University of Virginia Library

GLOSSARY
The numbers at the right-hand side of the page indicate the parts numbered in the preceding diagrams.

Aeronautics—The science of aerial navigation.

Aerofoil—A rigid structure, of large superficial area relative to its thickness, designed to obtain, when driven through the air at an angle inclined to the direction of motion, a reaction from the air approximately at right angles to its surface. Always cambered when intended to secure a reaction in one direction only. As the term "aerofoil" is hardly ever used in practical aeronautics, I have, throughout this book, used the term SURFACE, which, while academically incorrect, since it does not indicate thickness, is a term usually used to describe the cambered lifting surfaces, i.e., the "planes" or "wings," and the stabilizers and the controlling aerofoils.

Aerodrome—The name usually applied to a ground used for the practice of aviation. It really means "flying machine," but is never used in that sense nowadays.

Aeroplane—A power-driven aerofoil with stabilizing and controlling surfaces.

Acceleration—The rate of change of velocity.

Angle of Incidence—The angle at which the "neutral lift line" of a surface attacks the air.

Angle of Incidence, Rigger's—The angle the chord of a surface makes with a line parallel to the axis of the propeller.

Angle of Incidence, Maximum—The greatest angle of incidence at which, for a given power, surface (including detrimental surface), and weight, horizontal flight can be maintained.

Angle of Incidence, Minimum—The smallest angle of incidence at which, for a given power, surface (including detrimental surface), and weight, horizontal flight can be maintained.

Angle of Incidence, Best Climbing—That angle of incidence at which an aeroplane ascends quickest. An angle approximately halfway between the maximum and optimum angles.

Angle of Incidence, Optimum—The angle of incidence at which the lift-drift ratio is the highest.

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Angle, Gliding—The angle between the horizontal and the path along which an aeroplane at normal flying speed, but not under engine power, descends in still air.

Angle, Dihedral—The angle between two planes.

Angle, Lateral Dihedral—The lifting surface of an aeroplane is said to be at a lateral dihedral angle when it is inclined upward towards its wing-tips.

Angle, Longitudinal Dihedral—The main surface and tail surface are said to be at a longitudinal dihedral angle when the projections of their neutral lift lines meet and produce an angle above them.

Angle, Rigger's Longitudinal Dihedral—Ditto, but substituting "chords" for "neutral life lines."

Angle, Pitch—The angle at any given point of a propeller, at which the blade is inclined to the direction of motion when the propeller is revolving but the aeroplane stationary.

Altimeter—An instrument used for measuring height.

Air-Speed Indicator—An instrument used for measuring air pressures or velocities. It consequently indicates whether the surface is securing the requisite reaction for flight. Usually calibrated in miles per hour, in which case it indicates the correct number of miles per hour at only one altitude. This is owing to the density of the air decreasing with increase of altitude and necessitating a greater speed through space to secure the same air pressure as would be secured by less speed at a lower altitude. It would be more correct to calibrate it in units of air pressure. [1]

Air Pocket—A local movement or condition of the air causing an aeroplane to drop or lose its correct attitude.

Aspect-Ratio—The proportion of span to chord of a surface.

Air-Screw (Propeller)—A surface so shaped that its rotation about an axis produces a force (thrust) in the direction of its axis. [2]

Aileron—A controlling surface, usually situated at the wing-tip, the operation of which turns an aeroplane about its longitudinal axis; causes an aeroplane to tilt sideways. [3]

Aviation—The art of driving an aeroplane.

Aviator—The driver of an aeroplane.

Barograph—A recording barometer, the charts of which can be calibrated for showing air density or height.

Barometer—An instrument used for indicating the density of air.

Bank, to—To turn an aeroplane about its longitudinal axis (to tilt sideways) when turning to left or right.

Biplane—An aeroplane of which the main lifting surface consists of a surface or pair of wings mounted above another surface or pair of wings.

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Bay—The space enclosed by two struts and whatever they are fixed to.

