accessory gear train. A group of gears that drive an accessory from the crankshaft of a reciprocating engine or from the compressor drive shaft of a gas turbine engine.
accessory section (reciprocating engine). The portion of an aircraft engine crankcase on which such accessories as magnetos, carburetors, generators, fuel pumps, and hydraulic pumps are mounted.
access panel. An easily removable panel that allows access to some portion of an aircraft structure for inspection and maintenance.
accident. An event that happens by chance or from some unknown cause. An accident is usually thought to be an unfortunate situation or event.
accumulated error. The sum of all the errors occurring in the operation of a system or in the manufacture of a part.
If the errors are in opposite directions, they cancel, but if they are in the same direction, the accumulated error is greater than any of the individual errors.
accumulator (British terminology). An electrical storage battery.
accumulator (electronic computer). A device in a digital computer that stores a number and, upon the receipt of a second number, adds the two and stores the sum.
accumulator (hydraulic system component). A component in a hydraulic system that allows a noncompressible fluid, such as oil, to be stored under pressure. An accumulator has two compartments separated by a flexible or movable partition such as a diaphragm, bladder, or piston. One compartment contains compressed air or nitrogen, and the other is connected into the source of hydraulic pressure.
When oil is pumped into the accumulator, the partition moves over and increases the pressure of the air. This air pushing against the partition holds pressure on the oil.
An accumulator in an aircraft hydraulic system acts as a shock absorber and provides a source of additional hydraulic power when heavy demands are placed on the system.
accumulator air preload (precharge). The charge of compressed air or nitrogen in one side of an accumulator. The air preload is normally about one third of the system hydraulic pressure. When fluid is pumped into the oil side of the accumulator, the air is further compressed, and the air pressure and the fluid pressure become the same.
If the air preload pressure is too low, there will be almost no time between the regulator reaching its kick-in and kick-out pressures, and the system will cycle far more frequently than it should.
If there is no air pressure gage on the accumulator, the amount of air preload may be found by watching the hydraulic system pressure gage as the pressure is slowly bled off the system. The pressure will drop slowly, until a point is reached at which it drops suddenly. This point is the air preload pressure.
accuracy. A measure of the amount of error, or difference between an actual value and its indicated value. Accuracy is usually expressed in terms of percentage of the full range of measurement.
For example, if voltage is measured on a voltmeter having a full-scale range of ten volts, and the meter has an accuracy of plus or minus two percent of its full-scale reading, the voltage indication will be accurate to within 2% of ten volts, or it will be accurate within plus or minus 0.2 volt.
|
