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Terms & Definitions


Absolute Altitude
The measureable height of an aircraft above the actual terrain.
Absolute Ceiling
The maximum altitude above sea level at which an aircraft can maintain level flight under Standard Air conditions.
Accelerated Stall
Any stall made to occur at other than 1g.
Accessory Group
Mechanical and electrical units mounted on an engine necessary for its operation, such as starter, magnetos, fuel pumps, etc.
Adcock Range
National low-frequency radio navigation system (c.1930-c.1950) replaced by an omnirange (VOR) system. It consisted of four segmented quadrants broadcasting Morse Code "A" (dot-dash) and "N" (dash-dot) signals in opposing quadrants so that pilots could orient their position relative to a "beam" broadcasting a steady tone, and a Morse Code station identifier. Using a "build-and-fade" technique, a pilot could (ideally) pinpoint his location by the strength or weakness of a signal.
Automatic Direction Finding via automated radio.


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.
Cabane Strut
A wing strut which is attached to the fuselage.


The curvature revealed by a cross-section of a wing.


An aircraft that flies tail first, with its main lift surface at the aft end of its structure.
Type of combustion chamber for jet engines in which individual flame tubes are mounted inside an annular or circular chamber.
A fixed wing which has no external wires for bracing.
Centre of Gravity / C of G
The pivotal point within the aircraft mass around which all forces are balanced,
Centre of Pressure
The point of an airfoil where there is the most concentrated lift.
Radar reflective and dispersing material released from an aircraft to confuse enemy radar equipment.
The width of the wing measured parallel to the centre line of the aircraft from the leading edge to trailing edge.
Conical Wing
A straight leading edge on a Rogallo wing produces a Conical sail.
Control Bar
The bar below the frame that controls the direction of the glider via weight shift. On the early Rogallos the control bar was two parallel bars from which the pilot ‘hung’ by the armpits. Later control bars are triangular.
Control surfaces
The air deflection surfaces which control roll, pitch, and yaw of an aircraft.
Convection currents
A series of localised air currents which are both ascending and descending. They are the cause of turbulence and can also provide lift.


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.
Co-Axial Propellers
Two propellers mounted one behind the other and driven independently in opposite directions.
Compressibility Drag
The increase of drag arising from the compression of air when flying at high speeds.
Constant Speed Propeller
One which governs an engine speed. The blade pitch being increased or decreased automatically to achieve this.
Pointing the nose slightly upwind to counteract drift and maintain a track.
Cross Spar
The lateral tube of a hang glider which connects both wing spars and the keel spar and maintains their spread. The control bar is mounted directly below the cross spar.
Cyclic Pitch Control
Means of changing the pitch of a helicopter rotor blades progressively, to provide a horizontal thrust component for flight in any horizontal direction.


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 angle which the spanwise axis of an aerofoil makes the fuselage when the wing or tailplane tip is higher than its root attachment (positive dihedral). The upward angle of the wings on the vertical plane for the purpose of greater stability.


Diurnal Winds
The daily wind pattern over a particular area.
A steep downward flight through the air.
The force of wind resistance which opposes the forward motion:
Drag chute
A heavy duty parachute attached to the aircraft structure to slow the aircraft on landing.
The crabbing motion – the angle between the actual forward motion and the direction the nose is pointed.
A triangular shape – generally of the wing.
A wrought alloy of aluminium with small quantities of copper, magnesium and manganese added.
Dust devil
An upward spiral of air that picks up dust and debris and usually indicates thermal activity.
Electronic Counter Measures – Airborne equipment used to reduce the effectiveness of an enemy’s radar or other devices which generate electromagnetic radiation.
Electronic Flight Information System
Movable control surface on the trailing edge of an aircraft’s tailplane to control pitching movement.
The streamlining of a surface to reduce the drag
The fixed, vertical surface at the tail to which the rudder is attached.
The raising of an aircraft nose to arrest sink and reduce speed.


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.
International Air Transport Association
International Civil Air Organisation
Identification Friend or Foe – An electronic device to interrogate approaching aircraft.
Instrument Flight Rules – Flight by reference to on board instruments under conditions of poor visibility or darkness.
Instrument Landing System
Incidence angle
Angle between the chord of a wing and the horizontal centre line of the aircraft


Induced drag
Drag created by the generation of lift.
Agreed International Standard Atmosphere to permit accurate comparison of performance figures – 1013.2 millibars at 15 deg C.
Jet assisted takeoff – utilising solid or liquid fuel rockets to augment the takeoff power of an aircraft’s engines.
Kinetic heating
Heating of an aircraft’s structure as a result of air friction.
Usually a tethered heavier than air aircraft, sustained in the air by its aerofoil surfaces inclined to the wing to generate lift.
Kilo-Newton – measurement of force. The force necessary to provide a mass of 1 kg with an acceleration of 1 m/sec.
Landing weight
The maximum weight at which an aircraft is permitted to land.
Landing wires
External bracing wires which support the wings when the aircraft is on the ground.
Lift / drag ratio
Leading edge
The front edge of an aerofoil which first meets the airstream in normal flight.
The force generated by an aerofoil section, acting at right angles to the airstream flowing past it .
Translated from Czech – berserk-head-ache.
It begins as an outside climbing snap roll but becomes a tail-over-nose tumble of one-and-a-half rotations for a properly executed Lomcevak. Usual recovery is a vertical dive.
To enter a Lomcevak, from upside-down position apply hard down elevator and ailerons in the direction of the desired roll with hard full opposite rudder. Controls remain in this position throughout the entire manoeuvre, however engine power is reduced immediately following entry. Critical functions determining whether the inverted snap roll progresses into the end-over-end tumble are exact airspeed, angle of climb and the ‘G’ break on entry. These factors vary with different aircraft but are 130 mph, 45 degrees and 4 – 5 ‘G’ in a Great Lakes, slightly higher in the Pitts Special.


A main structural load bearing fore and aft axis member within the fuselage.
A long range radio based navigational aid
A means of recording speed as a ratio of the speed of sound in the same ambient conditions.
Named after the Austrian physicist Ernst Mach
Magnetic Anomaly Detector – carried by maritime reconnaissance aircraft to locate submarines beneath the surface.
Distress call
A structure in which the outer skin carries the primary stresses and is free from internal bracing.
National Advisory Committee for Aeronautics (later NASA)
National Aeronautics and Space Administration
North Atlantic Treaty Organisation


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.    


Operational Conversion Unit
A flapping wing aircraft
Operational Training Unit
Landing an aircraft at an abnormally high rate of descent or low landing speed.
The angle of incidence at which a propeller or rotor blade is set.
The angular motion about the lateral axis.
Pitot tube
A small open ended tube for measuring airspeed and pressure.
Artificially increased pressure in an aircraft to compensate for the reduced external pressure as the aircraft gains altitude.
The first airworthy example of a new aircraft design or variant.


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.


VHF Omni-directional Receiver
Vertical / Short take-off and landing
Vertical take-off and landing
A conical streamer on an airfield to indicate wind direction and strength at ground level.
A metallic material, in strip lengths that was dropped to confuse enemy radar.
A small, stabilizing, rudderlike addition to the tips of a wing to control or employ air movement.


Wing loading
The gross take-off weight of an aircraft divided by its wing area.
Wing warping
A method of lateral control used by early builders where the wing is flexible and is twisted or warped by the pilot to provide roll control.
A small upright structure attached to the wing tip to reduce drag by reducing wing tip vortices.
Works number
The movement of an aircraft about its vertical axis.
The control wheel of an aircraft, akin to an automobile steering wheel.
Using kinetic energy of an aircraft’s motion to gain height.



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