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Aeroplane Monthly - Airplanes glossary Category: Travel and Transportation > Airplanes Date & country: 14/12/2007, UK Words: 962

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:

Horn Balance
A small balanced area at the tip of a control surface, usually projecting forward of the main surface.

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.

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

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.

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.

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.

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.

IATA
International Air Traffic Association.

ICAN
International Commission for Air Navigation.

Ice Accretion
The formation of ice on the exposed surfaces of an aeroplane in flight.

Identification Light
A light situated on or near a ground beacon and serving to identify it when seen from the air.

IHP
Indicated Horse Power.

Immelmann Turn
An obsolete term for a half roll off the top of a loop - a useful manoeuvre, particularly in air fighting, for reversing direction and gaining height. It took its name from the famous German pilot of World War One, Max Immelmann, who is credited with having introduced the manoeuvre and who certainly used it to good effect in air combat in the Fokke…

Impellor
The rotor of a centrifugal supercharger.

In-Line engine
An engine with its cylinders arranged in one or more vertical rows running parallel to the longitudinal axis of the aircraft.

Incidence Wires
The diagonal wires or cables on a biplane, triplane or quadruplane which brace each pair of front and rear interplane or centre section struts. They get their name from the fact that they hold the planes at their correct angle of incidence.

Independent Air Force
A force formed on June 5, 1918 for the strategic bombing of Germany to be performed quite apart from the Army Cooperation work, then the chief occupation of the British Air Forces. By the end of World War One it comprised nine bomber squadrons and one night fighter squadron and had dropped 543 tons of bombs. 'Independent Air Force' was really a mis…

Indian Air Force
This Service was formed in October 1932.

Indicated Airspeed
The airspeed as shown by an airspeed indicator. The reading only agrees with the true airspeed if atmospheric conditions are 'standard'. As height increases the indicated airspeed falls below the true airspeed.

Indicated Horse Power
The power of an engine calculated from the pressure in the cylinders during each working stroke. In effect it is the total power developed by the engine without allowing for the power lost in mechanical friction. The IHP is obtained from the following formula:

Induced Drag
That part of the drag which is caused by vortices at the wing tips. It is the drag which results from the lift. Pushing a wing through the air, to generate lift in it, causes violent disturbance of the air at the tips. That expresses itself in turbulence or vortices which tend to withhold the wing from moving forward although in fact they are mainl…

Induction Manifold
A branched pipe which distributes the fuel mixture evenly to the cylinders of an internal combustion engine.

Inertia Starter
a device for starting aero engines consisting of a large flywheel which is set in motion by hand or mechanical means. When the flywheel is turning rapidly it is suddenly connected to the engine and its momentum rotates the crankshaft.

Inflation
The process of introducing a gas into the envelope or gas bag of an aerostat.

Inflow
The increase in air velocity in front of a propeller produced by its rotation.

Instability
The tendency of an aeroplane to depart involuntarily from the set line of flight. Instability may express itself in yawing (swinging to right or left), rolling or porpoising (following an undulating path). Such faults may arise from a variety of causes, eg insufficient fin area, too short a fuselage, inefficient tailplane, failure to compensate in …

Instructors' Certificates
In Great Britain these take the form of an endorsement by the Air Ministry on either an 'A' or a 'B' Pilot's Licence. The endorsement may be made on the recommendation of the Guild of Air Pilots and Air Navigators.

Instrument Flying
The art of flying an aeroplane solely by instruments without reference to any external datum or horizon.

Intake air heater
A device for raising the temperature of the air entering the carburetter to prevent icing.

Inter-cylinder Baffle
A plate fixed between the cylinders of an air cooled engine to direct the cooling air on to the cylinders.

Interceptor Fighter
A specialised single-seat fighter of short duration with a minimum of equipment and relatively light armament. A high rate of climb and high maximum speed are characteristics of this class of fighter, the chief function of which is to make contact with enemy aircraft at short notice.

Intercooler
A device installed on the delivery side of a supercharger to cool either the compressed air or the fuel mixture as it passes to the cylinders.

Interference
The increase in drag and, in certain cases, the reduction in lift caused by the interference of the airflow round one body with that round an adjoining body.

Internal combustion engine
An engine in which the combustion of the fuel takes place within the cylinder.

International Power
The b.h.p. an engine is rated to develop at full throttle and at the highest crankshaft rpm which may be maintained in climbing flight for periods exceeding 5min. This power is developed in Standard Atmosphere at the lowest height at which full throttle is permissible at that particular engine speed. In effect the International Power works out to b…

International Standard Atmosphere
An imaginary atmosphere used in comparing the performance of aircraft. It assumes at mean sea level a temperature of 15° C and a pressure of 1,013·2 millibars, and a fall in temperature of 6·5°C per 1,000m of increased height from sea level up to 11,000m, above which height the temperature is assumed constant at 56·5°C.

Interplane Interference
The interference between the airflows round the planes of a biplane. This is one of the serious drawbacks to the biplane arrangement. Interplane interference (sometimes termed 'biplane effect') may be reduced by having the gap between the planes at least equal to the maximum chord and by the use of positive stagger, that is to say, by having the to…

Interplane Strut
A structural member in a biplane, triplane or quadruplane which braces the mainplanes to each other. Interplane struts are usually of streamline sections and are attached to the planes at the spars.

Interrupter Gear
An obsolete gear designed to make possible the firing of a machine-gun or guns through the disc of a revolving propeller. The interrupter gear should not be confused with the synchronising gear; the former interrupts the firing of the gun when the blades of the propeller are in the way, the latter fires the gun when the blades are clear. The latter…

Invar
A nickel iron containing 36 per cent of nickel. It has an exceedingly low rate of expansion and has a high resistance to water corrosion.

