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

De-Icer
A device for dispersing ice which has formed on any part of an aeroplane, particularly the wings and control surfaces. The best-known type is the Goodrich de-icer. In this system pulsating rubber overshoes are fitted along the leading edges of the surfaces. The rubber tubes can be inflated and deflated alternately to crack off the ice.

Dead Reckoning
In air navigation the estimation of true direction and speed of an aeroplane during flight, and hence of its distance from any known point at any moment.

Decalage
Decalage is the angle between the chord line of the upper plane and that of the lower plane and is positive when the top plane is at a greater angle of incidence than the bottom. The reason for giving a different angle of incidence to the upper and lower wings of a biplane is to shorten the aeroplane's take-off run and adjust its landing characteri…

Decorations
In the Royal air Force, the Air Force Cross, the Air Force Medal, the Distinguished Flying Cross and the Distinguished Flying Medal.

Delayed Drop
A parachute descent begun by a free fall of greater duration than that normally allowed for the opening parachute to clear the aeroplane. Falling freely in the air, the average rate of descent of a man is constant at 119 m.p.h. The rate after the parachute has opened is 14 m.p.h. at sea level - approximately equal to a jump from a 10ft wall.

Depression
A region of relatively low barometric pressure. The winds circulate in an anti-clockwise direction around its centre in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere. A Depression is sometimes called a 'Low.'

Detachable Pack
A parachute pack which can be quickly attached to and detached from the parachute harness.

Dew Point
The lowest temperature to which air can be cooled at constant pressure without causing condensation and hence the formation of cloud.

DF
Direction-Finding Wireless Telegraphy.

DFC
Distinguished Flying Cross.

DFM
Distinguished Flying Medal.

DGCA
Director-General of Civil Aviation.

Diesel
The name given to a compression-ignition engine after its inventor, Rudolf Diesel. In the Diesel cycle the heavy oil fuel is ignited by the heat of compression of the air in the cylinder. The chief advantages of compression-ignition engines are their lower specific fuel consumption, the use of cheaper fuel, reduced risk of fire, and the absence of …

Differential Ailerons
Ailerons interconnected so that the aileron which moves upwards moves through a larger angle than the other which moves downwards. The reason for this is to increase the drag as well as the lift of the wing with the upgoing aileron and at the same time to keep down the drag of the downgoing aileron because of its smaller movement.

Diffusion
Function of a carburettor. The diffusion tube is perforated to assist in atomising the fuel before it is introduced into the choke tube.

Dihedral Angle
The angle at which the port and starboard mainplanes of an aeroplane or glider are inclined upwards to the lateral axis. When they are inclined downwards the angle is termed Anhedral or Negative Dihedral; an older term was Kathedral.

Direct-drive Aero-engine
An engine in which the propeller is driven at crankshaft speed without reduction gear. In most modern aero-engines the speed of rotation of the propeller shaft is geared down so that it revolves at only about one-half the crankshaft speed. In this manner a bigger propeller can be used and the great drag caused by the high speed of the tips of the b…

Direction Finder
(DF) Radio apparatus the function of which is to determine the bearing of a distant radio transmitter.

Directional gyro
More properly called Direction Indicator. An instrument to indicate any change in the direction of an aeroplane. Deviation from a straight course is shown by marks along a graduated card kept at a fixed datum by a gyroscope.

Directional Instability
A flying defect in an aeroplane which causes it to tend to deviate from a straight course by a combination of side-slipping and yawing movements whenever the pilot attempts to keep it on a level keel by moving the ailerons.

Dirigible
A steerable airship (the term does not denote a rigid airship.)

Disc Area
In a gyroplane or helicopter the area of the circle described by the tips of the blades.

Disc Loading
The product of the loaded (gross) weight of the gyroplane or helicopter divided by the disc area of its rotor.

Disposable Load
Same as Useful Load. The difference between the loaded weight (gross) and the empty weight of an aeroplane. It includes Payload or Military Load.

