[AR] Re: Skylon Progress (was Re: Silicon Carbide)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 1 Dec 2018 16:55:15 -0500 (EST)
On Fri, 30 Nov 2018, Rand Simberg wrote:
What would have been your idea for "different" ?
Something based on fundamental research into the nature of supersonics,
the cause of wave drag and entropy in the wake, and figuring out what to
do about it...
Translation: Rand has been involved with some folks who've been pursuing
such ideas, so that's the only acceptable approach. :-)
In fairness, their ideas *are* very interesting, and if their concept for
essentially shock-free supersonic flight works, it could make a big
difference to aviation. It does seem like something that would be worth
at least a modest amount of high-risk-high-payoff R&D funding.
(More precisely, I should say "shock-free supersonic *lifting* flight".
If you read old aerodynamics books, you find that people noticed the
possibility of shock-free supersonic flight a long time ago. One of the
shock-free shapes, the "Busemann biplane", appeared in the same paper that
first proposed swept-back wings. But nobody could find a shape that would
produce *lift* without shock waves -- the Busemann biplane is shock-free
only at zero angle of attack -- so the idea gradually got forgotten.)
However, it's not necessarily the *only* way to get good supersonic L/D.
Concorde didn't do too badly, even the traditional approaches can do
significantly better now, and there are other poorly-explored options,
like compression lift.
Finally, trying to rein in this digression a bit, it doesn't seem very
relevant to rocketry, or even Skylon. :-) Almost certainly, a more
efficient supersonic aircraft would have to be tightly optimized for
cruise at one specific speed, so this wouldn't be very useful for
"accelerator" missions like space launch. (Except insofar as easy
availability of commercial supersonic aircraft might make air launch more
attractive as a starting point for a rocket.)
Henry
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