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Silent sonic boom...Supersonic business jet?

Lord Blackadder

Lord Blackadder

macrumors P6
Original poster
May 7, 2004
15,746
5,633
Sod off
Just saw this very cool concept 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...
 
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:
 
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
 
stuartluff said:
Maybe NASA could look into something like this. Producing sound to create silence. Its not as stupid as I make it sound. :D
Click to expand...

Destructive interference, and it's not stupid. That's how noise-cancelling headphones work! ;)
 
here is another image of the sound barrier.
really cool
300px-FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg
 
I was doing my thesis on this...

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.)
 
ehurtley said:
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.)
Click to expand...

Wasnt the concorde scrapped because of fuel inefficiency? (as well as the 'one and only' crash) :confused:
 
ehurtley said:
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.)
Click to expand...

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.
 
Lord Blackadder said:
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.
Click to expand...

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.)
 
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.
 
Now after reading the article, I think they should change the name from sonic boom, to sonic pop! :D

ehurtley said:
<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>
Click to expand...
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. :)
 
Raid said:
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. :)
Click to expand...

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.
 
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.

TH20G3.jpg


Being an aerospace engineer, I love me some plots. :D
 
Don't panic said:
here is another image of the sound barrier.
really cool
300px-FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg
Click to expand...

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.
 
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.
 
uaaerospace said:
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.
Click to expand...

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