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

Spinner
A streamline fairing fitting co-axially over the hub or variable pitch mechanism of a propeller, and rotating with it.

Spiral
A continuous banked turn made during a glide with the engine stopped or 'ticking-over'.

Spiral Instability
A particular case of lateral instability, in which the banking angle is always too great, causing side-slipping.

Split Flap
A flat plate, hinged along its leading edge, and mounted on the underside of the trailing portion of a wing. Split flaps are used to increase the lift of a wing at comparatively low forward speeds and to steepen the glide in approaching to land.

Spoiler
A device to reduce lift of a wing surface in order to increase sinking rate of a glider or aeroplane.

Sponsons
Short wing-like projections on each side of the lower portion of a flying-boat hull to maintain its lateral balance on the water. They are usually of aerofoil section to give some return for their parasitic influence on aerodynamic performance. They serve as useful landing platforms as well as their main purpose of giving stability on the water, an…

Sporting Events
The range of events of a racing and competitive character allied with social intercourse which are exemplified in the Flying Club organisations of pre-Second World War days. Some association of the interest in the spotting of aircraft with sporting flying may be envisaged for the future.

Spotter
Any person who practises aircraft recognition. Industrial raid spotters were employed by vital factories and organisations during the Second World War.

Squadron
A Royal Air Force formation of two or more flights.

Squall
A strong wind of short duration usually associated with a change of wind direction. This distinguishes a squall from a gust, which is a sudden increase of strength of any wind. A line squall advances over a large area and is caused by the displacement of colder air.

Stabilisers
Originally the pressure-inflated fabric fins at the rear of a dirigible airship or kite balloon. Now loosely applied to all fixed stabilising fins. In America the term for tailplane.

Stability
Stability is the property possessed by aircraft (aerostat or aerodyne) in more or less degree which enables it to return to normal conditions of flight automatically after a disturbance of its course. Lateral stability is the maintaining of the horizontal attitude of the wings or envelope to the horizon. Longitudinal stability is the maintaining of…

Stagger
The 'set' of the wings of a biplane in relation to one another in side elevation. In positive stagger the upper wing is in front of the lower, and in negative stagger the reverse arrangement applies. Wings directly above one another are said to have no stagger.

Stall
The wing of an aeroplane is said to stall when the smooth flow over the top surface breaks down and degenerates into turbulence. Reverse flow may even be present. The lift of the wing then drops suddenly and with it controllability. A dive is necessary to pick up speed and restore the flow. Most wings stall normally at 15°, or at 25° with slots.

Starboard
A nautical term borrowed for flying terminology indicating the right-hand side of an aeroplane when looking forward from the pilot's seat.

Stars
The heavenly bodies are of great utility in the navigation of aircraft and a study of the stellar system is included in all initial training courses for air crews.

Starter
A device for starting aero-engines. Several different types exist, the more modern of these being operated by induced gas, compressed air, electricity or an explosive charge. Hand or auxiliary engine starters, and priming the induction in conjunction with a starting magneto, are other means used for starting.

Static Balance
When a propeller, mounted in a steel spindle and resting on knife edges, remains at rest it is said to be statically balanced.

Station
A term applied to Royal Air Force aerodromes and depots.

Steel
A high-grade iron alloy with a content of carbon and sometimes with other elements added, such as nickel. Stainless steel has a high chromium content and is non-corrosive.

Stem
The principal frame member in the bows of a flying-boat hull. It runs downwards from the deck to the keel.

Step
A break in the planing bottom of a flying-boat hull which assists 'unsticking' from the water.

Sternpost
The rearmost vertical member of a fuselage or hull.

Storm
A term given to any violent atmospheric disturbance.

Strain
The distortion of any body caused by forces acting on it.

Stratosphere
The outer layer of the atmosphere beginning at about 35,000ft defined as the strata of air in which the temperature gradient remains constant - at about -70°F.

Stratus
A fog-like layer of low cloud.

Streamline
A form designed to reduce resistance to motion through a fluid and to eliminate eddies. A good streamline form appears to have a longitudinal section rather like an elongated peardrop with the wider end foremost. First used on airships.

Streamline Wires
First introduced after research at Farnborough, streamline or Raf-wires are rolled to an oval section and are used for external bracing, particularly of biplanes.

Stress
The product of the load on a body divided by the area subjected to load, originally expressed in foot-pounds per square inch. A body is in tension when the force tends to pull it apart. It is in compression when the force tends to squeeze the body together. The change in shape caused by tension or compression is called strain. Stress divided by str…

Stressed Skin
The form of aircraft construction in which the external skin carries part or all of the main loads.

Stringer
A secondary member of an aeroplane structure, usually running parallel to the mainspars or longerons, which assist in maintaining the external form.

Structure
The basis framework or skeleton of aircraft. or other engineering construction.

