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equivalents where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').
Absolute ceiling. The greatest height which can be reached by an aerodyne or aerostat in Standard Atmosphere. The theoretical height at which the rate of climb is zero.
Backing. A change of wind in an anticlockwise direction. This is the opposite of Veering, which is a change of wind in a clockwise direction.
Cabane. The term for a tripod or similar arrangement of struts, usually at the centre-section of a biplane. Sometimes called a pylon.
Damping Factor. With regard to the stability of an aeroplane, the rate of change in the violence of any movement from the level path.
Earth. Used, in connection with the radio apparatus carried by an aeroplane, to describe the metallic portions of an airframe which are connected by bonding wires to give electrical continuity and so to serve the purpose of an "earth".
H-Engine. An aero-engine with its cylinders arranged in two banks, which, with crankshafts between them, represent the form of an "H" in end view.
IATA: International Air Traffic Association.
Katabatic Wind: A local wind produced by the downward motion of cold air off high ground. On clear nights in hilly country, when the air over the higher ground cools because of the radiation into space, it becomes heavier than the air farther from the surface and thus flows downhill on to lower ground. This flow is the Katabatic wind.
NACA: The National Advisory Committee for Aeronautics in the United States of America - a body specially concerned with research and experiment (superseded by NASA - National Aeronautics & Space Administration - in 1958).
Observation Mirror: An engraved mirror used for bombing training in the same way as a camera obscura. The bomber flies over the mirror, which is suitably mounted on the ground. A light is flashed in the aeroplane at the release point of the bomb and this is plotted on the mirror. In this way the accuracy of the "bombing" can be determined.
Pack: The canopy and shroud lines of a parachute packed within the pack cover.
Safety-belt: A strong belt of webbing about 4 inches wide with a quick release device which keeps the wearer in his seat in an aeroplane. For violent aerobatics a more elaborate harness is worn.
Undercarriage: The main alighting gear of an aeroplane or floatplane. Modern undercarriages are usually retractable to reduce drag.
Valve: A mechanism which may be opened or closed to permit or restrict the passage of a fluid or gas through an orifice.
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.
"X" Engine: An aero-engine with four rows of cylinders forming in end view the letter "X."