Distinguished Flying Cross (DFC)
An award granted to Commissioned Officers of the Royal air Force and of the Fleet Air Arm while serving under an Air Officer Commanding-in-Chief in the RAF for exceptional valour, courage or devotion to duty whilst flying in active operations against the enemy. The DFC was instituted by Royal Warrant on June 3, 1918. The colours of the ribbons are …

Distinguished Flying Medal (DFM)
An award granted to Non-commissioned Officers and Airmen of the Royal Air Force and of the Fleet Air Arm while serving under an Air Officer Commanding-in-Chief in the RAF for exceptional valour, courage or devotion to duty whilst flying in active operations against the enemy. The DFM was instituted by Royal Warrant on June 3, 1918. It bears the sam…

Distress Signal
Civil aircraft in danger and in need of immediate assistance have international signals laid down for use.

Dive
A steep descent with the nose down. A 'Terminal Velocity Dive' is the steepest dive in which the aeroplane accelerates until its drag becomes equal to the thrust of gravity pulling it downwards so that the speed remains constant. The terminal velocity of a World War Two single-seat fighter was around 650 m.p.h.

Doldrums
The region of calms and variable winds in equatorial seas, often accompanied by heavy rain, thunderstorms and squalls.

Doping
A system of chemical treatment of the fabric used for the covering of structural parts of aeroplanes to protect, strengthen, tauten and render it airtight.

Dorsal
A term used to denote the longitudinal member which runs from bow to stern along the top centre line of the hull of a flying-boat. Applied to a gun turret means that on top of the fuselage. Derived from the back fin of fish.

Dover Control
A device linking the throttles of multi-engined aeroplanes so that the throttles can be opened simultaneously or differentially.

Downwash
A term applied to airstream deflected downwards behind a lifting aerofoil. The angle of downwash is the angle of the inclined airstream relative to the longitudinal axis of the aeroplane. The downwash behind the mainplane may have an important influence on the tailplane.

Drag
The total resistance of an aeroplane along its line of flight. The total drag is made up of a number of components.

Drag Axis
, the straight line though the Centre of Gravity parallel to the airstream.

Draught
The vertical distance from the loaded waterline to the lowest point of the hull of a flying-boat or the floats of a float seaplane.

Drift
The movement of an aeroplane in a horizontal plane through the influence of a cross-wind. Drift makes necessary the deflection of the longitudinal axis of the aeroplane away from the line of track to be followed. That is to say an aeroplane must be headed slightly towards a beam wind to avoid being drifted off its course.

Drift Indicator
An instrument by which the speed and the direction of the wind can be determined from an aeroplane in flight.

Drift-angle
The angle between the longitudinal axis of an aeroplane and the track along which it is flying. A drift-angle sight or drift sight is an instrument for determining the angle of drift. It may employ direct vision or may be periscopic.

Drizzle
Rain in which the drops are very small.

Drogue
A conical canvas sleeve open at both ends with a metal hoop at the larger end, used as a sea anchor by seaplanes. In lighter form a drogue is towed behind an aeroplane to serve as a target for aircraft or anti-aircraft guns.

Dry Weights
A term applied to the weight of an aero-engine. The gross dry weight includes the whole of the engine, including propeller hub and stub exhausts, but excluding radiator, tanks, fuel, oil or instruments. The net dry weight of the engine is the gross dry weight not including exhaust stubs, starting units or accessories.

DSR
Director of Scientific Research.

DTD
Director of Technical Development.

Dual Control
Flying controls which are duplicated in an aeroplane either for instruction or so that one pilot may conveniently relieve another.

Ducted Cooling
A system of low velocity cooling in which the cooling air is constrained to flow in ducts to the radiators or the cylinder fins of an aero-engine. By means of ducted cooling the cooling drag is greatly reduced, and can, in theory, be made to add thrust.

Duralumin
The name for a wrought light alloy material extensively used for aircraft construction. Duralumin, commonly abbreviated to 'Dural', is an aluminium alloy containing approximately 4 per cent copper, 0·6 per cent magnesium, 0·6 per cent manganese ore, 0·3 per cent iron. Its specification numbers are L1, L3, L37, L39, T4, DTD 147 and 150. As Duralumin…

Dust Devil
A small whirlwind formed by strong convection over hot desert regions. It raises dust or sand in a vertical column which progresses across country.

Dust Interference
Interference with radio reception in an aeroplane flying through a dust storm, and is caused by the accumulation of static charges produced by the impact of particles on the airframe.

Dust Storm
A squall in desert regions which carries dust or fine sand to a height of several thousand feet.

