Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 419974 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #180 on: 03/29/2015 09:56 AM »
I'm going to a talk entitled "Precooled propulsion key to 21st century spaceflight" by Richard Varvill of REL tomorrow. I will try and either record audio or make notes to post here, but does anyone have any burning questions that I might attempt to put to him?

Edit - Just realised tomorrows talk will be broadcast live - http://www.develop3dlive.com/d3d-live-stream-gmt/   - starting at ~14:20 GMT

I'll still try and make notes but if people want to better understand what Mr Varvill will be saying it may be better to watch his talk.
This looks interesting but I missed it.

Is there any idea when they will post this years videos?

Failing that can you give a brief outline of key points?
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #181 on: 04/01/2015 12:32 PM »
Re Richard Varville's talk at Develop3D.  I asked them on their Facebook page about the video and they answered:
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Develop3D Yep, all the videos from #D3DLive will be posted online soon. Stay tuned for the release announcement in the coming weeks

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #182 on: 04/01/2015 01:28 PM »
Re Richard Varville's talk at Develop3D.  I asked them on their Facebook page about the video and they answered:
Quote
Develop3D Yep, all the videos from #D3DLive will be posted online soon. Stay tuned for the release announcement in the coming weeks
I'll have to look out for that.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline topsphere

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #183 on: 04/01/2015 01:58 PM »
I'm going to a talk entitled "Precooled propulsion key to 21st century spaceflight" by Richard Varvill of REL tomorrow. I will try and either record audio or make notes to post here, but does anyone have any burning questions that I might attempt to put to him?

Edit - Just realised tomorrows talk will be broadcast live - http://www.develop3dlive.com/d3d-live-stream-gmt/   - starting at ~14:20 GMT

I'll still try and make notes but if people want to better understand what Mr Varvill will be saying it may be better to watch his talk.
This looks interesting but I missed it.

Is there any idea when they will post this years videos?

Failing that can you give a brief outline of key points?

I'm afraid I forgot to bring a pen and paper :(

It was a good talk, nothing that seemed a new revelation, but then I haven't been following the technical development too closely.

He started off very generally, talking about justifying re-use vs expendable, background and history (HOTOL/work at rolls-royce), then background of skylon, went into quite a bit of detail about the mechanics of the SABRE engine, then current status of REL and future applications.

I'll leave you to pass judgement until you've seen the video, though.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #184 on: 04/02/2015 09:32 AM »
I'm afraid I forgot to bring a pen and paper :(
Not a problem. We'll wait for the videos.
Quote
It was a good talk, nothing that seemed a new revelation, but then I haven't been following the technical development too closely.

He started off very generally, talking about justifying re-use vs expendable, background and history (HOTOL/work at rolls-royce), then background of skylon, went into quite a bit of detail about the mechanics of the SABRE engine, then current status of REL and future applications.

I'll leave you to pass judgement until you've seen the video, though.
It's the current status part that's likely to change over time.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #185 on: 04/03/2015 06:14 AM »
Below are some thoughts on Skylon areodynamics, and safety. I could be making some incorrect assumptions here, so am happy to hear corrections.

Much has been made of how the Skylon aerodynamics are much improved over HOTOL due to the new airframe configuration: it now requires much less trim even as the fuel tanks empty and it transitions to rocket power.

Thats a welcome advance, but it seems to me that re-entry could still be challenging for a Skylon shape - at least more challenging than with capsules. I certainly believe that when flying during ascent it will be stable and easy to trim - those canards are far forward of the center of mass & pressure and so up to the task.

But the early stages of atmospheric entry are not at all like climbing, winged flight. With the nose high, the wings are essentially drag devices, and inasmuch as Skylon is an aircraft its in a free-fall stall. Unlike a capsule, the Skylon shape is complex and extends far away from the center of lift, so any net forces from the extremities are on long moment arms and need to be dealt with. And unlike a capsule it will not be passively stable. That said, my guess is that Skylon must be actively flown' on the canards during re-entry in the period when the atmosphere overpowers the RCS, and before Skylon is flying forwards - on wings like an aircraft.

The Skylon images indicate that there are elevons on the wings, but during high-alpha entry they seem close to the center of lift and so would not offer as much leverage as the canards (or the equivalent body flap at the rear of the space shuttle orbiter).

If Im right, failure of the canard actuator would be disastrous. I don't believe a thin movable aero surface like that has been flown from orbital speed through entry heating, and to sea level - the most recent public documents on Skylon state that the canards will need to be actively cooled.

