In article ,
Bob Engelhardt wrote:

Eric R Snow wrote:
... two big glowing lights appeared behind the jet and the
contrail disappeared. ... I think
we must have been seeing afterburners. ...

Hmmm ... I wonder why the contrail disappeared. With all that much more
fuel being burned and water vapor being created, I would think that the
contrail would get even bigger. Anybody know? Bob

Seems I remember hearing somewhere about a chemical that could be
introduced into the exhaust that would suppress and/or eliminate vapor
trails. IIRC something was/is particularly nasty about it, toxic,
corrosive or some such. It was for the cloak and dagger types, recon,
stealth and all that.

Just Googled around for a second, take a look at this...

http://www.google.com/search?q=paten...=Google+Search

Erik