Balance—Equilibrium maintained by the controlling mechanism, or by the automatic action of balancing-surfaces—as distinguished from the equilibrium preserved by stabilizing surfaces.
Balancing Plane—The surface which is employed either intentionally, or automatically, to restore a disturbed balance.
Biplane—The type of aeroplane which has two main supporting surfaces or planes, placed one above the other.
Body—The central structure of an aeroplane, containing the machinery and the passenger space—as distinguished from the wings, or planes, and the tail.
Brace—A construction member of the framing of aircraft which resists a compression strain in a diagonal direction—as distinguished from a “stay,” or “diagonal,” which supports a pulling strain; also from a strut which supports a compression strain in a vertical direction.
C
Camber—The distance from the chord of the curve of a surface to the highest point of that curve, measured at right angles to the chord.
Caster, or Castor, Wheel—A wheel mounted on an upright pivoted shaft placed forward of its axle, so that it swivels automatically to assume the line of travel of an aeroplane when landing: used in the alighting gear. To be distinguished from a fixed wheel, which does not swivel.
Cell—A structure with enclosing sides—similar to a box without top or bottom stood upon one side. The vertical walls of the cell give lateral stability, and its horizontal walls fore-and-aft stability.
The first Santos-Dumont biplane, constructed of cells.
Centre of Gravity—That point of a body where its weight centres. If this point is supported, the body rests in exact balance.
Centre of Lift—The one point at which the lifting forces of the flying planes might be concentrated, and produce the same effect.
Centre of Resistance—The one point at which the forces opposing the flight of an air-craft might be concentrated, and produce the same result.
Centre of Thrust—The one point at which the forces generated by the revolving propellers might be concentrated, and produce the same effect.
Chassis—The under-structure or “running-gear” of an aeroplane.
Chord—The straight line between the two ends of an arc of a circle or other curved line.
Compound Control—A mechanical system by which several distinct controls are operated through different manipulations of the same lever or steering-wheel.
Compression Side—That side of a plane or propeller blade against which the air is compressed—the under surface of a flying plane, and the rear surface of a revolving propeller.
Curtain—The vertical surface of a cell—the wall which stands upright.
D
Deck—A main aeroplane surface. The term is used generally in describing biplanes; as the upper deck, and the lower deck; or with aeroplanes of many decks.
Demountable—A type of construction which permits a machine to be easily taken apart for transportation.
Derrick—A tower-shaped structure in which a weight is raised and allowed to fall to give starting impetus to an aeroplane.
Dihedral—That form of construction in which the wings of an aeroplane start with an upward incline at their junction with the body of the machine, instead of stretching out on a level.
Dirigible—The condition of being directable, or steerable: applied generally to the balloons fitted with propelling power, or airships.
Double Rudder—A rudder composed of two intersecting planes, one vertical and the other horizontal, thus enabling the operator to steer in any direction with the one rudder.
Double-Surfaced—Planes which are covered with fabric on both their upper and lower surfaces, thus completely inclosing their frames.
Down-Wind—Along with the wind; in the direction in which the wind is blowing.
Drift—The recoil of an aeroplane surface forced through the air: also the tendency to float in the same direction as the wind.