trickle charge (batteries). A continuous, low-current charge used to keep storage batteries fully charged at all times. A trickle charge puts just enough current into the battery to restore the electrical energy lost through the internal resistance of the battery.
trickle charger (battery charger). A small transformer-rectifier connected across a storage battery to charge it at a slow rate. Trickle chargers are limited to a small amount of current by an internal circuit breaker that opens the primary circuit if the battery requires too much current.
tricycle landing gear (aircraft landing gear). A type of aircraft landing gear that uses two main wheels located behind the center of gravity and a nose wheel well ahead of the center of gravity. The ease of ground handling of aircraft with tricycle landing gear has made this the most widely used landing gear configuration.

trigger pulse. A pulse of electrical energy used to initiate an operation in certain types of electronic equipment.
trigonometry (mathematics). The branch of mathematics that deals with the relationships between the angles and the lengths of the sides of a triangle.
trijet (airplane type). A jet-propelled aircraft that has three engines. The Boeing 727, the McDonnell-Douglas MD-11, and Lockheed L-1011 are all trijet airplanes.
trimetrogon. A method of aerial mapping in which three photographs are taken at the same time of the area being mapped. One photograph is taken vertically downward and the other two are oblique photographs, taken at two different angles. The three photographs are studied with special instruments that show the contours of the terrain. Maps are made from these photographs.
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.
trimming (gas turbine engine operation). The procedure of adjusting the fuel control of a gas turbine engine so the engine produces the correct maximum RPM and idling RPM, and functions properly under acceleration and deceleration. Trimming is done to adjust the engine performance to agree with the performance specifications published by the engine manufacturer.
trim tab (aircraft controls). A small movable control mounted on a primary control surface. The trim tab is adjustable in flight to change the aerodynamic load on the control surface. The aerodynamic load produced by the trim tab deflects the control surface enough for it to trim the aircraft for hands-off flight at any normal speed.
trinomial (mathematical term). An algebraic expression that has three terms. A2 + 2AB + B2 is a trinomial.