'statement' saying such seems to have amounted to a couple of sentences in the general summery of work done and no attention was called to it...)

Conversely the 'idea' of 'deep-cooled' turbojets AND LH2 rockets on the same airframe have been suggested many times but the fact they are two separate systems always shows degraded performance. Even 'combined cycle' systems with everything integrated STILL showed the rocket and air-breathing being 'fed' seperatly. So ya there is a need to "show" it works in the real world and not just that the math works. ('cause Scramjet math has ALWAYS worked so getting them flying is "simply" an engineering problem right? :) )

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Actually they dug up the top aerodynamics guy at the time and he said they never tested the shape for low speed handling. No point. It's never going to land. TBH that's probably the case for any existing shape.

And if need be use a parachute but I'll point out that one aspect this is SUPPOSED to test is flight from 'launch' to high mach which you'd think is going to be at LEAST subsonic. And with that amount of effort I'd probably shoot for a shape that can be used for full range testing. In the D-21 case I suspect since you'd have to rebuild the wings and leading edges anyway they could 'fix' the low speed handling since you're working your way UP in speed anyway.

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Looking at the D-21's internal structure what struck was how SR71 it was. Basically, take an SR71, chop off the wings past the engine nacelles (and the nacelles themselves), then core out the fuselage and stick the ramjet in there. No doubt it was considerably more subtle than that but that's the high level view I got.

Probably not THAT much more subtle considering how much effort went into the aerodynamic of the SR. After all there's good reason to go with a 'known' shape for approximately the same job :) Which is why the RATTLRS looks the way it does :)

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Now this works better. When this Idea came up I was thinking more of the V-1 but with proven high Mach flight to go on...
My instinct is LH2 storage is going to be the big issue for any test design. A design that gives you a solid centre body to put an LH2 tank inside seems easier. Of course if you goal is to demonstrate "mad design skillz" then the LH2 wet wing is definitely the way to go. But there's a very fine line between mad skillz, and just plain mad. :)

Well to be honest the PRIMARY reason I recalled the X-7 was the mental picture of the FTV with its nose spike stuck in a huge "target" labled "It will never work" and the subtitle "Nailed it!" but that's just me...

Figuring the 'fuselage' design and construction can piggyback off what REL has already done is worth some thought. The biggest difference is the single engine close to the body but given the design you have less 'shock-impingement' issues to deal with.

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IIRC HMX was involved with MIPCC and said they could get their hands on a couple of F106's, which had a pretty big weapons bay. They reckoned with upgraded leading edges it could hit M5. Junking all that 1950's era SAGE computer hardware should've lightened it up considerably.

I think MLorry was the one pushing the F106, and there was a group of F106 fans that submitted a plan to use them but it was rejected by DARPA because it was 'too small' for the 'required' payload. (Which was when it became a 'suspicion' that this wasn't a 'research' project... The other hint was numerous articles from the lead scientist about how the 'operational' system would work)

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I think this is the issue with adapting existing designs. No existing design (except the X-15, X37b and Shuttle) were designed to fly above roughly M3.5. True they wouldn't have to last long (for engine and trajectory test get up to the right altitude/speed, switch over and get stable combustion in rocket mode. 10s of seconds after transition?) but it's a gamble. And you'd probably need a pilot as well.

Well Northrup DID suggest a redesign of the T-38 into an 'aerospace' trainer that could hit Mach-3.3 and over 200,00ft:
http://ghostmodeler.blogspot.com/2012/09/talons-in-space-northrops-n-205-proposal.html

And of course the NF-104:
https://en.wikipedia.org/wiki/Lockheed_NF-104A

But anything would take a large amount of work to use I agree, so starting from scratch might be more practical. Needing a 'pilot' is going to be a design decision as you can, (we've been doing it since radio control was invented) make a drone out of anything.

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Agreed. But now you have 2 goals.
1) Build a vehicle that can test the engine/inlet over its planned Mach and altitude range
2) Design it as a pre-production prototype for an actual vehicle with a specific purpose.

And that's often exactly the case with either or both contractor/customer overreach on a design :) (About even which one does the 'overreach' and more often than not is can be mutual : ) ) Frankly even if it IS a 'pure' test vehicle contractors will tend to 'suggest' it can be turned into an operational vehicle with "just a bit" more money and effort. More often than not this doesn't work BUT...

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One of the ways APD said they cut development costs by 1/3 was not to include support for things like reparability or maintainability. The language is quite important. It's a demonstrator, not a prototype.

The 'problem' though is that can often lead to asset being even "cheaper" (by creative accounting) if it is expendable in every test. As far as I can tell EVERY Scramjet "demonstrator" has been expendable for that very reason so the 'logic' is obviously compelling. On the other hand IF the vehicle IS reusable then the "logic" of some sort of operational or "long-term" research program use is just as compelling. Again pointing to the X-7, it was an engine and aerodynamic data test vehicle and very good at both for its time. That didn't stop it being pitched as everything from a supersonic target drone to a recon or attack missile. None of which it was very good at and something which a 'point' design did better.

Then there is the X-15 which was never 'planned' to be anything but a test vehicle. (Though the Douglas design was in fact more 'aimed' at a possible 'operational' follow on for the Navy even though they frankly had no clue what they'd use it for) That didn't stop North American from proposing all sorts of projects with the basic and advanced versions of the airframe. They key is both the X7 and X-15 were designed and used for the job they were made for and any "other" tasking was going to take some (in many cases significant) redesign and rebuilding. Hence they DID the job they were designed for and while possibly could have been used for other purposes in the end it would take time and money to do so.

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The X-33 programme should have taught people what happens when you make one vehicle do both. You end up with no vehicle and no improvement in your ability to design one, unless you count "Designing multi lobed conformal composite LH2 tanks is hard." Did it really need a $1.5Bn programme to "discover" this?

Actually there were a lot of lessons learned from the overall program, (a couple of the big ones being listen to your sub-contractors when you supposedly hire them for their expertise, and don't assume you can do something radically difficult when the people you hire are TELLING you it's radically difficult simply because you have a history of doing so, you can't win every time) but the ONE the was NOT learned, (even though it is often touted as "proof") is that SSTO or low-cost access is not possible. Similarly "lessons learned" from the NASP program include not making the whole program dependent on a single technology that at the time hadn't worked outside a laboratory and the risks of program bloat and unrealistic expectations. Yet the most often cited "lesson" is usually that "air-breathing propulsion" has no place in space launch without a shred of actual 'proof' to support it.

More often than not the actual "lessons" versus the assumed "lessons" are more directed towards bias's and desired outcomes than what was really learned. Never forget the biggest obstacle that any new idea has to overcome is the fallacy of "If it worked someone would have done it by now" :)

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OTOH setting aside some resources in the design (details TBD in discussion with interested parties) would give a resource other groups could use as a "flying laboratory" once it'd proved SABRE can do what they claim it can do.
REL recovers some costs, the groups get access to the first reusable hypersonic test vehicle in 50 years. Everyone wins.

In theory anyway :)

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The "demonstrator" becomes essentially a "prototype" and the costs go up 10x (or more)?
I really hope REL management don't go down this road. :( It ties so much that is completely irrelevant to the engine/inlet demonstration. Fly the engine over as much of the trajectory as possible. Show it works with the inlet design. Show it can do AB/rocket transition to stable combustion. All else is nice to have

Keep in mind that REL may have little or no input on the matter. To be honest they are really just the 'engine contractor' and most everything else is going to be what the rest of the consortium decides. All the more reason to push for essentially an flying engine test bed and not much else.

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I hope not, but aerospace contractors can be very persuasive when they have something that could (sort of) plausibly meet a long held desire. That's basically how NASP sank close to $3Bn. The PI told a really good story. Which in the end was exactly what it turned out to be.

NASP suffered (a LOT) from hypersonic and Scramjet advocates finally getting access to an 'blank check' with little or no oversight or actual understanding of the challenges by those who were supposed to provide the oversite. And the advocates not only didn't try to stop the spiral they egged it on by adding "requirements" specifically to drive the program into certain directions no matter the TRL of the technology needed. Frankly the INITIAL program of a hypersonic, (up to mach-10) demonstrator was a good idea but once the whole program became dependent on a single propulsion system and the 'goal-post' of flight speed began to creep up the whole thing was doomed.

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I wonder if anyone's counted up how many of those hypersonic programmes demonstrators there have been, along with
a)How many of them failed in flight with little or no data gathered?
b)How many of the programmes delivered all the data they promised by the end?

The 'figures' are available and with enough creative accounting they will tell what every result you want them to :) Seriously MOST programs have been 'successful' to some degree and few research programs deliver "all" the data they promise in the end. Take the X-15 for example. Almost 200 flights and in the end it only barely 'touched' the 'promised' speed levels, (the program was literally based on gaining "hypersonic" data which meant above Mach-5 and it was severely damaged at those speeds) and only about half its altitude goals.

"Most" Scramjet tests simply list "positive thrust achieved" or that the vehicle was 'accelerated' but neglect to provide actual figures. Which is because when they do the "acceleration" and/or "thrust over drag" is miniscule at best. Sure it CAN accelerate something to much higher speeds EVENTUALLY but probably not before it runs out of fuel. Sure you got a "Scramjet" to burn at Mach-5 to 7 but you've done that in a lab and in 'real-life' it has little utility if any. So why use a Scramjet when a rocket will actually do better?

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I came across a NASA study (didn't copy it) that had a diagram of a M8 passenger aircraft (SCramjet naturally) and its temperatures. Most of it was 800-1000c with the nose at 2200c.
Now where can REL find a jobbing shop that does Titanium, superalloys or ceramics?

I'd be surprised if it wasn't using 'heat-pipes' to the fuel for a heat sink :)

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Expendability means everything on every flight is a one-shot deal. That sounds a great deal for the contractors, not so good for the customers.

One of SABRE's goals is T/W ratio of about 14:1, about 7x (or at least 3.5x)better than any SCramjets I'm aware of. How does that affect the reusability/expendability calculation?

Yes it means everything is 'expended' on each flight but the calculations often show that's less costly over a few flights than making it reusable. We've seen the 'math' before with ELV versus RLV so it obviously "makes sense" at some point. T/W probably isn't a metric at all since there are expendable turbojets and rocket motors. The main 'metric' I assume is how many flights are planned, (and what kind of flight program overall) against the cost of an few (less costly) expendable vehicles versus a few (more costly) reusable ones. This is where the question becomes 'gray' because if your only testing a few key areas, (actual versus projected T/W, transition and stable combustion for example) then it might make sense to fly only a couple of mission to those specific points which would lean towards expendable. On the other hand if you want to get a complete data set from subsonic through hypersonic then it may make sense to build a couple of reusable flight vehicles for more upfront money.

Part of the problem of looking for 'other users' is frankly it's probably questionable if anyone else would 'need' the capability AND if the vehicle flight parameters (or the flown test parameters) may not adversely affect each other. (Example is the X-15 and the dummy Scramjet) The suborbital and micro-payload "markets" aren't that obvious and the temptation is to make a sub-scale 'demonstrator' (if you go the reusable route) that might be capable of delivering an upper stage and payload to orbit (Cube or micro-sat size) JUST because you're already making a 'demonstrator' in the first place.

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As NASA noted, plume heating is one of the "known unknowns."
Yes, it would be nice to get a jump on scoping how serious an issue (is it an issue?) this is.
But for now just getting something into the air seems adequately ambitious enough to me.