I'm sure the cooling mechanism and the actuators will be expertly designed, but with a spacecraft that's expected to fly many times, we can worry about what happens when statistically unlikely events occur. Id love to hear how REL would respond to questions about cooling mechanism and/or actuation mechanism failures.

----------------------------------

Since were not likely to hear from REL on these things, lets do some speculating:

+ The canards could be designed to require active cooling under normal conditions, but survive (need replacement) if it fails.
+ A second redundant pair of canards could be added to the rear of the fuselage, i.e. a tailplane/horizontal stabilizer.

If you were to add those additional aerosurfaces you get some other benefits too. It would give greater control authority which could conceivably help the self-ferry case on shorter runways: the additional surfaces would allow the nose to be pulled up earlier, putting more air under the wings leading to an earlier take-off. Similarly, all four surfaces could serve as air-brakes after landing, reducing roll-out distance.

And while were talking about self-ferry, if the engines could be gimbaled above the horizon, that too would help pick up the nose as the engines are behind the landing gear. I suppose it would also mean less rocket blast hits the runway which is a good thing.
« Last Edit: 04/03/2015 06:42 AM by adrianwyard »

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #186 on: 04/04/2015 04:00 PM »
Re the need to cool the canards:

It turns out BOR-4 used a vapor cooling system - a passive one - for its fins:

Quote
The structure of the heat shield of the wings was different from the remainder of the body. Indeed, because of the aerodynamic profile of the lifting body the wings were thin and could not support the heavy tiles. The interior cavity of wing was filled by a porous matter (the same as felt which holds the tiles on the fuselage) and impregnated with a special composition based on water. Thus, the vapor was used for cooling the structure during the intense heating on the return trajectory.
From: http://www.buran-energia.com/bor/bor-desc.php

So something like that could be used for Skylon. Obviously the advantage of a passive system is you don't need to worry about what happens when the coolant circulation system fails.

And perhaps you could do both: an active system that, when failed, leaves enough residual vapor/transpiration capacity to survive one entry?

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #187 on: 04/04/2015 11:36 PM »
Re the need to cool the canards:

It turns out BOR-4 used a vapor cooling system - a passive one - for its fins:
So something like that could be used for Skylon. Obviously the advantage of a passive system is you don't need to worry about what happens when the coolant circulation system fails.

And perhaps you could do both: an active system that, when failed, leaves enough residual vapor/transpiration capacity to survive one entry?
REL probably chose water cooling over something like heat pipes because the system has been flight tested at least once.

There is a declasified test report for a warehead test in the late 70s or early 80s on DTIC about it. Since it was a warhead design the structure was "thin" as they don't aim to decellerate much before detonation.

People call this "active" cooling but there is typically no actual "pump" involved. It's just water being allowed to boil and heat out of the surfaces.

RCC is good to 3000c in vacuum. it's likely to be SiC coated, like the Shuttle nose and leading edge sections, so good to somewhere like 1500 to 1800c without cooling.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Space OurSoul

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #188 on: 04/06/2015 04:24 PM »
the additional surfaces would allow the nose to be pulled up earlier, putting more air under the wings leading to an earlier take-off. Similarly, all four surfaces could serve as air-brakes after landing, reducing roll-out distance.

And while were talking about self-ferry, if the engines could be gimbaled above the horizon, that too would help pick up the nose as the engines are behind the landing gear. I suppose it would also mean less rocket blast hits the runway which is a good thing.

Early rotation: Once you're out of ground effect, I think the design would already be at optimal angle-of-attack for the take-off airspeed regime.

High gimbal: That would represent a new stress dynamic for transmitting thrust to the airframe: Now a shear on the engine itself and a torque on the wings. So a bigger mass penalty in the structure? And air is a capricious thing: I think you'd still want thrust running through the center-of-mass or who knows what-all instabilities you'd run into in the turbulent lower atmosphere (where, granted, aero surfaces are good at helping (although less so at low airspeeds)).

The effect of either approach is to trade higher drag for increased lift. I'm not sure that lift is the right variable to optimize for: I would have thought that optimizing for early acceleration (i.e _lower_ drag) would actually be what you want. (The way I though of it, probably simplistically, is that if you had high lift but traded a lot of fuel to get it, all you'd end up with would be a slightly less-fueled ship a few meters higher off the ground, going at the same speed. All your fuel's energy went into adding turbulence to the atmosphere.)

