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have a hand pump as a backup in case the power pump fails.
hand tools. A general name for all of the hand-held tools a technician uses when performing aircraft
maintenance.
hangar. A building used to house aircraft.
hangar rash. Scrapes, bends, and dents in an aircraft structure that are caused by careless handling, usually
when the aircraft is being moved inside the hangar.
hard (physical condition of a material). Compact, solid, and difficult to bend or deform.
hardboard. A composition material made by bonding sawdust and chips of wood with an adhesive under
heat and pressure.
hard bronze. A high-strength copper alloy made of 88% copper, 7% tin, 3% zinc, and 2% lead.
hard-drawn copper wire. Copper wire that has not been annealed after it was formed by pulling it through
dies. Pulling the wire through dies reduces its diameter to the desired size. It also work hardens the wire
and increases its tensile strength.
hardenability (metals). The ability of a metal to be hardened by either heat treatment or cold-working.
hardened steel. Steel that has been heated red-hot and then quenched in brine, water, or oil. Hardened steel
is strong but brittle.
hardener (plastic resin component). A material used with a plastic resin to improve its hardening.
hardening (metal heat treatment). A step in the heat treatment of metal in which the metal is made hard
but brittle. Most ferrous metals (metals containing iron) are hardened by heating them to a specified
temperature and then quenching them in oil, water, or brine. Other metals can be hardened only by
cold-working them: by rolling them between steel rollers or by bending or hammering them.
hard-facing. A method of increasing the hardness of the face of a steel tool to keep it from being worn
away in normal use. Hard-facing is done by welding, plating, or spraying a hard material, such as a carbide,
on the surface of the tool.
hard landing (aircraft operation). An airplane landing in which enough forces have been transmitted into
the structure to have likely caused damage.
hardness. The ability of a material to resist being scratched. Hardness is measured using the Mohs scale,
which rates the hardness of a material by comparing it with ten minerals that have been given Mohs
hardness values from one to ten.
These minerals range from talc, whose Mohs hardness is one, through gypsum, calcite, fluorite,
apatite, orthoclase, quartz, topaz, corundum, to diamond. Diamond has a Mohs hardness of ten.
hardness test. A test that can be made of either metallic or non-metallic materials to determine their
physical condition. A cone- or a ball-shaped tool is forced into the surface of the material, and the diameter
or depth of the penetration caused by a given amount of force is measured. The diameter or depth of the
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 291
penetration is related to the hardness and the strength of the material. See Rockwell hardness tester and
Brinell hardness test.
hard rubber. Rubber that has been vulcanized under high temperature and pressure to make it hard. Hard
rubber is used as an electrical insulator and for the handles of many different types of tools.
hardware. A general term for all of the small components, such as nuts, bolts, screws, and washers used to
assemble an aircraft or aircraft engine.
hardware (computer operation). The physical equipment used in computer operation.
hardwood. Wood from a broadleaf tree that sheds its leaves each year.
hard X-rays. X-rays that have a great deal of penetrating power. The penetrating power of X-rays is
determined by the amount of voltage applied to the anode of the X-ray tube. The higher the voltage, the
harder the X-ray (the greater its penetrating power).
harmonic. A vibration whose frequency is an even multiple of another vibration. The first harmonic of a
400-Hz vibration has a frequency of 400 Hz. The frequency of the first harmonic is the same as the
fundamental frequency. The second harmonic has a frequency of 800 hertz, and the third harmonic has a
frequency of 1,200 hertz.
harness (electrical). A bundle of wires routed through an aircraft structure, connecting electrical
components to each other and to the power bus.
Hartley oscillator. A popular electronic oscillator circuit which uses a tapped coil in parallel with a
capacitor to determine the frequency of the AC the circuit produces. Energy from the collector of a
transistor, or the plate of a vacuum tube, passes through one half of the coil and induces a voltage in the
other half.
This induced voltage is applied to the base of the transistor, or the grid of the vacuum tube, with a
polarity that causes the circuit to oscillate, or produce alternating current.
　
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