What you describe, Tom, is condensation in high humidity air experiencing
the reduction of pressure (and therefor temperature) as it is accelerated
over the lifting surface of the aircraft. The resulting condensate flows off
the trailing edge of the wings before evaporating in a sub-saturated
environment.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html







"Tom Bennett" wrote in message
...
This morning I noticed a large, fairly low-flying, 4- engined passenger
jet go overhead through a clear blue sky (it appeared to be still in
takeoff mode from Stansted).

What immediately struck me was that it was creating a large sheet of
condensation (?) in its wake, the sheet forming a delta shape, with the
apex somewhere just under the body of the aircraft. The condensate only
lasted a few seconds before it evaporated, but the continuous production
of it looked as if the plane was trailing a large white sheet behind it.

I've seen planes form short-lived vortices of condensation from the
wingtips, but never anything as extensive as this.

It looked quite spectacular as it went overhead. I assume that pressure
differences over the wings was reducing the temperature in air that was
close to saturation(?)

- Tom
Blackmore, Essex.