Author Topic: Reaction engines Flight Test Vehicle speculation  (Read 11798 times)

Offline RanulfC

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #20 on: 04/28/2018 08:43 pm »
Katana wrote:
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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

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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)

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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 :)

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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
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline RanulfC

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #21 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
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #22 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.
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Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #23 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 “speed and Isp requirements” 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.
« Last Edit: 04/29/2018 04:48 pm by Katana »

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #24 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.
« Last Edit: 04/29/2018 05:15 pm by Katana »

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #25 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.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #26 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.
« Last Edit: 04/30/2018 05:49 am by Katana »

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #27 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. ]
« Last Edit: 04/30/2018 04:56 pm by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline RanulfC

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #28 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
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #29 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...)
« Last Edit: 05/02/2018 06:24 am by john smith 19 »
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Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #30 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?
« Last Edit: 05/01/2018 06:00 pm by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #31 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.

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #32 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.
« Last Edit: 05/03/2018 12:18 am by Katana »

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #33 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.
« Last Edit: 05/03/2018 06:46 am by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #34 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?

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #35 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?
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #36 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.

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #37 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.
« Last Edit: 05/04/2018 05:40 pm by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Katana

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #38 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.
« Last Edit: 05/05/2018 06:17 am by Katana »

Offline john smith 19

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Re: Reaction engines Flight Test Vehicle speculation
« Reply #39 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.

« Last Edit: 05/05/2018 10:17 am by john smith 19 »
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