Chapter XXI: Glossary of Aeronautical Words

In the following list are the most common of the aeronautical words and phrases. Many of these words are of French origin, and in such cases are marked "Fr." In cases of English words, the French equivalents follow in parentheses. When a French word or term is given it is in italics, unless it is in common use in this country. Words marked (*) are the revisions adopted by the National Advisory Board of Aeronautics at Washington, D. C., and include the term "Airplane," which was intended to supplant the more common "Aeroplane." These revisions have not met with universal adoption, for the older words are too well established to admit of change.

A

ABSOLUTE UNITS.
Units given in terms of mass. For expression in terms of pounds
(Gravitational units) they must be multiplied by some factor
involving the value of gravitation. Thus, to convert units of
mass into pounds, the mass must be multiplied by the value of
gravitation, 32.16 being the average figure taken for this
quantity. To convert the absolute lift factors given by the
N.P.L. into pounds per square foot per mile per hour, multiply
the absolute value by O.005IV².

ABSOLUTE ZERO.
The temperature at which heat ceases to exist. This is 461
degrees below the Fahrenheit zero, or 273 degrees below the
Centigrade zero.

ACCELERATE.
To increase in speed.

_ACIER_ (Fr.)
Steel.

AERODONETICS.
A word originated by Lanchester to denote the science of
stability.

AEROCURVE.
See AEROFOIL.

AEROFOIL.*
A thin wing-like structure designed to obtain lift by the
reaction of moving air upon its surfaces.

AERODYNAMICS.
A science investigating the forces produced by a stream of air
acting upon a surface.

AERODYNAMIC RESISTANCE.
The resistance caused by turbulence or eddies.

AERODROME.
A flying field. This word was also used by Langley to describe an
aeroplane.

AEROSTAT.
A lighter than air machine.

AEROSTATICS.
The science of lighter than air machines, or devices sustained by
flotation.

AEROPLANE. (Fr. L’Avion.)
A heavier than air craft sustained by fixed wing surfaces driven
through the air at the same velocity as the body of the machine.
Auxiliary surfaces are provided for stabilizing, steering, and
for producing changes in the altitude. The landing gear may be
suitable for either land or water, although in the latter case it
is generally known as a "Seaplane." The Committee equivalent is
"Airplane."

AILERON.*
A movable auxiliary surface used in maintaining lateral balance.

_AILE_ (Fr.)
Wing.

AIRBOAT.
An aeroplane provided with a light boat hull in which the pilot
and passenger are enclosed.

AIRCRAFT.*
Any form of craft designed for the navigation of the air. This
includes aeroplanes, balloons, dirigibles, helicopters,
ornithopters, etc.

AIRPLANE.*
See aeroplane.

AIRSHIP.
A lighter than air craft provided with means of propulsion.

AIR-SCREW.
See PROPELLER.

ALTIMETER.*
An instrument used for determining the height of aircraft above
the earth.

ALTITUDE.
Height of aircraft above sea level—generally given in feet.

AMPHIBIAN.
An aeroplane equipped with landing gear for both land and water.

ANEMOMETER.*
An instrument for measuring the velocity of the wind.

ANGLE OF INCIDENCE.
The angle made by a surface or body with an air stream. In the
case of curved wings, the angle is measured from the chord of the
curve.

ANGLE OF ATTACK.*
See Angle of Incidence.

ANGLE OF ENTRY.
The angle made with the chord of a wing section by a line drawn
tangent to the upper curved face, and at the front edge.

ANGLE OF TRAIL.
The angle made by a line drawn tangent to the upper surface at
the trailing edge.

ANEMOGRAPH.
An instrument used for graphically recording the velocity of air
currents.

APTEROID ASPECT.
A wing is in apteroid aspect when the narrow edge is toward the
wind.

_ARETIER ARRIERE_ (Fr.)
See Trailing Edge.

_ARETIER AVANT_ (Fr.)
See Leading Edge.

_ARBRE_ (Fr.)
Shaft.

ASPECT RATIO.*
The ratio of the wing span to the chord (length divided by
width).

_ATTERRISSAGE_ (Fr.)
Landing Gear.

_ATTACHES_ (Fr.)
Fastenings.

AUXILIARY SURFACE.
A surface used for stability or for the control of the aeroplane.

AVIAPHONE.
An electric system of communication between the passenger and
pilot.

_AVION_ (Fr.)
See Aeroplane.

AXIS OF PITCH.
The axis taken parallel to the length of the wings, and through
the center of gravity. This is sometimes called the "Y" axis.

AXIS OF ROLL.
An axis passing fore and aft parallel to the center line of the
propeller. This axis is sometimes called the "X" axis.

