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Supersonic Flight Without The Sonic Boom
fname writes "Here's a story from Spaceflight Now about a new test aircraft that can travel at supersonic speeds without triggering a sonic boom. The technology works by modifying the shape of the plane. Although it's been believed to be possible for a long time, this is the first actual flight test, barring black box projects I suppose."
It seems it merely muffles the sonic boom. The technology doesn't completely silence it.
It is felt that the SST movement (i.e. concorde) was derailed by the american plane maker (i.e. Boeing) which got enough lawmakers to say that the concorde could not fly over the USA (i.e NY to LA) because of the sonic boom.
if a SST can go supersonic without the boom, then development of new craft could take place, because new markets could open up...
This is important because the main reason super sonic airplanes are not used more often for civils is because of the sonic boom. The sonic booms can be very loud and disturbs urban areas. The Concord, for example, had to wait to be very far away from populated areas before getting into super sonic speeds. This rwas costly, since the Concord was design to have optimal fuel efficiency at super sonic speeds.
"There is no teacher but the enemy."-Mazer Rackham
The reason to do this is to allow supersonic transports to fly over inhabited areas. The sonic boom from the Concorde, for example, is shockingly loud, it would never be tolerated.
What the article doesn't say, but was reported in Aviation Week a few weeks ago, is that this technique (and certainly this airplane) only reduces sonic booms -- it doesn't eliminate them. This demonstration is to show people that the math is right; that the sonic booms can be reduced through shaping. It is still unclear whether it is possible to build a practical airplane with a tolerable (negligible) sonic boom. Perhaps this could be combined with other techniques (the Russians have been working with exciting a plasma in front of the airplane, for instance) and together you could get a minimal boom.
Probably the parent article was questioning the need for supersonic travel at all -- whether it's worth the cost. It will almost certainly be less fuel efficient than subsonic travel. Travel in general is less fuel efficient than staying home. Living is less fuel efficient than dying.
thad
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I happened to notice a show (On The Edge) on the Discovery Wings channel covering a lot of this. Not as in depth, of course, but interesting nonetheless.
Submited on september 6, 2003:
Northrop, working with the Pentagon and NASA sucessfully tested a "quiet" supersonic flight wednesday at California's Edwards Air Force Base. In the tests, an F-5E aircraft with a modified nose section flew supersonically through the test range, shortly thereafter, an unmodified F-5E flew supersonically through the same airspace, with the sensors showing a clear reduction in the intensity of the sonic boom produced by the F-5E modified fuselage.
You can't take the sky from me...
This was also covered in Flight International (subscribers - I read the paper version in the library), in a bit more depth. The classic sonic boom was described as "N-shaped" and gives a crack-crack effect. This modified it to more of a "table-top", and was said to sound like a long rumble.
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"When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of the meager and unsatisfactory kind."--Lord Kelvin
The article doesn't give one single blessed number that would enable anyone to judge how effective the experiment was.
I'm not sure what the right measurement would be... decibels? sones? psi? pascal-seconds? Or average blood pressure increase in human subjects in Hgmm? But the article doesn't say.
Not even the usual marketing claim, like "42% less boom than traditional aircraft, yet still has that same great NASA 'look'"
Something about "We were all blown away by the clarity of what we measured" just doesn't do it for me.
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That is differnt. It is for a single shockwave. What this article deals with is multiple shockwaves.
The examples are ATF, Eurofighter, Viggen, Suhoy S27 and later, so on so forth. All of these have shapes designed specifically to split the shockwave into a series of shockwaves to improve lift and maneuvrability at hypersonic speeds. As a result the noise is muffled as a side effect. From there to muffling it completely is just one step.
In btw, I am glad that it was done on the F5. It is the only US bird that has some resemblance of grace and beauty in the air.
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Wow, you sure put a lot of effort into that reply. It must burn you to know that Karl S. Kruszelnicki Pty Ltd had the gall to blatantly plagiarise it and copyright it, no less.
It all goes downhill from first post
Quite possibly, fluid dynamics applies to both liquids and gasses.
Supersonic vehicles actually generate two booms- one for the nose and one from the tail- that's why this has the nose glove and the modified tail.
Incidentally, the size of the boom is related to the size of the aircraft, military planes are much smaller and hence give much less problems.
Interestingly, Concorde's nose is sharp- this is aerodynamically efficient, but generates bad sonic booms- it would be much better to use a rounded nose from that respect. Detailed changes to the tail section (other than the ones shown here) can also greatly reduce the shockwave. If you've seen Thunderbirds, some of the airliners shown there are strongly reminiscent of the kinds of shapes that probably help out, (strangely enough, that's probably because they got fairly good advice when designing their models.)
I think that the vehicle shown in the photo has a compromise nose shape- it's sharp on top to give better aerodynamics, but rounded underneath to project a weaker sonic boom downwards. Atleast that's my take on what they've done- IANAA. (I Am Not An Aerodynamicist).
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"For those who have asked how much of a reduction in sonic boom was achieved:
The following URL says the peak pressure was reduced by one third, but there was very little difference in the sound of the boom on the ground. This was a better result than expected, since they did not expect to hear _any_ difference.
After all, this was _not_ an attempt to fly supersonically without generating a sonic boom, despite the misleading title of this thread. Instead, it was a (very successful) attempt to valid the CFD models used to design the aircraft nose modifications and predict the reduction of the pressure wave on the ground.
Now that they have proved that their method works, they can work on more noticeable reductions.
http://209.157.64.200/focus/f-news/973267/posts
For starters, you don't have to "throw out" the Concorde as BA/AF are doing that for you. They even refused to sell one to Virgin Airways as Branson might find a way to make the flight profitable and would thereby kill BA/AF's hopes of pushing all of the Concorde folks into the 747 first class section.
There are two other reasons why you won't see the Concorde flying supersonic over the continental USA, with or without a sonic boom:
1) There are far too many other slow aircraft flying at or near Concorde altitudes. Considering the fuel costs involved in getting to supersonic speeds (max drag between 0.97M and 1.4M), the economics of trans-continental supersonic flight would require sterile airspace for end-to-end clearance. The lobby group for bizjet owners would never let that happen at their expense.
2) Even a reduced shock wave will have destructive powers if the aircraft is required to turn at supersonic speeds - the waves on the inside of the turn are concentrated toward a single point at which the N-wave would be amplified to an unacceptable level. Although it would be possible to structure straight-line routes between city pairs, the odds are pretty good that the flight would be unmanageable in terms of communication and coordination among ATC units.
Most planes I fly on cruise at about 35000'
That's because you fly commercial like me, prole. OTOH, Gulfstreams and other long range bizjets cruise in the 50k' range. Check out 'specifications' at thus URL: http://www.gulfstream.com/g550/
And while the Concorde ends its flight at 60K, it starts at 50 and gradually climbs as the weight of used fuel is lost. So not only is it ripping along at high speed but also constantly changing altitude. Not the kind of wild behavior you want over the continental US where there are a lot of the aforementioned bizjets puttering around at less than half the speed.