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southern hemisphere.
high blower (aircraft engine supercharger condition). The condition of supercharging of a reciprocating
engine in which a two-speed, single-stage internal supercharger is operating at its high-speed ratio. This
ratio is normally about ten times the speed of the crankshaft.
high-bypass turbofan engine. A turbofan engine in which the fan moves more than four times as much air
as is moved by the core engine compressor. This type of engine is said to have a bypass ratio of more than
4:1.
high-carbon steel. Steel that contains at least 0.50% carbon. High-carbon steel can be hardened to increase
its strength, but this causes it to become brittle.
high-frequency communications. Radio communications using frequencies between three and 30
megahertz. HF communication is used between aircraft and ground facilities in over water operations.
high-impedance voltmeter. A voltmeter whose meter movement requires very little current for full-scale
deflection. Most high-impedance voltmeters have a sensitivity of at least 20,000 ohms per volt, and when a
very-high-impedance voltmeter is needed, vacuum-tube or FET voltmeters are used. The sensitivity of
these meters is measured in megohms per volt. High-impedance voltmeters do not load the circuit, which
would give erroneous reading when voltage is measured across a high resistance.
high-level language (computer language). A computer language whose instructions are terms similar to
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 298
those used in normal communications. Statements in the high-level language entered into the computer
produce a series of machine-language instructions the computer can understand. BASIC, FORTRAN,
COBOL, and PASCAL are examples of high-level languages.
high-lift device (aircraft component). Any component used to increase the lift produced by an aircraft
wing. High-lift devices include leading edge flaps, slots, slats, trailing edge flaps, and boundary layer
control systems. High-lift devices allow the wing to reach a higher angle of attack and thus produce more
lift, before the airflow over its surface separates and the wing stalls.
high metal ion concentration cell corrosion. Corrosion that results from a concentration of metallic ions
in the electrolyte. The area of high concentration of metallic ions is the cathode of the cell.
high-pass filter (electronic circuit). A type of electronic filter that passes, with little opposition,
alternating current above a certain frequency. A high-pass filter blocks direct current, and blocks or reduces
the amplitude of all alternating current having a frequency lower than that for which it is designed.
high-potential test (ignition lead test). A test used to determine whether or not the insulation around
certain shielded wires in an ignition system can withstand the high voltage they carry without leaking an
excessive amount of current to ground.
A high potential (high voltage) is placed between the center conductor and the metal shield around
the outside of the insulation. An indicator light glows if the leakage current between the two conductors is
excessive. A high-potential test is often called a high-pot test.
high-pressure compressor (gas turbine engine component). The second-stage compressor in a
dual-spool gas turbine engine. The high-pressure compressor, called the N2 compressor, is the one that is
rotated by the starter for starting, and the one whose RPM is controlled by the fuel control.
high-pressure oxygen system. An oxygen system installed in an aircraft in which gaseous oxygen is
carried in steel bottles under a pressure of between 1,800 and 2,000 pounds per square inch.
high-pressure turbine (gas turbine engine component). The stage, or stages, of turbines used to drive the
high-pressure (N2) compressor in a two-spool, axial-flow gas turbine engine.
high-Q circuit (electronic circuit). An electronic circuit having a high ratio of circuit impedance to
resistance. Q is a measure of the efficiency of a reactive circuit.
high-rate discharge (battery operation). Discharge of a battery at the highest rate it is likely to encounter
in service. This is also called the cold-cranking discharge rate.
high-resistance connection (electrical circuit). A connection in an electrical circuit which has an
excessive amount of resistance. High-resistance connections are caused by corrosion, loose fasteners, and
cold-solder joints.
high-speed steel. Steel alloys used to make metal-cutting tools. These alloys retain their strength and
hardness when operating at high temperatures.
high-speed taxiway. A long-radius taxiway designed and provided with lighting or marking to define the
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
　
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