Boom—A term usually applied to the long spars joining the tail of a "pusher" aeroplane to its main lifting surface. [4]

Bracing—A system of struts and tie wires to transfer a force from one point to another.

Canard—Literally "duck." The name which was given to a type of aeroplane of which the longitudinal stabilizing surface (empennage) was mounted in front of the main lifting surface. Sometimes termed "tail-first" aeroplanes, but such term is erroneous, as in such a design the main lifting surface acts as, and is, the empennage.

Cabre—To fly or glide at an excessive angle of incidence; tail down.

Camber—Curvature.

Chord—Usually taken to be a straight line between the trailing and leading edges of a surface.

Cell—The whole of the lower surface, that part of the upper surface directly over it, together with the struts and wires holding them together.

Centre (Line) of Pressure—A line running from wing-tip to wing-tip, and through which all the air forces acting upon the surface may be said to act, or about which they may be said to balance.

Centre (Line) of Pressure, Resultant—A line transverse to the longitudinal axis, and the position of which is the resultant of the centre of pressure of two or more surfaces.

Centre of Gravity—The centre of weight.

Cabane—A combination of two pylons, situated over the fuselage, and from which anti-lift wires are suspended. [5]

Cloche—Literally "bell." Is applied to the bell-shaped construction which forms the lower part of the pilot's control lever in a Bleriot monoplane, and to which the control cables are attached.

Centrifugal Force—Every body which moves in a curved path is urged outwards from the centre of the curve by a force termed "centrifugal."

Control Lever—A lever by means of which the controlling surfaces are operated. It usually operates the ailerons and elevator. The "joy-stick." [6]

Cavitation, Propeller—The tendency to produce a cavity in the air.

Distance Piece—A long, thin piece of wood (sometimes tape) passing through and attached to all the ribs in order to prevent them from rolling over sideways. [7]

Displacement—Change of position.

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Drift (of an aeroplane as distinct from the propeller)—The horizontal component of the reaction produced by the action of driving through the air a surface inclined upwards and towards its direction of motion plus the horizontal component of the reaction produced by the "detrimental" surface plus resistance due to "skin-friction." Sometimes termed "head-resistance."

Drift, Active—Drift produced by the lifting surface.

Drift, Passive—Drift produced by the detrimental surface.

Drift (of a propeller)—Analogous to the drift of an aeroplane. It is convenient to include "cavitation" within this term.

Drift, to—To be carried by a current of air; to make leeway.

Dive, to—To descend so steeply as to produce a speed greater than the normal flying speed.

Dope, to—To paint a fabric with a special fluid for the purpose of tightening and protecting it.

Density—Mass of unit volume, for instance, pounds per cubic foot.

Efficiency—
Output
Input

Efficiency (of an aeroplane as distinct from engine and propeller)—
Lift and Velocity
Thrust (= aeroplane drift)

Efficiency, Engine—
Brake horse-power
Indicated horse-power

Efficiency, Propeller—
Thrust horse-power
Horse-power received from engine
(= propeller drift)

Note.—The above terms can, of course, be expressed in foot-pounds. It is then only necessary to divide the upper term by the lower one to find the measure of efficiency.

Elevator—A controlling surface, usually hinged to the rear of the tail-plane, the operation of which turns an aeroplane about an axis which is transverse to the direction of normal horizontal flight. [8]

Empennage—See "Tail-plane."

Energy—Stored work. For instance, a given weight of coal or petroleum stores a given quantity of energy which may be expressed in foot-pounds.

Extension—That part of the upper surface extending beyond the span of the lower surface. [9]

Edge, Leading—The front edge of a surface relative to its normal direction of motion. [10]

Edge, Trailing—The rear edge of a surface relative to its normal direction of motion. [11]

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Factor of Safety—Usually taken to mean the result found by dividing the stress at which a body will collapse by the maximum stress it will be called upon to bear.

Fineness (of stream-line)—The proportion of length to maximum width.

