I recently acquired a jpg claiming to be a photograph of a sonic boom. Can this be possible? If so what exactly are we seeing? What is the cloud made out of?
(pic avail.)
I’ve seen film footage of a plane reportedly breaking the sound barrier and there was a misty cone-shaped bow wave appearing intermittently around the nose of the plane.
I think it’s just water vapour turning visible due to pressure changes (just like it does when air passes over the wings of an ordinary jet liner) - whether this is precisely due to the sound barrier having been broken or if it is just because the plane in question is generally going very fast, I’m not sure.
This Picture ? (They also have a movie of the event). The cloud is water vapor that’s been compressed by the shock wave. The temperature and humidity have to be just right to form such a nice cloud.
Yes, thankyou. The footnote did suggest that the photographer must have the right weather conditions ( in particular humidity ) as well as a whole lot of luck. The resulting cloud was uniformly conical which (to me) made it appear to be a possible phony.
Thankyou for the insight.
A supersonic shock wave can be photographed using the Schlieren technique. This involves having a black and white striped background for the photo. Since the refractive index changes in the shock wave, it can be seen as distortion in the photgraph of the black and white stripes as the object making the wave goes by.
The cloud that appears on the top of the wing or around various parts of the plane doesn’t necessarily indicate that the speed of sound has been exceeded, although it can. What it does mean is that the relative humidity of the air over the surface is at 100%, or close to it, so that when the air expands and therefore cools, moisture condenses out. I have seen it on rotation at takeoff at LAX and Boston which are on the coast and can have high relative humidity at times.
I’ve seen a picture of a car breaking mach, and you could see a line extending from the front where the sonic boom was kicking up dust. Fairly impressive.
In the strictest sense, a sonic boom can’t be photographed because it’s just sound. You can photograph it’s effects, though, which is what these pictures are.
I saw a show (Nova maybe) that was about scientests photographing the actual shockwaves. They needed a super-bright light source to do it, so they had a fighter fly supersonically directly between the camera and the sun. It worked, you could see the actual shockwaves in the air (not just vapor).
Air is invisible. What you saw was the rate of refraction changing as the air changed density.
The photos bernse was talking about are a special kind of Schlieren photos.
This PDF explains how those photos were taken: http://techreports.larc.nasa.gov/ltrs/PDF/NASA-97-1psfvip-lmw.pdf
More photos and info here.
http://www.eng.vt.edu/fluids/msc/gallery/shocks/g2af18.htm
http://www.dfrc.nasa.gov/gallery/photo/Schlieren/HTML/EC94-42528-1.html
This page shows a conical cloud around a jet, but says the jet is probably subsonic: http://www.eng.vt.edu/fluids/msc/gallery/conden/bhf14.htm
You are of course correct. I just wanted to make it clear that it wasn’t vapor that was seen.
Thanks for the links!
Here’s a really cool MPEG VIDEO of a flyby with sonic-boom cloud:
http://faculty.rmwc.edu/tmichalik/movies/F-18.MPG
Other collections of photos and videos:
http://www.wilk4.com/misc/soundbreak.htm
http://faculty.rmwc.edu/tmichalik/physmov.htm