Strut
A member of a structure which takes compression stress along the direction of its length. The interplane struts of a biplane are the most graphical example in aeroplane structures.

Stub
Another name for a sponson or similar short projection from an aeroplane.

Stunts
a colloquial name for aerobatics.

Submarine
A small ship specifically designed to submerge and proceed under water to avoid detection and so take advantage of the element of surprise, one of the most telling tactics of warfare.

Suction
A lowering of pressure in a confined space causing a fluid to enter, or one body to adhere to another, under atmospheric pressure.

Super-Compression Engine
A high-compression engine designed for full-power operation only above a predetermined height. At lower levels the throttle opening is controlled by a throttle gate.

Supercharger
A device which forces a greater weight of charge into the combustion chamber of an aero-engine than would be taken in by normal induction, particularly in reduced atmospheric pressure at great heights.

Superheat
A term used in airship piloting to denote the difference in temperature between the gas in the airship's envelope and the surrounding atmosphere.

Supersonic Speed
A speed greater than the speed of sound through the medium concerned. The speed of sound in air is about 770 m.p.h. at sea level, falling to about 660 m.p.h. at 36,000ft. At supersonic speeds bodies have high drag and cause a loud noise, as with the propeller tips of the Harvard.

Supporting Surfaces
The lifting surfaces of an aeroplane or glider.

Surface Friction Drag
The drag caused by the actual contact of the air flowing over a body with the surface of that body.

Surface Radiator
An aero-engine's radiator so mounted as to form an integral part of one or more of the aeroplane's external surfaces. These radiators were used on some of the later Schneider Trophy floatplanes, but fell from favour following the introduction of the ducted radiator.

Sutton Harness
A system of four straps used to hold a pilot in his seat during aerobatics. It consists of two straps passing over the pilot's shoulders and two others over the thighs. The four meet in a quick-release pin in front of the pilot's chest.

Sweep Back
The mainplanes of many aeroplanes are so designed as to appear bent backwards in plan, the tips being aft of the centre section. The angular set back of the planes is known as 'sweepback.'

Swinging Base
Another term for a compass base which is a circular level piece of ground on which aeroplanes are stood while their compasses are calibrated. Lines marking the points of the compass are usually marked out on the base so that the aeroplane can be correctly aligned in each direction.

Switch Off
Term used in starting an aero-engine to ensure that the ignition switches are off.

Synchronising Gear
A mechanism designed to permit the firing of a machine-gun or guns through the disc of a revolving propeller. The best known synchronising gear was that developed by George Constantinesco in 1917, which remained in use until the introduction of wing-mounted guns shortly before the Second World War.

Synchroscope
An instrument for indicating whether two engines are running at the same speed.

Synoptic Weather Chart
A chart showing the weather by means of pressure variations at a given time over a particular area.

Tab
A small hinged flap usually set in the trailing edge of a control surface. Its purpose is so to adjust the control that the aeroplane is properly trimmed when the controls are centralised.

Tachometer
A revolution indicator (or 'rev counter').

Tail Heaviness
The faulty characteristic of an aeroplane caused by the Centre of Gravity (c.g.) being too far back or by badly trimmed elevators.

Tail Unit
The complete assembly of tail surfaces, comprising fin, rudder, tailplane and elevators.

Tail-first Aeroplane
Often called a 'canard', a form of aeroplane design in which the tail precedes the main supporting surfaces. Notable examples were the early Santos-Dumont types, the Aeronautical Syndicate Valkyrie of 1910/12, and the German Focke-Wulf Ente of 1927.

Tail-setting Angle
The acute angle formed by the chord line of the mainplane and that of the tailplane.

Tailbooms
Elongated girder or tubular structures used on some aeroplanes instead of the normal fuselage to carry the tail.

Tailless Aeroplanes
A basic aeroplane design, first evolved by Lt J.W. Dunne in 1907. It dispenses with tail surfaces carried on a fuselage or tailbooms. The wings are swept back in plan and the control surfaces are usually carried at the wing tips. The Westland-Hill Pterodactyl of 1926-30 was a notable example.

Tailplane
The fixed horizontal tail surface of an aeroplane.

Tailskid
A lever and shoe which, mounted on a fixed bracket and fulcrum, takes the weight of the rear end of the fuselage on the ground. Nowadays it is usually replaced by a tailwheel.

Tailslide
The backward and downward movement of an aeroplane which has been stalled after too steep a climb.

Tailwheel
The small wheel which takes the weight of an aeroplane fuselage on the ground at the tail.

Take-off
The movement of aircraft from a position of rest to the moment they are airborne.

Tanks
Fuel containers on aircraft.

Taxying
Manoeuvring aircraft on the ground or on water.

