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Terms & Definitions


The science of air in motion.
Above ground level – altitude.
A control surface on the trailing edge of the wing which creates bank or helps reduce roll.
Air foil / Aerofoil
Any surface designed to react to the air through which it moves. Four basic typpes:
- Symetrical – curved on top and bottom
- Flat bottomed
- Under cambered – the bottom surface follows the camber of the upper surface; as in a flixible wing
- Reflexed – characterised by the turned up trailing edge
The main structure of an aircraft.
The speed of the aircraft through the air.
Angle of Attack
The angle of the wing in relation to the direction of the wind’s motion. The angle is created by the intersection of the line of the chord of the wing and wind flow.
An electrolytic process of corrosion protection for aluminium.
The point of an angle made by the two wing leading edges.
Above sea level – altitude 
Aspect ratio
Wingspan divided by average chord.
For Rogallo wing – square of the wingspan divided by wing area.


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 line of any of the three planes (longitudinal, lateral, or vertical) that pass through an aircraft’s centre of gravity.
The angle of lean to the side, or roll.
Strips of light wood or fibreglass inserted into pockets at the trailing edge of a wing to reduce flutter.


The upward curve of the flexibly lifting surface when filled with air. Billow substantially influences the handling on a hang glider.
The type of aircraft that has two wings, one above the other.
The curvature revealed by a cross-section of a wing.


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.


Cylindrical wing
A helical twist of the leading edge of a Rogallo hang-glider produces a cylindrical sail.
Outrigger cables which counteract the tendency of the leading edge to bend while in flight.
The force of wind resistance which opposes the forward motion:
The crabbing motion – the angle between the actual forward motion and the direction the nose is pointed.
A triangular shape – generally of the wing.
The upward angle of the wings on the vertical plane for the purpose of greater stability.


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.
Induced drag
Drag created by the generation of lift.
N Number
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.    


Parasitic Drag
Drag created by the aircraft structure.


Rigid Wing Hang Glider
Both leading edge and trailing edges are attached to and supported by the frame. Use various lateral controls, like tip rudders, spoilers or natural rudders to augment weight shift control. Sink rates vary from 180-250 fpm and the glide ratio is usually above 8-1.
Standard Rogallo – Hang gliders with the leading edge of usually between 15 and 20 feet long and the keel the same. The nose angle is between 80 and 90 degrees with a sail billow of 3 to 5 degrees. The trailing edge is unconnected to the frame. The glide ratio is in the range of 4-1 to 6-1.




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