Oh I agree but that does feed back into the expendable/reusable equation. And the design, and the engine placement, and.. Well you get the picture :)

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This being a UK project I think the question is "how small can they make a SABRE engine affordably?" :)

Well that IS the reason you reach out to moneybag.. er that is the US right? ;)

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The recording of the BIS meeting from the head of the TF1 test stand project said the test engine is basically a SABRE 4 engine but with "1 of everything."
previous posters on that thread mentioned that SABRE is roughly a 4 segment pre-cooler, dual LOX pump, dual LH2 pump engine.

So logically the test engine will be 1 pre cooler segment, 1 LOX, 1LH2 pump. The LH2 pump is from the Ariane programme, but REL remain coy about wheather it's from a Vulcain or a Vinci engine. The former is way too big for the test stand (and still too small for the full Skylon sized SABRE) and the latter is a little undersized, but probably has enough margin to cope.

The implication is you just need to make multiple copies of those parts to upscale to a full Skylon sized SABRE. The joker is the LHe circulator which they describe as OTS, so probably too heavy for flight. There aren't too many uses for these outside of a)Air separation plants and b) Some high temperature nuclear reactors. By the end of the test programme I expect they will have a much better idea of what the issues of building one in house will be to meet the Skylon weight budget.

And really that's the whole nutshell right there. You probably NEED to flight test some type of engine to get an idea of what works subscale, what doesn't and what you can podge together to get it to work. The big risk is if you don't get it right then it may not work and then the whole concept is circular-filed as 'not-working' when it was actually a question of design. This is the stuff that keeps designers awake at night and causes ulcers but it's also a point your kinda of 'happy' to have gotten to.

Randy
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/29/2018 10:45 am
And more sophisticated don't forget :) The intake design had a series of internal segments to help handle the changing airstream as it went along. IIRC the work also spawned a suggested version of the F4 that had variable intakes similar t that of the F-15 for the same reason.
Impressive. I'm guessing inlet technology to run from M0-5.5+ will be even more critical.
Quote from: RanulfC
I was hoping for some 'new' and possibly more detailed information but ah well :)
The closest was a description of (roughly) a miniature Skylon, 3.5m span x 9m long, which IIRC was the Methane fueled inlet test vehicle. It's target was a 1000Kg mass.

Quote from: RanulfC
We tend to make a lot about Boeing because they are clearly an "airframe" manufacturer whereas BAE isn't as 'big' a name at this time. Mostly Boeing "VC" arm is there to invest in "interesting" technology that Boeing wants to keep abreast of but not enough to take on internal spending and effort. On the other hand if this propulsion system tests out then they will have a 'foot' in the door as it were. IIRC Airbus was considering a similar effort but I don't recall if they actually put anything into it. Yet...
Actually BAe do build complete airframes. The trouble is the only two that comes to mind as new build are the "Hawk" trainers and the Typhoon. Hawk is a 40 year old design. Typhoon, being a multi national European design will have issues pending Brexit.
Quote from: RanulfC
Given how much Scramjet hasn't yet lived up to the hype... And then there's the significant inertia of the concept of 'air-breathing' rocket engines that don't 'need' to have the air turned to a liquid first. Granted the information was THERE even in the late 50s but the 'institutional thinking' was stuck on LACE despite the subcontractors noting it wasn't true. (Then again consider the 'statement' saying such seems to have amounted to a couple of sentences in the general summery of work done and no attention was called to it...)
Exactly. Hence the critical need to get a vehicle to fly as much as possible of the trajectory, ideally beyond the AB/Rocket transition.
Quote from: RanulfC
Conversely the 'idea' of 'deep-cooled' turbojets AND LH2 rockets on the same airframe have been suggested many times but the fact they are two separate systems always shows degraded performance. Even 'combined cycle' systems with everything integrated STILL showed the rocket and air-breathing being 'fed' seperatly. So ya there is a need to "show" it works in the real world and not just that the math works. ('cause Scramjet math has ALWAYS worked so getting them flying is "simply" an engineering problem right? :) )
It seems the maths of SCramjets has always been shown to work. It's just that pesky engineering.
TBH to LACE and "cryojet" designs (which IIRC is what SABRE would be classified by William Escher as).frost control and the size of the precooler have been the issues Historical designs had tubes 10x the dia of the REL types and what is basically a more "fractal" plumbing layout.
I think the question is how far did earlier designs manage to share the core systems. It would seem not much, whereas SABRE shares inlets, pumps, pre-burners etc. It's only more recently they've gone with more separation of thrust chambers, giving an AB thrust chamber much closer to conventional gas turbine pressures.

Quote from: RanulfC
And if need be use a parachute but I'll point out that one aspect this is SUPPOSED to test is flight from 'launch' to high mach which you'd think is going to be at LEAST subsonic. And with that amount of effort I'd probably shoot for a shape that can be used for full range testing. In the D-21 case I suspect since you'd have to rebuild the wings and leading edges anyway they could 'fix' the low speed handling since you're working your way UP in speed anyway.
Yes, the only part of the D-21 designed for recovery was the "hatch" housing all the control gear, sensors etc. Apart from the fact it needs one engine and can hit more than M3 (but not sure how much more than) the D-21 layout doesn't have that much going for it as a model for a M6 test vehicle.
Quote from: RanulfC
Probably not THAT much more subtle considering how much effort went into the aerodynamic of the SR. After all there's good reason to go with a 'known' shape for approximately the same job :) Which is why the RATTLRS looks the way it does :)
I suspected it was something like that.

Quote from: RanulfC
Well to be honest the PRIMARY reason I recalled the X-7 was the mental picture of the FTV with its nose spike stuck in a huge "target" labled "It will never work" and the subtitle "Nailed it!" but that's just me...
I like that as well. :-)
Quote from: RanulfC
Figuring the 'fuselage' design and construction can piggyback off what REL has already done is worth some thought. The biggest difference is the single engine close to the body but given the design you have less 'shock-impingement' issues to deal with.
This is where it gets tricky.
The trouble is all the high mach designs I know of are
a) Air launched
b) Used actively cooled walls (mostly M3 and higher airliner studies).
a)Means they don't have to worry too much about take off mass and b is quite a complex design (interestingly they seemd to have gone with direct cooling from the LH2 in the tanks, rather than Helium loops (which in hindsight looks like asking for trouble to me). 

So maybe the simplest answer is to you use the construction technique they are planning to use on Skylon?

I will note that the FTV's goal is not that of the X-15. The core goal of the X-15 was to find out what happens to an airframe when it's "soaked" to thermal equilibrium with the environment. AFAIk the nearest thing in the UK to this was the Bristol 188, but apparently it didn't have the endurance to reach full soaking temperature.

This "Over and under" style has been used in a few ramjet missiles and recon drones up to about M4 (with the X-7). While I think it solves the LH2 storage issue the X-15 showed just how damaging shock/shock interferrence can be with the dummy SCramjet, mostly it seems not from the spike on the front, but from the outer edge of the inlet cowling hitting the airframe and fin shocks. There is also the issue this engine will definitely be running and therefor generating an exhaust plume

The obvious approach is to put the engine nacelle as far back as possible, like the V1. However now you're back in HOTOL territory, with high forebody lift with a back end heavy shape.
Quote from: RanulfC
I think MLorry was the one pushing the F106, and there was a group of F106 fans that submitted a plan to use them but it was rejected by DARPA because it was 'too small' for the 'required' payload. (Which was when it became a 'suspicion' that this wasn't a 'research' project... The other hint was numerous articles from the lead scientist about how the 'operational' system would work)
Highly suspicious. That said the X-15 "payload" was 1300lbs of instrumentation. Because of how early they started the planning for this they went with film cameras recording osciloscope traces rather than digital tape recorders. Obviously today with micro SD cards running 64GB you can collect a fair bit of information in a considerably smaller package.
Quote from: RanulfC
Well Northrup DID suggest a redesign of the T-38 into an 'aerospace' trainer that could hit Mach-3.3 and over 200,00ft:
http://ghostmodeler.blogspot.com/2012/09/talons-in-space-northrops-n-205-proposal.html

And of course the NF-104:
https://en.wikipedia.org/wiki/Lockheed_NF-104A

But anything would take a large amount of work to use I agree, so starting from scratch might be more practical. Needing a 'pilot' is going to be a design decision as you can, (we've been doing it since radio control was invented) make a drone out of anything.
I'd not heard of the T38 conversion. Very dramatic. Big doubts about the structural heating theough. :-( .
I think both RC and full AGV technology has come a very long way, but the list of vehicles possibly available is pretty small. Throw in the need to run LH2/LO2 (or even Methane) and it shrinks even further.

Quote from: RanulfC
And that's often exactly the case with either or both contractor/customer overreach on a design :) (About even which one does the 'overreach' and more often than not is can be mutual : ) ) Frankly even if it IS a 'pure' test vehicle contractors will tend to 'suggest' it can be turned into an operational vehicle with "just a bit" more money and effort. More often than not this doesn't work BUT...
My instinct with this is it depends to what degree "hooks" allow a design to transition into something more "operational."
Note that (according to Jenkins book) the core X-15 mission goals were done by 1963. The rest were flights on behalf of other people, or seperately funded, to test equipment, study the upper atmosphere etc.
In the same way I think there are other groups around the world who would be interested in fying their instrumentation not as an operational vehicle, but to help them design theirs.

Quote from: RanulfC
The 'problem' though is that can often lead to asset being even "cheaper" (by creative accounting) if it is expendable in every test. As far as I can tell EVERY Scramjet "demonstrator" has been expendable for that very reason so the 'logic' is obviously compelling. On the other hand IF the vehicle IS reusable then the "logic" of some sort of operational or "long-term" research program use is just as compelling. Again pointing to the X-7, it was an engine and aerodynamic data test vehicle and very good at both for its time. That didn't stop it being pitched as everything from a supersonic target drone to a recon or attack missile. None of which it was very good at and something which a 'point' design did better.
Personally I think the itearative nature of inlet development makes a reusable vehicle cheaper in the long run. The desire to make an LH2 monocoque seems to skew all attempts, when separating the LH2 as an inner tank makes life a lot simpler.

Quote from: RanulfC
Then there is the X-15 which was never 'planned' to be anything but a test vehicle. (Though the Douglas design was in fact more 'aimed' at a possible 'operational' follow on for the Navy even though they frankly had no clue what they'd use it for) That didn't stop North American from proposing all sorts of projects with the basic and advanced versions of the airframe. They key is both the X7 and X-15 were designed and used for the job they were made for and any "other" tasking was going to take some (in many cases significant) redesign and rebuilding. Hence they DID the job they were designed for and while possibly could have been used for other purposes in the end it would take time and money to do so.
Which IMHO is how an X programme should be.
Quote from: RanulfC
Actually there were a lot of lessons learned from the overall program, (a couple of the big ones being listen to your sub-contractors when you supposedly hire them for their expertise, and don't assume you can do something radically difficult when the people you hire are TELLING you it's radically difficult simply because you have a history of doing so, you can't win every time) but the ONE the was NOT learned, (even though it is often touted as "proof") is that SSTO or low-cost access is not possible. Similarly "lessons learned" from the NASP program include not making the whole program dependent on a single technology that at the time hadn't worked outside a laboratory and the risks of program bloat and unrealistic expectations. Yet the most often cited "lesson" is usually that "air-breathing propulsion" has no place in space launch without a shred of actual 'proof' to support it.
All true, sadly (with the exception that the X-33 somehow "proves" SSTO is impossible, when all it shows is something is impossible if you impose enough irrelevent and unneccessary constraints).
Quote from: RanulfC
More often than not the actual "lessons" versus the assumed "lessons" are more directed towards bias's and desired outcomes than what was really learned. Never forget the biggest obstacle that any new idea has to overcome is the fallacy of "If it worked someone would have done it by now" :)
Good point. The price of wisdom is enternal vigilance against learning the wrong lessons. :-( .
Quote from: RanulfC

Quote
OTOH setting aside some resources in the design (details TBD in discussion with interested parties) would give a resource other groups could use as a "flying laboratory" once it'd proved SABRE can do what they claim it can do.
REL recovers some costs, the groups get access to the first reusable hypersonic test vehicle in 50 years. Everyone wins.