But I realize that it's a very complicated optimization problem: Less time on the runway may well translate to mass savings in the undercarriage, less brake-cooling water to carry, etc. And if you really can get into ground-effect flight earlier, it might be a very efficient regime in which to accelerate.


A few threads back I floated the notion of dorsal re-entry. Imagine a configuration like SR-71 with two vertical stabilizers, one at each wingtip and no canard. It rolls down the runway "upside-down" with the stabilizers doubling as undercarriage. The payload doors are underneath at this time, and the top is unbroken TPS out of FOD danger from objects on the runway. During re-entry, the ship lies on its back, stabilizers sticking up out of the heating. It then flips over, probably subsonic, and lands like it takes off.
The relevance to the current discussion is that you now have two configurations (albeit, obviously, tightly linked!) that can be optimized: the take-off can favor low-speed aerodynamics, and the re-entry can favor dynamic stability.
While this approach might help for roll stability, I'll admit it doesn't much address the point that you raised which I think was focused on pitch. It does seem like some kind of aero-surface, ideally far from the center of lift, would help for that flight regime you mentioned.

 

All these thoughts make me realize, yet again, what a difficult optimization problem Skylon represents. I wonder if REL ever had a bash at "genetic" programming: iterating randomly tweaked designs, simulate over the whole mission, repeat.

But I talk too much.
</uninformed guesses>
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Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #189 on: 04/06/2015 10:29 PM »
All these thoughts make me realize, yet again, what a difficult optimization problem Skylon represents. I wonder if REL ever had a bash at "genetic" programming: iterating randomly tweaked designs, simulate over the whole mission, repeat.
This is the challenge to building Skylon. Any changes you make to improve some part of the trajectory have to either improve the whole of the trajectory or leave the rest unaffected.

Once you realize this you realize just how tricky it is to make changes to the design and how carefully the REL team have had to think this through.

In one of the periodic update reports REL have submitted to IAC they mentioned the use of Monte Carlo simulation methods to refine the design.

The upside is this task is still simpler than the various attempts at SCramjet powered vehicles that incorporate the inlet into the front of the vehicle.
« Last Edit: 04/06/2015 10:30 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Online Asteroza

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #190 on: 04/06/2015 11:38 PM »
Using the dorsal surface as the heatshield has merits, but necessitates the "barrel roll of death", as opposed to the "swoop of death" required for nose first reentry VTVL SSTO's. I think an unbroken TPS is preferable, and makes certain other things (beamed thermal propulsion receiver) easier to integrate into the airframe. Ventral opening payload bay also allows easy payload load/unload via a scissor lift cargo transfer vehicle/pit, as opposed to a gantry crane. The kicker is payloads and airframe have to handle long durations in both flipped and unflipped flight modes, which makes systems design more complicated. I suppose doing the flip always clockwise, and the unflip counterclockwise, might make it a bit easier, especially with a passenger module and the rotating seat frames.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #191 on: 04/07/2015 05:00 PM »
Below are some thoughts on Skylon areodynamics, and safety. I could be making some incorrect assumptions here, so am happy to hear corrections.

Much has been made of how the Skylon aerodynamics are much improved over HOTOL due to the new airframe configuration: it now requires much less trim even as the fuel tanks empty and it transitions to rocket power.
I've read your posts a few more times and I'm still not clear what  you're worried about. Is it a pitch failure? Is it a roll failure?

BTW The Shuttle control system also had a period its control surfaces were not fully effective and RCS thrusters were used together with the aero surfaces. Later development programmes found ways to make more effective use of the control surfaces (differential use of the 2 section rudder IIRC) that reduced RCS propellant usage substantially. [EDIT Point is this is not a new phenomena and has been dealt with before. Skylon's maximum nose up would also be about 20deg below Shuttles peak (50deg Vs 70deg). I'm quite sure that REL have flown Skylon through many simulated trajectories to check what happens in these cases ]

BTW it's SOP to have triply redundant actuators for large aircraft. You're postulating simultaneous failure of all drive loops and a possible cooling failure as well.

Probaballistic risk assessment would suggest that failure mode is very remote, but I don't have stats for the simultaneous failure of all flying controls on large aircraft to give a number.  I can say the goal for blind landing systems was 1 failure in every billion operating hours across all aircraft it was installed in and AFAIK it was achieved.

