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 GMTI'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.
Develop3D Yep, all the videos from #D3DLive will be posted online soon. Stay tuned for the release announcement in the coming weeks
Re Richard Varville's talk at Develop3D. I asked them on their Facebook page about the video and they answered: QuoteDevelop3D Yep, all the videos from #D3DLive will be posted online soon. Stay tuned for the release announcement in the coming weeks
Quote from: topsphere on 03/25/2015 12:01 pmI'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 GMTI'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.
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.
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?
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 we’re 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.
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.
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.
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.
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.
Quote from: adrianwyard on 04/03/2015 06:14 am 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 we’re 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>
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.
Assessments of Skylon tend to focus on it having 'near impossible' SSTO performance,
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.
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.
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.
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."