Flying Position—A special position in which an aeroplane must be placed when rigging it or making adjustments. It varies with different types of aeroplanes. Would be more correctly described as "rigging position."

Fuselage—That part of an aeroplane containing the pilot, and to which is fixed the tail-plane. [12]

Fin—Additional keel-surface, usually mounted at the rear of an aeroplane. [13]

Flange (of a rib)—That horizontal part of a rib which prevents it from bending sideways. [14]

Flight—The sustenance of a body heavier than air by means of its action upon the air.

Foot-pound—A measure of work representing the weight of 1 lb. raised 1 foot.

Fairing—Usually made of thin sheet aluminum, wood, or a light construction of wood and fabric; and bent round detrimental surface in order to give it a "fair" or "stream-like" shape. [15]

Gravity—Is the force of the Earth's attraction upon a body. It decreases with increase of distance from the Earth. See "Weight."

Gravity, Specific—
Density of substance
Density of water.

Thus, if the density of water is 10 lb. per unit volume, the same unit volume of petrol, if weighing 7 lb., would be said to have a specific gravity of 7/10, i.e., 0.7.

Gap (of an aeroplane)—The distance between the upper and lower surfaces of a biplane. In a triplane or multiplane, the distance between a surface and the one first above it. [16]

Gap, Propeller—The distance, measured in the direction of the thrust, between the spiral courses of the blades.

Girder—A structure designed to resist bending, and to combine lightness and strength.

Gyroscope—A heavy circular wheel revolving at high speed, the effect of which is a tendency to maintain its plane of rotation against disturbing forces.

Hangar—An aeroplane shed.

Head-Resistance—Drift. The resistance of the air to the passage of a body.

Helicopter—An air-screw revolving about a vertical axis, the direction of its thrust being opposed to gravity.

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Horizontal Equivalent—The plan view of a body whatever its attitude may be.

Impulse—A force causing a body to gain or lose momentum.

Inclinometer—A curved form of spirit-level used for indicating the attitude of a body relative to the horizontal.

Instability—An inherent tendency of a body, which, if the body is disturbed, causes it to move into a position as far as possible away from its first position.

Instability, Neutral—An inherent tendency of a body to remain in the position given it by the force of a disturbance, with no tendency to move farther or to return to its first position.

Inertia—The inherent resistance to displacement of a body as distinct from resistance the result of an external force.

Joy-Stick—See "Control Lever."

Keel-Surface—Everything to be seen when viewing an aeroplane from the side of it.

King-Post—A bracing strut; in an aeroplane, usually passing through a surface and attached to the main spar, and from the end or ends of which wires are taken to spar, surface, or other part of the construction in order to prevent distortion. When used in connection with a controlling surface, it usually performs the additional function of a lever, control cables connecting its ends with the pilot's control lever. [17]

Lift—The vertical component of the reaction produced by the action of driving through the air a surface inclined upwards and towards its direction of motion.

Lift, Margin of—The height an aeroplane can gain in a given time and starting from a given altitude.

Lift-Drift Ratio—The proportion of lift to drift.

Loading—The weight carried by an aerofoil. Usually expressed in pounds per square foot of superficial area.

Longeron—The term usually applied to any long spar running length-ways of a fuselage. [18]

Mass—The mass of a body is a measure of the quantity of material in it.

Momentum—The product of the mass and velocity of a body is known as "momentum."

Monoplane—An aeroplane of which the main lifting surface consists of one surface or one pair of wings.

Multiplane—An aeroplane of which the main lifting surface consists of numerous surfaces or pairs of wings mounted one above the other.

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Montant—Fuselage strut.

Nacelle—That part of an aeroplane containing the engine and pilot and passenger, and to which the tail plane is not fixed. [19]

Neutral Lift Line—A line taken through a surface in a forward direction relative to its direction of motion, and starting from its trailing edge. If the attitude of the surface is such as to make the said line coincident with the direction of motion, it results in no lift, the reaction then consisting solely of drift. The position of the neutral lift line, i.e., the angle it makes with the chord, varies with differences of camber, and it is found by means of wind-tunnel research.

