As Lusche said, if you shoot the wing tip off a drone or kill the pilot, it just blows up. Midway's idea would have the plane spiral down to the ground. If frame rate is an issue, there could be a check box in the options menu for "death animations", or something like that.

I'm not so sure about there not being a pilot in the drones though. I've had drones blow up on me later on in my bombing run, with no real damage done from an attacker. No puffy or ack firing when this happened. I came to the conclusion that the pilot in the drone was wounded, then died. I've also had my lead shot out from under me, switch to the next plane only to find the pilot is already wounded.
P.S.: I had to post this afterwards...Kept giving me an 80 character limit. Something has changed in the last few hours?

EDIT: Oh...dur... Figured it out. heh Wish I did a few moments sooner.
