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Fake sonic booms

rwguinn said:
It is my understanding that the shock comes off the front and back of the airplane--every one I've ever heard was a double boom--and I spent 4 years at Edwards doing flight test.
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If you want to get really, really technical about it, most supersonic aircraft throw off a whole series of oblique shocks, as you can see in a Schlieren image of a test article. Here's one for a T-38: NASA Image

Now every one of those shocks is a pressure discontinuity. Air hits the shock at one speed and angle, and leaves it at a different speed and angle. It's kind of like light waves "bending" when they hit glass or water at an angle -- think of the shocks defining the edges of the glass, not describing the fluid flow. What's happening is the supersonic freestreem is coming straight at the aircraft, and it's being forced to turn, first by the aircraft's nose, then the inlets or wing roots, the canopy, the structure, tail surfaces, etc. Each turn sets up its own shock.

The air also has to turn back to the direction of the freestream after the aircraft has passed. That's the "tail" shock. This and the nose shock are the strongest ones, because they correspond to the greatest amount of turning. The other shocks, all the little ones inside the cone of the nose shock, are much weaker -- they only turn the fluid a little bit, and the fluid is already mostly going the direction it needs to after encountering the nose. Correspondingly, the pressure discontinuities here are much smaller.

Now, again, with the Shuttle, because the Shuttle is the only aircraft that doesn't fit entirely within the cone of its own nose shock, it actually gives off two of them. So its "double boom" is two booms of extremely high amplitude. The Shuttle, like all other aircraft, has all of these other little shocks and also a tail shock as well, so it's not really a "double boom" and with sensitive equipment you can see all of these. But it is much more likely to sound like a double boom than any other vehicle.

rwguinn said:
Just FYI, Ryan, et al. The SR-71 sonic boom is a (Fairly) long, drawn-out thing, and not of a particularly high amplitude.
When I was at Edwards in the 1970's we flew the YF-12/SR aircraft with F-104 chase (only for T-O, landing, and refuel, of course). The SR-71 bOOm was a kaaaaa-boooooom.
The F-104 was a very sharp, rifle-like CRACK-crack! of a very, very short duration--and BTW-I've actually SEEN the shocks from a 104 on the lakebed!
The Flight Sciences guys told me that that was due to the fact the aerodynamic length of the SR is around 1000 feet, and the F-104 is more like 10 feet. Not being a fluids guy, I dunno.
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Cool. I believe the long SR-71 boom, it was a very long aircraft and highly optimized for low drag, so the nose shock would have been relatively weak, perhaps comparable to the secondary shocks. It also would have entrained the air for some distance so the tail shock would be delayed quite a bit, I don't know about 1000 feet but it's possible. The Shuttle, in contrast, is trying to be as draggy as possible, so its wake is almost certainly turbulent and the tail shock would follow it closely...

As for the F-104, I wonder if you weren't hearing only the nose shock, but instead hearing it directly and then reflected off the lakebed? All of these effects will echo off of hard surfaces.
 
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R.Mackey said:
If you want to get really, really technical about it, most supersonic aircraft throw off a whole series of oblique shocks, as you can see in a Schlieren image of a test article. Here's one for a T-38: NASA Image

Now every one of those shocks is a pressure discontinuity. Air hits the shock at one speed and angle, and leaves it at a different speed and angle. It's kind of like light waves "bending" when they hit glass or water at an angle -- think of the shocks defining the edges of the glass, not describing the fluid flow. What's happening is the supersonic freestreem is coming straight at the aircraft, and it's being forced to turn, first by the aircraft's nose, then the inlets or wing roots, the canopy, the structure, tail surfaces, etc. Each turn sets up its own shock.

The air also has to turn back to the direction of the freestream after the aircraft has passed. That's the "tail" shock. This and the nose shock are the strongest ones, because they correspond to the greatest amount of turning. The other shocks, all the little ones inside the cone of the nose shock, are much weaker -- they only turn the fluid a little bit, and the fluid is already mostly going the direction it needs to after encountering the nose. Correspondingly, the pressure discontinuities here are much smaller.

Now, again, with the Shuttle, because the Shuttle is the only aircraft that doesn't fit entirely within the cone of its own nose shock, it actually gives off two of them. So its "double boom" is two booms of extremely high amplitude. The Shuttle, like all other aircraft, has all of these other little shocks and also a tail shock as well, so it's not really a "double boom" and with sensitive equipment you can see all of these. But it is much more likely to sound like a double boom than any other vehicle.



