F

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where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').

---

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 higher factor of safety than those intended for normal level flying only.

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 manœuvre 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.

Fédération Aéronautique Internationale. Founded in June 1905 by Major Moedebeck, Fernand Jacobs and the Count de la Vaulx in Brussels to regulate aeronautical sport internationally throughout the World. All world records in flying are homologated and officially recognised by the FAI.

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 manœuvres 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 manœuvre 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.

Flap. A hinged surface, usually at the trailing edge of a wing, used to increase the lift of a wing at slow speeds, to steepen the glide and to act as an air brake during the approach and landing.

Flap Angle. The angle between the chord of the wing and the chord of the flap. Flaps are often lowered about 5° to assist take-off and usually about 30° to 45° for landing.

Flare. (i) A pyrotechnic flare attached to the underside of the wing of an aeroplane to illuminate the ground for a night landing. Parachute flares are used to illuminate targets for night bombing.

(ii) The outward slope of the hull of some designs of flying-boats from the chine to the gunwale.

(iii) The action of "holding the aircraft off", i.e. reducing the descent rate, during landing.

Flarepath. A line of lights laid out on an aerodrome or surface of a harbour to act as a guide for aeroplanes taking off or alighting.

Flat Spin. A spin in which the tail of the aeroplane drops and the machine rotates in an almost horizontal plane. Recovery from a flat spin is difficult and sometimes impossible. Low-wing monoplanes are more prone to the flat spin than any other type of aeroplane so that an anti-spin parachute is usually carried on trials. This small parachute is attached to the tail and can be released if necessary. It pulls up the tail of the aeroplane and makes possible recovery from the spin. It can then be jettisoned.

Flattening Out. In approaching to land an aeroplane, the transition from the gliding approach to the position to alight is termed "flattening out."

Fleet Air Arm. Descended from the Royal Naval Air service - which, with the Royal Flying Corps, became part of the Royal Air Force on April 1, 1918 - the Fleet Air Arm was formed in April 1924. It was then a part of the RAF, under the operational control of the Admiralty only when afloat. The Fleet Air Arm comprised all aircraft carried on ships of the Royal Navy. For 14 years the FAA was under the administrative control of the Air Ministry and remained part of the RAF.

In 1937 the Government decided to transfer the whole control of the FAA to the Royal Navy. The personnel of the FAA was then about 3,000. The transfer did not take place at once, but on May 24, 1939, the administrative as well as the operational control was assumed by the Admiralty.

The Fleet Air Arm distinguished itself in action in World War Two - particularly in the spotting of the Graf Spee (Fairey Seafox), in the action at Taranto (Fairey Swordfish), in action off Norway and against German and Italian dive bombers in the Mediterranean (Blackburn Skuas, Gloster Sea Gladiators and Fairey Fulmars), in the battle of Cape Matapan (Fairey Albacores and Fairey Swordfish) and in the destruction of the Bismarck (Fairey Albacores and Fairey Swordfish).

When war began the Royal Navy had seven aircraft carriers with six more being constructed. Since the outbreak a programme of converting merchant ships into auxiliary carriers has been started and many are now in service. The carriers completed at the outbreak of the war were, in order of age, Argus (14,000 tons, about 20 aircraft), Hermes (12,900 tons, about 20 aircraft), Eagle (20,400 tons, about 21 aircraft), Courageous (22,500 tons, about 48 aircraft), Glorious (22,500 tons, about 48 aircraft), Furious (22,450 tons, about 33 aircraft) and Ark Royal (22,000 tons, about 60 aircraft).

Six aircraft carriers had been officially named in the course of construction when the war began. They were the Illustrious (23,000 tons, about 60 aircraft), Victorious (23,000 tons, about 60 aircraft), Formidable (23,000 tons, about 60 aircraft), Indomitable (23,000 tons, about 60 aircraft), Implacable (23,000 tons, about 60 aircraft) and Indefatigable (23,000 tons, about 60 aircraft).

The Courageous was sunk by torpedoes in September, 1939, Glorious was sunk off Norway in June, 1940, Hermes was sunk off Trincomalee in April 1942, Ark Royal torpedoed off Gibraltar in November 1941 and Eagle was sunk in the Mediterranean in August 1942.

Flettner Rotor. A cylinder rotated with forward motion to provide lift at right angles to its path. Flettner rotors have been used to provide lateral control in place of ailerons, without outstanding results.