In theory anyway :)
That's basically what I'm suggesting. Of course the devils in the details.....

Quote from: RanulfC
Keep in mind that REL may have little or no input on the matter. To be honest they are really just the 'engine contractor' and most everything else is going to be what the rest of the consortium decides. All the more reason to push for essentially an flying engine test bed and not much else.
True. It will depend if REL is funding the FTV or there is a consortium in place. That's when the issue of governence comes in and things can get tricky. Again.
Quote from: RanulfC
NASP suffered (a LOT) from hypersonic and Scramjet advocates finally getting access to an 'blank check' with little or no oversight or actual understanding of the challenges by those who were supposed to provide the oversite. And the advocates not only didn't try to stop the spiral they egged it on by adding "requirements" specifically to drive the program into certain directions no matter the TRL of the technology needed. Frankly the INITIAL program of a hypersonic, (up to mach-10) demonstrator was a good idea but once the whole program became dependent on a single propulsion system and the 'goal-post' of flight speed began to creep up the whole thing was doomed.
Let's be clear. The FTV relies on SABRE. Propulsion has always been the key issue. Or rather, the insistance by the US hypersonic community that only SCramjets can meet the speed and the Isp requirements. It's interesting to consider what would be flying today if they had not become infected with this particular meme. :-(.

Quote from: RanulfC
The 'figures' are available and with enough creative accounting they will tell what every result you want them to :)
Now that I can believe. :-( .
Quote from: RanulfC
Seriously MOST programs have been 'successful' to some degree and few research programs deliver "all" the data they promise in the end. Take the X-15 for example. Almost 200 flights and in the end it only barely 'touched' the 'promised' speed levels, (the program was literally based on gaining "hypersonic" data which meant above Mach-5 and it was severely damaged at those speeds) and only about half its altitude goals.
I think that's a bit harsh. AFAIK it met all core goals. especially the prolonged effect on airframe heating. The real damage happened when they mounted that dummy SCramje to the lower fin. No one saw the massive effects of shock/shock interferrence heating.
Quote from: RanulfC
"Most" Scramjet tests simply list "positive thrust achieved" or that the vehicle was 'accelerated' but neglect to provide actual figures. Which is because when they do the "acceleration" and/or "thrust over drag" is miniscule at best. Sure it CAN accelerate something to much higher speeds EVENTUALLY but probably not before it runs out of fuel. Sure you got a "Scramjet" to burn at Mach-5 to 7 but you've done that in a lab and in 'real-life' it has little utility if any. So why use a Scramjet when a rocket will actually do better?
SCramjet advocates seem to be saying a) "Convetionl ramjet fuel consumption deteriorates badly above M5 and b) You have to factor in all the free reaction mass in the air.
Given SCramjet T/W is pretty poor that acceleration had better be phenomenial to make up for it, and it doesn't sound like it is.
Not to mention the only reliable SCramjet test vehicle for a full size SCramjet is another full size SCramjet vehicle. :-( .

Quote from: RanulfC
I'd be surprised if it wasn't using 'heat-pipes' to the fuel for a heat sink :)
That's the weird thing now I come to think of it. They seem to cool the skin panels directly from the LH2 supply, no intermediate HX. No heat pipes. It seems hard to believe no one considers this an issue.
Quote from: RanulfC
Yes it means everything is 'expended' on each flight but the calculations often show that's less costly over a few flights than making it reusable. We've seen the 'math' before with ELV versus RLV so it obviously "makes sense" at some point. T/W probably isn't a metric at all since there are expendable turbojets and rocket motors. The main 'metric' I assume is how many flights are planned, (and what kind of flight program overall) against the cost of an few (less costly) expendable vehicles versus a few (more costly) reusable ones. This is where the question becomes 'gray' because if your only testing a few key areas, (actual versus projected T/W, transition and stable combustion for example) then it might make sense to fly only a couple of mission to those specific points which would lean towards expendable. On the other hand if you want to get a complete data set from subsonic through hypersonic then it may make sense to build a couple of reusable flight vehicles for more upfront money.
Fair point. I guess the question is wheather you're validating what you already know to be true, or you're finding out what "true" means?
Quote from: RanulfC

Part of the problem of looking for 'other users' is frankly it's probably questionable if anyone else would 'need' the capability AND if the vehicle flight parameters (or the flown test parameters) may not adversely affect each other. (Example is the X-15 and the dummy Scramjet) The suborbital and micro-payload "markets" aren't that obvious and the temptation is to make a sub-scale 'demonstrator' (if you go the reusable route) that might be capable of delivering an upper stage and payload to orbit (Cube or micro-sat size) JUST because you're already making a 'demonstrator' in the first place.
We may be talking at cross purposes here.
I'm talking about "users" in the X-15 sense of additional research groups who might want to install other instrumentation. AFAIK most of the people who have an interest in this area use sounding rockets and balloons. Sounding rockets don't really do constant altitude and balloons are difficult to recover.
My favorite example was the UV spectrometer looking through a window in the top of the telemetry hardware bay.  This would have been completely impossible without the bay being designed for access from above, hence looking up at the sky was relatively easy.

My interest is in what other early design choices could make the FTV more "experimenter friendly" ?

Quote from: RanulfC
Oh I agree but that does feed back into the expendable/reusable equation. And the design, and the engine placement, and.. Well you get the picture :)
It's a Gordian Knot alright. But you've got to start somewhere. Only making a single engine is a serious limit on options here. With two they'd be lloking at something a lot more Skylon like. With three they might be able to approach the EU to do some structures testing. LAPCAT looked at the engines for a hypersonic aircraft but there was a sibling programme for the vehicle structure (can't recall the name. Choose any of the usual adjectives and nouns for this stuff and I'm pretty sure you'll a project that's used that combination over the decades. :-( ).
I wonder if it's too late for REL to set up EU office in say Bruxxels staffed with French and German speakers?
Quote from: RanulfC
Well that IS the reason you reach out to moneybag.. er that is the US right? ;)
Well, you are the country that gave the world "No Bucks, no Buck Rogers" :-)
Quote from: RanulfC
And really that's the whole nutshell right there. You probably NEED to flight test some type of engine to get an idea of what works subscale, what doesn't and what you can podge together to get it to work. The big risk is if you don't get it right then it may not work and then the whole concept is circular-filed as 'not-working' when it was actually a question of design. This is the stuff that keeps designers awake at night and causes ulcers but it's also a point your kinda of 'happy' to have gotten to.
My experience in other areas is that you can usually come up with two or three ways to do something. On paper they all look about equal. Pros and cons for all of them. Historically this was decided by the core developent team
a) Going to a bar
b) Talking it out
c) Drinking themselves into a stupor
d) Implementing the choise.

Although I'm sure a similar process could be carried out at your nearest favorite coffee house.

I can understand some REL fearing the outcome but I don't think any fear the process.
Some have waited half a lifetime to demonstrate their proposals are correct. Younger staff memebers weren't born when REL was founded. They have (literally) waited a lifetime for their efforts to pay off.
Fear of getting it wrong? Certainly.
Fear of trying. Never.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 04/29/2018 03:42 pm
Let's be clear. The FTV relies on SABRE. Propulsion has always been the key issue. Or rather, the insistance by the US hypersonic community that only SCramjets can meet the speed and the Isp requirements. It's interesting to consider what would be flying today if they had not become infected with this particular meme. :-(.


SCramjet advocates seem to be saying a) "Convetionl ramjet fuel consumption deteriorates badly above M5 and b) You have to factor in all the free reaction mass in the air.
Given SCramjet T/W is pretty poor that acceleration had better be phenomenial to make up for it, and it doesn't sound like it is.
Not to mention the only reliable SCramjet test vehicle for a full size SCramjet is another full size SCramjet vehicle. :-( .

I suspect NOTHING between M5 and M10 could satisfy the ďspeed and Isp requirementsĒ of end user. The actual need of end user is even NOT  "speed and isp". Especially given the revolutionary success (and effort) of recon satellites and stealth subsonic cruise weapons (on the side of microelectronics), while hypersonic excludes stealth.

But SCramjet developers could justify their activity as "technology demonstrators", while testing conventional ramjets for top speed can't.

Many people have waited half their lives to see a SCramjet (but not conventional ramjet) before X-43. They need the process (up to X aircraft), not the outcome (to end user). Cancelling SCramjet programs to fund convential ramjet are UNFAIR to them.

Optimizing ramjet technology is even not the RESPONSIBILITY of NASA, but one (of many) choice of defence contractors while defining their products. To go faster? to go smarter and more silent?

Similar situation above applys to SABRE/Skylon vs. optimized SR71 style turboramjet with Inconel airframe. The latter could certainly go beyond M5, but choosing payload to get PAID is another story.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 04/29/2018 05:02 pm
The 'problem' though is that can often lead to asset being even "cheaper" (by creative accounting) if it is expendable in every test. As far as I can tell EVERY Scramjet "demonstrator" has been expendable for that very reason so the 'logic' is obviously compelling. On the other hand IF the vehicle IS reusable then the "logic" of some sort of operational or "long-term" research program use is just as compelling. Again pointing to the X-7, it was an engine and aerodynamic data test vehicle and very good at both for its time. That didn't stop it being pitched as everything from a supersonic target drone to a recon or attack missile. None of which it was very good at and something which a 'point' design did better.

Then there is the X-15 which was never 'planned' to be anything but a test vehicle. (Though the Douglas design was in fact more 'aimed' at a possible 'operational' follow on for the Navy even though they frankly had no clue what they'd use it for) That didn't stop North American from proposing all sorts of projects with the basic and advanced versions of the airframe. They key is both the X7 and X-15 were designed and used for the job they were made for and any "other" tasking was going to take some (in many cases significant) redesign and rebuilding. Hence they DID the job they were designed for and while possibly could have been used for other purposes in the end it would take time and money to do so.

Both X-7 and X-15 are proved worthy to be reuseable, while X-43 and X-51 are proved worthy to be expendable.

X-7 provide iterative testing of RJ43 ramjet (for BOMARC) from concept to product. Similar Bumblebee program for Talos ramjet costed a great number of expendable protypes, and left out many problems in operational version, leading to late product modification.

https://www.okieboat.com/Talos%20history.html

X-15 provided system level testing for manned hypersonic flight before Shuttle.

X-43 and X-51 had little goal other than scramjet and airframe, while their expendable solid boosters are large and expensive, maybe more expensive than vehicle.

