=Section=--Any separate part of the top surface, that part of the bottom surface immediately underneath it, with their struts and wires.
=Spar=--Any long piece of wood or other material.
=Spar, Main=--A spar within a surface and to which all the ribs are attached, such spar being the one situated nearest to the centre of pressure. It transfers more than half the lift from the ribs to the bracing. [29]
=Spar, Rear=--A spar within a surface, and to which all the ribs are attached, such spar being situated at the rear of the centre of pressure and at a greater distance from it than is the main spar. It transfers less than half of the lift from the ribs to the bracing. [30]
=Strut=--Any wooden member intended to take merely the stress of direct compression.
=Strut, Interplane=--A strut holding the top and bottom surfaces apart. [31]
=Strut, Fuselage=--A strut holding the _fuselage longerons_ apart. It should be stated whether top, bottom, or side. If side, then it should be stated whether right or left hand. _Montant_. [32]
=Strut, Extension=--A strut supporting an "extension" when not in flight. It may also prevent the extension from collapsing upwards during flight. [33]
=Strut, Dope=--A strut within a surface, so placed as to prevent the tension of the doped fabric from distorting the framework. [34]
=Serving=--To bind round with wire, cord, or similar material. Usually used in connection with wood joints and wire cable splices.
=Slip, Propeller=--The pitch less the distance the propeller advances during one revolution.
=Stream-Line=--A form or shape of detrimental surface designed to produce minimum drift.
=Torque, Propeller=--The tendency of a propeller to turn an aeroplane about its longitudinal axis in a direction opposite to that in which the propeller revolves.
=Tail-Slide=--A fall whereby the tail of an aeroplane leads.
=Tractor=--An aeroplane of which the propeller is mounted in front of the main lifting surface.
=Triplane=--An aeroplane of which the main lifting surface consists of three surfaces or pairs of wings mounted one above the other.
=Tail-Plane=--A horizontal stabilizing surface mounted at some distance behind the main lifting surface. _Empennage_. [36]
=Turnbuckle=--A form of wire-tightener, consisting of a barrel into each end of which is screwed an eyebolt. Wires are attached to the eyebolts and the required degree of tension is secured by means of rotating the barrel.