Flick Roll. A rapidly executed roll in a horizontal plane in which the aeroplane is turned completely around its longitudinal axis by use of both rudder and elevators and continues in level flight. A flick roll is in reality a horizontal spin and the aeroplane is temporarily out of control during its course. The flick roll was first demonstrated on a Bristol Scout in 1914 and was popular as a spectacular aerobatic during the age of small manœuvrable single-seat fighter biplanes. Powerful elevators are needed to force a modern aeroplane into a flick roll.

Flight. (a) The act of flying.

(b) A unit of a formation of aeroplanes of the Royal Air Force. A flight usually consists of three aeroplanes, but may also be four, five or six.

(c) The aeronautical weekly journal founded by Stanley Spooner in January 1909.

Flight Engineer. A member of the crew of a large aeroplane who controls the engines in the air, thus relieving the pilot of an onerous duty.

Flight Lieutenant. A commissioned rank in the Royal Air Force equivalent to Lieutenant in the Royal Navy and Captain in the British Army. The rank may be distinguished by two sleeve stripes and two stripes on the coat shoulder straps.

Flightpath. The path of the centre of gravity of an aeroplane relative to the air. If the aeroplane is climbing steeply or gliding flatly the flightpath may be at an angle less acute than the attitude of the longitudinal axis of the machine.

Flight Sergeant. A non-commissioned rank in the Royal Air Force which corresponds with Chief Petty Officer in the Royal Navy and Colour Sergeant, Chief Quarter Master Sergeant, etc in the British Army. The pay of a Flight Sergeant in 1942 varied from 7s 9d per day to 12s per day on ground duties up to 15s 6d per day for a Flight Sergeant Pilot or Flight Sergeant Observer.

Flightway. A specified air space beyond the end of a runway of an aerodrome. Obstructions must be kept below the specified heights in the flightways.

Float. (a) When approaching to alight, the distance travelled horizontally in the air after flattening out and before touching down. The better streamlined the aeroplane the greater its float, unless fitted with flaps. Flaps act as air brakes and shorten the float and they make possible landing in a smaller space.

(b) A watertight body of streamlined form which gives buoyancy and stability on the water to a seaplane or flying-boat and enables it to take off and alight. There are four types of float (in America called "pontoons").

(i) Main float - usually two, sometimes one.

(ii) Wingtip floats - to provide stability for flying-boats or single-float seaplanes.

(iii) Tail float - used with the short main floats of old-type seaplanes.

(iv) Inboard floats - perform the same function as wing-tip floats but are mounted close to the hull.

Float Seaplane. A seaplane provided with floats (American pontoons) as its means of buoyancy on the water.

Floating Ailerons. Ailerons so connected that they remain free, while the control column is centralised, to preserve a negative angle of attack in relation to the air flow whatever the angle of the mainplane.

Floodlight. Wide angle lights used on an aerodrome to illuminate all or part of the landing area at night.

Flotation Gear. Emergency flotation equipment installed in landplanes liable to fly over the sea to give them buoyancy should they be forced down on the water. Flotation gear usually consists of watertight bags or compartments in the fuselage.

Flutter. Usually applied to wings or ailerons - the unstable oscillation caused by interaction between aerodynamic forces, elastic reactions in the structure and the force of inertia. Unless damped quickly flutter will break a wing. The cure is usually to dispose the weights so that the centre of gravity of the wing is as far forward as possible. Ailerons, elevators and rudders are mass-balanced to prevent flutter.

Flutter Speed. The lowest airspeed at which flutter occurs in a given aeroplane.

Flying Blind. Flying solely by instruments in thick cloud or darkness.

Flying-boat (Boat Seaplane). A seaplane in which the main body or hull provides the means of support on the water.

Flying Clubs. The Flying Club movement began with the advent of the light aeroplane in 1924. The Clubs received a Government subsidy up to the outbreak of World War Two which made possible the training of pupils - particularly the Civil Air Guard - at reasonable rates.

Flying Controls. The mechanism whereby the pilot operates the control surfaces from the control column.

Flying Instruments. (i) The Air Speed Indicator (ASI) linked to the Pitot Tube and the Static Tube to measure the air pressure and hence the forward airspeed.

(ii) Altimeter, which is in reality a barometer measuring pressures and recording them as heights.

(iii) Artificial Horizon, which indicates whether the aeroplane is banking, climbing or diving (worked by a gyroscope).

(iv) Turn and Bank Indicator, partly worked by a gyroscope and partly consisting of a simple pendulum.