Interesting to note the X-43 was a pure research program conducted by a tiny team of ex-X30 engineers, not too different from REL as ex-HOTOL engineers.
https://www.amazon.com/Road-Mach-10-Lessons-Research/dp/156347932X

X-51 was designed or at least shaped and pitched as a missile demonstrator. However after flight tests, interest for scramjet missiles in US ceased, including DMRJ and TTRJ programs of OrbitalATK.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/29/2018 08:04 pm
Many people have waited half their lives to see a SCramjet (but not conventional ramjet) before X-43. They need the process (up to X aircraft), not the outcome (to end user). Cancelling SCramjet programs to fund convential ramjet are UNFAIR to them.
Not really. Supersonic combustion was demonstrated at Johns Hopkins in 1960.  It's just very difficult to get any actual net thrust out of it.

Quote from: Katana
Optimizing ramjet technology is even not the RESPONSIBILITY of NASA, but one (of many) choice of defence contractors while defining their products. To go faster? to go smarter and more silent?
The first A in NASA is "Aeronautics," so yes it can be part of their task.
Quote from: Katana
Similar situation above applys to SABRE/Skylon vs. optimized SR71 style turboramjet with Inconel airframe. The latter could certainly go beyond M5, but choosing payload to get PAID is another story.
Actually a bit doubtful. The study on the D-21 to carry a new air breathing engine reckoned it could go to M4.5, but above that they were doubtful the structure could survive. The target of DRACO was to go to M6. Since the D-21 was structurally similar to the SR71 it is likely the SR71's limits would be quite similar.
Interesting to note the X-43 was a pure research program conducted by a tiny team of ex-X30 engineers, not too different from REL as ex-HOTOL engineers.
https://www.amazon.com/Road-Mach-10-Lessons-Research/dp/156347932X
In what way?

X30 blew close to $3Bn and produced nothing. The whole US SCramjet effort has (over 6 decades) swallowed  $10Bn+ in 2018 $ and failed to produced a single operational vehicle.

HOTOL cost less than $10m and paved the way for a step change in Isp and an actually viable SSTO.
In fact REL has no interest in building a "flight demonstrator," they want to build a vehicle they can sell.
That's the difference between companies that want to build products and researchers who want to build research programmes.

$3Bn would have had a full size SABRE running by now.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 04/30/2018 05:42 am
For structure surviveability, airframe design of D-21 with Inconel material of X-15 should be capable of going to speed near X-15.

Also the limitations of airframe is not the limitations of ramjet, you can use any airframe proposed for SABRESkylon demonstrator and fit in a turboramjet.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 04/30/2018 06:28 am
For structure surviveability, airframe design of D-21 with Inconel material of X-15 should be capable of going to speed near X-15.
Possibly. But LH2 is both much colder and much more voluminous than JP7. It's not the materials, it's the actual layout that seems unfriendly to the task.
Quote from: Katana
Also the limitations of airframe is not the limitations of ramjet, you can use any airframe proposed for SABRESkylon demonstrator and fit in a turboramjet.
True. But then you have the limitations of the turboramjet, which are known and not really relevant to this thread.

For some idea of the sort of parameters the FTV might collect here is the initial design study for the SCramjet that crashed the X-15 A2.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19650011864.pdf

I found the issues around collecting valid pressure reading particularly interesting. I wonder how far we've come in 5 decades?
[EDIT
This paper discusses some of the issues of too slow or too low a resolution sampling system

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19850008594.pdf

applied to the Shuttle Orbiter system. ]
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: RanulfC on 05/01/2018 04:06 am
Katana wrote:
Quote
Many people have waited half their lives to see a SCramjet (but not conventional ramjet) before X-43. They need the process (up to X aircraft), not the outcome (to end user). Cancelling SCramjet programs to fund convential ramjet are UNFAIR to them.

I fully understand that people have been 'waiting' for flying Scramjets for 'half-their-lives' and somewhat sympathize but I'll point out while it might SEEM 'unfair' to have their test programs canceled in favor a more proven technology, (and note I and JS19 don't appear to be arguing out-right cancelation but cutting back in favor of broader research and development, exactly the OPPOSITE of what the Scramjet advocates have been pushing for 'half-their-lives') those same people have rather unfairly dedicated their time and effort (lives if you will) to ensuing that the majority of funding, support and effort have in fact been spent on Scramjets to the detriment of any other propulsion scheme.

"Conventional" ramjets "top speed" was felt by the majority of engineers that worked with and on them to be in the mid-hypersonic range where Scramjets were only supposed to be beginning 'effective' operation. And considering there is enough practical evidence that such speeds are very likely to be operationally applicable, (ASALM test article reaching Mach-5.5 with a FIXED inlet design and still accelerating for example) the obvious question is why is there an 'assumption' bias against them in favor of Scramjets? Those people have had almost a decade of Scramjet "flights" at this point so in the nature of 'fairness' shouldn't other propulsion schemes get their chance now?

The thing was, at the time, it was felt that you could not achieve supersonic combustion in a 'ducted' system so there was no incentive to work within the typical 'ramjet' ducting. Something most Scramjet advocates seem to forget that INITIALLY propulsion by "supersonic combustion" was not even the idea behind the researched and developed. It was all about the possible lift the could be generated at very high altitudes and speeds. (Getting to that point either with 'conventional' turbojets/ramjets or rockets mostly) Dumping some fuel into the supersonic airstream would generate lift factors at 100,000ft equivalent to those at 40,000ft per area of lift. What little 'propulsive' effect that could be generated MIGHT offset the drag factors of some 'simple' ducting (short sections of duct offset from the fuselage or wing surface) or the drag-shocks formed by the propellant injection itself but that was about it.

That's STILL 'about it' today as the Scramjet has not proven to be the 'accelerator' engine it's been touted to be. The thing is the 'advocates' still refuse to consider and have in many cases actively fought research and development in any other propulsion system OTHER than Scramjet even when such was specifically directed at a near-or-operational system rather than 'research' work.

Quote
X-51 was designed or at least shaped and pitched as a missile demonstrator. However after flight tests, interest for scramjet missiles in US ceased, including DMRJ and TTRJ programs of OrbitalATK.

Let's be honest, the X-51 was disappointing managing at best to go from Mach-4.8 (booster burn out) to only Mach-5.1 and unable to accelerate further before it ran out of fuel. Such a vehicle being 'pitched' in any form as a "missile demonstrator" concept it going to be rapidly dismissed. NASA's X-43, (also a Boeing design) had hit speeds of up to Mach-9.6, (from the same booster burn out speed mind you) and over double the X-51 altitude, (that's important) and again a CONVENTIONAL fixed-inlet ramjet did Mach-5.5 at 40,000ft so of COURSE the 'requirement' for a Scramjet is going to be questioned. I have little doubt that IF, (big if mind you since the amount 'stated' towards the research and the actual planned spending is VASTLY different) the current (supposed) "possible operational hypersonic weapon system" goes anywhere it will be based on a "conventional" ramjet rather than a Scramjet. (Given that LM absorbed Martin Marietta after all the ones who designed and built the ASALM)

But let's also be honest that Scramjet research and development is actually NOT going away anytime soon:
https://www.c4isrnet.com/industry/2018/01/24/darpa-envisions-a-hybrid-engine-to-reach-hypersonic-speeds/

Despite the switch in main contractor:
http://www.airforcemag.com/Features/Pages/2018/April%202018/Lockheed-Martin-Gets-928-Million-Hypersonic-Missile-Contract.aspx

ARRW, ("Arrow") will be getting about a third of the money, while the DARPA TBG and HAWC programs will be getting the lion's share of the money.
https://breakingdefense.com/2018/03/dod-boosts-hypersonics-136-in-2019-darpa/ (Which by the way is less than a "billion" despite the headlines saying different) And both the HAWK and Advanced Full Range Engine concepts are planned to use Scramjets so saying "interest" has "ceased" is very misleading. It would be better to say that while 'interest' is still there the requirement for actually developing a hypersonic weapon has moved towards using a more practical, near-term propulsion system than the Scramjet. (Considering the "contract" neither specifies a time-frame or any numbers, both of which are listed as 'undefined' I have my doubt that this is actual 'progress'. Especially since they are attaching things like a new multi-service "AI" development center into the mix as a 'requirement' over and above the propulsion system itself)
https://breakingdefense.com/2018/04/usaf-announces-major-new-hypersonic-weapon-contract/
https://breakingdefense.com/2018/04/pentagon-run-ai-center-coming-hypersonics-work-in-progress/
https://breakingdefense.com/2018/04/big-hypersonic-news-coming-faster-progress-likely-roper/

And not exactly enthused about Michael (we know him from the also 'undefined' production and acquisition process behind Constellation) Griffen being the one 'pushing' both the development of 'hypersonic weapons' AND 'streamlining' defense acquisition process.
https://breakingdefense.com/2018/04/whack-7-dod-agencies-hasc-chairs-bill-proposes/

Quote
For structure survivability, airframe design of D-21 with Inconel material of X-15 should be capable of going to speed near X-15.

The D-21 was designed to fly at best around Mach-4, (Mach-3.35-ish listed but seen references to Mach-4 top speed) the X-15 on the other hand was always supposed to hit speeds in excess of Mach-5. Oddly enough the "X-20" was initially proposed to research speeds from Mach-6+ (where the X-15 program was supposed to top out) to Mach-20 but went from test vehicle to prototype vehicle as participants in the program dropped to just the Air Force who had to 'justify' it as a weapons system. Notably "RATTLRS" (http://www.designation-systems.net/dusrm/app4/rattlrs.html) was supposed to be only Mach-3 yet has a form more suited to much higher speeds.

Quote
Also the limitations of airframe is not the limitations of ramjet, you can use any airframe proposed for SABRE/Skylon demonstrator and fit in a turboramjet.

For what purpose? Granted a turboramjet 'could' hit speeds in excess of Mach-5, (Mardquart tests in the early 60s showed a 'free-wheeling' compressor system could survive up to Mach-6 for short periods) the entire exercise is to test deep-cooling and the use of the SABRE flow-path and concept so having a 'turboramjet' onboard makes no sense. SABRE has a rocket whereas a turboramjet does not. We still talking a possible applications towards an "operational" vehicle? That would strictly depend on the airframe ability to accept different engines for different tests.

Randy
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/01/2018 05:05 pm
Katana wrote:
I fully understand that people have been 'waiting' for flying Scramjets for 'half-their-lives' and somewhat sympathize but I'll point out while it might SEEM 'unfair' to have their test programs canceled in favor a more proven technology, (and note I and JS19 don't appear to be arguing out-right cancelation but cutting back in favor of broader research and development, exactly the OPPOSITE of what the Scramjet advocates have been pushing for 'half-their-lives') those same people have rather unfairly dedicated their time and effort (lives if you will) to ensuing that the majority of funding, support and effort have in fact been spent on Scramjets to the detriment of any other propulsion scheme.
Indeed. IMHO there are a number of groups who could benefit from more basic data with which to refine their models/hardware.
Quote from: RanulfC
The thing was, at the time, it was felt that you could not achieve supersonic combustion in a 'ducted' system so there was no incentive to work within the typical 'ramjet' ducting. Something most Scramjet advocates seem to forget that INITIALLY propulsion by "supersonic combustion" was not even the idea behind the researched and developed. It was all about the possible lift the could be generated at very high altitudes and speeds. (Getting to that point either with 'conventional' turbojets/ramjets or rockets mostly) Dumping some fuel into the supersonic airstream would generate lift factors at 100,000ft equivalent to those at 40,000ft per area of lift. What little 'propulsive' effect that could be generated MIGHT offset the drag factors of some 'simple' ducting (short sections of duct offset from the fuselage or wing surface) or the drag-shocks formed by the propellant injection itself but that was about it.
That is a very interesting side light on the history of the subject.
Quote from: RanulfC
That's STILL 'about it' today as the Scramjet has not proven to be the 'accelerator' engine it's been touted to be. The thing is the 'advocates' still refuse to consider and have in many cases actively fought research and development in any other propulsion system OTHER than Scramjet even when such was specifically directed at a near-or-operational system rather than 'research' work.
I've not seen a SCramjet that reached operating speed on anything but a damm big rocket.