Cool. I believe the long SR-71 boom, it was a very long aircraft and highly optimized for low drag, so the nose shock would have been relatively weak, perhaps comparable to the secondary shocks. It also would have entrained the air for some distance so the tail shock would be delayed quite a bit, I don't know about 1000 feet but it's possible. The Shuttle, in contrast, is trying to be as draggy as possible, so its wake is almost certainly turbulent and the tail shock would follow it closely...

As for the F-104, I wonder if you weren't hearing only the nose shock, but instead hearing it directly and then reflected off the lakebed? All of these effects will echo off of hard surfaces.
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Well-there were 2 lines of dust that went past us at a high speed coincident with the "cracks". And they were reeeeal close together.
(He was pretty low, however)
 
R.Mackey said:
Talking to the Shuttle was quite popular. We got a lot of contacts on Mir because, first of all, they were on orbit for a long, long time, and second, not too many people seemed to know about it.

Shuttle was different. Lots of competition. We could get a weak signal with no direction-finding at all, but if we wanted them to talk to us in the limited time available, we needed to have a nice, strong, readable signal, and we needed to get on it as soon as the track began. Being on the West Coast helped, but we had to be right on it as soon as they came over the horizon.

Although I also seem to recall my dad had an ace in the hole -- 2 meter simplex is supposed to be limited to 5 watts, if I remember right, but he had a 1500 W amplifier on standby, just in case it didn't work out, so as not to disappoint the kiddies. Never needed it, though. :p
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I remember talking to MIR a few times- it helped running around 500 watts (In FM mode the loudest signal overrides all the others.) But to me the most amazing ham communications coup was when my friend K2RIW was able to copy the astronauts in the Apollo Command Module while in lunar orbit using a homemade dish antenna. The "we never went to the Moon" wackos always seemed to have a hard time explaining how that worked if the astronauts really were just in Earth orbit.

This woman needs to be removed from her teaching position post haste.
 
Hamradioguy said:
But to me the most amazing ham communications coup was when my friend K2RIW was able to copy the astronauts in the Apollo Command Module while in lunar orbit using a homemade dish antenna. The "we never went to the Moon" wackos always seemed to have a hard time explaining how that worked if the astronauts really were just in Earth orbit.
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That's pretty impressive.

Of course, here at NASA, we did the same thing, except our "homemade dish antenna" was 64 meters wide... Before my time, alas.

More importantly, the Soviets also tracked the flight. With the Doppler shifts for orbits, differential between the command module and lander, occlusion behind the Moon, etc., etc. Absolutely no way in the world one could fake all that.
 
R.Mackey said:
Absolutely no way in the world one could fake all that.
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Just wait til Dan Brown gets around to it.

Wait...He sorta already did in Deception Point. Okay, not a moon landing plot, but preposterous all the same.
 
R.Mackey said:
That's pretty impressive.

Of course, here at NASA, we did the same thing, except our "homemade dish antenna" was 64 meters wide... Before my time, alas.

More importantly, the Soviets also tracked the flight. With the Doppler shifts for orbits, differential between the command module and lander, occlusion behind the Moon, etc., etc. Absolutely no way in the world one could fake all that.
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The brits were also watching.

http://wapedia.mobi/en/Goonhilly_Satellite_Earth_Station

But, I guess we were in on it so that doesn't count.

Woof!
 
This "teacher" probably cannot even remotely grasp the technical aspects of the unique sonic boom the Shuttle creates. And, I doubt she could grasp the technical near impossibility of faking a unique sonic boom such as this.

I have watched the shuttle docked with the ISS through my telescope using a satellite tracking program. You can't see fine detail, but you can easily recognize the general shapes of the various ISS components as well at the shuttle itself. I wonder how this so called "teacher" would explain away this fact.

L.
 
Lupie said:
I have watched the shuttle docked with the ISS through my telescope using a satellite tracking program. You can't see fine detail, but you can easily recognize the general shapes of the various ISS components as well at the shuttle itself. I wonder how this so called "teacher" would explain away this fact.

L.
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That's easy. Every telescope has a mini CGI projector built in, just to create fake images of the shuttle.


And before you ask, yes, even the telescope you made yourself, Mr. NASA Shilly Person!
 
I saw, with my naked eyes, the Shuttle and Mir during one of their link-ups. That same night my wife and I laid in the park across the street watching satellites go by.
 
Lisa Simpson said:
My niece is taking an elective class this year at her middle school called "pop culture". Frankly, I'm pissed off over it anyway as they got rid of computer class for learning Marilyn Monroe's real name, but whatever. Thanks to the Governator, California kids are getting a top notch education in useless crap.

