L
Lateral—From side to side; that is, crossing the length fore-and-aft, and generally at right angles to it.
Land-speed—The speed of aircraft as related to objects on the ground. See [Air-speed].
Landing Area—A piece of land specially prepared for the alighting of aeroplanes without risk of injury.
Leeway—Movement of a machine aside from the intended course, due to the lateral drift of the whole body of air; measured usually at right angles to the course.
Lift—The raising, or sustaining effect of an aeroplane surface. It is expressed in the weight thus overcome.
Lighter-than-air—A term used to designate aircraft which, owing to the buoyancy of the gas attached, weigh less than the volume of air which they displace.
Longitudinal—In a lengthwise, or fore-and-aft direction.
M
Main Plane—The principal supporting surface of an aeroplane. In the biplane, or the multiplane type, it denotes the lowest surface, unless some other is decidedly larger.
Main Landing Wheels—Those wheels on the alighting gear which take the shock in landing.
Mast—A vertical post or strut giving angular altitude to guys or long stays. Also used (erroneously) to designate a spar reaching out laterally or longitudinally in a horizontal position.
Monoplane—An aeroplane with one main supporting surface. A Double Monoplane has two of such surfaces set one behind the other (tandem) but on the same level.
Multiplane—An aeroplane having several main planes, at least more than three (for which there is the special name of triplane).
N
Nacelle—The framework, or body, of a dirigible balloon or airship.
Negative Angle of Incidence—An angle of incidence below the line of travel, and therefore expressed with a minus sign. Surfaces bent to certain curves fly successfully at negative angles of incidence, and exhibit a comparatively large lift.
O
Ornithopter—A type of flying machine with wing surfaces which are designed to raise and sustain the machine in the air by flapping.
P
Panel—Another name for [Curtain]—which see.
Parabola—The form outlined when a cone is cut by a plane parallel to a line drawn on its surface from its apex to its base. Declared to be the correct scientific curve for aeroplane surfaces, but not so proven, as yet.
Pilot—A term widely used for an operator, or driver, of any form of aircraft.
Pitch—The distance which a propeller would progress during one revolution, if free to move in a medium which permitted no [slip] (which see); just as the thread of a bolt travels in the groove of its nut.
Plane—Speaking with exactness, a flat spread of surface; but in aeronautics it includes also the curved sustaining surfaces of aeroplanes.
Polyplane—Another term for Multiplane.
Port—The left-hand side of an aircraft, as one faces forward. See [Starboard].
Projected Area—The total area of an irregular structure as projected upon a flat surface; like the total area of the shadow of an object cast by the sun upon a plane fixed at right angles to its rays.
Propeller Reaction—A force produced by a single revolving propeller, which tends to revolve the machine which it is driving, in the contrary direction. This is neutralized in various ways in the machines driven by single propellers. Where two propellers are used it is escaped by arranging them to move in opposite directions.