Angle, Rigger's Longitudinal Dihedral—Ditto, but substituting “chords” for “neutral life lines.”
Angle, Pitch—The angle at any given point of a propeller, at which the blade is inclined to the direction of motion when the propeller is revolving but the aeroplane stationary.
Altimeter—An instrument used for measuring height.
Air-Speed Indicator—An instrument used for measuring air pressures or velocities. It consequently indicates whether the surface is securing the requisite reaction for flight. Usually calibrated in miles per hour, in which case it indicates the correct number of miles per hour at only one altitude. This is owing to the density of the air decreasing with increase of altitude and necessitating a greater speed through space to secure the same air pressure as would be secured by less speed at a lower altitude. It would be more correct to calibrate it in units of air pressure.
Air Pocket—A local movement or condition of the air causing an aeroplane to drop or lose its correct attitude.
Aspect-Ratio—The proportion of span to chord of a surface.
Air-Screw (Propeller)—A surface so shaped that its rotation about an axis produces a force (thrust) in the direction of its axis.
Aileron—A controlling surface, usually situated at the wing-tip, the operation of which turns an aeroplane about its longitudinal axis; causes an aeroplane to tilt sideways.
Aviation—The art of driving an aeroplane.
Aviator—The driver of an aeroplane.