TRUSS: The framing by which the wing loads are transmitted to the body; comprises struts, stays, and spars. UNDERCARRIAGE: See Landing gear. VENTURI TUBE: A short tube, flaring at the front end, and constricted approximately midway of its length, so that, when fluid flows through it, there will be a suction produced in a side-tube opening into the constricted throat. This tube, when combined with a Pitot tube or with one giving static pressure, forms a pressure nozzle, which may be used as an instrument to determine the speed of an aircraft through the air. WARP: To change the form of the wing by twisting it. WASH IN: See Droop. WASHOUT: A permanent warp of an aerofoil such that the angle of attack decreases toward the wing tips. WEIGHT, GROSS: See Load, full. WING: The aggregate sustaining structure on the right or left side of an airplane, comprising both planes and trussing. (Thus, “detachable wings” and “folding wings.”) WING FLAP: See Aileron. WING LOADING: The weight carried per unit area of supporting surface. WING MAST: The mast structure projecting above the wing, to which the top load wires are attached. WING RIB: A fore-and-aft member of the wing structure used to support the covering and to give the wing section its form. WING SPAR OR WING BEAM: A transverse member of the wing structure. YAW: _Yawing_.—Angular motion about the normal axis. _Angle of_.—The angle between the direction of the relative wind and the plane of symmetry of an aircraft. ZERO LIFT LINE: The limiting position in an aerofoil section of the line of action of the resultant air force when the position of the section is such that the lift is zero. Transcriber’s Notes Page 59—Changed Farmborough to Farnborough Page 148—changed Chatterick to Catterick Page 165—changed condension to condensation Page 248—Space left for unknown word [not below the rank of ] Page 251—changed Clefden to Clifden Page 298—changed Porta Delgada to Ponta Delgada Page 298—changed reconnoissance to reconnaissance Page 354—Captain E. Libby no number of planes brought down recorded Page 365—changed axes to axis