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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equivalents where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').

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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.

Kaus: South-easterly or easterly winds in the Persian Gulf which herald the approach of a winter depression. They are usually associated with wet and cloudy weather.

Keel: (1) A longitudinal centre member running the length of a hull or float. (2) An internal or external framework integral with the underside of a rigid airship and serving to distribute the concentrated loads along the hull. (3) A rigid or articulated framedwork in a semi-rigid airship serving the same purpose as (2), but in this instance transmitting the loads direct to the envelope.

False Keel: A member fitted under the main keel to deepen it or to protect the hull (or float) plating from damage when the seaplane is aground or drawn up on a slipway.

Keel Angle: The angle formed by the straight lines joining the central keel and the chines at any particular section of a hull or float.

Khamsin (pronounced Khumseen): A hot dry Southerly wind blowing over Egypt in front of depressions passing Eastward along the Mediterranean. This wind is similar to the Sirocco.

Kharif: An intermittent but severe dust storm that blows from May to September in Somaliland.

King-post: A compression member which, together with suitable bracing wires, limits the deflection of a major member (such as a spar) which has to resist bending loads. King-posts raised above the wings of early flying boats were used to reinforce the interplane bracing.

King's Cup Air Race : A handicap air race open only to British and Empire pilots flying British or Dominion aeroplanes, competed for annually up to the outbreak of World War Two. The Cup was originally presented by King George V and the race was first held in 1922. On that occasion it was won by the late Captain F.L. Barnard in a D.H.4A (RR Eagle VIII) at an average speed of 120 m.p.h.

Kinetic Pressure: The increase in pressure which arises when a stream of fluid meets an obstruction. Air has many of the properties of a fluid and the pedestrian has to overcome kinetic pressure in meeting a high wind. In the reverse sense, kinetic pressure is built up in front of an aeroplane by reason of its movement through relatively still air.

Kite: An aerodyne not mechanically driven and normally moored to the ground, or towed by a line. Kites are the oldest form of aircraft and have been made and flown by the Chinese from ancient times. Their aerodynamic principle is analogous to that of an aeroplane. At the beginning of the 20th Century experiments were made with man-lifting kites for military purposes. Since then kites have been used for meteorological purposes and, in special circumstances, in place of barrage balloons.

Kite Balloon: A captive balloon so shaped as to derive stablility and aerodynamic lift from the relative wind. There are two types of kite balloon:

(1) The Observation Balloon: This is provided with a basket for one or more observers who are connected by telephone with the ground and can thus signal the results of artillery fire to the battery concerned and perform other types of observation. The observation balloon was much used during World War One. Captive balloons are used for training parachute troops.

(2) The Barrage Balloon: Balloon barrages were first introduced during World War One and were employed on a large scale in World War Two as a deterrent to dive bombers. They were used to protect important land areas and merchant ships in convoy.

Knot: A nautical unit of speed being equal to one nautical mile (6,080ft) per hour. To convert knots to miles per hour multiply by 1·15.