I think this one is my favorite at our club fun fly's:

Each Pilot draws an envelope before the flight, then he has to climb to altitude in a certain amount of time (i.e. 60 seconds), he then kills the engine....a helper then opens the envelope for him, and it has a specific time on it (each envelope is different) and he has to try to keep the plane aloft for that time....person that lands the closest to his drawn time is the winner.