Quote from: RanulfC
Let's be honest, the X-51 was disappointing managing at best to go from Mach-4.8 (booster burn out) to only Mach-5.1 and unable to accelerate further before it ran out of fuel. Such a vehicle being 'pitched' in any form as a "missile demonstrator" concept it going to be rapidly dismissed. NASA's X-43, (also a Boeing design) had hit speeds of up to Mach-9.6, (from the same booster burn out speed mind you) and over double the X-51 altitude, (that's important) and again a CONVENTIONAL fixed-inlet ramjet did Mach-5.5 at 40,000ft so of COURSE the 'requirement' for a Scramjet is going to be questioned. I have little doubt that IF, (big if mind you since the amount 'stated' towards the research and the actual planned spending is VASTLY different) the current (supposed) "possible operational hypersonic weapon system" goes anywhere it will be based on a "conventional" ramjet rather than a Scramjet. (Given that LM absorbed Martin Marietta after all the ones who designed and built the ASALM)
Agreed. And I'll bet LM are very careful to phrase things with enough get outs to do so.
But this is pretty  OT for the goal of this thread.

Quote from: RanulfC
And not exactly enthused about Michael (we know him from the also 'undefined' production and acquisition process behind Constellation) Griffen being the one 'pushing' both the development of 'hypersonic weapons' AND 'streamlining' defense acquisition process.
https://breakingdefense.com/2018/04/whack-7-dod-agencies-hasc-chairs-bill-proposes/
True. But close to a billion is way more than the usual DARPA grant funding. It actually sounds like they want to build some hardware.  [EDIT Isn't that more like a Phaase 3 award size? ]

Quote from: RanulfC
The D-21 was designed to fly at best around Mach-4, (Mach-3.35-ish listed but seen references to Mach-4 top speed) the X-15 on the other hand was always supposed to hit speeds in excess of Mach-5. Oddly enough the "X-20" was initially proposed to research speeds from Mach-6+ (where the X-15 program was supposed to top out) to Mach-20 but went from test vehicle to prototype vehicle as participants in the program dropped to just the Air Force who had to 'justify' it as a weapons system. Notably "RATTLRS" (http://www.designation-systems.net/dusrm/app4/rattlrs.html) was supposed to be only Mach-3 yet has a form more suited to much higher speeds.
The DRACO study I quoted seemed pretty confident of M4.5. M5.0+ was pushing it. Pushing it 1.5x its design speed is (I think) pretty good. Pushing it 2x? That's like Peace Jack saying "Yeah. Phantom II can do M4. No worries," while anyone who actually knew about structures is thinking "This is going to be trouble." :-(

Quote from: RanulfC
For what purpose? Granted a turboramjet 'could' hit speeds in excess of Mach-5, (Mardquart tests in the early 60s showed a 'free-wheeling' compressor system could survive up to Mach-6 for short periods) the entire exercise is to test deep-cooling and the use of the SABRE flow-path and concept so having a 'turboramjet' onboard makes no sense. SABRE has a rocket whereas a turboramjet does not. We still talking a possible applications towards an "operational" vehicle? That would strictly depend on the airframe ability to accept different engines for different tests.
I think he may be.

I'm thinking in terms of a traditional X programme. Maybe the demo engine is close to viable as a saleable product, but it's goal is to drive the data to design the full scale SABREs, LAPCATs, etc.

The vehicles key goal should remain "Fly the SKYLON trajectory AFAP and do so beyond AB/rocket transition until the rocket has got stable combustion."
Obviously the closer you can match that profile the better for Skylon (or other SABRE LV) concepts.
an "extended" goal would be to see how far you can push the envelope beyond that, given how every m/s in the booster gets you closer to orbit and (assuming a TSTO) one less for the US to produce (at the US trade rate of 1Kg of stage mass gain --> 1Kg of payload loss).

I also think the FTV can help with those "Shouldn't be a problem, but" areas.

I'm thinking of things like automated propellant fill and drain, ideally through the wheel wells to reduce the number of openings in the TPS. Propellant sub cooling (to improve range) and eliminate boil off (or perhaps it should be designed from the start for ZBO over a 2 hour hold period).
Likewise (possibly) upgrading to water cooled brakes with a functional test of the system. Potentially a vehicle ending experiment but very useful for the follow on programme given the substantial mass of brake systems (cutting 500Kg from the dead weigh of an A380 over it's 30 year operating life...)
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/01/2018 05:35 pm
Getting more directly back on topic.

My ROM for the vehicle and total propellant is 23500 Kg (excluding the engine but not the nacelle or pylon mass)

What I don't think people realize is how big that makes it with LH2.

Assuming SABRE 4 cycle REL reckon LH2 use is 2x usual O/F ratio. O/F for LO2/LH2 is somewhere between 5 and 6 to 1. So SABRE 4 shifts that to something like 5 or 6 to 2.

So assuming 6 to 2 (or 3 to 1) and 12tonnes of propellant to keep the math simple that's 9t of LO2 to 3t of LH2.

But that's 7.5m^3 (assuming LO2 subcooled to 1200Kg/m^3) but nearly 39 m^3 for the LH2 at 77Kg/m^3
Assuming the fuselage is road transportable at 14 feet in dia that gives 14.3 m^2.
That gives a LOX cylinder 0.53m long and a LH2 cylinder 2.73m long. That's 10.5ft long in total.
Of course with tank ends and wrapping it in a Sears-Haacke body that will be considerably longer. Likewise I'd assume the LH2 tank will be split with the LO2 tank in the middle for CoG control.

Note this is for a FTV that's a bit <50% structure, but Skylon is more like 25% structure, significantly increasing propellant load, but making the structural issues harder (Eyes on the prize. The #1 goal is engine and inlet testing. Structural verification would be a nice-to-have).

The questions are
a) Can you wrap a fuselage and wings around this (and the nacelle and pylon) in less than 11.5t?
b) What sort of flight duration could you manage?
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 05/03/2018 12:00 am
The biggest problem about a M6 vehicle is no customer really needs it, either for recon aircraft or strike missile. The absence of real need and real programs left the area to be occupied by SCramjet researchers who only want to build research programs.

For old ramjet / turboramjet, they are capable to reach M6 with moderate cost. But choice of whether to use them are decided by weapon manufacturers, they favor smart and stealth subsonic systems instead of going stupidly fast and hot.

Scramjet behaves even worse, but could be justified as a fancy research program and pushed by interest groups behind it. The more fancy and impractical, the more possibility of getting funded when there is no real customer need to achieve.

Same problem exists for SABRESkylon if REL want to sell the vehicle, though considering customer need too early may spoil the test vehicle.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 05/03/2018 12:07 am
Getting more directly back on topic.

My ROM for the vehicle and total propellant is 23500 Kg (excluding the engine but not the nacelle or pylon mass)

What I don't think people realize is how big that makes it with LH2.

Assuming SABRE 4 cycle REL reckon LH2 use is 2x usual O/F ratio. O/F for LO2/LH2 is somewhere between 5 and 6 to 1. So SABRE 4 shifts that to something like 5 or 6 to 2.

So assuming 6 to 2 (or 3 to 1) and 12tonnes of propellant to keep the math simple that's 9t of LO2 to 3t of LH2.

But that's 7.5m^3 (assuming LO2 subcooled to 1200Kg/m^3) but nearly 39 m^3 for the LH2 at 77Kg/m^3
Assuming the fuselage is road transportable at 14 feet in dia that gives 14.3 m^2.
That gives a LOX cylinder 0.53m long and a LH2 cylinder 2.73m long. That's 10.5ft long in total.
Of course with tank ends and wrapping it in a Sears-Haacke body that will be considerably longer. Likewise I'd assume the LH2 tank will be split with the LO2 tank in the middle for CoG control.

Note this is for a FTV that's a bit <50% structure, but Skylon is more like 25% structure, significantly increasing propellant load, but making the structural issues harder (Eyes on the prize. The #1 goal is engine and inlet testing. Structural verification would be a nice-to-have).

The questions are
a) Can you wrap a fuselage and wings around this (and the nacelle and pylon) in less than 11.5t?
b) What sort of flight duration could you manage?

Between X7 and D21: BOMARC / SR71 /original Skylon style. Wing mounted engines, and central fuselege almost fully occupied by tanks.

Virtually strech a LH2 rocket stage with boosters and add wings.

More basic question than flight duration: top speed.

Going barely to M5 in airbreathing mode does not even need LOX, but has little customer value.

Testing of rocket mode may push the vehicle to M8~10 and change everythig, but could push the program more to TSTO systems, even to candidate of XS1.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/03/2018 06:14 am
Virtually strech a LH2 rocket stage with boosters and add wings.

More basic question than flight duration: top speed.

Going barely to M5 in airbreathing mode does not even need LOX, but has little customer value.
Actually it would have very limited value to REL either.
AFAIK REL does not have the facilities on the ground to demonstrate air breathing to rocket transition on the ground.
Quote from: Katana
Testing of rocket mode may push the vehicle to M8~10 and change everythig, but could push the program more to TSTO systems, even to candidate of XS1.
The number 1 purpose of this vehicle is to demonstrate the parts of the SABRE cycle that are different from a  conventional rocket engine and to gather data to help REL design any future engine.
Once that is achieved then in principal however high a Mach number it operates too is a problem of Nacelle and aerodynamics and materials design. The engine is running entirely on internal propellants by then.

This is not a development programme for a vehicle. When I refer to customers I mean research groups who would like to use it to gather data over part of the flight path.
What data they might want, and what features they might like in the vehicle to collect it, are very on topic for this thread.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 05/03/2018 01:01 pm
Flight profile 1: airbreathing to M5, rocket to M7~10, reentry.
Flight profile 2: airbreathing to M5, rocket to M7~10, rocket deceleration to M5, reentry.

BTW is it possible for SABRE to operate in VTVL mode without wings?
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/03/2018 04:36 pm
BTW is it possible for SABRE to operate in VTVL mode without wings?
In principle yes.

Why would you want to?
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 05/04/2018 09:58 am
BTW is it possible for SABRE to operate in VTVL mode without wings?
In principle yes.

Why would you want to?
Use rocket style airframe to simplify early tests.
Core fuel tank + side "booster" mounted engine nacelles.
Could be done soon when engines are ready, compared to typical time cost of M3+ aircrafts.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/04/2018 05:31 pm
Use rocket style airframe to simplify early tests.
Core fuel tank + side "booster" mounted engine nacelles.
Could be done soon when engines are ready, compared to typical time cost of M3+ aircrafts.
It's often said that rocket stages are not leggo and that you can't mix and match stages to create new vehicles. You seem to want to turn the X-7 drone into a VTO rocket.

