Control line (called U-Control in some countries) is a simple way of controlling a flying model aircraft. The aircraft is connected to the operator by a set of wires, which work the elevator of the model. This allows the model to be controlled in the pitch axis. It is constrained to fly on the surface of a hemisphere by the control wires.
Competitions for control line aircraft are held in various classes. These include
- precision aerobatics (aka stunt)
- team racing
- naval carrier
Precision aerobatics consists of flying a set of maneuvers (all based on the loop) which are judged by a panel of judges for accuracy and other factors. "Stunt" models tend to be among the larger Control Line models, spanning around 45 inches (1.1 m). They are often powered by a two-stroke engine in the 6-10 cc (0.40-0.60 cu) range. The aircraft is almost always fitted with flaps, which work in conjunction with the elevator, to increase the pitch maneuverability. When up-elevator is applied, the flaps on the wings go down, and vice versa. "Stunt" models are often beautifully painted, since the judging of the manoeuvers is partly aesthetic, and a "pretty" model might help the score.
Team racing is an event for two-person teams - the pilot and the pit crew. There are various classes of team race - A and B (for different engine sizes), Goodyear (certain restrictions on the shape of the model) and so on. However, the basic idea of all the events is that a number of models (often three or four) fly together, aiming to complete a given number of laps before any of the others. The model is also required to make a pit-stop during the race, where it is refuelled, the engine restarted, and the model re-launched. This is the job of the pit crew. There are rules about how the pilots must walk around each other, and how to pass (harder than you might think - remember each model is on the end of a pair of control lines).
Combat is an event where highly maneuverable flying-wing aircraft are flown two-up. Each model tows a paper streamer, and the aim is to cut the oponent's streamer as many times as possible with your propellor. A point is scored for each cut. As combat models are fast and twitchy, and are chasing each other around, the mortality rate of the models is high. Deliberate collisions are not allowed, but plenty of accidental ones happen. Combat is a very exciting event, particularly for the pilots but also for spectators.
Navy carrier is an event where semi-scale models of real naval aircraft are flown. Takeoff and landing are from a simulated aircraft carrier deck, with arrestor wire. The aim of the flight is to have a number of fast laps, flown as fast as possible, followed by a number of slow laps, flown as slow as possible. This is followed by the carrier deck landing, attempting to snag the arrestor wire. Carrier models usually have a third control line, worked by a finger trigger in the handle. This line allows the throttle setting of the engine to be controlled. Often, a carrier model will have flaps. However, unlike a "stunt" model, these are worked separately from the elevator. A large amount of flap is usually applied during the "slow" laps.
Scale is an event where an accurate scale model of a real aircraft is flown. Scoring is based partly on static judging, for how closely the aircraft resembles the full-size, and how well it is finished, and partly on the flight performance. Extra points are often awarded for "working" features of the model, such as retracting undercarriage, droppable bombs, and so on. Certain more complex scale models us a fly-by-wire approach to allow a multitude of extra working features. A radio-control transmitter can be adapted to send its signal along the elevator control lines, instead of broadcasting them. Standard servos can then be used in the model.