Terms & Definitions
The autogiro has an engine-driven propeller like a fixed-wing aeroplane, and a rotor which is not engine-driven but is purely and simply a rotating wing. In flight the propeller drives the Autogiro forward, while the motion of the air now turns the rotor automatically (known as auto-rotation). As the rotor turns, air passes over its aerofoil shaped blades, developing lift in the same way as the wing of an aeroplane. As long as the Autogiro maintains a forward speed the rotor will develop sufficient lift to keep the machine airborne. If forward speed drops the rotor will still be turned, but lift will be reduced, and the Autogiro will glide to earth.
(In the direct take-off type of Autogiro, the rotor is geared to the engine temporarily prior to take-off, permitting a jump-start, without forward run.)
The Convertiplane is an aircraft which takes off as a helicopter and "converts " into an Autogiro or fixed wing aeroplane for forward flight. Its rotor is engine-driven and it takes of like a normal helicopter. In the air, engine power is gradually transferred from the rotor to orthodox propellers. These propellers provide thrust (and counter torque), and the rotor is used solely to provide lift and control, as in an Autogiro.
Convertiplanes usually have small fixed wings as well as a rotor, and these provide most of the lift required in cruising flight, with the rotor in auto-rotation. Examples are the Farfadet, McDonnell XV-1, and Rotodyne.
Other types of convertiplane have rotors that tilt through 90 degrees to serve as propellers for cruising flight. Examples are the Bell XV-3 and Transcendental Model I-G.
The helicopter's rotor is turned continuously by the engine, and provides both lift and propulsion. It creates sufficient lift to keep the helicopter airborne without any forward speed. Thus the helicopter can take off and land vertically, and hover. Progress in any direction is achieved by tilting the whole rotor assembly, to provide thrust as well as lift: for example, by tilting it forward the helicopter is propelled forward. A helicopter can, therefore, fly forward, backward or sideways. Most single-rotor helicopters have a small tail rotor to counter torque of the main rotor, which would otherwise tend to rotate the whole fuselage in the opposite direction to the rotor.
The United States did not formally register aircraft until 1927. In January 1927 temporary numbers were issued to existing aircraft. Later in 1927 permanent registrations began to be issued (with NC26: 1 to 25 were reserved by the Dept of Commerce). The US used a NC / C / R / NR / NS / X / NX prefix depending upon the licence status.