outside calipers. A measuring device having two inwardly curved, hinged legs. The calipers are closed until the points of the legs just touch the outside of the device to be measured, and the distance between the two points is measured with a steel scale.
“Over” (air traffic control). A term used in air traffic control to indicate “My transmission is ended; I expect a response.”
overboost (reciprocating engine operation). A condition of excessive manifold pressure in a reciprocating engine. Overboosting occurs when the supercharger is operated at too high a speed.
overcompounded generator (electrical generator). An electrical generator which has both a series and a shunt field with the effect of the series field being greater than that of the shunt field. The output voltage tends to increase as the electrical load increases.
overcompounded motor (electric motor). A compound-wound motor (a motor having both a series and a shunt field) in which the series field has the greater effect on the motor characteristics. The shunt, or parallel, field attempts to hold the speed of the motor constant as the load changes, but the series field causes the motor to speed up as the load increases.
In a flat compounded motor, the effects of the two fields cancel, and the motor speed remains relatively constant as the load changes. In an overcompounded motor, the series winding has the greater effect, and the motor tries to speed up as the load increases.
overcurrent protection device. A device in an alternator or generator control system that reduces the output voltage when excessive current flows.
overhaul (maintenance procedure). The maintenance procedure in which a device is disassembled to the extent needed to determine the condition of all its parts. Each part is inspected, and, if damaged or excessively worn, it is repaired or replaced. The device is then reassembled and tested, and if it functions as it should, is returned to service.
overhead-cam engine (type of reciprocating engine). A reciprocating engine in which the camshaft is located in the cylinder head. The valves are opened by rocker arms that are actuated by the cam lobes. The valves of engines that have the camshaft in the crankcase are actuated by pushrods and rocker arms.
overhead-valve engine (type of reciprocating engine). A reciprocating engine in which the intake and exhaust valves are located in the cylinder head. This type of engine is also called a valve-in-head engine.
overheat warning system (fire warning system). A type of warning system that warns the flight crew that an engine nacelle or wheel well is too hot for normal operation, but there is no localized high temperature that indicates the presence of a fire.
overinflation valve (aircraft wheel component). A valve used in some large aircraft wheels that mount tubeless tires. The valve opens and relieves the excess pressure if the tire is accidentally overinflated.
overlying center (air traffic control). The ARTCC facility that is responsible for arrival/departure operations at a specific terminal.
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