AXIS OF YAW.
A vertical axis, passing through the center of gravity, around
which the machine swings when being steered in a horizontal
direction under the action of the rudder. This is the "Z" axis.

B

BALSA WOOD.
A very light wood obtained from South America. It is lighter than
cork.

BALLOON.*
A form of aircraft of the lighter than air type comprising a gas
bag and car. It is not provided with a power plant, and depends
upon the buoyancy of the gas for its sustentation. A balloon
restrained from free flight by means of a cable is known as a
"Captive balloon." A kite balloon is an elongated form of captive
balloon, fitted with a tail to keep it headed into the wind, and
is inclined at an angle so that the wind aids in increasing the
lift of the gas.

BALLONET.*
A small air balloon within the main gas bag of a balloon or
dirigible used for controlling the ascent or descent, and for
keeping the fabric of the outer envelope taut when the pressure
of the gas is reduced. The ballonet is kept inflated with air at
the required pressure, the air being controlled by a valve or by
regulating the speed of the blower.

BANK.* To incline the wings laterally when making a turn so that a
portion of the lift force will be opposed to the centrifugal
force.

BAROGRAPH.* (Fr. _Barographe_.)
An instrument used for recording pressure variations in the
atmosphere. The paper charts on which the records are made are
used for determining the altitude of aircraft.

BAROMETER.
An instrument used for measuring variations in the atmospheric
pressure, but is not provided with a recording mechanism as in
the case of the barograph.

BEAUME.
A scale of density or a hydrometer unit used in measuring the
density of fluids. On the Beaume scale water is 10.00, while on
the "Specific gravity" scale water is 1.00. The Beaume scale is
generally used for gasoline and oils.

BENDING-MOMENT.
The moment or "Leverage" that tends to bend a beam.

_BEQUILLE_ (Fr.)
Tail Skid.

_BERCEAU de MOTEUR_ (Fr.)
Engine Bed.

BIAS LAID FABRIC.
Fabric laid on the wing structure with the seams at an angle with
the ribs.

_BIPLACE_ (Fr.)
Two Seater.

BIPLANE.* (Fr. _Biplan_.)
An aeroplane with two superposed lifting surfaces.

BODY. See FUSELAGE.

BODY RAILS.
See LONGERONS.

_BOIS_ (Fr.)
Wood.

_BOIS CREUS_ (Fr.)
Hollow wood construction.

BOMBER.
An aeroplane used for bombing operations.

BOOM. The fore and aft beams running from the wings to the tail in a
pusher type biplane.

_BORD de ATTACQUE_ (Fr.)
Entering or leading edge.

_BORD de SORTIE_ (Fr.)
Trailing edge.

BLADE, PROPELLER.
(Fr. _Pale-Helice_.)

_BOULON_ (Fr.)
Bolt.

_BOUSSOLE_ (Fr.)
Compass.

_BRAS de AILE_ (Fr.)
Wing Spar.

_BREVET_ (Fr.)
Flying permit or license.

BRAKES, AIR.
Small adjustable flaps used in increasing the head resistance
during a landing, thus decreasing the speed.

BURBLE POINT.
The angle at which the lift of a wing section reaches a maximum.

BUOYANCY.
The static force due to a difference in density. The difference
in density between the gas in a balloon envelope and the outside
air determines the sustaining or buoyant force of a balloon.

BUS. A slow fairly stable aeroplane used in training schools.

C

CABLE. (Fr. _Cable_.)
A wire rope built up of a number of small strands.

_CABRE’_. * (Fr.)
A flying attitude in which the angle of incidence is larger than
normal with the tail well down.

CAMBER.*
The convexity, or rise of a lifting surface, measured from the
chord of the curve. It is usually given as the ratio of the
maximum height of the curve to the length of the chord. Top
camber refers to the upper surface, and bottom camber to the
lower surface.

_CABANE_ (Fr.)
The center struts rising from the top of the body to the upper
wing, or the short struts used for the bracing of the overhanging
portions of a biplane wing. Usually cabane denotes the center
cell struts.

_CANARD_ (Fr.)
A machine in which the elevator and stabilizer are in front. The
canard type flies "Tail first."

_CAPOT_ (Fr.)
Cowl or motor hood.

CAPTIVE BALLOON.*
See Balloon.

CAPACITY.*
The lifting capacity is the maximum flying load of an aircraft.
The carrying capacity (live load) is the excess of the lifting
capacity over the dead weight of the aeroplane, the latter
including the structure, power plant and essential accessories.

_CARLINGUE_ (Fr.)
Cock-pit.

CATA-HEDRAL.
A negative dihedral, or wing arrangement, where the wing tips are
lower than the center portion.

