Electro-Mechanical Services Glossary

This page is designed to help you learn and understand the different functions that individual parts have on aircraft.

Actuators

 An Actuator is a mechanical device for moving or controlling a mechanism or system. It is a transducer that accepts a signal and converts it to a physical action. In other words, and actuator causes an action to occur relating to the data that was sent to it by via NCAP. Data written to an actuator is held in an input register until the trigger is received. Actuators also convert various forms of energy into rotating or linear mechanical energy. 

Linear Actuators

 Linear Actuators generally consist of a DC or AC motor connected to a screw drive through a set of gears. The screw drive is set inside of a tube which also has screw threads along the inside of the tube. When the motor turns, the screw turns inside the tube and (since the screw is firmly attached to the housing the screw cannot move) the tube is moved in or out (depending on the direction of the motor's rotation). To reverse the direction of the actuator, you simply reverse the polarity of the electrical connection on the actuator. Example of Linear Actuator P/N 6026C0001-01, Cargo Door Latch Actuator Assembly, consists of a housing assembly, control housing assembly, and a 28-vdc motor. The control housing assembly contains limit switches and a switch actuator controlling the direction and length of extension or retraction of an acme screw actuator.

Rotational Actuators

 A device that converts electric energy into controlled rotary force; usually consist of an electric motor, gear box and limit switches. Rotary actuators are compact, simple and efficient actuators that rotate an output shaft through a fixed arc to produce oscillating power. They require limited space and simple mountings and can produce high instant torque in either direction. Example of Rotary Actuator R6180 Series is an electromechanical device of the R887, R887M1 and R887M2 APU Inlet and Exhaust door actuation systems which converts electrical energy into mechanical controlled rotary motion. Designated APU Inlet and Exhaust Door Actuator, it operates the two Inlet and Exhaust doors of the APU compartment. 

Outflow Valve

 An outflow valve for a cabin pressure control system of an aircraft cabin includes an aft door that is modified to disrupt or increase speed of cabin air flowing past the aft door and out of the outflow valve. The aft door may be modified by notches formed in its leading edge. In the alternative, the aft door may be modified by through-holes formed behind the leading edge. The outflow valve also includes a forward door. Bolt heads or a baffle may protrude form an inner surface of the forward door to disrupt or slow down cabin air flowing over the inner surface of the forward door and out of the outflow valve. Example of Outflow Valve P/N 711003 consists of an aluminium gate that rotates within a rectangular aluminium frame. Rotary actuators (AC and DC) are mounted on each end of the frame. 

Wheel Speed Transducer

 The wheel speed transducer assembly consists primarily of a rotor and shaft assembly and a coil and bobbin assembly contained within a housing. The housing is comprised of a stator and a bearing in which the rotor shaft rotates. The shell of the housing is permanently formed into a one- piece assembly by brazing. An adapter is provided for mounting the transducer in the aircraft axle. Example PN 40-817  Wheel Speed Transducer (WST) is part of the aircraft Brake Control System (BCS). The (WST) generates signal directly proportional to the aircraft wheel speed of use by the BCS Skid Control Unit (SCU) to prevent wheel skid or lockup. The WST transducer output is also used by the SCU to indirectly operate the aircraft ground spoilers. 

Landing Light

 Example of Landing Light PN 45-0123-1, the landing light is used during aircraft landing and takeoff operations. It provides high-intensity illumination of the flight path. The landing light is extended during operation and retracted during normal flight. The landing light consists of the lamp support ring assembly, gearbox assembly, motor assembly and drive gears. The landing light is factory preset to move to an extended position of 73 degrees. It can be adjusted to extend to any position between 70 and 100 degrees. 

APU Starter

 The Auxiliary Power Unit or APU is a small turbine engine mounted between the main wheel wells. The primary purpose of an aircraft APU is to provide power to start the main engines. The APU is started by an electric motor, with power supplied by a battery or external power source (ground power unit), after the APU accelerates to full speed, it can provide a much larger amount of power to start the aircraft's main engines, either by turning an electrical generator or by providing compressed air to the air turbine of the starter motor. Example of APU Starter motor is PN 519852-4 engine starter motor is a brush-type, direct-current, series-wound motor with four fields poles. It has a stator assembly, an armature assembly with commutator and four brush assemblies. 

Pressure Switch

 A pressure switch is a mechanical device which converts a pressure change into an electrical function. The pressure change might be measured as pressure, vacuum, or differential between two pressure inputs. In every case, the pressure switch will employ a diaphragm, piston, or other pressure-responsive sensor, which has been coupled to the mechanical means of actuating a switch. Example of Pressure Switch P/N 42D185 

Servo Actuator

 The servo drive is the SP-50 aileron surface actuator unit. When the servo drive is coupled through the airplane's aileron servo stop mechanism, the servo drive controls the deflection of the roll control surfaces.The  Servo Drive consists of the following: A. Split field DC series motor and tachometer. B. Power gear train. C. Synchro control transformer. D. Electric engage power clutch. E. Interlock switches. F. Radio interference filter assembly. G. Splined output shaft.

Transmitter

Transmitter is a electronic device or tool which sends or receives a signal through electromagnetic radiation. The control Surface position transmitter, NCL type number H504A is a tandem transmitter which forms part of the electromechanical family of transmitters known as synchros. The Surface Position Transmitter, unit P/N 4004-01 is a synchro transmitter providing angular position information as a function of input shaft rotation.

Tach Generator

Tachometer generators and tachogenerators are small AC or DC generators that output a voltage in proportion to the rotational speed of a shaft. They are capable of measuring speed and direction of rotation, but not position. The frequency of the AC produced by the tachometer generator is proportional to the speed of the engine. The  Tachometer Generator P/N 2CM9-Series consists of a driven permanent magnet rotor and a stator in which voltage is induced as the rotor turns.