Aviation Maintenance Terms beginning with H

Heat

The total kinetic energy of the molecules of any substance.

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Henry

The basic unit of inductance, symbolized with the letter H. An electric circuit has an inductance of one henry when current changing at the rate of one ampere per second induces a voltage of one volt into the circuit.

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Hermaphrodite caliper

Generally used as a marking gauge in layout work. It should not be used for precision measurement.

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Hidden lines

Indicates invisible edges or contours.

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Horsepower

A measure of power equal to 550 foot-pounds per second or 33,000 foot-pounds per minute and 746 Watts.

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Hot start

Occurs when the engine starts, but the exhaust gas temperature exceeds specified limits. This is usually caused by an excessively rich air-fuel mixture entering the combustion chamber.

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Humidity

The amount of water vapor in the air.

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Hung start

Occurs when the engine starts normally, but the rpm remains at some low value rather than increasing to the normal starting rpm. This is often the result of insufficient power to the starter, or the starter cutting off before the engine starts self-accelerating.

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Hydrometer

An instrument for determining the specific gravity of liquids.

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Hypotenuse

The side of a right triangle that is opposite the right angle. The hypotenuse is the longest side of a right triangle

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