CATAPULT.
A device for launching an aeroplane from the deck of a ship or
other limited space. The first Wright machines were launched with
a catapult.

CELL. (Fr. _Cellule_.)
The space included between adjacent struts of a biplane. The
space between the center struts is the "Center Cell."

CEILING.
The maximum altitude to which an aeroplane can ascend.

_CEINTURE de SURETE_ (Fr.)
Safety Belt.

CENTER OF PRESSURE (C. P.)*
The point of application of the resultant of all aerodynamic
forces on an aeroplane wing. If the wing is supported at the
center of pressure it will be in equilibrium.

CENTER OF GRAVITY.
The point at which an aeroplane will balance when freely
suspended.

CENTER OF BUOYANCY.*
The point at which the resultant of all the buoyant forces act.

_CHARNIERE_ (Fr.)
Hinge.

CHASSIS.
The landing wheels and their frame. This is also called the
"Landing gear" in English, or the "Train de Atterrissage" in
French. The chassis carries the load when resting on the ground
or when running over the surface.

CHORD.*
This has two meanings. The chord is the width of a wing or its
shortest dimension. The chord is also the straight line drawn
across the leading and trailing edges of a wing section.

CHASER. (Fr. _Avion de Chasse_.)
A small, fast machine used in scouting or fighting. This type is
also known as a "Speed scout."

_CHARA-A-BANC_ (Fr.)
A two seater aeroplane in which the pilot and passenger are
seated side by side.

_CLOCHE_ (Fr.)
A type of control column used on the old Type XI Bleriot.

COCK-PIT.
The part of the body occupied by the pilot or passenger. The
openings in the body cut for entrance and exit are the "Cock-pit
Openings."

_COMMANDES A PONT_ (Fr.)
Control bridge or Deperdussin yoke.

_COMPTE TOURS_ (Fr.)
Tachometer or speed indicator.

COMPONENTS.
The individual forces that make up a total resultant force.

CONTROLS.* (Fr. _Commandes_.)
The complete system used for steering, elevating, balancing, and
speed regulation. When controls are operated by hand they are
known as "Manual Controls."

CONTROL BRIDGE. (Fr. _Commandes A Pont_.)
The "U" shaped lever used with the Deperdussin control system.
Sometimes known as the "Yoke."

CONTROL STICK. (Fr. _Manche A Balai_.)
A simple control lever capable of being moved in four directions
for elevation, depression and lateral balance.

CONTROL SURFACES.
The adjustable surfaces used for directing and balancing
aircraft. On an aeroplane these are represented by the rudder,
elevator, and ailerons.

_CONTREPLAQUE_ (Fr.)
Three-ply wood.

_CORDE_ (Fr.)
Cord or wire.

_CORD A PIANO_ (Fr.)
Piano or solid hard wire.

CORD WINDING. (Fr. _Transfil_.)
A winding wrapped around wooden struts to prevent splintering or
complete fracture.

_COSSE_ (Fr.)
Thimble for cable connections.

_COUSS IN_ (Fr.)
Cushion.

COVERING, WING. (Fr. _Entoilage_.)
The fabric used in covering the wing structure.

CRITICAL ANGLE.*
The angle of attack or incidence at which the lift is a maximum.

COWL. (Fr. _Capot_.)
The metal cover surrounding a rotary cylinder motor.

_CROISILLONS_ (Fr.)
Bracing wires.

D

DAMPING.
The reduction of oscillation or vibration by the resistance of
the stabilizing surfaces.

DEAD LOAD.
The weight of the structure, power plant, and essential
accessories.

DEAD WATER.
The wake directly in the rear of a moving body or surface.

_De CHASSE_ (Fr.)
See CHASER.

DECALAGE.*
The difference in the angle of incidence between the upper and
lower wings of a biplane.

DEMOISELLE TYPE.
A small monoplane type developed by Santos Dumont.

DENSITY.
The specific weight, or the weight per cubic foot.

_DIEDRE_ (Fr.)
Dihedral angle.

_DERIVE_ (Fr.)
Fin.

DIHEDRAL ANGLE. (Fr. _Diedre_.)
When the tips of the wing are higher than at the center, the two
wing halves form an angle. The included angle between the two
halves, taken above the surface, is known as the "Dihedral
angle."

DIPPING FRONT EDGE.
A wing section in which the leading edge is well bent down below
the rest of the lower surface.

DIRIGIBLE.*
A lighter than air craft in which sustentation is provided by a
gas bag. It differs from a balloon in having a power plant, and
is thus capable of flying in any desired direction regardless of
the wind.

