A.I.D. Aircraft Inspection Directorate. A department of the Air Ministry whose duty is to see that aircraft and aircraft parts reach the standards laid down by regulations.
“A” Pilot’s Licence. A flying licence which permits the holder to fly wherever he desires and carry passengers or goods for private purposes.
Absolute Ceiling. The height above which an aeroplane is unable to climb farther.
Acorn. A small device fixed at the points of intersection of two bracing wires to prevent abrasion.
Aerobatics. Evolutions intentionally performed in an aeroplane which are not required in normal flying.
Aerodyne. A general term for all aircraft which are heavier than air.
Aerofoil. A surface which tends to rise when moved forward through the air. The plane or wings of an aeroplane.
Aerostat. A general term for all aircraft which are lighter than air.
Ailerons. Control surfaces near the tips of wings, and operating in opposite directions, which make an aeroplane bank.
Air Brakes. Surfaces on an aeroplane which may be turned to increase the wind resistance of the aircraft.
Air Log. An instrument which measures the distance an aircraft travels in relation to the air.
Air Scoop. A scoop in the front of a kite balloon through which air is forced by the wind to ballonets in the envelope.
Airframe. A complete aeroplane except for the engine or engines.
Airscrew Pitch. The distance forward which an airscrew would travel in making one turn if revolved without slip in a solid medium.
Altitude Control. A small lever next to the throttle lever for adjusting the mixture supplied to the engine when an aeroplane is flying high.
Amphibian. A floatplane or flying boat which is fitted with wheels to enable it to alight on land as well as on water.
Anemometer. A ground instrument which measures the speed of the wind passing by it.
Angle of Attack. Angle of incidence.
Angle of Incidence. Angle of attack. The angle between the horizontal axis of an aeroplane and the line joining the leading and trailing edges of the wings.
Apron. The hard surface laid round hangars and aerodrome terminal buildings to facilitate the movement of aircraft.
Artificial Horizon. A gyroscopically operated instrument which indicates the fore-and-aft and lateral attitude of an aeroplane in relation to the horizon.
A.S.I. Air speed indicator. This shows the speed of an aeroplane in relation to the wind and not to the ground.
Aspect Ratio. The ratio of the span of a plane to the mean chord of the plane.
Attitude. The position of an aeroplane in its three axes in relation to the earth.
Automatic Pilot. A gyroscopically operated device connecting up with the controls of an aeroplane which keeps the aeroplane in steady flight on any desired course
B
“B” Pilot’s Licence. A licence which permits the holder to carry goods or passengers for hire or reward.
Backing. The wind is said to be backing when it is changing in an anti-clockwise direction.
Balanced Controls. A type of control in which the pressure required to move control surfaces is reduced, generally aero-dynamically.
Ballonet. A compartment within an airship into which air may be pumped to compensate for volume changes in the gas due to temperature changes, or to alter the trim of the airship.
Barograph. A barometer which automatically records barometric pressure in relation to time.
Beaufort Notation. Numbers from o to 12 denoting wind strengths from less than 1 mile an hour to 75 miles an hour and over.
Blade Angle. The acute angle made by a line joining the edges of a propeller blade at any point, and the plane of rotation of the propeller.
Blimp. A small non-rigid airship.
Blind Flying. An alternative term for instrument flying.
Bonding. The electrical joining together of metal sheathing round cables or of other isolated metal parts of an aircraft.
Boost. The difference in pressure on a supercharged engine between the inlet-manifold pressure and atmospheric pressure.
Brake Horse-Power. The power output of an engine when measured at the point of attachment of the airscrew.
Bubble. The liquid cross-level which indicates when an aeroplane is flying with its wings in a correct position.
Bumping Bag. A partly inflated bag fitted beneath the car of an airship when moored near the ground to prevent damage to the car.
Bunt. The first half of an inverted loop followed by a half roll or the second half of a normal loop.
C
Camber. The curvature of the outside surface of an aerofoil.
Catapult. A device for shooting a glider or aeroplane into the air at a flying speed.
Centre of Gravity. The point at which the weight of an aeroplane is balanced in all directions. Generally it is a little aft of the landing wheels.
Centre of Pressure. The point on an aerofoil where the line of the resultant aerodynamic force intersects the line joining the leading and trailing edges of the aerofoil.
Centre Section. The portion of the top plane of a biplane immediately above the fuselage, and the struts which support it.