Dynamic Lift
The lift from the envelope of a balloon or airship or the fuselage of an aeroplane caused by its passage through the air.

Dynamotor (Usually Dynamo)
A battery-driven generator which supplies power for a radio installation. It consists of low- and high-tension armature windings running in a common field system.

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'.

Economical Cruising Power
The percentage of the maximum level horse-power of an aero-engine at which the specific consumption is the lowest. Usually about 62·5 per cent of the maximum power.

Economical Cruising Speed
The speed at which an aeroplane achieves its greatest range in still air. This speed is usually about 85 per cent of the maximum speed. Maximum range is attained at a speed about 40 per cent greater than the stalling speed. Maximum duration is obtained at a speed about 20 per cent greater than the stalling speed.

Eddy
The irregular motion of a fluid - in aeronautics, air - when flowing above a certain speed or around an object. In eddy motion the flow moves in irregular swirls.

Eddy Drag
The portion of the drag of a body which is caused by the eddies formed in flowing around the surface.

Edge
(a) Leading Edge - The forward edge of an aerofoil (including a propeller blade, strut, or any streamlined body). (b) Trailing Edge - The rear edge of an aerofoil, strut, or any streamlined body).

Elastic Limit
Applied to materials for aircraft construction, the limit of stress or force which can be exerted on a body without causing permanent distortion of the stressed body.

Elasticity
The material of a body is said to be elastic up to the point at which the whole of the strain, or distortion of the body, disappears when the stress, or force, which has produced it is removed.

Electrical Starter
An electric motor turned by batteries in an aeroplane or externally, used to rotate an aero-engine to start it.

Electrically Heated Clothing
Flying suits which are heated by electricity through the medium of thin, high-resistance wires enclosed in glass insulators and inserted at points vulnerable to cold. In modern flying clothing only the gloves and boots are heated to give protection against the severe cold at great heights.

Elektron
A magnesium alloy increasingly used in the form of castings for aircraft components. Elektron was developed in Germany during the 1914-18 War as a substitute for aluminium alloy. Elektron is unusually light and has a specific gravity of about 1·8 compared with the 2·8 of aluminium alloy.

Elevator
Control surface hinged to the trailing edge of the tailplane to provide longitudinal control. By raising the elevators the tail is depressed and the nose raised, and vice versa.

Empennage
A general term, now little used, to refer to the tail unit of an aeroplane. Empennage includes tailplane, elevators, fins and rudders.

Endurance
The maximum time which an aeroplane can continue to fly without refuelling. The speed for maximum endurance is normally about 20 per cent above the stalling speed, changing as the stalling speed varies with the constant diminution in weight caused by the burning of fuel.

Engine
A loose term used for the aero-engine which provides the motive power for any flying machine or airship. Aero-engines are both liquid-cooled and air-cooled. The former have less drag, the latter need less maintenance because of the absence of 'plumbing.'

Engine Instruments
The most common instruments concerning the aero-engine used in the cockpits of modern aeroplanes are:

English Channel
The first people to fly across the English Channel were Blanchard and Jeffries in a gas balloon - Jan 7, 1785. The first flight across the English Channel in an aeroplane was made by Louis Blériot in a Blériot XI monoplane (25 h.p. Anzani engine) in 37 minutes - July 25, 1909.

Envelope
The gas container of a balloon or airship or the outer cover surrounding the gas bags.

Equivalent Full-throttle Power
The theoretical brake-horsepower which a supercharged aero-engine would develop if run at full throttle and maximum rpm at sea level. In practice the power cannot be attained because the loads on the engine would be too great. For instance, the equivalent full-throttle power of the Rolls-Royce Merlin II would be about 1,900 h.p., although only 1,03…

Eta Patch
A fan-shaped patch of fabric and webbing secured to the envelope of a balloon to hold rigging.

Evaporative Cooling
A cooling system for aero-engines which makes use of the 'latent heat of evaporation' by allowing the cooling fluid to boil, then condensing the steam from it and returning it to the cylinder jackets. The Rolls-Royce Goshawk engine of 1932 was designed on this principle, but was not really successful.

