Not only that, but even an aircraft with full inverted oil/fuel systems can't sustain zero 'g' for any length of time (I believe) -- after all, if there's no applied 'g' there's no way of recovering the oil...
For this reason the aircraft I fly has a limit of 3 minutes for sustained -ve 'g', but only 15 seconds (IIRC, don't have the books to hand) for knife-edge or zero 'g' flight.
Last edited by Dimensional; 2nd October 2005 at 13:47.