Centrifugal Force. The force which tends to move a revolving body in a direction away from the axis of rotation.
Certificate of Airworthiness. A certificate issued by the Air Ministry which has to be renewed yearly, and which certifies that the aircraft concerned reaches the standards laid down by regulations.
Chocks. Triangular-sectioned devices, generally built up of wood, which are placed in front or behind aeroplane wheels to prevent the aeroplane from moving when on the ground.
Chord. The width of a wing from its leading edge to its trailing edge.
Compass Base. A circular concrete area marked with compass points on which adjustments are made to an aircraft’s compass.
Compass Course. The bearing on which an aeroplane will fly so that it follows the desired true course irrespective of drift and magnetic variation.
Compressed Air Starter. A starting device which causes an engine to rotate by the injection of compressed air into the cylinders.
Compression Ignition. A method of igniting the gases in the cylinders of an engine solely by the heat produced by compression.
Contact. The expression used by engineer or pilot when starting an aeroplane engine to denote that the ignition switches are in the right position for starting.
Control Column. The upright control, surmounted by a wheel in large aircraft, by which the pilot operates the ailerons and elevators of an aeroplane.
Course and Distance Calculator. A device for quickly calculating the course to fly for a cross-country flight in varying strengths and directions of wind.
Course and Speed Computer. A similar device to a course and distance calculator.
C.P. Airscrew. A propeller of controllable pitch.
Crankcase Sump. A part of the crankcase of an engine in which oil is collected and fed back to the oil pump.
D
Drag. The force acting on an aeroplane in a backward direction when it is in flight.
Drag Wires. Wires which transfer the drag ol the wings to the fuselage of an aeroplane.
Differential Ailerons. Aileron controls so arranged that the rising control surface moves more than the other and so reduces drag effects.
Dihedral. The angle from the horizontal at which the wings of an aeroplane are inclined upwards from the fuselage to give the aeroplane lateral stability.
Directional Gyro. A gyroscopically operated instrument which indicates when an aeroplane is turning and the amount it turns to port or starboard.
Drag Axis. A line passing through the centre of gravity of an aeroplane and parallel to the effective direction of the wind made up by the movement of the aircraft and the direction of the natural wind.
Drift. The amount which a side wind will blow an aeroplane off its true course when flying on the equivalent magnetic course.
Drogue. A sea anchor in the form of a conical device open at both ends.
Drift Angle Sight. An aircraft instrument for enabling the amount of drift of the aircraft to be measured by watching the ground through the instrument.
Dynamic Lift. The lift of an airship obtained by its movement through the air.
E
Elevators. Control surfaces at the tail of an aeroplane by means of which the aeroplane is made to climb, glide or dive.
Endurance. The time which an aeroplane can remain in flight without refuelling. Generally given for normal cruising speed.
Envelope. The gas container of a balloon or airship of any type.
F
Fairing. External shaping, round any structure, fitted with the object of reducing the wind resistance of the structure.
Fin. A vertical surface at the tail of an aeroplane to which the rudder is attached and which gives the aeroplane directional stability.
Flat Spin. A spin in which the longitudinal axis of the aeroplane is more nearly horizontal than vertical.
Flaps. Surfaces at the trailing edges of wings which can be lowered to act as air brakes or to increase the lift of the wings.
Floatplane. A seaplane which is supported on the water by one or more floats.
Flutter. A rapid backwards and forwards movement of a control surface or wing which tends to increase in intensity once it has started.
Flying Boat. A seaplane in which the body or hull supplies the support when on the water.
Flying Wires. Lift wires. Wires which transfer the lift of the wings of an aeroplane in flight to the fuselage.
Free Balloon. A balloon which is free to be blown along with the wind.
Fuselage. The main body of an aircraft to which the wings, tailplane, etc, are attached.
G
Gale. A wind of a strength equivalent to values between 32 and 63 miles an hour.
Gap. The distance between the upper and lower planes of a biplane.
Gliding. An aeroplane is said to be gliding when it is descending in an ordinary flying attitude.
Gravity Tank. A fuel tank from which the fuel runs to the engine by the aid of gravity alone.
Gross Weight. The maximum permissible weight according to regulations of an aircraft when fully loaded with crew, fuel and pay load.
Gyroplane. An aircraft whose support in flight is obtained from one or more freely revolving rotors.
H
H Engine. An engine in which the cylinders are arranged to form an H when viewed from the end.