DISC AREA OF PROPELLER.*
The total area of the disc swept out by the propeller tips.

DISCONTINUITY.
Interruption in direction, or breaks in stream line flow. A body
causing eddies or turbulence causes "Discontinuous flow." The
surface separating the eddies and the continuous stream is called
a "Surface of Discontinuity."

DISPLACEMENT.
The volume or space occupied by a floating body.

DOUBLE CAMBER.
A wing section in which both the top and bottom surfaces are
given a convex camber or curvature.

DOPE. (Fr. _Enduit_.)
A solution used for protecting and stretching the wing fabric.

DRAG. The resistance offered to the forward motion of a surface or body
moving through the air. As defined by the Advisory Committee this
is the total resistance offered by the craft and includes both
the resistance of the wings and body. This conception is
confusing, hence the author has considered drag as being the
forward resistance of the wings alone. The resistance of the
structure is simply called the "Head resistance," and the sum of
the resistances is the "Total resistance." This nomenclature was
in existence before the Advisory Board proposed their definition.

DRIFT. As defined by the Advisory Board, the drift is the horizontal
resistance offered by the wings alone. This is confusing since
previous works defined "Drift" as the amount by which an aircraft
was driven out of its normal path by wind gusts. According to
usage, "Drift" is the sidewise deviation from the normal flight
path.

DRAG WIRES.
The bracing wires used for resisting the drag stresses set up in
the wing.

DRIFT INDICATOR.
An instrument for indicating the amount by which an aircraft is
blown out of its path by side winds.

DUAL CONTROL.
A double system of control that can be operated both by the pilot
and passenger.

DUTCH ROLL.
A combined side roll and fore and aft pitch. The machine rolls
from side to side in combination with an up and down motion of
the nose.

DYNAMIC PRESSURE.
The pressure due to the impact of an air stream.

E

ECCENTRIC LOAD.
A load acting to one side of the center line of a beam or strut.

_ECOLE_ (Fr.)
School.

_ECROU_ (Fr.)
Nut.

EDDY. An irregularly moving mass of air caused by the breaking up of a
continuous air stream, or by "Discontinuity."

EFFICIENCY.
The efficiency of a lifting surface is generally expressed by the
ratio of the lift to the drag, or the "Lift-drag ratio." The
efficiency of a propeller is the ratio of the work usefully
applied to the air stream in regard to the power supplied to the
propeller.

ELEVATOR.*
The hinged horizontal tail surface used for maintaining
longitudinal equilibrium and for ascent or descent.

_EMPENNAGE_ (Fr.)
The group of tail surfaces, including the elevator and
stabilizer.

_ENDUIT_ (Fr.)
Dope.

ENGINE ROTATION.
According to the Advisory Board, an engine is turning in
right-hand rotation when the output shaft stub is turning
anti-clockwise.

ENGINE BEARERS (BED). (Fr. _Berceau du Moteur_).
The timbers or fuselage members upon which the engine is
fastened.

ENGINE SPIDER or BRACKET. (Fr. _Arraignee Support de Moteur_.)
A perforated metal support for a rotary cylinder motor.

ENTERING EDGE. (Fr. _Bord D’Attaque or Aretier Avant_.)
The front edge, or air engaging edge, of an aerofoil or lifting
surface. It is also called the "Leading Edge."

_ENTOILAGE_ (Fr.)
Wing fabric or covering.

ENVELOPE.
The gas bag of a balloon or dirigible.

_ESSIEU_ (Fr.)
Axle.

_ENVERGURE_ (Fr.)
Wing span.

EXPANDING PITCH.
A system in which the pitch increases or "expands" towards the
tips of the propeller.

F

FABRIC, WING. (Fr. _Entoilage_.)
The cloth used for covering the wing and control surface
structures.

FAIRING. (Fr. _Fusele_.)
Wood coverings used to streamline steel struts or other
structural members.

FERRULES.
Sheet steel caps used for the ends of the interplane Struts.

FIN. (Fr. _Derive_.)
A fixed vertical stabilizing surface used for damping out
horizontal vibration and oscillations.

FINENESS RATIO.
The ratio of the maximum length to the width of a streamline
body.

FITTINGS. (Fr. _Ferrures, Godets_.)
The metal parts used for making connections between the
structural parts of an aeroplane.

FIXED TAIL.
(See STABILIZER.)

FLACCID BLADE PROPELLER.
A propeller having a cloth covered frame work on which the fabric
is free to adjust itself to the air pressure.

FLAPS, ELEVATOR. (Fr. _Volets de Profondeur_.)
See ELEVATOR.

FLEXIBLE SHAFT. (Fr. _Transmission flexible_.)
Used for tachometer drive.