Newton's Laws of Motion—1. If a body be at rest, it will remain at rest; or, if in motion, it will move uniformly in a straight line until acted upon by some force.
2. The rate of change of the quantity of motion (momentum) is proportional to the force which causes it, and takes place in the direction of the straight line in which the force acts. If a body be acted upon by several forces, it will obey each as though the others did not exist, and this whether the body be at rest or in motion.
3. To every action there is opposed an equal and opposite reaction.

Ornithopter (or Orthopter)—A flapping wing design of aircraft intended to imitate the flight of a bird.

Outrigger—This term is usually applied to the framework connecting the main surface with an elevator placed in advance of it. Sometimes applied to the "tail-boom" framework connecting the tail-plane with the main lifting surface. [20]

Pancake, to—To "stall "

Plane—This term is often applied to a lifting surface. Such application is not quite correct, since "plane" indicates a flat surface, and the lifting surfaces are always cambered.

Propeller—See "Air-Screw."

Propeller, Tractor—An air-screw mounted in front of the main lifting surface.

Propeller, Pusher—An air-screw mounted behind the main lifting surface.

Pusher—An aeroplane of which the propeller is mounted behind the main lifting surface.

Pylon—Any V-shaped construction from the point of which wires are taken.

Power—Rate of working. [21]

Power, Horse—One horse-power represents a force sufficient to raise 33,000 lbs. 1 foot in a minute.

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Power, Indicated Horse—The I.H.P. of an engine is a measure of the rate at which work is done by the pressure upon the piston or pistons, as distinct from the rate at which the engine does work. The latter is usually termed "brake horse-power," since it may be measured by an absorption brake.

Power, Margin of—The available quantity of power above that necessary to maintain horizontal flight at the optimum angle.

Pitot Tube—A form of air-speed indicator consisting of a tube with open end facing the wind, which, combined with a static pressure or suction tube, is used in conjunction with a gauge for measuring air pressures or velocities. (No. 1 in diagram.)

Pitch, Propeller—The distance a propeller advances during one revolution supposing the air to be solid.

Pitch, to—To plunge nose-down.

Reaction—A force, equal and opposite to the force of the action producing it.

Rudder—A controlling surface, usually hinged to the tail, the operation of which turns an aeroplane about an axis which is vertical in normal horizontal flight; causes an aeroplane to turn to left or right of the pilot. [22]

Roll, to—To turn about the longitudinal axis.

Rib, Ordinary—A light curved wooden part mounted in a fore and aft direction within a surface. The ordinary ribs give the surface its camber, carry the fabric, and transfer the lift from the fabric to the spars. [23]

Rib, Compression—Acts as an ordinary rib, besides bearing the stress of compression produced by the tension of the internal bracing wires. [24]

Rib, False—A subsidiary rib, usually used to improve the camber of the front part of the surface. [25]

Right and Left Hand—Always used relative to the position of the pilot. When observing an aeroplane from the front of it, the right hand side of it is then on the left hand of the observer.

Remou—A local movement or condition of the air which may cause displacement of an aeroplane.

Rudder-Bar—A control lever moved by the pilot's feet, and operating the rudder. [26]

Surface—See "Aerofoil."

Surface, Detrimental—All exterior parts of an aeroplane including the propeller, but excluding the (aeroplane) lifting and (propeller) thrusting surfaces.

Surface, Controlling—A surface the operation of which turns an aeroplane about one of its axes.

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Skin-Friction—The friction of the air with roughness of surface. A form of drift.

Span—The distance from wing-tip to wing-tip.

Stagger—The distance the upper surface is forward of the lower surface when the axis of the propeller is horizontal.

Stability—The inherent tendency of a body, when disturbed, to return to its normal position.

Stability, Directional—The stability about an axis which is vertical during normal horizontal flight, and without which an aeroplane has no natural tendency to remain upon its course.