Everest
A Westland Wallace and a Houston-Westland P.V.3 biplane flew over Mount Everest (29,028ft) for the first time on April 3, 1933. The expedition which made this flight, and another on April 19, 1933, was named the Houston Mount Everest Expedition and was led by Air Commodore P.F.M. Fellowes. The pilots were Lord Clydesdale and Flt Lt D.F. McIntyre. I…

Exhaust
The burnt gases discharged from an aero-engine. About 47 per cent of the latent energy in the fuel supplied to an aero-engine is normally wasted in the exhaust.

Exhaust Branch Pipe
A short pipe which conveys exhaust gases from the cylinder of an aero-engine to the exhaust manifold.

Exhaust Driven Turbo-supercharger
A type of supercharger specially suitable for high flying in which the rotor is turned by the exhaust gases. The chief difficulty in this form of supercharger is to find metals to withstand the intense heat.

Exhaust Flame-damper
An exhaust pipe designed to prevent exhaust gases from passing into the atmosphere while incandescent and thus visible at night.

Exhaust Gas Analyser
An instrument for indicating the quantity of carbon monoxide in the exhaust gases and so showing the efficiency with which the fuel is being consumed.

Exhaust Manifold or Collector Ring
A pipe or chamber into which exhaust gases are led from a number of cylinders through branch pipes. In Bristol radial engines the collector ring forms the nose of the cowling ring. This serves to cool the gases, but has the disadvantage of glowing red-hot at night. Most American radials have an exhaust collector ring inside the cowling behind the c…

Exhaust Stub Pipe
Stub exhausts were fitted to most fighters before ejector exhausts were developed. The stub exhausts discharge the gases straight into the atmosphere at right angles to the direction of flight. The ejector exhausts turn the gases and discharge them backwards, thus aiding propulsion.

Exhaust Tail Pipe
The pipe which leads the exhaust gases away from a manifold or collector ring.

Experimental Mean Pitch
The theoretical distance which a propeller advances along its own axis during one revolution when there is no slip.

Eye of Storm
The central calm area of a tropical cyclone.

FAA
Fleet Air Arm (in USA, Federal Aviation Administration).

Fabric
A material, usually of linen used for the outer covering of wings, fuselages and tail units of some aeroplanes. Fabric is usually of multi-ply weave.

Factor of Safety
A strength factor to which all aeroplanes are built. Thus a factor of safety of five means that any part of the aeroplane is designed to withstand five times its normal load before failing. A factor of safety of one would mean that the machine would be on the point of breaking at its normal load. Aeroplanes intended for high-speed aerobatics have a…

FAI
Fédération Aéronautique Internationale.

Fairing
A secondary structure added to reduce drag. Common examples of fairings are wing-root fillets and streamlining of struts.

Falling Leaf
An aerobatic manÅ`uvre of a purely spectacular variety. The aeroplane is first stalled and is then forced into a spin. As soon as the spin develops the controls are reversed so that a spin begins in the opposite direction.

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.

Feed Pipes
The oil pipes which convey lubricating oil from the oil tank to the aero-engine.

Figure of Eight
A series of reverse banking turns in which the aeroplane describes a horizontal figure of eight in the air. This was one of the required manÅ`uvres for the gaining of a civil pilot's 'A' Licence.

Fillet
A fairing at the junction of two surfaces to improve the airflow and so cut down drag. A fillet is often seen at the trailing-edge wing root.

Fin
A fixed vertical surface, usually at the tail, designed to contribute to both directional and lateral stability. Often called the 'tail fin' and usually used to carry the rudder. On lighter-than-air craft the term fin is also used to define the horizontal stabilising surfaces termed the tailplane in an aeroplane.

Fishtailing
Swinging the tail of an aeroplane from one side to another when coming in to land in order to shorten the glide and landing run. It is an alternative manÅ`uvre to sideslipping.

Fix
A navigational term. A 'fix' is the point of intersection of two position lines drawn on a map to determine the location of an aeroplane.

Fixed Aerial
The aerial of an aeroplane permanently attached at two points. Fixed aerials usually run from an aerial mast to the fin or from a wing-tip to the tail.

Fixed Loop-aerial
An aerial permanently fixed on an aeroplane and used as a homing receiver.

Flame-float
A 'firework' device which can be dropped from an aeroplane at night to burn on the water and so make possible the determination of drift.