People in general think of Radio Control as soon as model aircraft is mentioned, overlooking the two other branches of aeromodelling, Free Flight and Control Line. These two branches may lack the appeal of realism that Radio Control offers, but they compensate by offering unique and challenging competition opportunities.

What is Control Line?

In this flavor of model flying, C/L in short, also referred to as U-Control, the models are flown in a circle and controlled by a pilot in the center holding a handle connected to two thin steel wires. The wires connect through the inboard wing tip of the plane to a mechanism that translates the handle movement to the airplane elevator, allowing maneuvers to be performed along the airplane pitch axis.
A sketch:   By Yash Mulgaonkar
The pilot will turn to follow the model going round. (And you will get dizzy just the first few flights.) The combination of line length and flying speed is such that the lines are kept straight at a tension of several times the model weight, and overhead maneuvers are possible. So that is why I call it "A Hemisphere of Fun". You can actually reach anywhere on the surface of the hemisphere above you with a radius equal to the line length.

Over the years since its introduction in the late '30:s, control line flying has developed into a high level competition sport.

 

Speed

This is the all-out speed event.

Flight is timed over nine laps after the pilot has placed his handle in a pylon fork at the center, and the speed determined. In the international class, F2A, engine capacity is 2.5 cc (.15 cu.in.). The flight radius is 17.69 m, (58.04 ft.) making 9 laps equal to 1 kilometer. This was changed from the previous 15.92 m and 10 laps on 1st July, 1997. Top speeds are above 300 km/h (190 mph, 311 km/h was the winning speed in the 1996 World Championship, on short lines).
Engines have glow plug ignition, run on restricted fuel (80% methanol, 20% castor oil) and use resonant exhaust systems, "pipes". They operate at around 36,000 rpm and develop over 2 bhp.
Model designs are very exotic with inboard wing only and single blade propeller. There is no undercarriage, but a dolly that is dropped at take-off and a wire skid for landing. Weight is around 500 g (18 oz.). In addition to the FAI F2A class there are national classes for engine sizes between .8 cc and 10 cc, as well as pulse jet engines.

 

Aerobatics

This is precision flying with big, beautiful models.

Also called Stunt. A predetermined flight program with advanced maneuvers is to be performed, and points are given for the precision by a panel of referees. The international class, F2B, has a program of sixteen maneuvers, also involving square and triangular loops with corners specified at 1.5 m (5 ft.) radius. All maneuvers except the overhead eight should have their low level at 1.5 m (5 ft.) above ground. It takes some nerve to do this repeatedly with an airplane that has taken hundreds of hours to build. Models are often very attractive with a superb finish.
Wing span is around 1.5 m (6 ft.) and weight 1.5 - 2 kg ( 3-4 lb.). Wings have flaps that are coupled to the elevator. Line length is 15-21.5 m (50-70.5 ft.). Flying speeds are around 85 km/h (55 mph). Engines are of 5.6-10 cc (.35-.60 cu.in.) size and operate at relatively low rpm (9,000) with a rich fuel setting. As the engine leans out in response to the g forces of the maneuvers, power increases to compensate for the induced drag and keep speed up.

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