airplane and bullet shock waves

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BigFatKen

BigFatKen

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There has been some interesting discussions about bullet shock waves and flight distortions. I have never seen a contrail except at high altitudes. What are we looking at in above photo only a few hundred or thousand feet up?

See movie,12MB, with military ads but also some knive ads here:
http://shock.military.com/Shock/videos.do?displayContent=121687&ESRC=army-a.nl
 
Right.
Basically, the compression of the air in the shock wave zone behind the object forces together amospheric water molecules. These water molcules condense into small droplets (just like are present in a cloud). The small droplets diffract the light and appear white (again, just like clouds--or vapor trails).
It is very cool looking:D
Of course, if you are a big Art Bell fan, then that is the chemicals released by government agents to make you forget the visit last night by the aliens from another planet that have made a deal with the US to mining rights for your hind quarters:evil:
It could go either way.
 
picture

In the airplane picture it's not high pressure but a low pressure area that looks white. As the air expands in the low pressure it cools and the water condenses. It's not necessary to exceed the speed of sound or to create a shock wave to do this. It's commonly seen in sub-sonic scenarios.
 
And you don't have to go supersonic to create the extreme high pressure/low pressure areas. Take a look at a modern formula race car in a high humidty environment, and you'll see the same affect at the "wing" tips and other areas of high aerodynamic loading.
 
I used to fly a military surplus aircraft to airshows and such (Douglas AD-4N if you know what that is) and it had an extremely large wing that could produce massive lift.

On real humid days you could yank that thing into a high G turn and look out to see a water stream the size of a firehose squirting off the end of the wing.

Lots of fun to do :)
 
As previously mentioned

High humidity and lowered pressure can make nice contrails.
I've often watched landing planes throw off con trails in that low speed, high load condition.
 
I thought contrails had to do with the hot exhaust gas off the engines turning the moisture to steam, not about the pressure differential.
 
The photo is not of a contrail, but yes generally contrails are caused by warm moist exhaust hitting cold air.
And you don't have to go supersonic to create the extreme high pressure/low pressure areas. Take a look at a modern formula race car in a high humidty environment, and you'll see the same affect at the "wing" tips and other areas of high aerodynamic loading.
Click to expand...

Even easier, blow very hard into your hand (put your hand over your mouth so that you can create a high pressure area in your mouth). After about 30 seconds, relax the pressure, then open your mouth and slowly, very slowly, blow the air out:eek: .
You will see a small condensation cloud emerge.
Supersaturated moist air in mouth under pressure then cools.
Had an older kid show this to me when I was about 7 or 8, claimed that he smoked and some smoke was still stuck in his lungs.
 
WAtch any video with a jet yanking around in turns. The location varies between planes, but you'll get some somewhere.

Most of contrails are from moisture in the exhaust. You get a fair amount of it when you're burning several pounds of hydrogen-containing compounds every minute.
 
TEXASSIGMAN----you just made me realize how old I have become..worked on the AD's in the early 60's at NAS JAX. VA-44 RAG outfit....
 
Air shows show it very well. Whenever one of the Blue Angels dips and then yanks it up into a steep climb, you see twin contrails coming off the outer ends of the wings. Looks really cool if it's perfectly clear against the dark blue of the plane and the deep blue of the sky.
 
What you see in the pic is a Prandtl-Glauert condensation cloud -- a rare event which only occurs right around Mach 1. It is NOT the standard condensation trail you see coming off the wingtips of a jet executing a high angle of attack turn.

Here's an explanation, but you better have a degree in thermodynamics if you want to understand it --

http://www.fluidmech.net/tutorials/sonic/prandtl-glauert-clouds.htm


:)
 
The "sonic boom" of a supersonic aircraft is exactly the same thing as the "crack" of a passing supersonic bullet. The "contrail" is caused by condensation from the engines freezing at high altitude, and is caused by temperature and humidity conditions, not by supersonic flight (WWII bombers, far from supersonic, left high altitude vapor trails).

Jim
 
The "contrail" is caused by condensation from the engines freezing at high altitude, and is caused by temperature and humidity conditions, not by supersonic flight
Click to expand...

Jim, what you're describing is a simple vapor contrail. What is pictured in the OP is a Prandtl-Glauert cloud, sometime known as a Prandtl-Glauert singularity. It's a very different event from a vapor contrail or standard lift and vortex condensation.

Here are links to lots of pics of Prandtl-Glauert clouds:

http://www.galleryoffluidmechanics.com/conden/pg_sing.htm

Here's a particularly dramatic one formed around a low flying F14 --

http://www.galleryoffluidmechanics.com/conden/ef14b.htm
 
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