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View Full Version : Silent sonic boom...Supersonic business jet?


Lord Blackadder
Oct 10, 2006, 09:17 PM
Just saw this very cool concept (http://blogs.zdnet.com/emergingtech/?p=377) that NASA is working on.

It's simple: silence the sonic boom. This removes one of the reasons we don't have supersonic passenger aircraft. Of course, there are other major problems with SSTs (significantly louder and thirstier engines than subsonic aircraft) but it will be cool to see where this development may take us...

jamesmcd
Oct 11, 2006, 05:11 AM
I do understand the problems with sonic booms (I am a trainee pilot after all :cool: ), however actually witnessing a jet breaking the sound barrier is amazing :eek:

MacBoobsPro
Oct 11, 2006, 05:22 AM
Interesting but a little bit primitive in a technological way :D

I believe sounds can drowned out by conflicting sounds offset by a certain amount of time (milliseconds). It happens with gunshots often. If you fire a gun quickly enough the second bang from the second bullet cancels out the first bang from first bullet and the first bang cancels out the second bang. Its weird and I'm no expert on it by any means its something I saw on TV. There was an fake assasination set up that fired 6 bullets but only 3 were heard. Leading to believe there was a second gunman with a silencer somwhere. There wasn't.

Maybe NASA could look into something like this. Producing sound to create silence. Its not as stupid as I make it sound. :D

whooleytoo
Oct 11, 2006, 09:51 AM
Maybe NASA could look into something like this. Producing sound to create silence. Its not as stupid as I make it sound. :D

Destructive interference, and it's not stupid. That's how noise-cancelling headphones work! ;)

Sdashiki
Oct 11, 2006, 10:43 AM
This was on Digg the other day, fancy that!

http://www.micom.net/oops/F14aExplosion.wmv

sorry its wmv, couldnt find the YouTube video of it.


You can see the "sound barrier" as the pressure waves going across the plane, and then apparently he pulled up in a roll causing vibrations to explode...i think.

Don't panic
Oct 12, 2006, 03:52 PM
here is another image of the sound barrier.
really cool
http://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg/300px-FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg

Anonymous Freak
Oct 12, 2006, 04:23 PM
I was an Aerospace Engineering student in college, and was starting to do my thesis on this. There is some NASTY math involved with trying to design an aircraft to minimize sonic boom. I dropped out of college before finishing, but it is nice to see that someone is doing work on it.

As for being supersonic means being fuel-thirsty? There are a few aircraft out there that are counter to that idea. The Concorde is one (although it is more efficient subsonically, it is still reasonably efficient at supersonic speeds.) The F-22 is another (again, still more efficient in "miles per gallon" to go subsonic, but it's not a huge jump.) The SR-71 (and its predecessors in the A-12 line) and XB-70 are the major 'disprovers' of this. Both of those aircraft were more efficient at supersonic speeds than subsonic. (For example, the SR-71 had a Mach 3 range of about 3000 miles. At subsonic speeds, its range was approximately 1000 miles.)

MacBoobsPro
Oct 12, 2006, 04:27 PM
I was an Aerospace Engineering student in college, and was starting to do my thesis on this. There is some NASTY math involved with trying to design an aircraft to minimize sonic boom. I dropped out of college before finishing, but it is nice to see that someone is doing work on it.

As for being supersonic means being fuel-thirsty? There are a few aircraft out there that are counter to that idea. The Concorde is one (although it is more efficient subsonically, it is still reasonably efficient at supersonic speeds.) The F-22 is another (again, still more efficient in "miles per gallon" to go subsonic, but it's not a huge jump.) The SR-71 (and its predecessors in the A-12 line) and XB-70 are the major 'disprovers' of this. Both of those aircraft were more efficient at supersonic speeds than subsonic. (For example, the SR-71 had a Mach 3 range of about 3000 miles. At subsonic speeds, its range was approximately 1000 miles.)

Wasnt the concorde scrapped because of fuel inefficiency? (as well as the 'one and only' crash) :confused:

bigandy
Oct 12, 2006, 05:02 PM
Wasnt the concorde scrapped because of fuel inefficiency? (as well as the 'one and only' crash) :confused:

No. linkey (http://en.wikipedia.org/wiki/Concorde#Withdrawal_from_service)...

Lord Blackadder
Oct 12, 2006, 09:48 PM
As for being supersonic means being fuel-thirsty? There are a few aircraft out there that are counter to that idea. The Concorde is one (although it is more efficient subsonically, it is still reasonably efficient at supersonic speeds.) The F-22 is another (again, still more efficient in "miles per gallon" to go subsonic, but it's not a huge jump.) The SR-71 (and its predecessors in the A-12 line) and XB-70 are the major 'disprovers' of this. Both of those aircraft were more efficient at supersonic speeds than subsonic. (For example, the SR-71 had a Mach 3 range of about 3000 miles. At subsonic speeds, its range was approximately 1000 miles.)

