Aviation Maintenance Terms beginning with G
Galileo
A European satellite-based radio navigation system being developed that will provide a global positioning service.
Galling
Fretting or pulling out chunks of a surface by sliding contact with another surface or body.
Galvanic corrosion
Corrosion due to the presence of dissimilar metals in contact with each other.
Gas cylinder
A portable container used for transportation and storage of a compressed gas.
Gas generator
The basic gas turbine engine. It consists of the compressor, diffuser, combustor, and turbine. The gas generator is also called the core engine.
Gas Tungsten Arc Welding
(GTAW) an arc welding process which produces coalescence of metals by heating them with an arc between a tungsten (nonconsumable) electrode and the work. Shielding is obtained from a gas or gas mixture. Pressure may or may not be used and filler metal may or may not be used.
Gas turbine engine
An internal combustion engine that burns its fuel in a constant-pressure cycle and uses the expansion of the air to drive a turbine which, in turn, rotates a compressor. Energy beyond that needed to rotate the compressor is used to produce torque or thrust.
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 existing atmospheric pressure.
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.
General aviation
A term used to describe the total field of aviation operation except the military and airlines.
General Aviation Airworthiness Alerts
While these documents are no longer published, they are still available at www.faa.gov. These are used to alert technicians of problems that have been found in specific models of aircraft, and reported on Malfunction and Defect Reports. Airworthiness Alerts suggest corrective action, but compliance with the suggestion is not mandatory.
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
A device for converting mechanical energy into electrical energy.
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.
Geometric pitch
The distance a propeller would advance in one revolution if it were rotating in a solid.
Geopotential of the tropopause
The point in the standard atmosphere where the temperature stops dropping and becomes constant. This is the tropopause, or the dividing line between the troposphere and the stratosphere.
Gerotor pump
A form of constant-displacement pump that uses an external-tooth drive gear that meshes with and drives an internal-tooth gear that has one more space for a tooth than there are teeth on the drive gear. Both gears turn inside a close-tolerance housing. As the gears rotate, fluid flows between the teeth that are beginning to un-mesh, and is carried around the pump as the space continues to open up. On the discharge side of the pump, the teeth becomes smaller, fluid is forced out of the pump.
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 color cathode-ray-tube displays to replace a large number of mechanically actuated instruments.
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.
Glider
A heavier-than-air aircraft, that is supported in flight by the dynamic reaction of the air against its lifting surfaces and whose free flight does not depend principally on an engine.
Global Navigation Satellite System (GNSS)
The generic term for a satellite navigation system, such as GPS, that provides autonomous worldwide geo-spatial positioning and may include local or regional augmentations.
Global Positioning System (GPS)
A U.S. satellite-based radio navigation system that provides a global positioning service. The service provided by GPS for civil use is defined in the Global Positioning System Standard Positioning Service Performance Standard, 4th edition, dated September 2008, available at http://www.gps.gov/technical/ps/2008-SPS-performance- standard.pdf.
Global positioning system (GPS)
A navigation system that employs satellite transmitted signals to determine the aircraft’s location.
GNSS Time of Applicability
The time when the position output from the GNSS sensor is applicable.
GNSS Time of Measurement (TOM)
The time when the last GNSS signal used to determine the position arrives at the aircraft GNSS antenna.
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.
Gouge
A deep groove on a blade formed by a heavy pressure contact with a solid object.
Governor
A control used to automatically change the pitch of a constant speed propeller to maintain a constant engine rpm as air loads vary in flight.
Grain
The direction, size, arrangement, appearance, or quality of the fibers in wood or metal.
Grain- diagonal
Annual rings in wood at an angle with the axis of a piece as a result of sawing at an angle with the bark of the tree.
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.
Grommet
An insulating washer that protects the sides of holes through which wires must pass/or a metal or plastic drain attached to fabric on aircraft.
Gross thrust
The thrust produced by a turbojet or turbofan engine when the engine is static or not moving. The air is considered to have no inlet velocity, and the velocity of the gas leaving the engine is considered to be the acceleration factor.
Gross weight
The total weight of the aircraft including its contents.
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.
Ground Speed
The magnitude of the horizontal velocity vector (see velocity). In these minimum operational performance standards (MOPS) it is always expressed relative to a frame of reference that is fixed with respect to the earth’s surface such as the WGS-84 ellipsoid.
Ground Track Angle
The direction of the horizontal velocity vector (see velocity) relative to the ground as noted in ground speed.
Ground-boosted engine
An aircraft reciprocating engine with a built-in supercharger that boosts the sea-level rated horsepower of the engine.
Grounding
The term is usually applied to a particular form of bonding that is the process of electrically connecting conductive objects to either conductive structure or some other conductive return path for the purpose of safely completing either a normal or fault circuit.
Gudgeon pin
The British name for a wrist pin, or piston pin. See wrist pin.
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.
Gyrodyne
A rotorcraft whose rotors are normally engine-driven for takeoff, hovering, and landing, and for forward flight through part of its speed range, and whose means of propulsion, consisting usually of conventional propellers, is independent of the rotor system.
Gyroplane
A rotorcraft whose rotors are not engine-driven, except for initial starting, but are made to rotate by action of the air when the rotorcraft is moving; and whose means of propulsion, consisting usually of conventional propellers, is independent of the rotor system.
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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