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hook spanner. A type of wrench used to turn a splined shaft. Some hook spanners have a hinged hook that
allows them to be used on shafts of different diameters.
hopper. A funnel-shaped container with an opening in the top for loading and a smaller opening in the
bottom for dumping. Hoppers are used to store the abrasive in an abrasive blaster. The abrasive is loaded in
through the large opening, and it feeds out as needed through the small opening.
hopper-type oil tank (reciprocating engine oil tank). An oil tank, or reservoir, in which there is a hopper
around the outlet from the tank. When oil dilution is being used, the diluted oil fills the hopper before the
engine is shut down. Then, when the engine is started, the diluted oil is the first used. This diluted oil helps
start the engine in cold weather. As soon as the oil begins to warm up, oil around the outside of the hopper
feeds into the engine.
horizon. The line we see that forms an apparent boundary between the earth and sky.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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horizontally opposed engine (reciprocating engine). A reciprocating engine in which the cylinders are
arranged in two banks separated by 180°, with the cylinders and crankcase mounted in the aircraft so they
are flat. The cylinders are staggered, with one bank slightly ahead of the other. Staggering the cylinders
allows each piston to be connected to a separate throw of the crankshaft. Horizontally opposed engines are
called flat engines.
horizontal needle of the cross-pointer indicator (aircraft instrument). The horizontal needle of the
cross-pointer indicator of the Instrument Landing System (ILS) shows the pilot the vertical position of the
aircraft as it descends along the glide slope for an instrument approach.
If the horizontal needle is above the center mark, or doughnut, the aircraft is below the glide slope,
and the pilot should fly upward. If the needle is below the doughnut, the aircraft is too high and should
descend. The glide slope is sometimes called the glide path. See illustration for glide slope.
horizontal plane. A horizontal plane is one that is perpendicular to the gravitational field of the earth.
horizontal situation indicator. See HSI.
horizontal stabilizer (airplane control). The fixed horizontal surface on the tail of a conventional airplane.
The horizontal stabilizer is usually adjustable in flight to vary the down-load produced by the tail. This
allows the airplane to fly hands-off at any desired air speed.
horsepower. A measure of mechanical power equal to 33,000 foot-pounds of work done in 1 minute, 550
foot-pounds of work done in 1 second, or 746 watts of power.
One metric horsepower is equal to 75 meter-kilograms per second or 0.9863 English horsepower
horseshoe magnet. A permanent magnet formed in the shape of the letter U, the shape of a horseshoe. The
poles of a horseshoe magnet are close together, and the magnetic flux between them is concentrated.
hose. A flexible fluid line. A hose may have threaded fittings installed in its ends for attachment to other
fittings, or it may be slipped over a piece of rigid tubing and secured with hose clamps.
hot-blow forming (sheet metal forming). A method of forming sheet metal by forcing it into a die with
argon gas whose pressure is computer-controlled to maintain the correct rate of strain of the metal.
hot dimpling (sheet metal construction process). A process used to dimple, or indent, the hole into which
a flush rivet is to be installed. Some metals, such as magnesium and the harder aluminum alloys, cannot be
dimpled cold because they are likely to crack. These metals must be hot dimpled.
Hot dimpling equipment consists of a pair of electrically heated dies with a pilot that goes through
the rivet hole. The pilot is passed through the hole, and the heated dies are pressed together. The dies heat
the metal enough to soften it and force it into the shape of the die. This is the proper shape for the rivet
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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head.
hot section (gas turbine engine). The portion of a gas turbine engine that operates at high temperature.
The hot section includes the combustors, the turbine, and the exhaust system of the engine.
hot section inspection (gas turbine engine maintenance procedure). The inspection of the hot section of
a gas turbine engine.
hot spark plug (reciprocating engine ignition component). A spark plug with a long path for heat to
travel from the nose core insulator to the spark plug shell. Because the heat must travel a long distance
before it is transferred into the cylinder head, the nose core stays quite hot.
Hot spark plugs are used in low-powered engines because a cold spark plug would not get hot
　
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