Harness. The straps by which a parachute is attached to the body or the straps in an aeroplane to hold the pilot in his seat.
Helicopter. An aircraft designed for vertical ascent which obtains its lift mainly from one or more power-driven rotors.
I
Incidence Wires. Wires which brace the main planes of a biplane generally in the plane of two of the inter-plane struts.
Indicated Air Speed. The measurement of the speed of an aircraft which takes into account the density of the air as well as the air speed as shown by an A.S.I.
Inertia Starter. A device in which a flywheel is revolved at high speed and then connected to the engine via a slipping clutch.
Inherent Stability. A property of an aircraft design which tends to prevent the aircraft from being moved out of level flight.
Instrument Flying.Blind flying. Flying an aeroplane entirely by reference to instruments without visual reference to any external objects.
Interference. The effect which one body may have on the flow of air past another body.
International Standard Atmosphere. To permit comparisons between different aircraft, the temperature, density and pressure of the atmosphere is assumed to conform to a standard which specifies the values of these items for different heights.
Interplane Struts. The struts which join the two planes of a biplane on either side of the fuselage.
Interrupter Gear. A device which prevents the firing of a gun when the blades of the propeller are in the line of fire.
Inverted Engine. An engine in which the crankcase is above the cylinders.
Isobars. Lines drawn on weather charts joining places at which barometric pressure is equal.
Ignition Timing. The position of the piston of an engine in relation to top dead centre at which the spark occurs at the sparking plug.
Inclinometer. A fore-and-aft level in which liquid indicates the angle of climb or glide, or level flight, when an aeroplane maintains a steady attitude.
In-Line Engine. An engine in which the cylinders are placed vertically one behind the other, only one cylinder being visible from the end.
Inverted Loop. A loop begun with the aeroplane in a normal position of flight and made in a downwards direction.
J
Jettison Gear. Gear which enables fuel to be rapidly dropped should an emergency make this desirable.
Joystick. Common description for the control by which the pilot operates the ailerons and elevators of a light aeroplane.
Jury Strut. A temporary strut inserted to provide support, such as that inserted between the wings of a biplane when they are folded.
K
Kite Balloon. A captive balloon whose shape is such that it obtains lift and stability from the wind.
L
Landing Speed. The lowest air speed at which an aeroplane can make a safe landing.
Landing Wires. Anti-lift wires. Wires which carry the weight of the wings to the fuselage when the aircraft is on the ground.
Lateral Axis. A line passing through the centre of gravity of an aeroplane and parallel to the line joining the wing tips and also parallel to the ground when the aircraft is flying level.
Lateral Stability. The property of an aircraft which tends to make it return to level flight after having been forced into a bank by air disturbances.
Leading Edge. The edge of an aerofoil which first cuts the air during flight.
Left-Hand Airscrew. An airscrew which revolves in an anti-clockwise direction when an aircraft is looked at from behind.
Lift. The upward force acting on an aeroplane in flight.
Lift Axis. A line passing through the centre of gravity of an aeroplane at right angles to the drag axis, and parallel to the effective direction of the wind made up by the movement of the aeroplane and the direction of the natural wind.
Longeron. One of the principal members running fore and aft of a fuselage or hull.
Longitudinal Axis. A fore-and-aft line passing through the centre of gravity of the aeroplane and parallel with the airscrew axis.
Longitudinal Stability. The property of an aircraft which tends to make it return to level flight after having been forced into a climb or dive by air disturbances.
M
Magnetic Course. The magnetic bearing corresponding to a true course.
Magnetic Deviation. The number of degrees by which the reading of a magnetic compass in an aeroplane deviates from correct magnetic readings at various points of the compass because of the effect of metal in the aircraft.
Magnetic Variation. The number of degrees by which the magnetic north varies from the true north at a given point on the earth’s surface and during a given year.
Mass Balance. A weight fitted in front of the hinge of a control to prevent flutter of the control surface.
Millibar. One-thousandth part of the standard atmospheric pressure which will uphold a column of mercury 29.531 inches.
Monocoque. A type of fuselage or nacelle construction in which the stresses are taken mainly by the covering which gives shape to the structure.
N
Nacelle. A streamlined body carried by the wings of an aeroplane and generally housing an engine.
Navigation Flare. A flare dropped on to land to provide a point on which to take drift sights.
Non-Rigid Airship. An airship in which the shape of the envelope is retained by the pressure of the gas inside it.
