A strut for sidewise bracing in the framework of an aeroplane.

Lateral Stability

Lateral equilibrium in the side-to-side direction.

Lattice Girder

A girder with many crossed members, resembling in appearance a lattice window.


Lateral drift in the direction in which the air current is flowing due to the air current.


The ascensional force of an aeroplane surface.

Longitudinal Stability

Lengthwise stability.


An apparatus for generating electric current to produce a spark wherewith to ignite the explosive mixture in the cylinder of an internal-combustion motor.

Main Plane

The largest supporting wing in a multiplane.


A spar or strut for fastening trussing wires or stays to stiffen the planes.


An aeroplane with one or more supporting surfaces, all in the same plane.


A rail used as a track in starting some machines.


An aeroplane with more than one main supporting surface.


See Fuselage. In some monoplanes the enclosed, boat-like part of the body, containing the seat for the pilot and his passenger.

Negative Angle Of Incidence

The angle formed by a plane inclined downwardly to the direction of travel.

Ornithopter, Ornithoptere, Orthopter, Or Orthop-Tere

A machine which attains flight by bird-like flapping of wings.

Orthogonal Action

The vertical reaction of the air in affording equilibrium by means of wing motion.


The vertical planes in a box-like or cellular structure.

Pendular Movement

To-and-fro movement like that of a pendulum.


Lanchester's designation for the undulating course naturally adopted by plane surfaces when moving in the air.


The forward movement that would be produced by one turn of a propeller in a solid.


Literally a flat surface; in aeroplanes a flat or curved surface.

Poly Plane

See Multiplane.


The tower required by some types of aeroplanes to start. Also, the pillars that mark a definite course to be taken by a flying-machine at a flying-machine meeting.


A coil of piping or any circuitous conduit in which water is cooled by radiation after having circulated around the hot cylinder of an internal combustion engine.

Rarefaction Side

The side opposite the compression side, as, for example, the top of an aeroplane in motion.

Reactive Stratum

The compressed or rarefied layer of free air flowing along an aeroplane surface.

Rear Control

A stabilising tail surface which may also be a rear horizontal rudder.

Rising Angle

The maximum angle of ascension.


A horizontal or vertical plane used for steering.


See Skids.


A propeller.


A monoplane.


Aeroplane surfaces covered only on one side. Compare with Double-Surfaced.


Runners underneath some types of machines, used for landing.

Skin Friction

The friction of the air against surfaces.


The difference between the pitch of a propeller and its actual forward travel.

Soaring Flight

Flight with rigid wings.


A strut, a brace, etc.


Maintenance of balance in flight by automatic devices such as a shifting weight or a gyroscope (q. v.) ; or hand-operated devices such as ailerons, wing-tips, and plane-warping devices.


To maintain equilibrium by means of surfaces and not by mechanism.


The tail of a flying-machine.

Stabilising Plane

A surface for the maintenance of equilibrium; small horizontal planes hinged to the main planes, and suiting the angle of the wind.

Starting Frame

See Chassis.

Starting Rail

See Monorail.


A brace or wire in an aeroplane framework.

Steadying Vane

Small vertical planes, usually placed in the front control of the old Wright machine.

Straight Pitch

In propellers, a flat instead of a helical blade surface.


A turnbuckle.


A compression member in a structure. In biplanes the posts separating the main planes.

Supplementary Surface Or Auxiliary Surface

A small surface such as an aileron or wing-tip, which acts in unison with a larger one for a specific purpose.

Supporting Surfaces

The main planes.


A collective term for the framework and planes in the rear of the main plane.

Tail Planes

The rear planes supported by the tail framework.

Tail Wheel

A small wheel under the tail of some machines to support the tail on the ground.


A tension member in a framework; used also for wire stays.

Tractor Screw

A propeller set in front of the supporting surface instead of in the rear, so that the machine is drawn through the air and not pushed.


An aeroplane with three superposed supporting surfaces.


A combined right and left-hand screw for taking up the slack in a loose wire stay.


Moving against the wind.

Variable Pitch

In propellers, a varying angle of blade width in contradistinction to uniform pitch.


See Glide.


The wash of an aeroplane in flight.


The act of twisting a plane for the maintenance of equilibrium.


See Wake.

Wing Arc

The arc described by a moving wing.


A longitudinal strip so placed as to strengthen an aeroplane surface.

Wing Section

The longitudinal curvature with relation to the arc of travel.


A runner under a wing-tip.


The hinged outer side of a plane.


A wheel under a wing-tip to support the wing when the machine strikes on the ground.