There are also various beginner categories on the national level, to match the skills of every flyer.

The international class is F2C. A pilot and a mechanic compete as a team to fly small (350 grams)(12 oz.) 65 cm (25 in.) wingspan semi-scale racing models over a tarmac or concrete surface. Lines are 15.92 meters long (52.231 ft).
Three pilot + mechanic teams compete simultaneously in the same circle, and the object is to finish the determined course as fast as possible. The all-out important catch is that tank size is limited to 7 cc. (About one and a half teaspoon.) Thus 2-3 pitstops for refueling are needed during the race.
The mechanic stands at a pit area outside the marked flight circle. He will start the engine and release the model at the start signal and then stand alert for refuelling. The pilot will operate a fuel shutoff by a quick down elevator movement after the planned number of laps so that the model can approach the mechanic at optimum speed, around 50 km/h (30 mph). The mechanic will catch the model by the wing, fill the tank from a pressurized can by a hose and finger valve. Then restart the engine by hitting the carbon fiber/epoxy resin propeller with his finger. Ground time of a good pitstop is less than three seconds.
The race course is 10 km, corresponding to 100 laps. Flying speeds are around 200 km/h (125 mph), which means that the pilots have to turn one lap in 1.8 seconds. Line pull due to centrifugal force is 85 N (17 lb) (19 g:s). A faster model will overtake by the pilot steering it above the slower one while he moves his handle with lines over the opponent pilot's head. Conduct of both pilots and mechanics is subject to numerous regulations. Line tangles aren't as common as you might think, since the penalty normally is wrecked models. Natural selection at work.
After two rounds of elimination heats, the 6, 9 or 12 fastest teams enter two semifinal rounds, and the three fastest teams in the semifinals go to the final, which is run over the double course.
Maximum engine size is 2.5 cc (.15 cu.in.). Diesel, i.e. compression ignition engines are used. They are single cylinder two-stroke, designed and highly specialized for this purpose. At the world championship level it is not uncommon that the competitors design and build their own engines. Their output power is approaching .8 horsepower at 25,000 rpm. A drawing of engine and tank.
The fuel is 50% kerosene, 35% diethyl ether, 10% castor oil plus various additives, most notably amyl nitrate 1-3%. (And maybe a few specials, such as my own.) The tank 7 cc capacity leads to fuel economy tradeoffs to limit the number of pitstops to two. The fuel system includes a multifunction valve to ensure optimum starting, running, stopping and refuelling operations.

Top Pilots, E/Ch '97:
Gusev, RUS,
A Beliaev, RUS

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Mats Bejhem preparing for a Combat bout. (40k)

Kozyol, an Ukrainian combat engine.

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.