Originating in the early 1940s in America control-line operated model aircraft is the only branch of aeromodelling where the pilot maintains physical contact with the model. Using two thin lines varying in length from twenty to seventy feet depending on the size of the aircraft and power plant the pilot actually flies the craft. Inside the model a bell crank, triangular in shape, transfers the movement from the pilots handle via pushrods to the elevators and in some cases flaps. This movement causes the aircraft to climb and dive as the pilot moves the handle up or down. Control Line or c/l models are divided into various branches i.e. Aerobatic, Combat, Team Race, Speed, Scale and Sport. Each branch requires a different type of model and engine, but the skill to fly them remains a co-ordination of hand and eye timing. Costs vary considerably depending on the type of model plus engine.