Temperature
Degrees of heat. There is a temperature variation of 129 degrees Fahrenheit (71·5 degrees Centigrade) between sea level (59 degrees F International Standard Atmosphere) and a height of 40,000ft (-69·7 degrees F International Standard Atmosphere).

Tempering
The final stage in the treatment of high-grade steels which relieves strains in the material and produces any required combination of hardness and toughness.

Tensile Strength
The property of a material to resist a stress which tends to pull molecules apart.

Terminal Velocity
The maximum speed attainable by an aeroplane at its most acute diving angle, the engine and propeller operating under specified conditions.

Thermometer
An instrument for measuring temperatures. Three different systems are employed. The Fahrenheit scale records freezing point of water at 32 degrees and boiling point at 212 degrees; the Centigrade scale registers freezing point at 0 degrees and boiling point at 100 degrees; the Reaumur scale has a freezing point of 0 degrees and a boiling point of 8…

Thickness Ratio
In an aerofoil its chord divided by its maximum depth. In modern cantilever wings the average thickness ratio is about 6:1.

Three-point Landing
When the three wheels (or two wheels and tailskid) of an aeroplane touch down simultaneously on landing.

Thrust
The force exerted by a propeller along its thrustline.

Thunderstorm
Strong convectional movements in the atmosphere which give rise to intense vertical currents of air. Thunderstorms are usually heralded by towering cumulo-nimbus clouds followed by heavy rain or hail, thunder and lightning.

Tornado
A violent whirling windstorm of small radius which advances over land while circling round its centre. Strong ascending currents of air form in the region of a tornado. In West Africa a tornado is defined as a squall accompanying a thunderstorm.

Torque
The moment of the aerodynamic forces about the thrust line of a propeller which tends to turn the aeroplane in the opposite direction to that in which the propeller is rotating.

Townend Ring
A narrow-chord cowling ring round the cylinders of a radial engine to reduce drag and improve cooling. The Townend ring was the invention of Dr H.C.H. Townend in 1929. It caused a great reduction in the drag of radial engines and was widely used before the long-chord NACA cowling came into general use. Aeroplanes with Townend rings were the Vickers…

Track
A course followed by projection of the path of the centre of gravity of an aeroplane on to the surface of the Earth.

Track Angle
The angle, at any moment, between the track of an aeroplane and the Meridian, measured clockwise from 0 degrees to 360 degrees.

Tractor Aeroplane
An aeroplane which has a tractor propeller or propellers, i.e. mounted in front of the engines so as to pull the aircraft through the air. The opposite of a pusher aeroplane, which has its propeller(s) mounted aft of the engine.

Tractor Propeller
A propeller designed to pull on its propshaft. A tractor propeller is usually fitted in the nose or in the front of engine nacelles in the wings and is distinct from a pusher propeller which propels the aeroplane and is thus situated in the rear.

Trade Winds
Persistent winds which blow in latitudes 30 degrees North and South, towards the equitorial doldrums, north-east in the northern hemisphere and south-east in the southern hemisphere. The reverse winds above the trade winds are called the anti-trades.

Trailing Aerial
A weighted radio aerial which trails in flight, mounted in an aeroplane and usually capable of being wound in or out.

Trailing Edge
The rear edge of a streamlined body, aerofoil, or control surface.

Trainers
A generic term for aircraft used for flying training.

Transport
A civil or military aeroplane used for freight or troop carrying.

Tricycle Undercarriage
A landing gear which incorporates a nosewheel and two mainwheels which are located behind the Centre of Gravity so that the aeroplane remains in approximately flying attitude when on the ground.

Trim
The set or angle at which an aeroplane flies under given conditions.

Trimming Tabs
Small auxiliary movable tabs on the trailing edges of control surfaces. Originally designed to provide trim as an improvement on incidence gears, they were found to have a potent effect on the aerodynamic balance of control surfaces.

Triplane
An aeroplane with three mainplanes superimposed one above the other.

Troop Carrier
A transport aeroplane expressly designed or converted for carrying airborne troops.

Tropical Revolving Storms
The generic term for the type of cyclonic depression known in various parts of the world as hurricane, cyclone or typhoon.

Tropopause
The region of the atmosphere between the stratosphere and the troposphere.

Troposphere
The lower layer of the atmosphere in which the change of temperature with height is relatively large and decreases with an increase in height. The troposphere extends up to approximately 33,000ft.

Trough
A valley of low atmospheric pressure, as opposed to a ridge of high pressure.

True Air Speed
The speed of an aeroplane through the air in which it is flying, corrected for errors in Indicated Air Speed and contrasted with ground speed.

True Course
The angle between the longitudinal axis of an aeroplane and a true meridian.

Turbo-supercharger
An exhaust-driven supercharger, the advantage of which is that it can maintain sea-level engine performance at great heights. Disadvantages are high working temperature and excessive turbine speed.