The theoretical cost savings of this are counterbalanced by
a) Massively asymmetrical thrust, needing a fairly heavy thrust structure.
b) No aerodynamic lift to reduce those propellant mass loads, which are now at 180deg to thrust, not 90deg.
c) In HTOL Thrust (for supersonic aircraft) is 0.5-0.7xGTOW. For this it will need to be at least 1.15xGTOW
   IE 15-17.39tonnes, instead of the more like 28tonnes a HTOL vehicle would have available.
d) The trajectory will be nothing like that all known SABRE using concepts need to have validated.
e) If you're planning on a powered vertical landing you've lost even more of your GTOW to landing propellant. So

IOW what you might save on costs you lose on a vehicle that contributes very little to the big picture in engine or vehicle design.

There is an outside chance that cost might trump everything and a VTOL vehicle could carry enough propellant to take off, accelerate to the transition point and past it, then come back to land.

But I strongly doubt it.  :(

Anything less would not be worth the effort, as engine operation to that point can already be demonstrated on the ground.

I'd point out that a significant fraction of the cost of a new aircraft are the systems designed specifically for that aircraft.  28tonnes is in the range of a heavy fighter or a light regional airliners (like the Bombardier C series).

While I'd like a FTV to retire the risk of some of the systems in Skylon they don't have to exist first before it can fly. Depending on structural fraction it does not have to use the Skylon construction method. With no effective payload landing gear could be an OTS package. Flight surfaces could be hydraulic, not electric etc. Improving the TRL of all of these is nice to have, but not essential to the design functioning.

In fact the very first question, which I have taken as an article of faith, is can you build a HTOL vehicle around a 20 000 Kgf SABRE engine that will carry enough propellant to get it through the AB transition?
I've been presuming so.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 05/05/2018 06:06 am
Use rocket style airframe to simplify early tests.
Core fuel tank + side "booster" mounted engine nacelles.
Could be done soon when engines are ready, compared to typical time cost of M3+ aircrafts.
It's often said that rocket stages are not leggo and that you can't mix and match stages to create new vehicles. You seem to want to turn the X-7 drone into a VTO rocket.

The theoretical cost savings of this are counterbalanced by
a) Massively asymmetrical thrust, needing a fairly heavy thrust structure.
b) No aerodynamic lift to reduce those propellant mass loads, which are now at 180deg to thrust, not 90deg.
c) In HTOL Thrust (for supersonic aircraft) is 0.5-0.7xGTOW. For this it will need to be at least 1.15xGTOW
   IE 15-17.39tonnes, instead of the more like 28tonnes a HTOL vehicle would have available.
d) The trajectory will be nothing like that all known SABRE using concepts need to have validated.
e) If you're planning on a powered vertical landing you've lost even more of your GTOW to landing propellant. So

IOW what you might save on costs you lose on a vehicle that contributes very little to the big picture in engine or vehicle design.

There is an outside chance that cost might trump everything and a VTOL vehicle could carry enough propellant to take off, accelerate to the transition point and past it, then come back to land.

But I strongly doubt it.  :(

Anything less would not be worth the effort, as engine operation to that point can already be demonstrated on the ground.

I'd point out that a significant fraction of the cost of a new aircraft are the systems designed specifically for that aircraft.  28tonnes is in the range of a heavy fighter or a light regional airliners (like the Bombardier C series).

While I'd like a FTV to retire the risk of some of the systems in Skylon they don't have to exist first before it can fly. Depending on structural fraction it does not have to use the Skylon construction method. With no effective payload landing gear could be an OTS package. Flight surfaces could be hydraulic, not electric etc. Improving the TRL of all of these is nice to have, but not essential to the design functioning.

In fact the very first question, which I have taken as an article of faith, is can you build a HTOL vehicle around a 20 000 Kgf SABRE engine that will carry enough propellant to get it through the AB transition?
I've been presuming so.
Two booster engines to be symmetrical like conventional rockets with strap on boosters, nothing related to X7.

The X7 airframe may work up to M6, but would be infeasible for rocket mode operation to M10.

Even without VTOL, the vehicle need to be symmetrical in rocket mode, which exclude X7 and favors BOMARC/ SR71/ original Skylon.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/05/2018 10:08 am
Two booster engines to be symmetrical like conventional rockets with strap on boosters, nothing related to X7.
Are you saying you think REL would build two flight engines or two rocket engines?
Quote from: Katana
The X7 airframe may work up to M6, but would be infeasible for rocket mode operation to M10.
I'm talking about the X7 layout which is basically the same as the M2 Firebee II drone and Hound Dog missiles.
Quote from: Katana
Even without VTOL, the vehicle need to be symmetrical in rocket mode, which exclude X7 and favors BOMARC/ SR71/ original Skylon.
There have been a number of asymmetric thrust rocket concepts, IIRC one of the NLS designs for example.

I think everyone would prefer a symmetric vehicle wheather it looked like Skylon or not. Thrust is more balanced, there are more engine placement options and you have redundancy, which is important given the new engine has unknown reliability statistics (something else flight testing will discover).

It's wheather the budget will be available to allow it.  :( The minimal assumption is there will be enough for one engine, not two, so what can you do with that one engine?

Incidentally it turns out that through the 1970's and 80's NASA ran a number of studies for such an aircraft in the 40-60 000lb range as the "High Speed" or "Hypersonic Speed" Research Aircraft, partly to try out the various possible structural concepts they had seen on a scale that would give them a realistic test of the structural issues of a large aircraft.

They reckoned you could build a baseline aircraft out of fairly conventional Aluminium with active water/glycol cooling good at least to M6.

My instinct is for a passive heat pipes to move heat, eliminating the need for pumps and the large  numbers of fluid connectors that have to stay fluid tight over a very wide range of temperatures and pressures covering the wings and fuselage. I don't think their complexity was ever really addressed and it's a non trivial problem to solve.

Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: knowles2 on 05/05/2018 11:25 am
I wasn't sure if this should go in "Advance Concepts" or "Commercial" with the main SABRESkylon thread, but it's not meant to be a product and it' would certainly be advanced.  :)

REL have talked about the idea of a "Flight Test Vehicle" on a couple of occasions. Earlier ideas were for a scaled down Skylon, running LOX/Methane rockets while the current design, resembles the D-21 M3 reconnaissance  drone designed to launch off the back of a couple of modified SR71s in hte late 60's. then modified with a booster longer than the drone, was tested off a modified B52, before the whole project was cancelled.

However looking through the archives I located this.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000004765.pdf
and this.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990110312.pdf

Basically a late 90's plan to modify a couple of D-21 to demonstrate the "DRACO" Rock Based Combined Cycle engine some NASA centers were working on.  This system has multiple mode transitions in its flight trajectory and also featured a moving inlet spike to accommodate the speed changes.

In the process the second one discusses the D-21 in some detail, along with the LM Advanced Projects "Experimental Prototype" approach to cutting the development cost by about 1/3 (page 35 if you're interested).

Interestingly they reckoned you could  add a LOX tank between the fuel wing tanks and the engine duct, and they didn't think it would have thermal issues, although once you got above M3.5 the titanium skin and duct leading edge looked doubtful. Interestingly the issue around the LOX tank was not temperature related but pressurization. The D-21 was designed to operate its fuel tanks (there were 3, front, middle and back cross ways) at 1.5psi above the ambient pressure. Pressurizing the tanks to make the engine pressure fed was viewed as too dangerous.

On the upside the REL FTV is a clean sheet design with a thrust about 29x bigger than the D-21 ramjet. (Marquardt RJ43-MA-20S4) and recovery and reuse will be designed in from day one.

Beyond that we have a few data points.

The SABRE test engine is expected to have a thrust of 20 tonnes (44 000lbf) and according to the SEI study on the USAF TSTO design thrust needs to be at least 70% of GTOW, giving about 28500Kg of mass.

SABRE's T/W ratio is expected to be 14:1 so engine mass is say 1430Kg.
The D21 dry mass 5500lb vs fully loaded at 11200lb means it was 49% structure. It was stressed to withstand -2/+5g in both axial and directions normal to axial. So a lower peak acceleration should give a lighter structure.

28,500-1,430kg is a total mass of 27,070Kg. A 15% mass growth allowance means the maximum mass (structure and propellant) is 23,539Kg.

To put this in perspective 30tonnes is a small(ish) regional airliner or a large(ish) fighter aircraft.

My instinct is this layout is not a good fit to the issues around LH2 as a fuel, hence my interest in wheather it would be possible to make 2 engines and go with a "Mini Skylon" airframe.

Given the D-21 is going to be REL's FTV design to test inlet design and spike schedule what does that say about its capabilities?


My instinct is REL can go one of two ways on this.

A "bare bones" X-plane approach.
This is totally focused on flying SABRE through as much of its trajectory as possible and refining the inlet and spike performance to meet its goals. The vehicle structure is as simple as possible to do that.  Not intended to be anywhere close to deliver a substantial payload to orbit, or a 2nd stage to release.

A "Skylon risk retirement" approach.
This implements the FTV in technologies more like those planned for Skylon. IE a truss framework with appropriate levels of MLI and the SiC reinforced ceramic skin fabricated in corrugated panels.

Both options can help retire a number of operations features of a Skylon as well. EG fully automated fueling and de-fueling, although that would not be necessary for early tests. Likewise early tests could treat it as an RPV flown from a ground station, before moving to fully AGV status.

the big question would be what else  could it be used for ? What sort of things would 3rd parties like to test, and what sorts of instrumentation would they want to install to do so?
It all about funding, if REL can go for the mini skylon concept then they will because it means they go from mini to full scale pretty quickly.

But if they don't have the money for that they will knock up the cheapest vehicle they can to test their engine. Which will most likely be something that complete avoids anything use or developed in the US to avoid Itar.

Thing is they are a engine seller, they aren't interesting in building the actual craft, at least not yet, so all they need is something that proves the engines flies and at least make to sub orbit. You should be able to knock something up that does that for less than a 100 million.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: knowles2 on 05/05/2018 11:41 am
Quote
BAE are the steering force now in this, their actual percentage is pretty irrelevant but itís big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isnít civilian.
They are working with DARPA because they are willing to pay for testing of their pre cooler in a hypersonic tunnel. They are hoping this piece of data along with the other testing going on in the UK over the next 2-3 years that will unlock serious money either from BAE/Boeing/RR or from other investment funds around the UK, they want to avoid taking as much US money as possible to avoid getting entangled in ITAR. They

An Reaction Engines is just creating the engine, they want to sale that engine to anyone that wants one, if that includes the military then so be it, they aren't fuss, as long as no this top secret, classified,can't talk to anyone about it type restrictions are place on the program. In a ideal world they would want the military and civilian companies to buy their engines to mount of their own vehicles. Just like RR does.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: JCRM on 05/05/2018 11:37 pm
The form a test vehicle takes will depend on the requirements behind the funding.

REL worked on FSPLUK which if funded may provide a flight tested vehicle that could fly a SABRE.

But I can't see anyone funding a pure SABRE test vehicle until SABRE has been tested. BAe's initial estimates for a test vehicle was 1 billion

The Darpa funding has a potential phase 3, which covers flight testing (It also explicitly mentions dual use - civilian and military).

Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: knowles2 on 05/06/2018 12:52 am
The form a test vehicle takes will depend on the requirements behind the funding.

REL worked on FSPLUK which if funded may provide a flight tested vehicle that could fly a SABRE.

But I can't see anyone funding a pure SABRE test vehicle until SABRE has been tested. BAe's initial estimates for a test vehicle was 1 billion

The Darpa funding has a potential phase 3, which covers flight testing (It also explicitly mentions dual use - civilian and military).
BAE works on military funding scales, if they say it will cost a billion, a non military contractor probably could so it for a fraction of that price.

The vehicle only have to be something similar to SpaceshipOne,. Which cost around a 100 million dollars, even taking inflation into account it hard to get to BAE figure of a billion quid for a demonstrator vehicle.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Katana on 05/06/2018 05:26 am
Two booster engines to be symmetrical like conventional rockets with strap on boosters, nothing related to X7.
Are you saying you think REL would build two flight engines or two rocket engines?
Quote from: Katana
The X7 airframe may work up to M6, but would be infeasible for rocket mode operation to M10.
I'm talking about the X7 layout which is basically the same as the M2 Firebee II drone and Hound Dog missiles.
Quote from: Katana
Even without VTOL, the vehicle need to be symmetrical in rocket mode, which exclude X7 and favors BOMARC/ SR71/ original Skylon.
There have been a number of asymmetric thrust rocket concepts, IIRC one of the NLS designs for example.

I think everyone would prefer a symmetric vehicle wheather it looked like Skylon or not. Thrust is more balanced, there are more engine placement options and you have redundancy, which is important given the new engine has unknown reliability statistics (something else flight testing will discover).

It's wheather the budget will be available to allow it.  :( The minimal assumption is there will be enough for one engine, not two, so what can you do with that one engine?

Incidentally it turns out that through the 1970's and 80's NASA ran a number of studies for such an aircraft in the 40-60 000lb range as the "High Speed" or "Hypersonic Speed" Research Aircraft, partly to try out the various possible structural concepts they had seen on a scale that would give them a realistic test of the structural issues of a large aircraft.

They reckoned you could build a baseline aircraft out of fairly conventional Aluminium with active water/glycol cooling good at least to M6.

My instinct is for a passive heat pipes to move heat, eliminating the need for pumps and the large  numbers of fluid connectors that have to stay fluid tight over a very wide range of temperatures and pressures covering the wings and fuselage. I don't think their complexity was ever really addressed and it's a non trivial problem to solve.
Why you think REL can't afford to build two engines , for a test vehicle?

Building several more copies per batch only add minor cost to R&D. In fact they are really needed for backup, in case of damaging.

Solving the asymmetrical thrust problem needs additional procedures, which becomes really expensive.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/06/2018 06:08 am
Why you think REL can't afford to build two engines , for a test vehicle?

Building several more copies per batch only add minor cost to R&D. In fact they are really needed for backup, in case of damaging.

Solving the asymmetrical thrust problem needs additional procedures, which becomes really expensive.
Because the last REL presentation I've seen showed a test vehicle looking like a D-21 drone, whereas earlier ones (designed to fine tune the inlet design) was more Skylon like.  Historical learning curves for aircraft production are that when you double the number of items you drop the cost by 15%.

That said I would expect the precooler would be a 3rd generation unit ( the test stand ones in Colorado and the TF1 stand being the first two generations). The rest would be the second full  iteration of the design.

Pending an announcement from REL the conservative view is they are going to build one flight weight engine to test fly.  :(
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/06/2018 06:24 am
BAE works on military funding scales, if they say it will cost a billion, a non military contractor probably could so it for a fraction of that price.

The vehicle only have to be something similar to SpaceshipOne,. Which cost around a 100 million dollars, even taking inflation into account it hard to get to BAE figure of a billion quid for a demonstrator vehicle.
This is where it gets complicated. BAe is an investor (and having  an airframe mfg already was a late changed condition of the UK govt grant contract to REL)

TBH I don't believe there are any existing airframe mfgs with experience of the materials REL have baselined for the Skylon airframe, so the fact that BAe is a large military contractor is not a plus point. It basically means they are great at the paperwork of a government contract, like the F35.

No doubt the UK govt were persuaded that having someone who could design such a vehicle would "reduce risk" in their investment.

Personally I would have preferred someone who still built commercial jet aircraft (Bombardier in Belfast for example), but UK "industrial" policy (much like US DoD policy) mashed them all together (along with small arms, artillery, submarines, torpedoes and armored fighting vehicle makers) into BAe.  :(

[EDIT For those curious of what what some of the issue of a hypersonic vehicle are this is a NASA roundup paper of some of the issues (and ways to handle them) from 1968. Note a structural fraction of 25% for hypersonic aircraft was viewed as achievable without the use of a truss structure.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680017975.pdf

What has changed? Well FSW for metal joining, much cheaper  high resolution NDE of parts. Wider experience of diffusion bonding. Maximum operating temperature for some plastics exceeding 250c and some up to 350c. ]
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 05/21/2018 09:20 am
One problem area for space planes is the hydraulic system. Servicing the one on the Shuttle was a major PITA and needed a dedicated pump to stop it freezing.

All electric actuation looks to be less troublesome, given the wide thermal and pressure operating ranges the control system needs to operate over.  It is already standard on the Vega solid rocket and seems to have worked fine for main nozzle TVC, which calls for a fairly high thrust, high speed (but low angle) drive system. Likewise the X37b seems to be all electric, including all the landing gear associated equipment.

With this in mind I found a British PhD thesis  sponsored by landing gear mfg Messier Dowty (part of Saffran) on health monitoring for electrically actuated landing gear.

https://www.research.manchester.ac.uk/portal/files/54520238/FULL_TEXT.PDF

It mentions a £10m programme funded by the UK Dept of Trade & Industry called ELGEAR targetting this specific area.

Here is a presentation by Messier Dowty's parent company Saffran on the idea of electric landing gear, including brakes and steering.
http://www.icas.org/media/pdf/Workshops/2013/ICAS%20-%20Recent%20Advances%20and%20Future%20Electrical%20Landing%20Gear%20Systems%20Publish.pdf

This is paper from China on some of the detailed issues around this task and some of the type of electric motors that could be used.

http://www.icas.org/ICAS_ARCHIVE/ICAS2012/PAPERS/109.PDF

IMHO it would be easier to route electric cabling and cool EMA's than develop high temperature hydraulic actuators, their associated fluid and pump package. 
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 07/16/2018 08:35 pm
Why you think REL can't afford to build two engines , for a test vehicle?

Building several more copies per batch only add minor cost to R&D. In fact they are really needed for backup, in case of damaging.

Solving the asymmetrical thrust problem needs additional procedures, which becomes really expensive.
I'd agree.  A two engine vehicle just seems much easier to deal with, in terms of air flow and thrust and CoG shifts.

But the latest renderings show a single engine vehicle.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: knowles2 on 07/24/2018 02:29 pm
The UK has just announce it building a new fighter the tempest.

I think Reaction Engine can squeeze a bit of money out of this program. It could provide a continuous revenue stream by getting rolls royce to adopt it pre coolers for the fighter engine.

 Reaction Engine do claim they offer a lot of advantages,  https://www.reactionengines.co.uk/sabre/pre-cooled-turbojet.

This is Roll Royce video on the new engine https://www.youtube.com/watch?v=X8kTZ9I8f_U
Could the guy fit any more buzz words in this video! Improve thermal management is one of Reaction Engine claims through.
 
Also nearly all the partners involve in Tempest are now also actively involved in Reaction Engine.

I'm taking a little guess here but to be a truly next gen aircraft the Tempest will be base on a all electrical system. incorporate electrical landing gears and replace most of hydraulic systems with electrical systems, which should produce plenty of transferable knowledge to incorporate those technologies into skylon. 

Also could reaction engines take advantage of Project Magma https://www.baesystems.com/en/article/first-magma-flight-trials to further lighten skylon?

Project Tempest if the UK truly wants a true 6th gen aircraft, should mature all of these technologies making them cheaper to integrate them into Skylon and produce a even lighter vehicle and may be even a simpler spacecraft to build as well.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Star One on 07/24/2018 03:02 pm
The UK has just announce it building a new fighter the tempest.

I think Reaction Engine can squeeze a bit of money out of this program. It could provide a continuous revenue stream by getting rolls royce to adopt it pre coolers for the fighter engine.

 Reaction Engine do claim they offer a lot of advantages,  https://www.reactionengines.co.uk/sabre/pre-cooled-turbojet.

This is Roll Royce video on the new engine https://www.youtube.com/watch?v=X8kTZ9I8f_U
Could the guy fit any more buzz words in this video! Improve thermal management is one of Reaction Engine claims through.
 
Also nearly all the partners involve in Tempest are now also actively involved in Reaction Engine.

I'm taking a little guess here but to be a truly next gen aircraft the Tempest will be base on a all electrical system. incorporate electrical landing gears and replace most of hydraulic systems with electrical systems, which should produce plenty of transferable knowledge to incorporate those technologies into skylon. 

Also could reaction engines take advantage of Project Magma https://www.baesystems.com/en/article/first-magma-flight-trials to further lighten skylon?

Project Tempest if the UK truly wants a true 6th gen aircraft, should mature all of these technologies making them cheaper to integrate them into Skylon and produce a even lighter vehicle and may be even a simpler spacecraft to build as well.

None of this will happen as Tempest is designed to be sixth generation on a budget. Like with the B-21 in the US the rapid capabilities office running this program is looking to use off the shelf technologies as much as possible.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 07/24/2018 07:15 pm
The UK has just announce it building a new fighter the tempest.

I think Reaction Engine can squeeze a bit of money out of this program. It could provide a continuous revenue stream by getting rolls royce to adopt it pre coolers for the fighter engine.

 Reaction Engine do claim they offer a lot of advantages,  https://www.reactionengines.co.uk/sabre/pre-cooled-turbojet.


Could the guy fit any more buzz words in this video! Improve thermal management is one of Reaction Engine claims through.
Indeed. I call "House" on the Buzzword Bingo.  :)
However...
I think electric actuation is a technology that Skylon could use well and is becoming more mature. For the FTV I'm not sure if anything more than batteries would be needed (that are several decades more advanced than the ones planned for the DRACO conversion of the D-21). BTW the big points of what he was talking about are
1) Direct bonding of the magnets to the shaft, a more "unitized" construction
2) Magnets cease to work above their Curie Point, so putting those magnets deep inside the engine means magnet alloys that can operate at high (or higher) temperature.
 
Quote from: knowles2
Also nearly all the partners involve in Tempest are now also actively involved in Reaction Engine.

I'm taking a little guess here but to be a truly next gen aircraft the Tempest will be base on a all electrical system. incorporate electrical landing gears and replace most of hydraulic systems with electrical systems, which should produce plenty of transferable knowledge to incorporate those technologies into skylon. 
Quite likely.
 
Quote from: knowles2
Also could reaction engines take advantage of Project Magma https://www.baesystems.com/en/article/first-magma-flight-trials to further lighten skylon?