Using the dorsal surface as the heatshield has merits, but necessitates the "barrel roll of death", as opposed to the "swoop of death" required for nose first reentry VTVL SSTO's.
Or you could stick with Skylon's planned flight path and avoid either.   :)
Quote
I think an unbroken TPS is preferable, and makes certain other things (beamed thermal propulsion receiver) easier to integrate into the airframe.
The trouble is it relies on the whole surface remaining perfect for all missions.

That's simply unreasonable for a vehicle of this size and expected life time.   :( [EDIT NASA are doing it for Orion, SpaceX are not doing it for Dragon, and Dragon is planned to be reused ]
Quote
The kicker is payloads and airframe have to handle long durations in both flipped and unflipped flight modes, which makes systems design more complicated.
Very much more complicated.
Quote
I suppose doing the flip always clockwise, and the unflip counterclockwise, might make it a bit easier, especially with a passenger module and the rotating seat frames.
Doubtful. You're back with the making-the-structure-strong-in-2-axes-at-once issue.  :(

When people think of cranes around rockets I believe they are thinking of Saturn/Apollo (or SRB's) being assembled in a building so big it has its own weather.

But a Skylon hangar is more like a 3-4 storey building with 20 tonne gantry crane. This is far below the leading edge of crane technology. I'd expect 10s of suppliers globally could deliver such a system.
« Last Edit: 04/07/2015 05:15 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #192 on: 04/07/2015 05:32 PM »
My point (worry) could be summarized like this:

Skeptical assessments of Skylon tend to focus on it having 'holy grail' SSTO performance, and using unproven SABRE engines. But its return from orbit is also novel/unproven in terms of its shape and size. This part of the design challenge is rarely highlighted.

But just as with the SABRE engines, Skylon re-entry does not require any magical new technology (and it evidently didn't phase the ESA assessors) but it is a novel shape, and its development will involve more than just selecting high temperature materials and nailing them together.

My bet is the development plan will include high-fidelity testing of those canards as they move around in high-temperature >hypersonic air, and fully understanding the way the resultant shock patterns interact with the fuselage. Heating at the hinge seems like a good place to focus on.

The tip of the engine inlet cones are likely another hot-spot too, but modeling/testing that seems trivial compared to the canards.

Speculation: collaboration with US Air Force could provide an opportunity for the sort of testing I'm talking about here.

Edited for clarity.
« Last Edit: 04/08/2015 12:04 AM by adrianwyard »

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #193 on: 04/07/2015 06:16 PM »
Re take-off optimization (responding to full quote below):

I find these discussions great fun, but it's worth remembering that any 'winning' argument is probably wrong/incomplete as we're never privy to all the relevant factors.

That said, let me explain more about my thinking.

First of all, I should have emphasized I was talking about improving take-off for the self-ferry case; with little/no LOX and less LH2 on board the loads will be much less than with an orbital launch from its custom runway.

It seems to me highly desirable for Skylon to be able to self-ferry from regular runways, e.g. the Airbus runway in Toulouse (3.5km) to its own 5.5km orbital launch facility. I'm thinking about shortening take-off length in hopes that self-ferry could be made realistic.

In additional to delivering new vehicles, this would mean simplified recovery if it has to land at an alternate site. It would also mean a spare could be flown in - perhaps leased from another provider - if one had maintenance issues.

In terms of take-off aerodynamics, I'm pretty confident my idea (duplicate the canards to get double the lift/control authority) has merit theoretically. First of all, we can be sure that the wing is not optimized for short take off - many factors constrain it in other directions. Even commercial aircraft airfoils are not optimized for take-off, hence the need for high-lift devices such as flaps. The canards would essentially be the equivalent of flaps.

Imagine an extreme case: A Skylon with no canards, and wings much smaller than the current design: they generate so little lift that its still resting on its undercarriage when barreling down its 50km runway at 700mph. But at 700mph there is enough air flowing by to lift the vehicle IF the wings had some angle of attach with respect to the airflow. That's what the canards could do for this case, and that's why I suggested doubling up the canards could shorten the take-off length during self-ferry with the current design.

EDIT: my assumption is that the current canards are not already large enough to provide all the lift you'd require to pick the nose up for the shortest self-ferry take-off, and that duplicating them gives worthwhile redundancy.

And in terms of them causing drag which would hinder short take-off: they'd be feathered (so minimal drag) until they were used to rotate. In that respect, they are better than flaps on commercial aircraft.

the additional surfaces would allow the nose to be pulled up earlier, putting more air under the wings leading to an earlier take-off. Similarly, all four surfaces could serve as air-brakes after landing, reducing roll-out distance.