Normal Axis. A line passing through the centre of gravity of an aeroplane at right angles to the longitudinal axis and to the lateral axis.
O
Oleo Leg. A telescopic leg carrying a landing wheel in which movement is damped by oil having to be forced through small holes. The return action is by springing or compressed air.
Ornithopter. A flying machine which obtains its lift during flight from wings to which a flapping motion is imparted.
P
Pancake Landing. A landing in which the aeroplane is completely stalled a foot or so above the ground and allowed to drop.
Parachute Flare. A flare attached to a small parachute to illuminate the ground during night flying.
Payload. The portion of an aircraft’s load which provides revenue, such as passengers, mail and freight.
Pilot Parachute. A small parachute attached to the main parachute, and which pulls the main parachute from its pack.
Pitot-Static Head. A combination of pitot and static-pressure tubes connected to an A.S.I. to show the speed of an aeroplane.
Pitot Tube. A tube, open at one end, and facing into a current of air.
Porpoising. An undulatory movement of a seaplane when taxying.
Port. The left-hand side of an aeroplane when looking in. the direction of its flight. Indicated at night by a red light.
Power Loading. The normal weight of an aircraft (generally in pounds) divided by the normal horse-power of the engine or engines.
Pressure Height. The height at which the gas just fills the gasbags of a balloon or airship without causing pressure.
Pterodactyl. The name of an extinct flying reptile. The name has been adopted for a particular type of tailless aircraft.
Pusher Airscrew. A propeller which produces compression in its driving shaft and so pushes an aeroplane through the air.
R
Radial Engine. An engine in which the cylinders are stationary and arranged radially round a common crankshaft.
Range. The distance which an aeroplane can travel in given conditions without refuelling.
Rate of Climb Indicator. An instrument which shows the rate at which an aircraft is ascending or descending.
Rated Horse-Power. The horse-power which an engine is designed to give at full throttle at normal r.p.m. at a given altitude in international standard atmosphere.
Retractable Radiator. A radiator used by liquid-cooled aircraft which can be lowered into the propeller slipstream as desired to adjust the degree of cooling.
Rib. A member which gives the shape to the outer covering of a wing or control surface.
Rigid Airship. An airship having a rigid framework to maintain its shape with gasbags arranged inside the framework.
Rigging. The adjustment of the various components and surfaces of an aeroplane in relation to one another.
Rigging Position. The position of the fuselage in relation to the horizontal when the aeroplane is in level flight.
Ripping Line. A cord for tearing open a specially prepared panel in the envelope of a balloon.
Rolling Instability. Instability which makes an aircraft tend to roll from side to side after having been disturbed in a lateral direction.
Rotary Engine. An engine in which the cylinders are arranged radially round a fixed crankshaft, round which the cylinders revolve.
R.P.M. Abbreviation for revolutions per minute.
Rudder. Vertical control surface at the tail of an aeroplane by which the aeroplane is controlled directionally.
S
Seaplane. An aeroplane of any type which is designed to alight on and take off from water only.
Semi-Rigid Airship. An airship with a rigid keel to assist the gas in maintaining the shape of the envelope.
Service Ceiling. The height at which the rate of climb has fallen to one hundred feet per minute.
Servo Control. A control which aerodynamic-ally or mechanically relays back power to assist the effort applied by the pilot.
Sesquiplane. An aeroplane in which one set of wings is considerably smaller in area to the other and which is generally smaller in chord as well as in span.
Sideslip. The movement of an aeroplane at right angles to its forward direction of flight either because of incorrect use of the controls or intentionally.
Slipstream. A continuous stream of air passing a solid body, such as the backwards-moving air from an airscrew passing an aeroplane fuselage.
Slots. A Handley Page device fitted to the leading edges of aeroplane wings to retain a smooth flow of air over them at speeds below their normal stalling speed, and so to maintain lateral control of the aeroplane.
Spin. A downward movement of an aeroplane in the form of a spiral which may be made when the aeroplane is stalled.
Stagger. The amount by which the leading edge of the top plane of a biplane is ahead of the leading edge of the lower plane.
Stall. An aeroplane is said to be stalled when increases in the angle of incidence of its wings produce less lift instead of more lift.
Starboard. The right-hand side of an aeroplane when looking in its direction of flight. Indicated at night by a green light.
Static Lift. The lift of an airship obtained by the difference between the weight of the air displaced by the airship and the weight of the airship and the gas it contains.