FLOORING.
(Fr. _Plancher_.)

_FLASQUE D’HELICE_ (Fr.)
Propeller flange.

FOOT LEVER. (Fr. _Palomnier_.)
The foot lever generally used to operate the rudder.

FORMERS.
Supports used in giving a certain outline to the fuselage. The
formers are attached to the fuselage frame and in turn support
small stringers on which the fabric is fastened.

FRICTIONAL WAKE.
The following current of air in the rear of a moving body or
surface. Because of the friction, a portion of the air is drawn
in the direction of the motion.

FUSELAGE.
A structure, usually enclosed, which contains and streamlines the
power plant, passengers, fuel, etc. Sometimes called the "Body."

FUSELAGE BIPLANE.
See TRACTOR BIPLANE.

FUSIFORM.
Of streamline form.

G

GAP. The vertical distance between leading edges of the superposed
planes of the biplane or triplane.

GLIDING. (Fr. _Vol Plan_.)
With an aeroplane the weight of the machine can be made to
provide a forward component that will allow the machine to
descend slowly (without power) along an inclined line. This line
is known as the "Gliding Path."

GLIDING ANGLE.
The angle made by the gliding path with the horizontal is known
as the gliding angle. This may be expressed in degrees or in the
units of horizontal distance traveled per foot of fall.

GLIDER.
A small form of aeroplane without a power plant, which is capable
of gliding down from an elevation in the manner of an aeroplane.
With a proper direction and velocity of wind it can be made to
hold a constant altitude and can be made to hover over one spot
continuously.

_GOUVERNAIL_ (Fr.)
Rudder.

GUY WIRE.
A bracing wire.

H

HARD WIRE.
A solid tempered wire of high tensile strength used for aeroplane
bracing systems.

H.T. WIRE.
Another expression for hard or high tensile strength wire.

HEAD RESISTANCE.
The resistance of the structural parts of an aircraft. In an
aeroplane, the head resistance is the sum of the resistances of
the body, stays, struts, chassis, tail, rudder, elevators, etc.;
in fact, this includes everything with the exception of the wing
drag.

HELICOPTER.
A type of direct lift machine in which sustentation is performed
by vertical air screws or propellers.

HELIX. A geometrical curve formed by the combined advance and revolution
of a point.

_HELICE_ (Fr.)
Propeller or screw.

_HELICE TRACTIVE_ (Fr.)
Tractor propeller.

HYDROAEROPLANE.
See SEAPLANE.

HOLLOW WOOD CONSTRUCTION.
(Fr. _Bois Creus_.)

HOOD OF ENGINE.
(Fr. _Capot_.)

HYDROMETER.
An instrument for measuring the density of liquids.

I

ICTHYOID.
Fish or stream lined shape.

INCLINED PLANE.
A plane inclined to the wind stream so that the energy of the air
stream is broken up into the two components of lift and drag.

INCLINOMETER.
An instrument used for determining the angle of the flight path.

INCIDENCE.
See ANGLE OF INCIDENCE.

INCIDENCE, NEGATIVE.
The angle formed with the air stream when front edge of the
lifting surface dips below the apparent flight path.

INHERENT STABILITY.
Stability due to some fixed arrangement of the main or auxiliary
surfaces. A machine that requires mechanism or moving parts for
its stability is automatically but not inherently stable.

INTERFERENCE.
The crowding of the airstream in the gap of a biplane or triplane
causes the surfaces to "Interfere," and results in a loss of
lift.

J

JOY STICK.
See CONTROL STICK.

_JAMB de FORCE_ (Fr.)
Bracing strut.

_JANTE_ (Fr.)
Rim of wheel.

K

KITE BALLOON.
See BALLOON.

KILOMETER.
French metric unit of distance. One kilometer equals O.621
statute mile or O.5396 nautical mile.

KILOGRAM.
Metric unit of weight. One kilogram equals 2.205 Avoir. pounds.

KNOCKOUT HUB.
An aeroplane chassis wheel hub provided with removable bronze
bushings.

KEEL PLANE AREA.*
The total effective side area of an aeroplane which tends to
prevent skidding or side slipping.

L

LATERAL STABILITY.
Stability about the fore and aft axis.

_L’AVION_ (Fr.)
Aeroplane.

LAMINATED.
Built up in a series of layers.

LEEWAY.*
The angular deviation from a given course due to cross currents
of wind.

LEADING EDGE.
See ENTERING EDGE.

LIFT. The vertical component of the forces produced on an aerofoil by
an air current.

LIFT COEFFICIENT.
The lift per unit of area at a unit velocity (Ky). The American
lift coefficient is the lift in pounds per square foot at one
mile per hour.