And while were talking about self-ferry, if the engines could be gimbaled above the horizon, that too would help pick up the nose as the engines are behind the landing gear. I suppose it would also mean less rocket blast hits the runway which is a good thing.

Early rotation: Once you're out of ground effect, I think the design would already be at optimal angle-of-attack for the take-off airspeed regime.

High gimbal: That would represent a new stress dynamic for transmitting thrust to the airframe: Now a shear on the engine itself and a torque on the wings. So a bigger mass penalty in the structure? And air is a capricious thing: I think you'd still want thrust running through the center-of-mass or who knows what-all instabilities you'd run into in the turbulent lower atmosphere (where, granted, aero surfaces are good at helping (although less so at low airspeeds)).

The effect of either approach is to trade higher drag for increased lift. I'm not sure that lift is the right variable to optimize for: I would have thought that optimizing for early acceleration (i.e _lower_ drag) would actually be what you want. (The way I though of it, probably simplistically, is that if you had high lift but traded a lot of fuel to get it, all you'd end up with would be a slightly less-fueled ship a few meters higher off the ground, going at the same speed. All your fuel's energy went into adding turbulence to the atmosphere.)

But I realize that it's a very complicated optimization problem: Less time on the runway may well translate to mass savings in the undercarriage, less brake-cooling water to carry, etc. And if you really can get into ground-effect flight earlier, it might be a very efficient regime in which to accelerate.


A few threads back I floated the notion of dorsal re-entry. Imagine a configuration like SR-71 with two vertical stabilizers, one at each wingtip and no canard. It rolls down the runway "upside-down" with the stabilizers doubling as undercarriage. The payload doors are underneath at this time, and the top is unbroken TPS out of FOD danger from objects on the runway. During re-entry, the ship lies on its back, stabilizers sticking up out of the heating. It then flips over, probably subsonic, and lands like it takes off.
The relevance to the current discussion is that you now have two configurations (albeit, obviously, tightly linked!) that can be optimized: the take-off can favor low-speed aerodynamics, and the re-entry can favor dynamic stability.
While this approach might help for roll stability, I'll admit it doesn't much address the point that you raised which I think was focused on pitch. It does seem like some kind of aero-surface, ideally far from the center of lift, would help for that flight regime you mentioned.

 

All these thoughts make me realize, yet again, what a difficult optimization problem Skylon represents. I wonder if REL ever had a bash at "genetic" programming: iterating randomly tweaked designs, simulate over the whole mission, repeat.

But I talk too much.
</uninformed guesses>
« Last Edit: 04/07/2015 08:26 PM by adrianwyard »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #194 on: 04/08/2015 12:13 AM »
First of all, I should have emphasized I was talking about improving take-off for the self-ferry case; with little/no LOX and less LH2 on board the loads will be much less than with an orbital launch from its custom runway.

It seems to me highly desirable for Skylon to be able to self-ferry from regular runways, e.g. the Airbus runway in Toulouse (3.5km) to its own 5.5km orbital launch facility. I'm thinking about shortening take-off length in hopes that self-ferry could be made realistic.
On self ferry Skylon will be 150 tonnes lighter. That alone will shorten the takeoff substantially. It will accelerate substantially faster and its wing loading be substantially lower. 
Quote
In additional to delivering new vehicles, this would mean simplified recovery if it has to land at an alternate site. It would also mean a spare could be flown in - perhaps leased from another provider - if one had maintenance issues.
REL state the landing speed and sink rate is such that it could land on grass. Note landing, not take off.
Quote
In terms of take-off aerodynamics, I'm pretty confident my idea (duplicate the canards to get double the lift/control authority) has merit theoretically. First of all, we can be sure that the wing is not optimized for short take off - many factors constrain it in other directions.
Nevertheless it will take off in short order in air breathing mode.
Quote
Even commercial aircraft airfoils are not optimized for take-off, hence the need for high-lift devices such as flaps. The canards would essentially be the equivalent of flaps.

Imagine an extreme case: A Skylon with no canards, and wings much smaller than the current design: they generate so little lift that its still resting on its undercarriage when barreling down its 50km runway at 700mph. But at 700mph there is enough air flowing by to lift the vehicle IF the wings had some angle of attach with respect to the airflow. That's what the canards could do for this case, and that's why I suggested doubling up the canards could shorten the take-off length during self-ferry with the current design.

