TR unit. A transformer-rectifier unit. A TR unit reduces the voltage of AC and changes it into DC. 

Tractor powerplant.  An airplane powerplant in which the propeller is mounted in the front, and its thrust pulls the airplane rather than pushes it. 

Trammel (verb). To square up the Pratt truss used in an airplane wing. Trammel points are set on the trammel bar so they measure the distance between the center of the front spar, at the inboard compression strut, and at the center of the rear spar at the next compression strut outboard. The drag and antidrug wires are adjusted until the distance between the center of the rear spar at the inboard compression strut and the center of the front spar at the next outboard compression strut is exactly the same as that between the first points measured. 

Trammel bar. A wood or metal bar on which trammel points are mounted to compare distances. 

Trammel points.  A set of sharp-pointed pins that protrude from the sides of a trammel bar. 

Transducer. A device that changes energy from one form to another. Commonly used transducers change mechanical movement or pressures into electrical signals. 

Transformer rectifier.  A component in a large aircraft electrical system used to reduce the AC voltage and change it into DC for charging the battery and for operating DC equipment in the aircraft. 

Translational lift. The additional lift produced by a helicopter rotor as the helicopter changes from hovering to forward flight. 

Transonic flight.  Flight at an airspeed in which some air flowing over the aircraft is moving at a speed below the speed of sound, and other air is moving at a speed greater than the speed of sound. 

Transverse pitch.  See gauge. 

Triangle. A three-sided, closed plane figure. The sum of the three angles in a triangle is always equal to 180°. 

Tricresyl phosphate (TCP).  A chemical compound, (CH$_{3}$C$_{6}$H$_{4}$O)$^{3}$PO, used in aviation gasoline to assist in scavenging the lead deposits left from the tetraethyl lead. 

Trim tab.  A small control tab mounted on the trailing edge of a movable control surface. The tab may be adjusted to provide an aerodynamic force to hold the surface on which it is mounted deflected in order to trim the airplane for hands- off flight at a specified airspeed. 

Trimmed flight. A flight condition in which the aerodynamic forces acting on the control surfaces are balanced and the aircraft is able to fly straight and level with no control input. 

Trip-free circuit breaker.  A circuit breaker that opens a circuit any time an excessive amount of current flows, regardless of the position of the circuit breaker’s operating handle. 

Troubleshooting. A procedure used in aircraft maintenance in which the operation of a malfunctioning system is analyzed to find the reason for the malfunction and to find a method for returning the system to its condition of normal operation. 

True airspeed (TAS).  Airspeed shown on the airspeed indicator (indicated airspeed) corrected for position error and nonstandard air temperature and pressure. 

Trunnion.  Projections from the cylinder of a retractable landing gear strut about which the strut pivots retract. 

Truss-type structure.  A type of structure made up of longitudinal beams and cross braces. Compression loads between the main beams are carried by rigid cross braces. Tension loads are carried by stays, or wires, that go from one main beam to the other and cross between the cross braces. 

Turbine.  A rotary device actuated by impulse or reaction of a fluid flowing through vanes or blades that are arranges around a central shaft. 

Turn and slip indicator. A rate gyroscopic flight instrument that gives the pilot an indication of the rate of rotation of the aircraft about its vertical axis. A ball in a curved glass tube shows the pilot the relationship between the centrifugal force and the force of gravity. This indicates whether or not the angle of bank is proper for the rate of turn. The turn and slip indicator shows the trim condition of the aircraft and serves as an emergency source of bank information in case the attitude gyro fails. Turn and slip indicators were formerly called needle and ball and turn and bank indicators. 

Turnbuckle.  A component in an aircraft control system used to adjust cable tension. A turnbuckle consists of a brass tubular barrel with right-hand threads in one end and left-hand in the other end. Control cable terminals screw into the two ends of the barrel, and turning the barrel pulls the terminals together, shortening the cable. 

