Through the sound barrier!

[housefull]

I've read somewhere, these white clouds physically doesn't relate directly to the speed of sound. Don't remember exactly, it was told they appear on the speeds near to the speed of sound, that's why it is now official visual representative of sound barier braking.
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[Tinwolf]

Originally Posted by housefull

I've read somewhere, these white clouds physically doesn't relate directly to the speed of sound. Don't remember exactly, it was told they appear on the speeds near to the speed of sound, that's why it is now official visual representative of sound barier braking.
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I think it depends on several factors to do with air density, moisture content in the air etc. which is why the altitude at which contrails develop (if at all) changes all the time.
I`m sure someone will come on and give the scientific reasons but it stills looks super cool.

My most impressive memory of this effect was at an RAF Mildenhall airshow many many years ago on a very foggy, cr*ppy day when nothing was going to fly but a USAF F-4 did a few fast fly throughs each of which produced a big halo of condensation around the Rhino as it blasted through the air. Brilliant
The Phantom..... proof that given enough power anything will fly

[sicsok]

The phenomena is completely independent of the Mach number. Every time the moist air experiences sudden drop of pressure-the temperature drop that follows the pressure drop creates oversaturated humidity and thus-sudden condensation occurs. This happens on wing surfaces, canopies, wingtips, (and shockwaves if supersonic) etc. even at takeoff and landing speeds. The extent and the shape of the cloud may change somewhat by the speed regime but it mostly depends on the percentage in humidity and the severity of the pressure-change (pressure-gradient time derivative).
One rarely sees these aircraft-clouds on arid early-afternoon flights over the Chad desert by the Mirages, but at the humid Alps the wingtips "smoke" even until touchdown on the landings of the F.18-s.
BTW to Housefull:
At supersonic regimes the cloud does not form at the shockwave (where the pressure and temp. increases) but at the expansion waves - accross which the pressure (thus the temp.) drops. Plainly the first shockwave of the flying plane is at the nose or at the tip of the boom -if there is one), but no one have seen vapor there. At locations where the shape curves or folds mor streamwise or even (at the tail particularly) toward the vehicle's longitudinal center the expansion waves are formed.