LIFT CAPACITY.
See CAPACITY.

LIVE LOAD.
The live load generally includes the passengers, pilot, fuel,
oil, instruments, and portable baggage, although in some cases
the instruments are included in the dead load. The live load is
the difference between the total lift and the dead load.

LOADING (UNIT).
The unit loading is the load carried per square foot of wing
surface, or is equal to the total weight divided by the area.

LONGERONS.
The principal fore and aft structural members of the fuselage.

LONGITUDINALS.
See LONGERONS.

LONGITUDINAL STABILITY.
Stability in a fore and aft direction about the "Y" axis.

M

MASS. The quantity of matter. Is equal to the weight in pounds divided
by the gravitation, or generally to the weight divided by 32.16.

_MANDRIN de BOIS_ (Fr.)
Wood spar.

_MAROUFLAGE_ (Fr.)
Strut taping with fabric bands.

_MANCHE A BALAI_ (Fr.)
Control stick.

_MANETTE_ (Fr.)
Throttle.

_MAR, MONTANT_ (Fr.)
Interplane struts.

METACENTER.*
The point of intersection of a straight vertical line passing
through the center of gravity of the displaced fluid or gas, and
the line that formerly was a vertical through the center of
gravity before the body was tipped from its position of
equilibrium. There is a different metacenter for each position of
a floating body.

MONOPLANE. (Fr. _Monoplan_.)
A type of aeroplane with a single wing surface.

MONOCOQUE BODY (Fr.)
A body built up in tubular form out of three-ply wood, thus
virtually forming a single piece body.

_MONOPLACE_ (Fr.)
Single seater.

_MONOSOUPAPE_ (Fr.)
Single valve Gnome motor.

_MONTGOLFIER_ (Fr.)
Hot air balloon.

MULTIPLANE.
An aeroplane having the main lifting surface divided into a
number of parts.

N

NACELLE.
The body or fuselage of an aeroplane or dirigible. It generally
signifies a dirigible body. The short fuselage of a pusher type
is often called the nacelle.

NATURAL STABILITY.
See INHERENT STABILITY.

NEGATIVE AILERONS.
Ailerons making a negative angle with the wind when in normal
flight. The negative incidence of the ailerons is decreased on
the low side and increased on the high side so that the high side
is pushed down. This decreases the drag on the lower, inner wing
in making a turn, and therefore does not tend to stall the
machine.

_NERVURES_ (Fr.)
Wing ribs.

NORMAL PLANE.
A flat plane placed with its surface at right angles to the air
stream.

NORMAL PRESSURE.
The pressure at right angles to the surface of a plane.

NON-LIFTING TAIL.
A stabilizing surface arranged so that it carries no load in
normal flight.

NOSING.
The member used for the entering edge of the wing.

NOSE. The front end of the aeroplane.

NUT. (Fr. _Ecru_.)

O

_OBLITEUR RINGS_ (Fr.)
The special piston rings used on the Gnome motor.

ORTHOPTER.
Any type of wing flapping machine.

ORNITHOPTER.
A wing flapping machine that imitates bird flight.

ORTHOGONAL BIPLANE.
A biplane with the upper and lower leading edges in line.

OSMOSIS.
The transfer of hydrogen or other gas through a balloon envelope
by a molecular process. This must not be confused with leakage
due to holes.

OUTRIGGER.
See Boom.

O.W.L. TYPE.
A type of machine adapted for use over "Water and Land."

P

PANCAKE.
A straight vertical drop due to stalling.

PATH OF FLIGHT.
The path of the center of gravity of an aircraft in reference to
the air.

_PALONNIER_ (Fr.)
Foot bar or lever.

PANELS.
The wing sections included between adjacent struts.

_PATIN, PATINNAGE_ (Fr.)
Skids.

PARASOL TYPE.
A monoplane in which the wing is located above the body.

PENGUIN.
A training machine which cannot leave the ground.

PERSONNEL.
Pilot and passengers.

PETROL.
An English term for gasoline.

PHILLIP’S ENTRY.
See DIPPING FRONT EDGE.

PILOT. The operator of aircraft.

PILOT BALLOONS.
Small balloons sent up to determine the direction of the wind.

PITCH. The forward distance traveled through by one revolution of the
propeller.

PITCHING.
A fore and aft oscillation, first heading up and then diving.

PISCIFORM.
Fish form.

_PIQUE, VOL_ (Fr.)
Dive.

_PLAFOND_ (Fr.)
"Ceiling" or maximum altitude obtainable.

_PLAN CENTRAL_ (Fr.)
Center panel.

_PLANCHER_ (Fr.)
Flooring.

