Report Card for Donald Trump

[Warren Dew]

(01-16-2017, 03:54 PM)SomeGuy Wrote:

Quote:This is only true at constant altitude at subsonic speeds.

At supersonic speeds, the boundary layer speeds must remain subsonic due to speed of sound limitations, which changes how skin friction drag operates.

In addition, for both subsonic and supersonic speeds, higher speeds result in higher lift.  This permits aircraft to achieve adequate lift at higher altitudes where the air is thinner.  This in turn reduces drag.

Finally, at supersonic speeds, there is compressibility drag, but again, the compression wave can be used for lift.  This permits supersonic transports to cruise at much higher altitudes than subsonic transports, which again reduces drag relative to flying "in the soup".

You say all of that, and yet I don't think that this actually cancels out the inherent drag from moving through even a thin atmosphere at LUDICROUS speed.  There's a reason that all of the actual supersonic aircraft built optimize their airframes to minimize drag, and take advantage of vortex lift at slow speeds when taking off and landing.

I'm still not seeing the fundamental breakthrough that allows this to be done in a cost-efficient manner.

The Concorde had about the same fuel burn per passenger mile as the first generation 707.  There hasn't been any fundamental breakthrough in subsonic jets since then, despite a manyfold improvement in fuel economy; there was just incremental improvement, mostly from higher and higher bypass ratios, resulting in a high degree of optimization for subsonic jets.

I'd expect the same gradual improvement for supersonic jets once they become common.