_Starting Area_--An area of ground specially prepared to facilitate the starting of aeroplanes into flight. _Starting Device_--Any contrivance for giving an aeroplane a powerful impulse or thrust into the air. See Derrick. _Starting Impulse_--The thrust with which an aeroplane is started into the air for a flight. Most machines depend upon the thrust of their own propellers, the machine being held back by force until the engines have worked up to flying speed, when it is suddenly released. _Starting Rail_--The rail upon which the starting truck runs before the aeroplane rises into the air. _Starting Truck_--A small vehicle upon which the aeroplane rests while it is gaining sufficient impulse to take flight. _Stay_--A construction member of an aeroplane sustaining a pulling strain. It is usually of wire. _Straight Pitch_--That type of pitch (which see) in a propeller blade in which every cross-section of the blade makes the same angle with its axis of revolution. _Strainer_--Another term for Turnbuckle--which see. _Strut_--An upright, or vertical, construction member of an aeroplane sustaining a compression strain; as distinguished from a brace which sustains a diagonal compression strain. _Supplementary Surface_--A comparatively small surface used as an adjunct to the large surfaces for some special purpose; as, for instance, the preserving of balance, or for steering. _Sustaining Surface_--The large surfaces of the aeroplane whose rapid movement through the air at a slight angle to the horizontal sustains the weight of the machine. T _Tail_--A rear surface on an aeroplane designed to assist in maintaining longitudinal stability. It is in use principally on monoplanes, and is often so arranged as to serve as a rudder. _Tail Wheel_--A wheel mounted under the rear end of an aeroplane as a part of the alighting gear. _Tangent_--A straight line passing the convex side of a curved line, and touching it at one point only. The straight line is said to be tangent to the curve at the point of contact. _Tangential_--In the position or direction of a tangent. _Tangent Spoke_--A wire spoke extending from the outer edge of the hub of a wheel along the line of a tangent until it touches the rim. Its position is at right angles to the course of a radial spoke (which see) from the same point on the hub. _Tie_--A construction member connecting two points with a pulling strain. _Tightener_--A device for taking up the slack of a stay, or tie; as the turnbuckle. _Tractor Propeller_--A propeller placed in front, so that it pulls the machine through the air, instead of pushing, or thrusting, it from behind. _Triplane_--An aeroplane with three main surfaces, or decks, placed in a tier, one above another.