Static-Pressure Tube. A tube, closed at the end, but with small holes at the side, so designed that the internal air pressure will equal the external air pressure irrespective of forward movement.
Step. A shallow break in the smooth run of the under-surface of a hull or float to facilitate the take-off of aircraft.
Stratosphere. The outer layer of the atmosphere in which temperature varies barely at all with height.
Stub Pipe. A short pipe attached to a cylinder of an aircraft engine to carry away exhaust gasses.
Stub Plane. Projections from the hulls of flying-boats to increase their stability when taxying. An alternative for wing-tip floats.
Suck-In. An expression used by the pilot of an aeroplane when an engineer is swinging the propeller, to denote that the engine controls are properly set for mixture to be sucked into the engine.
Supercharged Engine. An engine in which the pressure at the inlet valves is increased mechanically above that of normal intake systems.
Superheat. The temperature difference between the gas in a balloon or airship and the surrounding air.
Sweep-Back. The angle at which the wings of an aeroplane are inclined backwards in relation to the fuselage.
Switches-Off. The expression used by engineer or pilot when an aeroplane propeller is being swung, to denote that the ignition switches are in the closed position in which the engine will not start.
Synchronizing Gear. A device which operates the firing mechanism of a gun by synchronizing it with the movement of the propeller.
T
Tachometer. A revolution indicator which indicates the number of revolutions a minute being made by an engine.
Tail Parachute. A parachute attached to the tail of an aircraft so that the tail may be raised if necessary to enable a pilot to stop a spin during test flights.
Tail Skid. A sprung member at the rear end of the fuselage of an aeroplane which takes the weight at the tail of the aircraft when it is stationary or taxying. It may be steerable with the rudder or free to move on its own.
Tail-Trimmer. A control to adjust the fore-and-aft trim of an aeroplane so that it will fly level without pressure being applied to the control stick.
Tail Unit. The combination of surfaces at the tail of an aeroplane made up of the tailplane, fin, rudder and elevators.
Tare Weight. The weight of an aircraft in flying condition, but without crew, fuel, oil, payload or removable equipment.
Terminal Nose Dive. A vertical engine-on dive at the highest attainable speed.
Thrust. The power produced by the airscrew, which tends to force the aeroplane along in a forward direction.
Townend Ring. A ring of aerofoil shape arranged round a radial engine to reduce the wind resistance by deflecting the passing air to the inside of the ring.
Tractor Airscrew. A propeller which produces tension on the driving shaft and so pulls the aeroplane along.
Trailing Edge. The edge of an aerofoil opposite the leading edge.
Tropopause. The dividing area between the stratosphere and troposphere.
Troposphere. The inner layer of the atmosphere in which temperature varies considerably with height.
True Course. The bearing of the desired course over the ground to be followed by an aeroplane.
Turn Indicator. A blind flying indicator which shows the rate at which an aeroplane is turning to port or to starboard. A sideslip indicator is generally combined with it.
U
Undercarriage. The complete assembly of wheels, axles, oleo legs, struts, etc., which form the landing gear. The wheels may be replaced by skis or floats in some instances.
Useful Load. The total load of an aircraft minus the tare weight.
V
V Engine. An engine in which the cylinders are arranged to form a V when viewed from the end.
Valve Timing. The position of the piston of an engine in relation to top dead centre at which an inlet or exhaust valve opens.
Veering. The wind is said to be veering when it is changing in a clockwise direction.
Venturi Tube. A specially shaped tube designed to produce a suction for driving gyroscopic aircraft instruments.
W
Wash-Out. A decreasing angle of incidence from the fuselage ends of wings towards their tips.
Water Recovery. The obtaining of water from the exhaust gases of an engine to act as ballast to replace the fuel consumed.
Weathercock Instability. A combination of sideslipping and yawing which tends to make an aeroplane turn left or right when it is kept level laterally.
Wind Tunnel. A device used in aerodynamic research and. testing which provides an artificially produced steady wind at desired speeds.
Wing Loading. The normal weight of an aeroplane (generally in pounds) divided by the number of square feet in the main plane or planes, including the aileron area.
Wing Span. The length of a plane from one wing tip to the other.
Y
Yawing. An aeroplane is said to be yawing when it is turning to left or right about an axis passing through the centre of gravity of the aircraft and vertical to the aircraft.
Z
Zoom. An aerobatic manoeuvre in which the momentum of forward or downward flight is used to gain height in a steep climb
