i think he means the fact that nasa is mostly expirementing with wingless lifting body type craft (wings would protrude from the shock cone and would be a source of immense drag). so nasa designs have a mostly flat long ship with stub wings and small control surfaces. nasas designs tend to favor scramjets though. the scimitar engine that reaction engines is developing is a completely different kind of engine. like saber it both compresses and cools intake air (air naturally gets hotter when you compress it). but where saber uses this as oxidizer in its 4 rocket engines and bypass air goes through the ring o ramjets to meet otherwise wasted hydrogen from the heat exchanger (under certain flight conditions, which i believe is between mach 1 and 5). scimitar has a a more traditional turbofan layout (all be it with the core nozzel resembling the rocket engine) with what looks like a 2 stage burner. from the image i would assume the bypass turbine and burner would be for subsonic operation, and the rocket-like nozzel for the hypersonic flight modes (this is just a guess though im trying to find more info).
using fuel to cool parts of the engine are nothing new, saturn-v's main booster did this, pumping fuel through piping in the bell before burning it to keep it from melting. but this is the first time ive seen a plan for an actively cooled engine. the fact that it has multiple applications (space and transport), means that the technology may turn out viable in one area or the other, and so both the lapcat and skylon are somewhat linked (hell they even have the same layout with slightly different wing configurations) in their fate. its certainly a lot better than using heavier than sane scramjet technology. nasa has a tendency to make baby steps where revolutions are needed. they really havent done anything to compare with what they pulled off with apollo. so i really hope reaction engines can deliver.
supposedly their preparing for a full test of the precooler and they got until april to get it working. and if they do it will impress investors and drum up some more government money. if they dont, well then they will likely need to find another source of funding. i really wish them the best though. it will bypass a lot of the babystepping thet seems to be going on with private space industry and backstepping with going on with nasa. if you want to get out of the gravity well this century on the cheap, this is gonna have to work. and of course it will certainly make faster than neccisary transport availible to all you rich snobs out there.
Yeah, independent from the engines, I was mostly referring to what NASA has found out about the optimal planforms for hypersonic flight. I might have linked this earlier in the thread but I don't feel like looking, so here's a summary:
http://www.grc.nasa.gov/WWW/BGH/index.htmlBasically, they've found that a lot of pointed surfaces are no longer the best way to go. Rather, it's best to design the aircraft so that it essentially rides on its own shockwave (hence the name of the X-51: WaveRider). It's not a new concept; it was something that was done on the XB-70 design back in the late 50s and early 60s. As Nuke mentioned, wings are more of an inconvenience at hypersonic speeds especially because leading edges are subject to massive heating; it's easier to just use a lifting body that rides the hypersonic shockwave for lift and avoid traditional wings, with the added benefit that it keeps a greater portion of the aircraft near the center of gravity, which adds stability and makes it easier to cool. I just don't even want to think about what happens if a piece comes off of one side of that Reaction Engines design at mach 5. Shear off a wingtip at 4,500 mph and there's gonna be some serious yawing problems. Again, I'll bring up the SR-71: back when the shock cones of its engines were controlled by analog computers, they would occasionally not be able to react to changing flight conditions fast enough; the shockwave generated by the front of the cone would normally ride just inside the lip of the inlet, but in those cases, it would be disrupted and blow out the front of the engine in spectacular fashion, called an "inlet unstart." There'd be some incredibly yawing of the plane until it either eventually stabilized itself or the pilot unstarted the other inlet. Yawing and shearing typically aren't very good for airframes - the SR-71 survived because it was made out of 80% titanium that, quirkily enough, they found was getting stronger over time because it was basically getting heat treated. I don't want to know what that kind of yaw would do to the Reaction Enginges design, though, especially with how long it is. Keep in mind how sensitive the industry is to accidents and that's a whole can of worms I'd rather avoid if I were them. One accident (that was a result of ground debris and nothing to do with the airframe or the maintenance or the pilot) sunk the Concorde.
Also, the lifting body design has another advantage at those speeds. Take a look at the X-43 and you'll notice that the intakes are at the bottom of the planform, with what we'd think of as the nose essentially forming a ramp down to the intakes. It helps it collect the rarefied air at the cruising altitudes of hypersonic flight. I'd be very worried about the amount of air the Scimitar engines would be able to collect at 90,000 ft+ using that A2's proposed nacelle design. Again, I'm not an expert on this and it'd be awesome if the A2 works - I'd love to fly in it at least once, just to see what it was like. But like I mentioned, it just seems too conventional - NASA's been working on this since the 50s, they've had several testbeds and recent successes. I like their chances of being right.
