An actuator is a type of transducer, a device that is capable of converting one form of energy into another. The energy may come from an electric current, hydraulic or pneumatic pressure.
A motor is an example of an actuator that transforms energy from electricity or fuel into the energy of circular motion. A linear actuator, on the other hand, converts the energy of rotary motion into linear motion. Piezoelectric actuators are an example of one type of linear actuator. These devices may be very small, as micro and mini actuators, or very large, as in the case of heavy-duty actuators.
Airplane automation is used for airplane flaps. The flaps are mounted by hinges onto the trailing edge of the wings of a fixed-wing aircraft. Their function is threefold:
1. Reduce stall speed.
2. Increase the angle of descent.
3. Reduce the pitch angle of the aircraft. During landing, this improves the pilot's view of the runway over the nose of the aircraft.
In order for landing gear to function properly, a number of different linear actuators must function. First, the door that holds the landing gear must open, which is done by linear actuators. Then the landing gear itself must be lowered with actuators when the plane is in position.
Immediately after touchdown, reverse thrust is used to provide the necessary deceleration of the aircraft. Here, the force provided by the airplane's exhaust is directed forward, against the direction of travel. Propeller-driven aircraft may also be able to use linear actuators to produce reverse thrust in flight. This allows rapid deceleration, quick speed changes the buildup of speed encountered in steep dives.