EDIT: my assumption is that the current canards are not already large enough to provide all the lift you'd require to pick the nose up for the shortest self-ferry take-off, and that duplicating them gives worthwhile redundancy.
If they can deliver enough lift to get the nose up for a fully loaded takeoff (which they are sized for) how likely is it they can't when the vehicle is 150 tonnes lighter?
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #195 on: 04/08/2015 12:13 AM »

Assessments of Skylon tend to focus on it having 'near impossible' SSTO performance,
For a VTOL SSTO, rather less so for an air breathing HTOL. This matter has been discussed before.
Quote
and using unproven SABRE engines. But its return from orbit is also novel/unproven in terms of its shape, size. And to land in one piece, those canards need to operate as expected.
Exactly like the control surfaces of any vehicle that use aerodynamic lift and exactly as the Shuttle design managed on  135 flights. Like the Shuttle it will probably have triply redundant actuator circuits.

It's the difference between "likely to fail" and "may fail in in 20 000 launches."
Quote
My bet is the development plan includes high-fidelity testing of those canards as they move around in high-temperature >hypersonic air, and fully understanding the way the resultant shock patterns interact with the fuselage. Cooling at the hinge seems like a good place to focus on.
At least part of that has already happened when DLR (who thought the canards too thin to survive the heating) did a major CFD exercise on it using their Tau CFD code and confirmed they will survive.

It's a pretty safe bet that such test work is part of the schedule for the Skylon project.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #196 on: 04/08/2015 12:43 AM »
I think you are under the impression that me naming the concerns of Skylon's skeptics, and asking questions means I've already decided Skylon is a flawed concept - and that you need to defend it. Not true.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #197 on: 04/08/2015 06:31 AM »
I think you are under the impression that me naming the concerns of Skylon's skeptics, and asking questions means I've already decided Skylon is a flawed concept - and that you need to defend it. Not true.
Not at all. I'm trying to understand what you're concerned about and you are not making your concerns any clearer.

You started with something about canards being too small then elevons being too close to the body and come up with a reason for having a more conventional tail. You talk about the canard actuators failing but seem to ignore they will likely be triply redundant and when this is mentioned you just seem to ignore it.

So what is the root cause of your worry?



"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #198 on: 04/08/2015 03:38 PM »
I'm not worried; at least not in the usual negative sense. I think I need to put more smileys in my posts because the 'worries' you see are born of an interest and enthusiasm with the engineering challenges Skylon represents. That's clearly not coming through.

If you reread my posts you'll see they go like this (with positive fanboi vibe now added in):

1] "Hey fellow-Skylon fans, I just realized that Skylon's re-entry will push the state of the art further forward than anything before it. How come no-one ever mentions that? More than any spacecraft before it, Skylon actually 'flies' in on the canards. How cool. Passively stable re-entry vehicles are for wimps. :-)"

2] "Wouldn't it be awesome if Skylon could take-off and land at regular airports? I know our friends at REL have already worked out how to make it take off in the shortest distance, but I'm just such a fan that I can't help but think about ways to improve Skylon. So, how about adding canards at the back to aid in earlier rotation. Probably a silly idea, I know."


Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #199 on: 04/09/2015 12:49 PM »

If you reread my posts you'll see they go like this (with positive fanboi vibe now added in):

1] "Hey fellow-Skylon fans, I just realized that Skylon's re-entry will push the state of the art further forward than anything before it. How come no-one ever mentions that? More than any spacecraft before it, Skylon actually 'flies' in on the canards. How cool. Passively stable re-entry vehicles are for wimps. :-)"
Perhaps because no spaceplane before it had cannards? The importance of trim was one of the big discoveries of the HOTOL project. Putting the engines on the wing tips is a big change. Skylon is designed to avoid the continuous "fluttering" of control surfaces the Shuttle used to keep it stable. You're assuming it will be unstable. That's not a given.

An interesting question is could it be stable enough to allow a human pilot to fly it without a computer in the loop to stabilize it.

That would make it a very exciting prospect for some potential customers.

Quote

2] "Wouldn't it be awesome if Skylon could take-off and land at regular airports? I know our friends at REL have already worked out how to make it take off in the shortest distance, but I'm just such a fan that I can't help but think about ways to improve Skylon. So, how about adding canards at the back to aid in earlier rotation. Probably a silly idea, I know."
Then you're missing the biggest issue of all. The huge noise level. It's not just the thrust it's the exhaust velocity for air/H2 is much higher than air/kerosene mixture. While OK for occasional takeoffs or emergency landings (which will be unpowered) it's most unlikley there will be fully fueled take offs from any regular airport.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

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