Tab. A small airfoil hinged to a control surface and used to move the larger surface or to trim or balance the plane. May be a balancing tab, servo tab, or trim tab. Taxi. To move an airplane over ground or water under its own power.

Thermal barrier, or heat barrier. Zone of speed at which friction heat generated by passage of an object through air endangers its operation.

Three·point landing. A landing in which the tail skid or tail or nose wheel of an airplane and its two main wheels touch ground at the same instant.

Torque. A force which produces twisting, such as rolling of an airplane in reaction to the rotating propeller or turning of a helicopter fuselage because of the revolving rotor.

Transonic. The transitional speed between subsonic and supersonic.

Turbofan. A jet engine of the bypass, or ducted-fan, type in which part of the air taken in at the front by a compressor or fan bypasses the combustion chamber to give extra, thrust; one type has a fan at the rear.

Turbojet. A jet engine with a turbine- driven compressor that takes in and compresses air for combustion of fuel, producing hot exhaust gases that rotate the turbine and create a jet steam for thrust.

Turboprop, or prop let. A jet engine whose exhaust gases drive a turbine- connected propeller and also produce thrust.

V

Visual night rules (VFR). Rules for minimum altitudes and limits of visibility to govern contact flight by visual reference to the ground.

W

Worm-up. Running an engine to heat it to operating temperature.

Wind sock. A cloth cone pivoted on a pole to show wind direction.

Wind tee. A pivoted T-shaped device that indicates wind direction.

Wing loading. Cross weight of loaded airplane divided by the wing area.

Y

Yaw. Movement about vertical axis.

Z

Zoom. A brief, steep climb.