|YF-12 Inlet Schematic|
It [the Blackswift conceptual design work] produced an aircraft configuration that could controllably take off, accelerate through subsonic, supersonic, transonic and hypersonic speeds. It was controllable and kept the pointy end forward.This is of course a response to their competitor who is quite a well-known advocate of wave-riders. A design technique recently demonstrated in small part (on a missile-like configuration which makes the "pointy end first" problem easier) with X-51.
We are not advocates of wave riders... You end up with a vehicle that is hard to take off and land, has little fuel volume and high transonic drag.
|LoFLYTE wind-tunnel model|
|D-21 Inlet Spike and Bleed Doors|
|D-21 Front-view showing Wing Anhedral|
One of the reasons that Lockheed and the Air Force were hesitant about sharing an SR-71 with NASA was changes that were made from the YF-12 inlet to make the SR-71 have a lower RCS. I'm not sure what those changes were, but from an external view you can see that the leading edge of the wing on the SR-71 is pushed right up to the inlet lip whereas there is a large gap between the inlet lip and the wing leading edge on the YF-12. This sort of little feature can act as a corner reflector and contribute significantly to the total cross section. That may be the change... or it may not ; - )