Equilibrator. A plane or other contrivance which makes for stability. F Flexed. A plane is said to be flexed when it curves upward forming an arc of a circle. Fin. A fixed vertical plane. Flying Machine. Literally a form of lighter than air craft; a gas-born airship. Following Edge. The rear edge of the plane or wing of an aeroplane. Fusilage. The body or framework of an aeroplane. G Glider. An aeroplane without motor power. Guy. A brace, usually a wire or cord used for tuning up the aeroplane. Gross Weight. The weight of the aircraft comprising fuel, lubricating oils, and the pilot. Gyroscope. A rotating mechanism for maintaining equilibrium. H Hanger. A shed for housing an aeroplane. Harbor. A shelter for aircrafts. Heavier Than Air. A machine weighing more than the air it displaces. Helicopter. A flying machine driven upward by rotary screws on vertical shafts. Helmsman. One in charge of the steering device. L Lateral Stability. Stability which prevents side motion. Loading. The gross weight divided by the supporting area measured in square feet. Longitudinal Stability. Stability which prevents fore and after motion or pitching. M Mast. A perpendicular stick holding the stays or struts which keep the planes rigid. Model Aeroplane. A toy aeroplane, reproducing a man-carrying machine. Monoplane. An aeroplane or heavier than air machine supported by a single main plane which may be formed of two wings extending from a central body. Motor. A contrivance for generating driving power. Multiplane. An aeroplane with more than three main planes one above another. N Nacelle. The car of a dirigible balloon, literally a cradle. Net Weight. Complete weight of the machine without pilot, fuel or oil. O Ornithopter. A machine supported and propelled by planes moving in imitation of birds; a flapping wing machine. Orthogonal. A flight maintained by flapping wings. P Plane. A surface or wing, either plain or flexed, employed to support or control an aeroplane. Pilot. One directing an aeroplane in flight. Pitch. Theoretical distance covered by a propeller in making one revolution. Pylon. Correctly, a structure housing a falling weight used for starting an aeroplane, commonly a turning point in aeroplane flights. Propeller. The screw used for driving an aeroplane, plane. R Rudder. A plane or group of planes used to steer an aeroplane. Runner. Strip beneath an aeroplane used for a skid. S Scale Model. A miniature aeroplane exactly reproducing the proportions of an original. Spar. A mast, strut, or brace. Stability. The power to maintain an even keel in flight.