H

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where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').

---

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.
Notable examples of this type of engine are the Napier series, the 16-cylinder Rapier, the 24-cylinder Dagger and the 24-cylinder Sabre. H-type engines were produced also by Hispano-Suiza and Jalbert-Loire.

Haar. A local name in Eastern Scotland for a sea fog which spreads inland.

Haboob. A disturbance of the line squall type which occurs in the Sudan during the rainy season and is usually accompanied by a dense sandstorm.

Hail. Precipitation in the form of hard pellets of ice which fall from cumulo-nimbus clouds and are often associated with thunderstorms.

Hand Starter. A mechanism for the rotation by hand of an aero-engine's crankshaft for starting.

Hangar. A building to house aircraft. This was originally a French term which came into use in this country before the Second World War.

Harmattan. A very dry North-East wind prevalent in West Africa during the dry season (November to March) carrying with it great quantities of dust from the Sahara.

Haze. Slight fog caused by the presence of solid matter such as dust, smoke, or hydroscopic particles carrying a deposit of water in air not saturated with water vapour.

Head Resistance. More correctly "drag." The total resistance of an aeroplane to forward motion along its line of flight.

Header Tank. A tank in the cooling circuit of liquid-cooled aero-engines in which coolant is received from the engine and distributed to the cooling elements of the radiator.

Heap Clouds. Clouds with vertical structure and usually found between 1,500ft and 20,000ft. They are:

(a) Cumulus. High flat-based clouds with rounded billowy summits.

(b) Fracto-cumulus. Broken masses of cumulus.

(c) Cumulo-nimbus. Heavy masses of cloud with solid bases and fibrous tops.

Heavier-than-air Craft. More correctly "aerodyne." Includes all aeroplanes, gliders, gyroplanes and helicopters.

Height Computer. A calculating device for converting indicated to true height by taking the density factor into consideration.

Helicopters. Aircraft deriving their lift from one or more mechanically driven rotors.

Helium. An inert colourless gas, one-sevcnth of the weight of air. It is preferable to hydrogen for use in airships because it is non-inflammable. Unfortunately it is very costly and is only found in workable quantities in North America, and it is twice as heavy as hydrogen.

High Clouds. Mean height of more than 20,000ft. Usually composed of ice crystals. They are:

(a) Cirro-cumulus (mackerel sky). Layer cloud of small white flakes or of small globular masses. Often resembles the ripples in the sand on the seashore.

(b) Cirro-stratus. A thin whitish veil which does not blur the outlines of the sun or moon but gives rise to haloes.

(c) Cirrus (Mare's tails). Detached clouds of delicate and fibrous appearance.

Hucks Starter. A device consisting of a lorry chassis fitted with an overhead shaft geared to the engine and provided with a dog which can be engaged with the boss of the propeller for starting purposes.

Hull. (i) The main structural and flotation body of a flying-boat or boat amphibian.
(ii) The structural framework of a rigid airship.

Humidity. The amount of water vapour per unit volume of air.

Absolute Humidity. The mass of water vapour per unit volume of air.

Relative Humidity. The ratio of the humidity of a given volume of air to its maximum possible humidity at the same temperature.

Hump. That point in the take-off run at which a seaplane passes from displacement lift to hydrodynamic lift. It represents the process of climbing, by means of the "step" in the floats or the hull and with the help of increasing speed, out of the water on to its surface.

Hump Speed. The speed of a seaplane at the hump point at which its resistance is a maximum.

Hurricane. (1) A wind of "Force 12" (e.g. maximum) on the Beaufort Scale of wind force. Rarely experienced except in tropical revolving storms or tornadoes. Velocity of 75+ m.p.h.

(2) The name given in the West Indies to tropical revolving storms.

(3) the famous Hawker single-seat fighter in use in many theatres of the Second World War.

Hydrodynamics. That part of the science of mechanics which deals with the dynamics of water and of the effects of the motion of water past bodies on its surface or immersed in it.

Hydrofoil. A surface immersed in water underneath the planing bottom of a hull or float to assist take-off with its hydrodynamic lift.

Hydrogen. The lightest known gas which has been, and still is, extensively used in airships and balloons. Its one great drawback is that it is highly inflammable and this undesirable characteristic has been the cause of many disasters. Because of this the heavier gas, helium, is more suitable for airship use.

Hydrogen has one-fourteenth the weight of air and is one-half the weight of helium. One thousand cubic feet of hydrogen will lift 70.746lb. One thousand cubic feet of helium will lift 65.57lb.

Hydromatic. The trade name for the Hamilton hydraulic constant-speed full-feathering propeller. It was built under license in the UK by the de Havilland Aircraft Co Ltd.

Hydroplane. A flat-bottomed craft designed to skim over the surface of the water.
Seaplanes are said to hydroplane as soon as they have passed the hump speed during take-off and are supported by the hydrodynamic lift of the hull or floats.

Hydrostatics. That part of the science of mechanics which deals with the equilibrium of stationary bodies immersed in water or on its surface.

Hydrovane. A planing surface sometimes fitted to landplanes to make possible an emergency alighting on water.

Hyetograph. A recording rain gauge.

Hygrograph. A recording instrument for measuring the humidity of the air.

Hygrometer. An instrument giving the humidity of the air at any instant.