Stability, Longitudinal—The stability of an aeroplane about an axis transverse to the direction of normal horizontal flight, and without which it has no tendency to oppose pitching and tossing.

Stability, Lateral—The stability of an aeroplane about its longitudinal axis, and without which it has no tendency to oppose sideways rolling.

Stabilizer—A surface, such as fin or tail-plane, designed to give an aeroplane inherent stability.

Stall, to—To give or allow an aeroplane an angle of incidence greater than the "maximum" angle, the result being a fall in the lift-drift ratio, the lift consequently becoming less than the weight of the aeroplane, which must then fall, i.e., "stall" or "pancake."

Stress—Burden or load.

Strain—Deformation produced by stress.

Side-Slip, to—To fall as a result of an excessive "bank" or "roll."

Skid, to—To be carried sideways by centrifugal force when turning to left or right.

Skid, Undercarriage—A spar, mounted in a fore and aft direction, and to which the wheels of the undercarriage are sometimes attached. Should a wheel give way the skid is then supposed to act like the runner of a sleigh and to support the aeroplane. [28]

Skid, Tail—A piece of wood or other material, orientable, and fitted with shock absorbers, situated under the tail of an aeroplane in order to support it upon the ground and to absorb the shock of alighting. [28a]

Section—Any separate part of the top surface, that part of the bottom surface immediately underneath it, with their struts and wires.

Spar—Any long piece of wood or other material.

Spar, Main—A spar within a surface and to which all the ribs are attached, such spar being the one situated nearest to the centre of pressure. It transfers more than half the lift from the ribs to the bracing. [29]

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Spar, Rear—A spar within a surface, and to which all the ribs are attached, such spar being situated at the rear of the centre of pressure and at a greater distance from it than is the main spar. It transfers less than half of the lift from the ribs to the bracing. [30]

Strut—Any wooden member intended to take merely the stress of direct compression.

Strut, Interplane—A strut holding the top and bottom surfaces apart.

Strut, Fuselage—A strut holding the fuselage longerons apart. It should be stated whether top, bottom, or side. If side, then it should be stated whether right or left hand. Montant. [32]

Strut, Extension—A strut supporting an "extension" when not in flight. It may also prevent the extension from collapsing upwards during flight. [33]

Strut, Undercarriage— [33a]

Strut, Dope—A strut within a surface, so placed as to prevent the tension of the doped fabric from distorting the framework. [34]

Serving—To bind round with wire, cord, or similar material. Usually used in connection with wood joints and wire cable splices.

Slip, Propeller—The pitch less the distance the propeller advances during one revolution.

Stream-Line—A form or shape of detrimental surface designed to produce minimum drift.

Toss, to—To plunge tail-down.

Torque, Propeller—The tendency of a propeller to turn an aeroplane about its longitudinal axis in a direction opposite to that in which the propeller revolves.

Tail-Slide—A fall whereby the tail of an aeroplane leads.

Tractor—An aeroplane of which the propeller is mounted in front of the main lifting surface.

Triplane—An aeroplane of which the main lifting surface consists of three surfaces or pairs of wings mounted one above the other.

Tail-Plane—A horizontal stabilizing surface mounted at some distance behind the main lifting surface. Empennage. [36]

Turnbuckle—A form of wire-tightener, consisting of a barrel into each end of which is screwed an eyebolt. Wires are attached to the eyebolts and the required degree of tension is secured by means of rotating the barrel.

Thrust, Propeller—See "Air-Screw."

Undercarriage—That part of an aeroplane beneath the fuselage or nacelle, and intended to support the aeroplane when at rest, and to absorb the shock of alighting. [37]

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Velocity—Rate of displacement; speed.

Volplane—A gliding descent.

Weight—Is a measure of the force of the Earth's attraction (gravity) upon a body. The standard unit of weight in this country is 1 lb., and is the force of the Earth's attraction on a piece of platinum called the standard pound, deposited with the Board of Trade in London. At the centre of the Earth a body will be attracted with equal force in every direction. It will therefore have no weight, though its mass is unchanged. Gravity, of which weight is a measure, decreases with increase of altitude.

