true wind direction. The direction, with respect to true north, from which the wind is blowing.
truncated cone. A cone with its point cut off in such a way that its top is parallel with its base.
TR unit. A transformer-rectifier unit. A TR unit reduces the voltage of alternating current and changes it into direct current.
trunnion. Projections from the cylinder of a retractable landing gear strut about which the strut pivots to 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 called compression struts. Tension loads are carried by stays, or wires, that go from one main beam to the other and cross between the compression struts.
T-seal. A form of two-way seal used in fluid power components. The cross section of the main seal element is in the shape of the letter T with the edge of the stem providing the sealing surface. The stem is backed up on both sides with Teflon backup rings.
TSFC (thrust specific fuel consumption). A measure of the fuel efficiency of a turbojet or turbofan engine. TSFC is the number of pounds of fuel burned per hour for each pound of thrust produced.
TSO (Technical Standard Order). An approval issued by the FAA for the manufacture of a component for installation on a certificated aircraft.
tubing cutter (mechanic’s hand tool). A small hand tool used to make a square cut across the end of a piece of soft metal or plastic tubing. The cutter consists of a set of rollers and a sharp-edged wheel that can be screwed down so it rolls over the surface of the tubing. The tubing is placed on the rollers, and the wheel is screwed down against the surface. The cutter is rotated around the tubing and the wheel is moved in so it cuts deeper into the tubing. This action is continued until the tubing is cut completely through.
tumble limit (gyroscopic flight instrument limitation). The number of degrees of pitch or roll an aircraft is allowed before a gyroscope in a gyroscopic flight instrument contacts the stops in its gimbal system and tumbles.
tuned circuit (electronic circuit). A resonant electronic circuit containing both inductance and capacitance.
Either the inductance or the capacitance can be adjusted to change the frequency to which the circuit is resonant.
tungsten. A hard, grayish-white, brittle, corrosion-resistant, metallic chemical element. Tungsten’s symbol is W, its atomic number is 74, and its atomic weight is 183.85. Tungsten, which melts at 3,400°C, is used for incandescent lamp filaments and as an alloying element to give steel toughness and strength at high temperature.
tunnel diode (electronic component). A semiconductor diode doped with a larger amount of impurity than is used in an ordinary diode. A tunnel diode has a negative resistance region. Forward current increases with an increase in forward voltage until peak current is reached. At this point, forward current decreases with an increase in forward voltage until a valley is reached. This region of decreasing forward current, with an increase in forward voltage, is called the negative resistance region. Tunnel diodes are used as high-speed switching diodes.
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