_PLAN FIXE de QUEUE_ (Fr.)
Stabilizer surface.

_PLAN de DERIVE_ (Fr.)
Stabilizing fin.

PITOT TUBE.
An instrument for measuring the velocity of an air current.

PONTOON.
Seaplane floats.

_POIGNEE_ (Fr.)
Handle.

_POMPE_ (Fr.)
Pump.

_POMPE A PRESSION_ (Fr.)
Pressure pump.

_POULIE_ (Fr.)
Pulley.

PROPELLER. (Fr. _Helice_.)
A device used in converting the energy of a motor into the energy
required for the propulsion of an aircraft. It consists of two or
more rotating blades which are inclined in regard to the relative
wind, and hence they act as rotary aeroplanes in creating a
tractive force.

PROPELLER ROTATION.
The direction of rotation is determined when standing in the slip
stream.

_PNEU_ (Fr.)
Pneumatic tire.

PTERYGOID ASPECT.
A wing flying with the long edge to the wind is said to be in
"Pterygoid Aspect."

PUSHER TYPE.
An aeroplane with the propeller in the rear of the wings.

PYLON. A marking post on an aeroplane course.

P

RACE OF A PROPELLER.
The air stream thrown by the propeller.

RADIAL MOTOR.
A motor with the cylinders arranged in radial lines around the
crankcase.

RAKED TIPS.
The tips are arranged at an angle with the wing so that the span
of the trailing edge is greater than that of the leading edge.

_RAYONS_ (Fr.)
Spokes.

REFLEX CURVE.
An aerofoil in which the trailing edge is given an upward turn.

_REMOUS_ (Fr.)
A downward current of air.

_RESERVOIR_ (Fr.)
Tank.

_RESERVOIR SOUS PRESSION_ (Fr.)
Pressure tank.

RESULTANT.
The total force resulting from the application of a number of
forces.

RETREAT.
Back swept wings with the tips to the rear of the wing center.

RIBS. The fabric forming member of the wing structure.

RUDDER, VERTICAL.
A control surface used for steering in a horizontal plane.

ROLL. Oscillation about the fore and aft axis.

S

SCREW. (Fr. _Helice_.)
See PROPELLER.

SEAPLANE.*
An aeroplane equipped with floats or pontoons for landing on
water.

SCOUT TYPE.
See CHASER.

SERVICE TANK.
The fuel tank feeding directly into the carburetors.

SET BACK WINGS.
A type of wing in which the leading edge is inclined backward as
in the Mann biplane. The trailing edge is straight.

SHOCK ABSORBERS.
An elastic device on the chassis or landing gear that absorbs
vibration by allowing a limited axle movement.

SIDE SLIP.*
Sliding down sideways, and toward the center of a turn. This is
due to an excessive angle of bank.

_SIEGE_ (Fr.)
Seat.

SIMILITUDE, LAWS OF.
The drag or resistance of a small aerodynamic body does not
increase in direct proportion with the area and speed. The laws
governing the relation between a model and a full size machine
are known as the laws of "Similitude."

SKIDS.* (Fr. _Patin, Pattinage_.)
Long wood or metal runners attached to the chassis to prevent the
"nosing over" of a machine when landing, or to prevent it from
dropping into holes or ditches on rough ground. It also acts when
the wheels collapse.

SKID CURTAINS.
Vertical side curtains or surfaces provided to reduce the
skidding action on turns or to prevent side slip.

SKIDDING.*
Sliding sideways away from the center of the turn. It is due to
insufficient banking on a turn.

SKIN FRICTION.
The resistance caused by the friction of the air along a surface.

SLIP.* Applied to propeller action, the slip is the difference between
the actual advance of an aircraft and the theoretical advance
calculated from the product of the mean pitch and the revolutions
per minute. When the propeller is held stationary, the slip is
said to be 100 percent.

SLIP STREAM.
The wind stream thrown by a propeller.

SOARING FLIGHT.*
The sustentation of a wing surface due to wind currents and
without the expenditure of other power. Soaring flight is
performed by gulls, buzzards and vultures, but no practical
machine has yet been built that will fly continuously without the
aid of power.

SPAN. (Fr. _Envergure_.)
The length or longest dimension of a wing, generally taken at
right angles to the wind stream.

SPAR. (Fr. _Bras D’Aile_.)
The main wing beams that transmit the lift to the body.

SPOKES.
(Fr. _Rayon_.)

SPREAD.*
See SPAN.

STABILITY.*
The property of an aircraft that causes it to return to a
condition of equilibrium after meeting with a disturbance in
flight.

STAGGER.*
The advance of the leading edge of the upper wing over that of
the lower wing.

