Sonic Booms explained...

[Sundog]

This explanation of sonic booms (http://www.youtube.com/watch?v=gWGLAAYdbbc) and it's effects is excellent. I only bring it up because I had to explain to my cousin's daughter, who thought she saw an airplane go supersonic because she saw shock waves around it, that it wasn't actually supersonic. This video does so with some great footage.

Although there is one error in it. There was one part where they refer to plane in it as an SR-71; it was actually a T-38. It was from the test NASA performed to use the sun as a back-light for Schlieren Photography (http://en.wikipedia.org/wiki/Schlieren_photography) of full sized aircraft.

[jmig]

Interesting and educational. For the pilot in the cockpit it is no big deal. You don't hear or feel anything different.

Must be part of Einstein's Relativity. LOL

[PRB]

The shock waves from the rocket was amazing!

It's interesting to note that the closer the super-sonic plane is to you when it passes, the closer together in time the two booms reach you. When it passes very close, the two booms are almost indistinguishable from each other (B-BOOM). But if the plane is very high, the booms are separated more (boom ... boom) I wonder what the reason is for this. Are the two shock waves traveling at different speeds? That doesn't make sense, since they are both traveling through the same air.

[jmig]

The shock waves from the rocket was amazing!

It's interesting to note that the closer the super-sonic plane is to you when it passes, the closer together in time the two booms reach you. When it passes very close, the two booms are almost indistinguishable from each other (B-BOOM). But if the plane is very high, the booms are separated more (boom ... boom) I wonder what the reason is for this. Are the two shock waves traveling at different speeds? That doesn't make sense, since they are both traveling through the same air.

The two booms, wing and tail surfaces, travel out as Vs the farther away the wider the Vs spread. So while the angle may be the same the distance between the two booms increases with the distance of the aircraft from the observer.

Does that help?

[Sundog]

The reason it sounds like two booms the farther away you get is that as it travels through the atmosphere it coalesces into what is known as an "N-Wave." Below is a link to a powerpoint presentation by DARPA regarding the low boom F-5E test bed that was flown that has an excellent graphic showing the sonic boom signature in the nearfield around the aircraft and how it changes shape into the N-Wave as it propagates.

You have to copy and paste the link into a new window for it to work.

<cite>http://www.sonic (http://www.sonic/)booms.org/F5SSBD/SSBD_SSBE_Program_040317.ppt</cite>

[Wing_Z]

Having been told as a child that thunder is "when the clouds bang together"...:d

Interesting that the NASA F-5 mods reduced the first overpressure but have the same negative secondary amplitude.
Wonder whether that reduces the overall effect - or does it just go boomBOOM ?

[Jagdflieger]

I've always wondered about the twin boom from an aeroplane. Thanks for the info and the link.

[exc141ac]

For the pilot in the cockpit it is no big deal. You don't hear or feel anything different.

Pilot training T-38 (early 70s) -- you file for supersonic flight, go to the area, clear, lower the nose, go to Mil Power, kick in the afterburners . . . the little Mach needle goes past 1.0

Biggest effect is visual: since the ABs bypasses the flow meters the fuel flow doesn't change past mil power,
but you can actually watch the fuel levels droping with the burners on.

[Sundog]

My former boss was a T-38 pilot, but he switched to helo's because he found flying around at altitude boring, lol.

But I do have a question for you guys in the supersonic club. When you go supersonic, do you notice it in terms of sound? What I mean by that is, do the noises emanating through the airframe change or is the noise of the airflow around the canopy what dominates anyway, so you don't really notice a difference in the hum? I say that because I assume you still hear the engines emanating through the airframe.