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 path of aircraft traveling at high speed (up to 60 knots) from the runway center to a point on the center of a taxiway. A high-speed taxiway is also referred to as a long-radius exit or turn-off taxiway and is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time.
high-strength steel. Steel whose tensile strength can be increased by proper heat treatment to between 50,000 and 100,000 pounds per square inch.
high-tension magneto (reciprocating engine ignition system). A self-contained ignition system used with a spark-ignition reciprocating engine. A high-tension magneto contains an alternating current generator that produces a flow of primary current, and a set of breaker points that interrupts this current the instant the spark is needed.
When the primary current stops flowing, its magnetic field collapses. The collapsing lines of flux cut across many thousands of turns of wire in the secondary winding of the built-in magneto coil and induces a high voltage into it. The distributor, which is a high-voltage selector switch, directs the high voltage from the magneto coil to the proper spark plug for ignition.