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where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').

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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Committee for Aeronautics in the United States of America - a body specially concerned with research and experiment (superseded by NASA - National Aeronautics & Space Administration - in 1958).

Nacelle: A body accommodating crew, load or engines of an aeroplane, glider or airship.

Navigation (Avigation): The science of determining and plotting the position of an aircraft and of determining the courses to steer to reach any required destination.

Navigation Flame-Float: A pyrotechnic device dropped from an aeroplane on to water for determining the drift-angle by night.

Navigation Flare: A pyrotechnic device dropped from an aeroplane on to land for determining the drift-angle by night.

Navigation Light: A light on an aeroplane to reveal its presence and direction of motion at night. A complete set of navigation lights comprise a red light on the port (left) wingtip, a green light on the starboard (right) wingtip and a white light at the tail.

Neck: A tube at the base of a balloon through which the gas is passed during inflation and through which it can escape when it expands.

Nimbo-stratus: A low, rainy layer of cloud, grey in colour.

Nitralloy: A steel that can be surface-hardened by the Nitriding process.

No-Lift Direction: That direction of the airflow over an aerofoil in which no lift is generated.

Non-Induced Drag: The total drag of an aeroplane or glider less the drag which results from the lift of the wings. More often called the parasitic drag.

Non-Rigid Airship: An airship without a rigid keel and depending on the pressure of the gas within the envelope to retain its shape.

Normal Axis: A line passing through the centre of gravity of an aerodyne which is vertical in straight and level flight.

Normal Flight: All manœuvres needed in ordinary flying, such as level climbing and gliding flight, turns and side-slipping, but excluding aerobatics.

Normalising: The object of normalising is to relieve the stresses and refine the crystal structure after it has been coarsened by previous hot working.

Normally Aspirated Engine: An aero-engine the cylinder charge of which is normally taken in at the existing atmospheric pressure and temperature.

Norte (pronounced "nortey"): A cold, dry wind from the north over the Gulf of Mexico.

Nor' Wester: A disturbance of the line-squall type associated with thunderstorms and experienced in Bengal and Assam.

Nose Cap: A hub fairing fitted to the front of the boss of a fixed-pitch one-piece propeller.

Nose-Dive: A steep descent with the nose of the aeroplane down. More correctly, simply "dive".

Nose-heaviness: The tendency of an aeroplane to lower its nose of its own accord when flying.

Nose Radiator: An aero-engine radiator installed in the nose of a fuselage or nacelle.

Nose Rib: A rib between the front spar and leading edge of a main plane, tailplane or control surface.

Nose Slot Cowling: An aero-engine cowling in which the cooling air is discharged in the low-pressure area near the nose.

NPL: The National Physical Laboratory - an official centre of scientific research in Great Britain

Nurse Balloon: A fabric container used either as a gas reservoir or to maintain a constant pressure in an aerostat's envelope on the ground.