initial cut on the engine, there will be a period of gliding but almost instantanious "drop like a brick" moments after and then of course that moment during your battle in-game, everyone looks up to catch a glimpse of the poor bastard flying it go up in a beautiful explosion.
I should be affraid for my characters life when I hear a chopper going down near me!
http://en.wikipedia.org/wiki/Equations_for_a_falling_body