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This glossary of historic aviation terms is reproduced from 'The Spotters Glossary' which appeared in 'The Aeroplane Spotter' from January 1940 onwards. 'The Aeroplane Spotter' was the first journal devoted exclusively to the study and practice of aircraft recognition.

We are pleased to have been able to reproduce the entire glossary from A-Z, offering a unique insight into aviation terminology (and therefore aviation history and technology) prior to and during the 1940s.

NB: In the interests of clarity we have substituted current equivalents where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').

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Wake: That part of a fluid, such as air, in which the pressure head has been changed by the passage through it of a body, such as an aerofoil.

Warm Front: A body of warm air advancing over a mass of cold air. Being forced upwards, it expands. Its moisture tends to condense in the lower temperatures at height, clouds form and rain is likely to fall.

Warning: Advance notice of the approach of a rapid change in meteorological conditions.

Wash-in: An increase of the angle of incidence of a wing towards the tips.

Wash-out: A decrease of the angle of incidence of a wing towards the tips designed to delay tip stalling.

Water Lines: The lines of a flying-boat, such as keelson and chines, which determine its behaviour when water-borne.

Water Spout: The equivalent of a tornado over water. It is visible because of condensation produced by the lowering of pressure within the core.

Water Tanks: Special model testing tank for ascertaining in advance the probable behaviour of flying-boat hulls when water-borne.

Weather: The state of the atmosphere with reference to climatic conditions.

Wedge: An area of high pressure radiating from an anticyclone, which when plotted as isobars appears as a wedge.

Weight: The relative mass of a body or the relative reaction on a body caused by some attractive force such as gravity.

Wetted Area: In aerodynamics, the total area of an aeroplane or airship exposed to airflow.

Whirlwind: A small region of air revolving rapidly round a low-pressure core and acting for some hundreds of feet up from the ground.

Wind: Air in motion in the atmosphere.

Windmill: A term at one time used to describe the action of a propeller when revolving freely under the forward airspeed of an aeroplane but without engine power. Also a colloquial term for the rotor of a gyroplane.

Wind Cone: An indicator of wind strength and direction erected on an aerodrome. It consists of an open-ended fabric sleeve attached to the top of a mast. Also called windsock.

Wind "T": A horizontal T-shaped marker placed on the surface of an aerodrome to indicate wind direction to the pilots of incoming aeroplanes.

Wind Tunnel: A chamber of tunnel shape in which experiments are made to collect aerodynamic data. A steady stream of air is blown through the tunnel by a large fan at a predetermined speed. This airflow reacts on aerofoil sections or aeroplane models mounted on sensitive balances which measure the force of reaction. Corrections have to be made for scale effect to facilitate the application of the data to the design of aeroplanes.

Wing: The main lifting surface of an aeroplane.

Wing Section: The form of the cross-section of an aerofoil which determines its aerodynamic characteristics, in particular the lift and drag coefficients and the lift-drag ratio.

Wing Plan: The shape of the wing or wings of an aeroplane as seen from directly above or below.

Wing Tip: The outboard end of a wing. The shape of wing tips is important aerodynamically and in aircraft recognition.

Wing Tip Float: A buoyant body of streamline shape attached to the wing tips of a flying-boat or single float seaplane to give it lateral stability when waterborne.

Wireless: Nowadays called radio, wireless apparatus is installed in aircraft for sending or receiving signals (through the ether waves) to and from other aircraft or ground stations.

Wiring: A term applied to the electrical circuits of an aeroplane. Electrical apparatus on aircraft is now so complex that servicing is only possible by the use of intricate wiring diagrams and wires of diverse colours on different circuits.

Wood Construction: Wood was mostly used to construct early aeroplanes. Since the early 1920s, metal construction has largely replaced wood construction for aircraft.

W/T: An abbreviation for wireless telegraphy, or radio communication by dots and dashes, as contrasted with wirelessed speech or R/T (radio telephony).