Anyway, the woman teaching the class believes in every conspiracy theory. JFK assassination magic bullet theory, bombs in the World Trade Center, moon Landing hoax - she believes them all. Not only does she believe we didn't land on the moon, she believes we've never been to outer space at all. When a student said "but what about the sonic booms" made by the re-entering space shuttles, she said "the government faked them".

So my question is - how difficult would it be to fake the double sonic booms we hear every time the shuttle comes home?
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Ya know, as soon as I think I'm getting staid in my life, I see something like this and realize I'm going to be an activist up to drawing my very last breath.

This person is allowed to be teaching??!! I'd create a sonic boom just by the speed with which I'd be heading to the principal's office of the school. I really don't give a damn if she's a human and has feelings. She is dangerous! And given enough rope - she'll probably be anti-fluoride, anti-vax, etc... This person shouldn't be allowed to teach any class.

And just what are the educational/training requirements for a teacher of "pop culture"?

Well, I've ready every issue of People Magazine,... ever!
You're hired!
 
She teaches other classes besides the pop culture class. English, I think. Not sure. None of my sons ever had her as a teacher.
 
While I'm not quite as vociferous about it as Foolmewunz here, I agree: The principal needs to be talked to. It's one thing to hold a weird belief, but if she's starting to propogandize to students, that's a whole other level right there. It's a real problem at that point. School is for learning, not agitprop. And preaching trutherism and other pseudoscientific conspiracy fantasy is the epitome of that.
 
R.Mackey said:
If you want to get really, really technical about it, most supersonic aircraft throw off a whole series of oblique shocks, as you can see in a Schlieren image of a test article. Here's one for a T-38: NASA Image

Now every one of those shocks is a pressure discontinuity. Air hits the shock at one speed and angle, and leaves it at a different speed and angle. It's kind of like light waves "bending" when they hit glass or water at an angle -- think of the shocks defining the edges of the glass, not describing the fluid flow. What's happening is the supersonic freestreem is coming straight at the aircraft, and it's being forced to turn, first by the aircraft's nose, then the inlets or wing roots, the canopy, the structure, tail surfaces, etc. Each turn sets up its own shock.

The air also has to turn back to the direction of the freestream after the aircraft has passed. That's the "tail" shock. This and the nose shock are the strongest ones, because they correspond to the greatest amount of turning. The other shocks, all the little ones inside the cone of the nose shock, are much weaker -- they only turn the fluid a little bit, and the fluid is already mostly going the direction it needs to after encountering the nose. Correspondingly, the pressure discontinuities here are much smaller.

Now, again, with the Shuttle, because the Shuttle is the only aircraft that doesn't fit entirely within the cone of its own nose shock, it actually gives off two of them. So its "double boom" is two booms of extremely high amplitude. The Shuttle, like all other aircraft, has all of these other little shocks and also a tail shock as well, so it's not really a "double boom" and with sensitive equipment you can see all of these. But it is much more likely to sound like a double boom than any other vehicle.



Cool. I believe the long SR-71 boom, it was a very long aircraft and highly optimized for low drag, so the nose shock would have been relatively weak, perhaps comparable to the secondary shocks. It also would have entrained the air for some distance so the tail shock would be delayed quite a bit, I don't know about 1000 feet but it's possible. The Shuttle, in contrast, is trying to be as draggy as possible, so its wake is almost certainly turbulent and the tail shock would follow it closely...

As for the F-104, I wonder if you weren't hearing only the nose shock, but instead hearing it directly and then reflected off the lakebed? All of these effects will echo off of hard surfaces.
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I just wanted to say, this is really some fascinating stuff. Thanks for taking the time to put this info into easily understandable terms.

L.
 
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Lupie said:
I just wanted to say, this is really some fascinating stuff. Thanks for taking the time to put this info into easily understandable terms.

L.
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+2

That's what I like so much about this place: most of the scary smart people can explain esoteric concepts in such a way that even I, the world's preeminent layperson, can understand.
 
R.Mackey said:
Yup, turbojets are noisy beasts. I've always thought the (similarly subsonic) Harrier was a noisy bird, but the Intruder/Prowler might be even worse...
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Probably the loudest sound I've ever heard. My father worked for McDonald Douglas as a stress engineer on the AV-8B. I dropped him off at work one day, and one was hovering around. It eventually hovered over near my car. At the time, I was a car stereo nut, and had 1500 watts of amplifiers pushing 8 12-inch woofers. I cranked the stereo to full blast, and the jet noise still drowned everything out. It was incredible.
 
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