You are correct, but the aircraft you're talking about are still less efficient than modern subsonic airliners. Fuel efficiency is always a relative term. The absolute fuel costs of running the Concorde are significantly higher than those of a 747, for example.

I hope that SSTs are someday back in the commercial fleet.

Anonymous Freak
Oct 13, 2006, 12:13 AM
You are correct, but the aircraft you're talking about are still less efficient than modern subsonic airliners. Fuel efficiency is always a relative term. The absolute fuel costs of running the Concorde are significantly higher than those of a 747, for example.

I hope that SSTs are someday back in the commercial fleet.

Quite correct. I wasn't attempting to say that an XB-70 used less fuel per mile than a 737. Just that it is more efficient at supersonic speeds than at subsonic speeds.

Also for the Concorde. Yes, it is more fuel inefficient than any other airliner, even at subsonic speeds. It's just that it is relatively efficient at supersonic speeds. (Relative to what most people think of when they think of supersonic: fighters, that can use up all their fuel in a matter of a couple minutes while travelling supersonic.)

Lord Blackadder
Oct 13, 2006, 09:20 AM
Fuel efficieny is such a big issue with airlines - any new SST will probably have to be significantly more efficient than the Concorde was in order to be viable. Having a better power to weight ratio will probably help.

MacBoobsPro
Oct 13, 2006, 09:29 AM
Ram Jets or Scram Jets (forget which is which) is the way to go me thinks. :)

Grimace
Oct 13, 2006, 09:42 AM
I think I bought memory from Ram Jet ! :D

Raid
Oct 13, 2006, 10:33 AM
Now after reading the article, I think they should change the name from sonic boom, to sonic pop! :D

<snip>For example, the SR-71 had a Mach 3 range of about 3000 miles. At subsonic speeds, its range was approximately 1000 miles.)</snip> Wasn't the SR-71 more efficient at supersonic because it's fuel seals and skin required thermal expansion before becoming leak proof? ... well ok maybe there were still some fuel efficiency gains at supersonic, but these things needed air-to-air refueling after take off and a warm up! So as long as you go supersonic your good, but don't leave it with a full tank on the tarmack. :)

Anonymous Freak
Oct 13, 2006, 10:37 PM
Now after reading the article, I think they should change the name from sonic boom, to sonic pop! :D

Wasn't the SR-71 more efficient at supersonic because it's fuel seals and skin required thermal expansion before becoming leak proof? ... well ok maybe there were still some fuel efficiency gains at supersonic, but these things needed air-to-air refueling after take off and a warm up! So as long as you go supersonic your good, but don't leave it with a full tank on the tarmack. :)

That's part of it. When it would go on missions, they would fill up halfway on the ground, take off, do a quick supersonic jaunt to heat the body up, then come down and refuel from a tanker.

The other part is that the engine is designed so that the inlet spike actually makes the engine compartment acts sort of as a ramjet at supersonic speeds. Estimates range that at Mach 3, between 40% and 80% of the thrust comes from this ramjet effect, not from the actual turbine jet engine.

uaaerospace
Oct 14, 2006, 09:22 AM
This figure shows one of the main problems with aircraft going supersonic. Drag increases tremendously as the flight speed approaches Mach 1. There is some optimization that can be done to minimize this increase, however it can't be completely eliminated. Notice this increase begins between Mach 0.8 and 0.9. It is no coincidence that modern airliners top out around M=0.86.

http://www.centennialofflight.gov/essay/Theories_of_Flight/Transonic_Wings/TH20G3.jpg

Being an aerospace engineer, I love me some plots. :D

uaaerospace
Oct 14, 2006, 09:42 AM
here is another image of the sound barrier.
really cool
http://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg/300px-FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg

I know it's popular belief that that photo was taken at the instant the sound barrier was broken, but that doesn't seem likely. More likely it was taken right before the Mach 1 condition (sound barrier broken). When M=1 is achieved, a shock forms along the frontmost part of the aircraft. It does not form far back as depicted in the photo. The F-18 is most likely in the transonic flight regime. In transonic flow, the flight speed is less than M=1, though the flow over the aircraft surfaces reaches or exceeds M=1. On the wing, this usually occurs at about the 60% chord (slightly behind the middle of the wing from front to back).

It's an awesome picture nonetheless. I have a 24x36in framed copy of it in my bedroom.

h?
Oct 14, 2006, 03:14 PM
That would be so good. I really wanted to go on concorde but never had a chance to do so. This would be cool to travel on.

IJ Reilly
Oct 14, 2006, 10:05 PM
This figure shows one of the main problems with aircraft going supersonic. Drag increases tremendously as the flight speed approaches Mach 1. There is some optimization that can be done to minimize this increase, however it can't be completely eliminated. Notice this increase begins between Mach 0.8 and 0.9. It is no coincidence that modern airliners top out around M=0.86.

Isn't it also true that supersonic aircraft fly at significantly higher altitudes than subsonic aircraft, and can take advantage of the thinner air?