Web (of a rib)—That vertical part of a rib which prevents it from bending upwards. [37a]

Warp, to—To distort a surface in order to vary its angle of incidence. To vary the angle of incidence of a controlling surface.

Wash—The disturbance of air produced by the flight of an aeroplane.

Wash-in—An increasing angle of incidence of a surface towards its wing-tip. [38]

Wash-out—A decreasing angle of incidence of a surface towards its wing-tip. [39]

Wing-tip—The right-or left-hand extremity of a surface. [40]

Wire—A wire is, in Aeronautics, always known by the name of its function.

Wire, Lift or Flying—A wire opposed to the direction of lift, and used to prevent a surface from collapsing upward during flight. [41]

Wire, Anti-lift or Landing—A wire opposed to the direction of gravity, and used to sustain a surface when it is at rest. [42]

Wire, Drift—A wire opposed to the direction of drift, and used to prevent a surface from collapsing backwards during flight.

Wire, Anti-drift—A wire opposed to the tension of a drift wire, and used to prevent such tension from distorting the framework. [44]

Wire, Incidence—A wire running from the top of an interplane strut to the bottom of the interplane strut in front of or behind it. It maintains the "stagger" and assists in maintaining the angle of incidence. Sometimes termed "stagger wire." [45]

Wire, Bracing—Any wire holding together the framework of any part of an aeroplane. It is not, however, usually applied to the wires described above unless the function performed includes a function additional to those described above. Thus, a lift wire, while strictly speaking a bracing wire, is not usually described as one unless it performs the additional function of bracing some well-defined part such as the undercarriage. It will then be said to be an "undercarriage bracing lift wire." It might, perhaps, be acting as a drift wire also, in which case it will then be described

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as an "undercarriage bracing lift-drift wire." It should always be stated whether a bracing wire is (1) top, (2) bottom, (3) cross, or (4) side. If a "side bracing wire," then it should be stated whether right-or left-hand.

Wire, Internal Bracing—A bracing wire (usually drift or anti-drift) within a surface.

Wire, Top Bracing—A bracing wire, approximately horizontal and situated between the top longerons of fuselate, between top tail booms, or at the top of similar construction. [46]

Wire, Bottom Bracing—Ditto, substituting "bottom" for "top." [47]

Wire, Side Bracing—A bracing wire crossing diagonally a side bay of fuselage, tail boom bay, undercarriage side bay or centre-section side bay. This term is not usually used with reference to incidence wires, although they cross diagonally the side bays of the cell. It should be stated whether right-or left-hand. [48]

Wire, Cross Bracing—A bracing wire, the position of which is diagonal from right to left when viewing it from the front of an aeroplane. [49]

Wire, Control Bracing—A wire preventing distortion of a controlling surface [50]

Wire, Control—A wire connecting a controlling surface with the pilot's control lever, wheel, or rudder-bar. [51]

Wire, Aileron Gap—A wire connecting top and bottom ailerons. [52]

Wire, Aileron Balance—A wire connecting the right-and left-hand top ailerons. Sometimes termed the "aileron compensating wire." [53]

Wire, Snaking—A wire, usually of soft metal, wound spirally or tied round another wire, and attached at each end to the framework. Used to prevent the wire round which it is "snaked" from becoming, in the event of its displacement, entangled with the propeller.

Wire, Locking—A wire used to prevent a turnbuckle barrel or other fitting from losing its adjustment.

Wing—Strictly speaking, a wing is one of the surfaces of an ornithopter. The term is, however, often applied to the lifting surface of an aeroplane when such surface is divided into two parts, one being the left-hand "wing," and the other the right-hand "wing."

Wind-Tunnel—A large tube used for experimenting with surfaces and models, and through which a current of air is made to flow by artificial means.

Work—Force X displacement.

Wind-Screen—A small transparent screen mounted in front of the pilot to protect his face from the air pressure.