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Show Me The Numbers!
To paraphrase the Cuba Gooding character from "Jerry Maguire."
I keep seeing these breathless articles in the popular media, and even the trade press, about reducing sonic boom, with its promise of practical commercial supersonic flight. The latest hype comes from Popular Science (via Clark Lindsey).
Why do I call them hype?
First, I have never, ever seen a single number in these articles indicating to what degree the boom is attenuated. Maybe it's just my suspicious nature, but I suspect that if we could see those numbers, we might be less impressed.
Second, there is never any mention in these articles about the other problem that is holding back practical supersonic flight, which is all of the drag associated with the shock. Even if by some legerdemain with vehicle contours they can reduce the boom sufficiently to allow overflight of land, the operating costs will remain horrific and unaffordable to most, because of the tremendous amount of wave drag from the shock system and skin drag from the huge swept delta wings that all of these concepts continue to employ.
That means that at best, it will remain another Concorde, though perhaps one that can fly coast to coast--an expensive ride only for the rich.
I find this topic particularly frustrating because I've been aware for a number of years of a technology with the potential to effectively eliminate shock, with both the sonic boom and the tremendous drag associated with it, but there has never been any interest in pursuing it, from either NASA or industry.
Anyway, I'll take this stuff seriously when I see some quantification of just how much they're reducing the overpressure, and some indication of understanding of the drag problem, instead of focusing entirely on the boom.
[Update in the afternoon]
Clark points out in comments that they do show some numbers in a slideshow.
Color me unimpressed. There's never been any doubt that one can reduce boom through body shaping--the issue is whether you can get enough reduction to solve the problem. This graph shows a softer peak, from a little over 1.2 PSF to about 9 PSF. So they're reducing it by about thirty percent.
Big whoop. Still gonna break windows.
Is there any reason to think that they can do significantly better than this graph would indicate, particularly for a large transport? There's none provided in the article. In fact, they even admit in the caption here, "Designers of the modified F-5E weren't trying to eliminate the sonic boom, but prove that aircraft shaping can lessen this signature of supersonic flight."
Big deal--we knew that.
And as Clark notes, there remains no mention of the drag issue.
Still looks like hype to me, similar to that over hypersonics. It may be beneficial for some military apps, but there's no reason to think that it will usher in a new era of commercial air transport, or even make supersonic bizjets practical, despite the pretty pictures.Posted by Rand Simberg at July 05, 2004 10:14 AM
WRT numbers, there is a graph for the PopSci article in the slideshow -
Rand, how similar is your proposed method to the systems used on the old Buccanneer attack plane the RN used to fly?Posted by Phil Fraering at July 5, 2004 03:34 PM
I don't know anything about that aircraft, but no one to my knowledge has implemented shock-free technology in any operational (or even test) aircraft.Posted by Rand Simberg at July 5, 2004 04:19 PM
Thanks Rand. You've convinced me there are significant problems with their approach. It looks like they also need to have a mechanical system to alter the nose shape to maintain the suppression as they build up to the "sweet spot" and then later while slowing down. That would seem to add a lot to the cost and hurt reliability as well.
It looks like they also need to have a mechanical system to alter the nose shape to maintain the suppression as they build up to the "sweet spot" and then later while slowing down. That would seem to add a lot to the cost and hurt reliability as well.
That's going to be practical issue with any design, including one that incorporates the technology with which I'm familiar. There will always be an optimal configuration for cruise--off-design conditions are always the hardest part. That's why they have flaps...
However, that having been said, true shock-free technology offers a path to much less dramatic modifications for take-off/landing (and eliminates the need for afterburners).Posted by Rand Simberg at July 5, 2004 06:34 PM
Rand, check out this link:
http://www.vectorsite.net/avbucc.htmlPosted by Phil Fraering at July 5, 2004 10:30 PM
(I forgot to mention: yes, it's a subsonic aircraft, generally, but you'll see what I mean when I say it has a similar system.)Posted by Phil Fraering at July 5, 2004 10:31 PM
Drag or lift/drag ratio
I thought the problem of supersonic cruise flight had already been solved by the old XB-70 bomber. Has any other supersonic aircraft, including the Concorde, ever used the principle of compression lift that was incorporated into the design of the XB-70?
I read somewhere that because of compression lift the XB-70's lift to drag ratio was actually better at supersonic speeds than at subsonic speeds!Posted by Brad at July 6, 2004 02:32 AM
Phil, that looks superficially like the concept, but it's just a blown control surface system, and has nothing to do with shock suppression.
As for the Valkyrie having a better supersonic than subsonic L/D, it could be, but they both still sucked.Posted by Rand Simberg at July 6, 2004 05:41 AM
sucky L/D ratios
Hmmm, I'm surprised about that. But if the L/D of the XB-70 sucks, then the L/D of a B-52G must really suck considering both planes have similar gross weights and maximum ranges but the cruising speed of the B-52G is 3.7 times slower than the XB-70.Posted by Brad at July 8, 2004 01:15 AM
L/D is a function of many more things than simply gross weight and maximum range (e.g., compare the wetted area of the wings of the two aircraft).Posted by Rand Simberg at July 8, 2004 04:48 AM
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