There's a lot of possibilities. Most require a stopwatch.

1) Timed glide. Pilot gets plane in take off position. Once ready, timer says "Go". Pilot has (timed) 30 seconds to climb as high as possible, then must "kill" the engine (no idling allowed). Glides as long as possible. Time stops when any part of the plane touches down. Longest glide wins event.

Variation on above. Pilot guesses how long his glide lasted. Closest wins.

2) Take off, once pilot is at a comfortable height, timer says go. Pilot has 20 or 30 or whatever, seconds to do as many loops, rolls, or both, as possible. Highest number wins.

Of course there are limbo contests; two 10 foot poles with crepe paper stretched between them. Keep lowering the paper until pilots don't make it, or don't try.

Or egg drops; paper cup rubber banded to top of plane. Egg inserted and pilot takes off. Once over target, pilot rolls (or loops) to drop the egg. Closest to target wins.

Any of these can have bomus points added for landing closest to a point or circle on the runway. (No taxiing allowed.)

Lots of others. Get creative.
Dennis-