In a circle laid over grass two pilots fly models that have strings with paper streamers attached to the tail. The object is to cut the opponent's streamer with your propeller, and to stay airborne. In the international class, F2D, the pilots are assisted by two mechanics each and are allowed one spare model per bout.
At the end of the 4 minute bout period, the cuts and airtime are given points and a winner of the bout is determined. The contest is run by matching competitors that haven't collected two losses until a single winner remains.
The models are able to loop/bunt at 140 km/h (90 mph) with a radius of less than 2.5 m (8 ft.) at the wiggle of your hand. That's g forces of 70 g:s!
They are at the extreme in simplicity, maneuverability and durability. Although they are strong enough to often survive ground hits at full speed, there is a considerable carnage in mid-air collisions during a competition. To enter a competition you have to bring a model stock of about half a dozen, except for the engines where three plus a spare inventory suffice if you bring equipment to clean out the soil from ground hits.