(v) Rate of Climb Indicator. Shows the rate of change of height by providing a visual indication of the air entering or leaving a "Thermos" flask.

(vi) Compass - An instrument which consists essentially of a magnetic needle free to swing and which, subject to correction for conflicting magnetic fields, always points to the magnetic North. It thus indicates the angle in the horizontal plane between the magnetic North and the longitudinal axis of the aeroplane.

(vii) Directional Gyros used to indicate any change in course, without continual reference to the compass, which must be mounted horizontally.

Flying Machine. A power-driven heavier-than-air craft. Includes all aeroplanes, helicopters and gyroplanes, but not gliders, sailplanes or airships.

Flying Officer. A junior commissioned rank in the RAF corresponding to a Sub-Lieutenant in the Royal Navy and a Lieutenant in the British Army.

Flying Position. The attitude of an aeroplane when it is flying straight and level.

Flying Speed. Maximum: The maximum airspeed of an aeroplane when flying level in Standard Atmosphere. Mimimum: The minimum airspeed at which an aeroplane can fly level in Standard Atmosphere.

Flying Wires. Those bracing wires in a biplane which transfer the lift of the wings to the main structure. Also known as "lift wires." They extend diagonally outwards and upwards. Anti-lift wires which take the weight of the wings on the ground extend outwards and downwards.

Fog. A condition of bad visibility in the lower atmosphere caused by the presence of particles of condensed moisture, of smoke, or of a mixture of the two held in suspension in the air.

Föhn (Pronounced "Furn"). A warm dry wind which blows down the northern slopes of the Alps when the general wind current comes over the mountains. Can be applied to any wind experienced under similar conditions.

Folding Wings. The mainplanes of an aeroplane designed to fold so that it may be stored in a confined space.

Force. That which produces or tends to produce a change of motion or shape of a body. Measured in pounds or dynes.

Forecast. A statement of weather to be expected over a given area or route during a definite period.

Forced Landing. The unpremeditated landing of an aeroplane usually caused by mechanical breakdown or bad weather.

Four-stroke engine. An internal-combustion engine in which explosion of the mixture in each cylinder occurs at every alternate revolution of the crankshaft. Nearly all aero-engines work on the four-stroke cycle at present.

Fracto-cumulus. Small cumulus clouds with ragged tops which continually change their form.

Fracto-nimbus. Low, dark, ragged clouds associated with bad weather.

Fracto-stratus. Layer cloud broken into irregular, ragged fragments.

FRAeS. Fellow of the Royal Aeronautical Society.

Free Balloon. A balloon intended for cross-country flying carried by the wind.

Freeboard. In a flying-boat hull, the vertical distance from the loaded waterline to the lowest opening through which water could enter the hull or to the level of the top decking if there is no opening below its level.

"Frise" Ailerons. Ailerons with their hinges a little back from their leading edges and so shaped that when the aileron is raised a horn projects into the airflow below the wing, thus creating turbulence and destroying lift. Their function is to equalise aileron drag in a banked turn. Named after Mr Frise, Chief Designer to the Bristol Aeroplane Co Ltd who invented them.

FRMetSoc. Fellow of the Royal Meteorological Society.

Front. A line of discontinuity between cold and warm masses of air.

Frost. A condition in which the temperature of the air is below the freezing point of water.

Froude's Law. A law used in Hydrodynamic calculations to convert the full size data obtained with scale models in testing tanks. It states that to get similar flow on model and full scale, the model should be towed at a speed equal to the full-scale speed multiplied by the square root of the scale of the model.

Fuels. Aero-engine fuels are either refined from crude petroleum or obtained from coal, the latter source being that on which Germany has had largely to depend.
The great majority of aero-engines run on what is so commonly termed "high grade aviation spirit," but a few compression-ignition engines running on heavier fuels are in service, notably in Germany.

Fuel-contents Gauge. A gauge for indicating the contents of a fuel tank ie full or empty etc.

Fuel-flow Meter. An instrument for indicating the rate of flow of fuel.

Fuel-jettison Gear. Gear to enable part of an aeroplane's fuel load to be discharged in case of emergency. This is particularly important with modern aeroplanes because of the high wing-loadings at take-off in general use - loadings too great for safe landing if one should become necessary soon after take-off.

Fuel Tank. A tank containing the fuel supply for an aero-engine.

Fuselage. The main body of a landplane, float seaplane, or float amphibian, providing accommodation for the crew and useful load.