Aviation Maintenance Terms beginning with G
Galling
Fretting or pulling out chunks of a surface by sliding contact with another surface or body.
Gasket
A seal between two parts where there is no relative motion.
Gauge (rivet)
The distance between rows of rivets in a multirow seam. Gauge is also called transverse pitch.
Gauge pressure
Pressure referenced from the existing atmospheric pressure.
Gear-type pump
A constant-displacement fluid pump that contains two meshing large-tooth spur gears. Fluid is drawn into the pump as the teeth separate and is carried around the inside of the housing with teeth and is forced from the pump when the teeth come together.
Generator
A mechanical device that transforms mechanical energy into electrical energy by rotating a coil inside a magnetic field. As the conductors in the coil cut across the lines of magnetic flux, a voltage is generated that causes current to flow.
Generator series field
A set of heavy field windings in a generator connected in a series with the armature. The magnetic field produced by the series windings is used to change the characteristics of the generator.
Generator shunt field
A set of field windings in a generator connected in parallel with the armature. Varying the amount of current flowing in the shunt field windings controls the voltage output of the generator.
Gerotor pump
A form of constant-displacement gear pump. A gerotor pump uses an external-tooth spur gear that rides inside of and drives an internal-tooth rotor gear. There is one more tooth space inside the rotor than there are teeth on the drive gear. As the gears rotate, the volume of the space between two of the teeth on the inlet side of the pump increases, while the volume of the space between the two teeth on the opposite side of the pump decreases.
Gimbal
A support that allows a gyroscope to remain in an upright condition when its base is tilted.
Glass flight deck
An aircraft instrument system that uses a few cathode-ray-tube displays to replace a large number of mechanically actuated instruments.
Glaze ice
Ice that forms when large drops of water strike a surface whose temperature is below freezing. Glaze ice is clear and heavy.
Glide slope
The portion of an ILS (Instrument Landing System) that provides the vertical path along which an aircraft descends on an instrument landing.
Goniometer
Electronic circuitry in an ADF system that uses the output of a fixed loop antenna to sense the angle between a fixed reference, usually the nose of the aircraft, and the direction from which the radio signal is being received.
Gram
The basic unit of weight or mass in the metric system. One gram equals approximately 0.035 ounce.
Graphite
A form of carbon. Structural graphite is used in composite structure because of its strength and stiffness. Halon 1301 is bromotrifluoromethane.
Greige (pronounced “gray”)
The unshrunk condition of a polyester fabric as it is removed from the loom.
Ground
The voltage reference point in an aircraft electrical system. Ground has zero electrical potential. Voltage values, both positive and negative, are measured from ground. In the United Kingdom, ground is spoken of as “earth.” Ground-power unit (GPU). A service component used to supply electrical power to an aircraft when it is being operated on the ground.
Ground effect
The increased aerodynamic lift produced when an airplane or helicopter is flown nearer than half wing span or rotor span to the ground. This additional lift is caused by an effective increase in angle of attack without the accompanying increase in induced drag, which is caused by the deflection of the downwashed air.
Guncotton
A highly explosive material made by treating cotton fibers with nitric and sulfuric acids. Guncotton is used in making the film base of nitrate dope.
Gusset
A small plate attached to two or more members of a truss structure. A gusset strengthens the truss.
Gyro (gyroscope)
The sensing device in an autopilot system. A gyroscope is a rapidly spinning wheel with its weight concentrated around its rim. Gyroscopes have two basic characteristics that make them useful in aircraft instruments: rigidity in space and precession. See rigidity in space and precession.
Gyroscopic precession
The characteristic of a gyroscope that causes it to react to an applied force as though the force were applied at a point 90° in the direction of rotation from the actual point of application. The rotor of a helicopter acts in much the same way as a gyroscope and is affected by gyroscopic precession.
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