I wouldn't say it's the only acceptable approach. It's the only approach
that will make supersonic transport practical for the mass market,
rather than a useful niche.
On 2018-12-01 13:55, Henry Spencer wrote:
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