Inversion
An increase of temperature with height through a given layer of air in place of the decrease which normally occurs.

Inverted Engine
An engine with its cylinders below the crankshaft. In single engine aeroplanes the use of an inverted engine usually improves the pilot's view in a forward direction.

Inverted Loop
An outside loop. One of the less common evolutions which come under the general heading of aerobatics. In an inverted loop the upper surfaces of the aeroplane are on the outside of the loop and the pilot must accordingly be firmly strapped in, as the tendency of centrifugal force is to catapult him out of his seat.

Inwales
The longitudinal members in a seaplane hull at the junction of the topsides and decking.

Iraqi Air Force
A service formed in 1931 in Iraq. Its equipment was of British and Italian manufacture and some of its aircrews were trained in this country.

Irreversible Control
A flying control so designed that, although it is easily moved by the pilot, it cannot be moved by the air forces acting on it. Controls are made irreversible as a precaution against flutter.

Isallobar
A line on a weather map drawn through points where similar changes in barometric pressure have occurred in a given period of time. Isallobars show regions of rising and falling pressure.

Isobar
A line on a weather map drawn through points of equal pressure reduced to mean sea level. Isobars show the pressure distribution at any given time.

Isotherm
A line on a weather map drawn through points of equal temperature. Isotherms are usually drawn to show average monthly or annual distribution of temperature over a given area.

Isothermal Layer
An obsolete term for the Stratosphere. Generally, any layer of the atmosphere in which there is no appreciable variation of temperature with height.

Izod Test
A test employed to determine particular characteristics of structural materials. The testing machine consists of a weighted pendulum which is arranged so as to strike and fracture a test piece of fixed dimensions after it has swung through a specified arc. The height swung by the pendulum after impact with the test piece provides a measure of the p…

Japanning
The application of an enamel coat by any process for protective or decorative purposes.

Joystick
A colloquial term for Control Column, the primary flying control of an aeroplane or glider which is linked to the ailerons and elevators. It controls the aeroplane in the rolling and pitching planes.

Junk Ring
A ring for maintaining a gas-tight seal between the cylinder head and the bore of a sleeve-valve on an aero engine.

Jury Strut
A strut inserted to provide temporary support for a structure. A common example is the strut used to support the wing structure of an aeroplane when folded.

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…

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.

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.

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 spe…

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 milit…

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:

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.

LAC
Leading Aircraftman - an RAF rank between Aircraftman 1st Class and Corporal, indicated by an 'airscrew' badge on the arms of the tunic.

Lagging
The extent to which a rotor of a gyroplane in flight is displaced rearwards by air resistance from its normal position relative to the rotor head. The amount of lag is limited by the action of the drag pivot, a damping device which gives the rotor flexibility in the plane of rotation.

Laminar Flow
Airflow free of turbulence, that is to say, free of any eddying motion - a smooth stream.

Laminar Flow Wing
An aeroplane wing of thin section designed so that turbulence is reduced to a minimum. The Davies wing is an example.

Land and Sea Breezes
Offshore and onshore winds which occur up to about 1,000ft at night and in the daytime respectively. They are caused by the more rapid heating and cooling of the air over land than over water. Thus during the day when the land heated by the sun becomes hotter than the sea, the air above is warmed and expands. When air expands, its pressure falls an…

Landing
The act of bringing an aeroplane under full control into contact with the ground.

Landing "T"
A large symbol shaped like a letter T which is the standard indicator used on landing areas to show the direction of the wind. The cross stroke of the T is up wind. Landing T indicators may be illuminated for use at night.

Landing Area
An area of smooth and level land or of sheltered water providing sufficient space for the take-off and alighting of an aeroplane.

Landing Flare
A pyrotechnic flare attached to the underside of an aeroplane which, when lighted by the pilot, provides a bright illumination of the ground beneath, thus facilitating landing at night.

Landing Ground
A selected piece of ground suitable for the landing of aeroplanes, but without the facilities of an aerodrome.

Landing Light
A lamp (or lamps) usually installed in the leading edge of the mainplane of modern aeroplanes for use in illuminating the surface on which the aeroplane is alighting.

Landing Run
The distance travelled over the ground by an aerodyne after landing. Thus it is the distance between the first point of contact with the ground and the point at which the aeroplane comes to rest.

Landing Speed
That speed at which an aeroplane with a normal type two-wheel undercarriage stalls when making contact with the ground in the course of a 'three-point landing.' Aeroplanes with tricycle undercarriages do not have an exact landing speed, but are flown on to the ground at some speed within a specified range and are 'pulled up' by wheel brakes.

Landplane
An aeroplane with a wheel undercarriage designed to operate from an aerodrome or aircraft carrier.

Laps
Defects in steel caused by splashing of the molten metal when pouring it into the ingot mould. They appear as a crack on the surface of the metal after rolling.

Lapse Rate
The rate at which temperature decreases with height. The average lapse rate in the troposphere is 3°F per 1,000ft, but the actual rate varies a good deal between the two extreme conditions of dry and saturated air.

Lateral Axis
An imaginary line passing through the centre of gravity and parallel to a line joining the wing tips. Movement about the lateral axis is termed 'pitching.'

Lateral Axis
The straight line through the Centre of Gravity parallel to a line which would join the wing tips.

Lateral Clinometer
An instrument used to indicate the direction of the resultant force, or apparent direction of gravity, in a transverse plane. Sometimes called the Cross-level.

Lateral Divergence
A combination of rolling, yawing and side-slipping of an aeroplane which precedes a spin or spiral descent with increasing rate of turn.