STABILIZER.* (Fr. _Stabilisateur_.)
A horizontal tail surface (fixed) used for damping out
oscillations and for promoting longitudinal stability.

STALLING.*
The condition of an aeroplane that has lost the speed necessary
for steerage way or control.

STALLING ANGLE.
See CRITICAL ANGLE.

STEERING WHEEL.
(Fr. _Volant_.)

STATOSCOPE.*
An instrument for detecting a small rate of ascent or descent.
Used principally with balloons.

STAY WIRE. (Fr. _Tendeur_.)
A wire or cable used as a tie to hold members together, or to
give stiffness to a structure.

STEP.* A break in the form of a float or flying boat bottom.

STREAMLINE.
A form of body that sets up no turbulence or eddies in passing
through air or liquid.

STRUT.* (Fr. _Mar, Montant_.)
A compression member used in separating the upper and lower wings
of a biplane, or the longerons of the fuselage.

SWEEP BACK.
See RETREAT.

T

TACHOMETER. (Fr. _Compte Tours_.)
An instrument for directly indicating the revolutions per minute.

TAIL.* (Fr. _Queue_.)
The rear part of an aircraft to which usually are attached the
rudder, stabilizer, and elevator.

TAIL SKID. (Fr. _Bequille_.)
A flexibly attached rod which holds the tail surfaces off the
ground, and breaks the landing shocks on the tail structure.

TAIL BOOM.
See BOOM.

TAIL DIVE.
A very dangerous backward dive.

TAIL SPIN.
A condition in which the tail revolves about a vertical line
passing through the center of gravity.

TANDEM PLANES.
A form of aeroplane in which the wings are placed one after
another.

TAUBE. An old type of German or Austrian aeroplane with back swept wing
tips.

TAXI. To run along the ground.

THIMBLE. (Fr. _Cosse_.)
An oval grooved metal fitting used for the protection of a cable
loop at the point of attachment.

THREE-PLY. (Fr. _Contreplaque_.)
A wood sheet composed of three layers of wood glued together, the
line of grain crossing at each joint.

THRUST.
The propulsive force exerted by a propeller.

THRUST DEDUCTION.*
The reduction of thrust due to a reduction of pressure under the
stern of the aircraft.

_TIRANT_ (Fr.)
Bracing tubes.

TORQUE.
The turning force or moment exerted by the motor.

_TOILE_ (Fr.)
Linen.

TORQUE WARP.
The amount of warp, or permanent set in the ailerons necessary to
overcome the torque or twisting effect of the motor. In some
machines the torque is overcome by changing the angle of
incidence at the wing tips.

TRACTOR BIPLANE.
A type of aeroplane in which the propeller is placed in front of
the wings so that it pulls the machine along.

TRAILING EDGE.
The edge of a wing at which the air stream leaves the surface.

_TRAIN D’ATTERRISSAGE_ (Fr.)
Landing gear.

_TRANSFIL_ (Fr.)
Cord winding on the struts.

TRIPLANE. (Fr. _Triplan_.)
An aeroplane with three superposed wings.

TURBULENCE.
The eddies or discontinuity caused by a body or surface passing
through the air.

U

USEFUL WEIGHT. The difference between the total lift and the dead load. This comprises the pilot and passenger, the weight of the fuel, baggage and instruments.

UNIT LOADING. The weight per square foot of main wing surface.

V

_VOL PLANE_ (Fr.)
See GLIDE.

_VOL PIQUE_ (Fr.)
See DIVE.

_VOLANT_ (Fr.)
Steering wheel.

_VERNIS_ (Fr.)
Varnish.

_VRIL_ (Fr.)
Spinning nose dive.

_VOLETS de PROFONDEUR_ (Fr.)
Elevator flaps.

W

WARP CONTROL.*
Lateral control obtained by twisting the wing tips.

WASHOUT.
Decreased camber or incidence toward the wing tips.

WEATHER-COCK STABILITY.
Stability in the line of travel, or with the relative wind, so
that the machine always tends to head into the wind.

WHALE TYPE.
A speed type biplane in which the body entirely fills the gap
between the upper and lower wings.

WHIRLING TABLE.
A testing device in which a model wing or body is placed at the
end of a revolving arm.

WINGS.* (Fr. _Aile_.)
The main supporting surfaces of an aeroplane.

WORKING FACE.
The face of a propeller blade lying next to the slip stream.

WAKE GAIN.*
Due to skin friction and eddies, a moving aircraft drags a
certain amount of the surrounding air with it. This reduces the
effective resistance of the hull and increases the effective
pitch of a pusher propeller since the latter acts on a forward
moving mass of air. This is "Wake gain."