The Aeroplane Speaks. Fifth Edition

=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. [2] =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. [3] =Aviation=--The art of driving an aeroplane. =Aviator=--The driver of an aeroplane. =Barograph=--A recording barometer, the charts of which can be calibrated for showing air density or height. =Barometer=--An instrument used for indicating the density of air. =Bank, to=--To turn an aeroplane about its longitudinal axis (to tilt sideways) when turning to left or right. =Biplane=--An aeroplane of which the main lifting surface consists of a surface or pair of wings mounted above another surface or pair of wings. =Bay=--The space enclosed by two struts and whatever they are fixed to. =Boom=--A term usually applied to the long spars joining the tail of a "pusher" aeroplane to its main lifting surface. [4] =Bracing=--A system of struts and tie wires to transfer a force from one point to another. =Canard=--Literally "duck." The name which was given to a type of aeroplane of which the longitudinal stabilizing surface (empennage) was mounted in front of the main lifting surface. Sometimes termed "tail-first" aeroplanes, but such term is erroneous, as in such a design the main lifting surface acts as, and is, the empennage.