Project Tempest if the UK truly wants a true 6th gen aircraft, should mature all of these technologies making them cheaper to integrate them into Skylon and produce a even lighter vehicle and may be even a simpler spacecraft to build as well.
This is rather more doubtful.
"Boundary Layer Control" or "blown flaps" have been demonstrated since the 1950's. The classic example was the "Buccaneer" (probably the closest to the Douglas A4 Skyhawk).

BLC allowed the Buccaneer wing to be 50% smaller that designs with similar specs. This is attractive. OTOH it took a substantial fraction of the engine thrust to do so and of course if the engine fails the consequences are serious. OTOH the wing mass reduction is significant. The question is wheather it is significant enough? [EDIT IE does the reduced vehicle dry mass outweigh the increased risk of losing the payload if there is an engine failure? ]

Fluidic controls are even more problematical if you've already gone to electric actuators.

Where you draw the line is a very tricky question. Necessary innovation (because you can't make the design work without it) versus unnecessary innovation, that adds cost, technical risk and potential delays.



Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: t43562 on 08/02/2018 01:50 am

Fluidic controls are even more problematical if you've already gone to electric actuators.

Where you draw the line is a very tricky question. Necessary innovation (because you can't make the design work without it) versus unnecessary innovation, that adds cost, technical risk and potential delays.

I saw Magma at the BAE Systems display at Farnborough and had a long chat with the gentleman demonstrating it.  He gave me the fluidic thrust vectoring nozzle for the previous aircraft (DEMON) to compare with the one for MAGMA which was 3D printed.

Both were made from Titanium but the DEMON one was about maybe 2KG and the MAGMA one was at most a couple of hundred grams. It was a great surprise.

I don't know about DEMON but the MAGMA one was "only" 2D and it is something that he says has potential to be included in Tempest.  It's like mouth with an (not quite) elliptical opening shape and there are openings at the top and the bottom for gas to be blown to influence the direction of flow of the exhaust.

My memory is that he said DEMON was over 100kg (140?) but that MAGMA is 20kg empty.   This is partly because they worked out how to supply air from the thrust engine instead of having 2 but perhaps mostly because of the carbon airframe.

MAGMA has conventional controls which are used to supplement the fluidics when larger forces are needed.  I think this shows they can perhaps be backups as well.

One of the big innovations in MAGMA was that they worked out that they couldn't supply more air for control but they could supply it at higher speed (supersonic) and this makes their fluidic controls much more efficient than with DEMON.

The main claim about fluidics from the MAGMA representative was that they are much lower maintenance since only a ball valve moves. The fluidic thrust vectoring is also good for this reason - meaning that whatever craft you have is much more likely to have high availability with this kind of thrust vector rather than a mechanical one.   It also pays for the vectoring system to be light because it makes CoG problems much less onerous.
 
I'm no expert but it just seemed like thrust vectoring a rocket nozzle with airflow would be a huge research project of its own and why would you want to do it for a launch vehicle?

As for replacing ailerons etc they mentioned that it got more challenging with larger aircraft but that the fact that large modern engines (as opposed to their model aircraft ones) had more compressors which might compensate.

That's all I could get - I leave you to judge if anything's applicable to SABRE-powered vehicles.


Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 08/02/2018 07:19 am
I'm no expert but it just seemed like thrust vectoring a rocket nozzle with airflow would be a huge research project of its own and why would you want to do it for a launch vehicle?
You'd be right but this is not how it works.  The flow is run through piping to vent through the trailing edge of the wings. AIUI SABRE thrust chambers, if not the whole nacelle, will swivel.
The point is that this is a research project. I'm very doubtful that this is necessary to make the design close. Plus I'm not sure SABRE has any provision to divert any of its feed air for other purposes. If it does this could be an option. Historical designs have used similar techniques to cut wing size (which lowers drag as well as T/O mass) but it's another dynamic system that becomes a "Criticality 1" system that simply cannot fail.
Quote from: t43562
As for replacing ailerons etc they mentioned that it got more challenging with larger aircraft but that the fact that large modern engines (as opposed to their model aircraft ones) had more compressors which might compensate.

That's all I could get - I leave you to judge if anything's applicable to SABRE-powered vehicles.
Personally I think more could be done with Skylon's wing design. I suspect it is fairly basic in shape and plan. As we move toward construction I think there is room for improvement, while keeping the aerodynamics within the known SoA.

My instinct is the model for this fluidic controls stuff is the acceptance of 2 engine airlines for flight over the oceans. This took a long process of accumulating flight hours to demonstrate the new engines had the reliability to operate for the extended periods needed. It helps this technology can fly in a hybrid configuration, allowing it to accumulate flight hours without failure being catastrophic.

While the current FTV that REL have shown pictures of looks like the Man. U test vehicle I think it adds design issues both to the engine and the vehicle that aren't needed. Conventional controls should be adequate. Also the operating speed range for the FTV and Skylon are way  beyond what the bulk of vehicles fitted with this technology will operate over.  We know aerosurfaces can operate to high Mach numbers, as Buran, Shuttle and the X37b have shown. Outside the atmosphere you need thrusters anyway.
Failure to make fluidic controls work on the FTV at M3+ wouldn't mean they aren't completely viable at 0-M2+, which is pretty much what all military (and < M1 for all civil) aircraft fly at.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: Asteroza on 08/05/2018 11:48 pm
Would fluidic nozzles win versus gimbals and associated structure to accommodate gimbaling? I get a sneaking suspicion that the mass and performance trades are real murky here. For instance, is there enough bleed air from the SABRE compressor to run fluidics? On a more conventional rocket engine, would turbine exhaust work? Shades of the TAN augmented nozzle work in a sense?

For Skylon, the nacelles have a serious bend to them, trying to matching between airflow flight angle and ideal thrust angle, which is probably not insignificant in terms of drag. Could one cheat with fluidics to effectively get more of the nozzle inline with the airflow and have variable thrust angle/trim?
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 08/08/2018 09:50 pm
Would fluidic nozzles win versus gimbals and associated structure to accommodate gimbaling? I get a sneaking suspicion that the mass and performance trades are real murky here.
And you'd be right. Multiplied by the TRL of the technology. Well understood and used many times over the last 60+ years versus (essentially) developed over the last decade with limited funding.

The hardware is not the whole story.  :( You must consider things like the design tools available to design new versions. Mature for mechanical TVC. But for fluidic, with supersonic flows? And bleeding off thrust right during take off?  That could turn a slight engine under performance into a crash (or it might not. The new tech brings greatly increased uncertainty).

Basically your swapping a well understood steering method, with equally well understood design methods, for a new approach that's have very limited hardware validation and a high risk of "Unknown unknowns" when you design and operate it over a range of at least 0-M6

The benefits, in terms of mass reduction and reliability increase by reducing the number of individual parts, would have to be huge to justify the (substantially) greater risk of using it. If they are not it's way more risk of the design not working (and over running on schedule and budget) for just too little gain.
Maybe  it can, but I'm very skeptical the case closes, in which case it would be novelty for novelty's sake, which is always a bad idea.
Quote from: Asteroza
For instance, is there enough bleed air from the SABRE compressor to run fluidics? On a more conventional rocket engine, would turbine exhaust work?
Unknown, and possible, if you can take the 3-5% of propellant diverted to the gas generator. SABRE, is more in the line of staged combustion engines, where everything that goes through the preburner ends up in the combustion chamber.
Quote from: Asteroza
Shades of the TAN augmented nozzle work in a sense?
Not really, that's way too far down stream.
Quote from: Asteroza
For Skylon, the nacelles have a serious bend to them, trying to matching between airflow flight angle and ideal thrust angle, which is probably not insignificant in terms of drag. Could one cheat with fluidics to effectively get more of the nozzle inline with the airflow and have variable thrust angle/trim?
Maybe. Estimates are that this angle was about 14Deg for SABRE 3 but SABRE IV has halved that to about 7 Deg.
Title: Re: Reaction engines Flight Test Vehicle speculation
Post by: john smith 19 on 12/31/2018 07:41 am
HMX supplied a link to the Boeing study for a replacement Shuttle called RASV

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780022223.pdf
Written in the late 70's and assuming technology that would not be available until the late 80's in time for the start of the development programme for a Shuttle replacement by the mid 90's

It's a long read but has a number of nuggets for anyone planning a ground based HTO as written by a company that makes very large aircraft.

The preferred architecture (selected by the client, not Boeing) was a rocket powered wheeled sled to accelerate the SSTO vehicle (at 6 degs to the horizontal) to 220m/s (Skylon takeoff is designed for c180 m/s) before braking through a combination of drag brakes, drag 'chutes and plates pressing onto an unmodified (but long) runway surface

For example.
Running the engines with a zero Net Positive Suction Head LH2 pump reduced vehicle mass by 1588Kg and a 1psi NPSH LO2 pump reduced it by 902Kg, both mostly due to reduced tank mass needed to carry the additional pressure loads. The sensitivities on LO2 tank mass were 101.36 Kg/psi  and 259.59 Kg/psi for the LH2 tank.

Boeing seemed confident that they could carry LO2 in "wet wings" using pin joined spars linking the top and bottom surfaces

Landing gear is the big subsystem mass (3.3% of dry weight, although in a table it's 3.5% of landed weight) and they have some ideas of how to reduce it. Page 33 also gives the detailed landing gear requirements in FAR25, which Boeing planned to meet. Tire design is also considered for both the sled and the orbiter. Tyre cords were still Nylon, today AFAIK they are mostly Kevlar. Note OTS wheels should be good enough for an FTV, testing the viability of a larger tire on the ultimate vehicle would be much more involved.
Boeing did not consider water cooling for Rejected Take Off, and how it could radically lower the T/O mass.

The report also notes that while OMS/RCS individually are quite small, all together they come up more than the landing gear. Even then looking at ways to combine RCS and OMS functions using main propellants rather than hypergolics was being considered.

The report also notes that the APU's of the Shuttle are sized by the power needs of main engine TVC, whereas previous generation engines (F1, J2 and RL10) all had "Accessory drives" to drive hydraulic pumps, creating a more self-contained engine package. It noted that having the SSME's (actually upgraded versions of the Shuttle engines) pump their own hydraulic fluid means a)Much smaller APU, b) Much smaller APU MMH tank.
In terms of FTV/Skylon usage that might translate to eliminating a separate APU/Fuel cell power package and batteries being sufficient for aero surface control and systems power. Rather than gear down the turbine speed for a hydraulic pump (part of what made the Shuttle APU a PITA to service) a directly connected generator or alternator and some power electronics could drive a set of electromechanical actuators directly.

One quite unexpected feature. The nose wheel well is basically buried in the LH2 tank. While there is a a double walled and vented cable conduit run through the LH2 tank the designers don't seem to trust running any hydraulic lines through it. Instead they have a totally separate MMH powered APU driving a small hydraulic pump for braking and steering. Something you'd definitely want to avoid on a modern design.

Primary electrical power is 400Hz 120/220V from alternators as it notes that such systems are 10-30% the mass of DC systems. OTOH they would be more difficult for regenerative control, where you can recover most of the power you used moving something to a far point as it coasts back to its neutral position.

In other ways the report makes for quaint reading. Aircraft hydraulic systems were expected to hit 5000psi by the 80's, which didn't happen till the late 90's, by which time electric or electrohydraulic systems had also appeared. Likewise mounting 12 6 single DOF vibrating string gyros for the IMU in a dodecahedron arrangement (for redundancy), when SoA are ring laser gyros. Much lighter and much more compact.