Appendix: The hose at the bottom of a balloon used for inflation. In the case of a spherical balloon it also serves for equalization of pressure.
Aspect ratio: The ratio of span to chord of an aerofoil.
Attitude: The attitude of an aircraft is determined by the inclination of its axes to the “frame of reference”; e. g., the earth, or the relative wind.
Aviator: The operator or pilot of heavier-than-air craft. This term is applied regardless of the sex of the operator.
Axes of an aircraft: Three fixed lines of reference; usually centroidal and mutually rectangular.
The principal longitudinal axis in the plane of symmetry, usually parallel to the axis of the propeller, is called the longitudinal axis; the axis perpendicular to this in the plane of symmetry is called the normal axis; and the third axis, perpendicular to the other two, is called the lateral axis. In mathematical discussions the first of these axes, drawn from front to rear, is called the X axis; the second, drawn upward, the Z axis; and the third, running from right to left, the Y axis.
Balancing flaps: See Aileron.
Ballonet: A small balloon within the interior of a balloon or airship for the purpose of controlling the ascent or descent and for maintaining pressure on the outer envelope so as to prevent deformation. The ballonet is kept inflated with air at the required pressure, under the control of valves by a blower or by the action of the wind caught in an air-scoop.
Balloon: A form of aircraft comprising a gas bag, rigging and a basket. The support in the air results from the buoyancy of the air displaced by the gas bag, the form of which is maintained by the pressure of a contained gas lighter than air.
Barrage.—A small spherical captive balloon, raised as a protection against attacks by airplanes.