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lubricating oil in a sump, or compartment, which is part of the engine itself. After serving its lubricating
functions, the oil drains back into the sump by gravity.
A dry-sump engine uses an external oil tank, and the oil, after flowing through the engine, is
moved by scavenger pumps to the external tank where it is stored until it is pumped through the engine
again.
wet-type vacuum pump. An engine-driven air pump which uses steel vanes lubricated with engine oil
drawn into the pump through holes in the base. The oil passes through the pump, where it seals and
lubricates, and is then exhausted with the air. Wet-type pumps must have oil separators in their discharge
line to trap the oil and return it to the engine crankcase.
wet wing (aircraft structure). A type of aircraft construction in which part of the wing structure is sealed
and used as a fuel tank. Wet wings are more properly called integral fuel tanks.
Wheatstone bridge (electrical circuit). A four-arm electrical bridge circuit used to measure resistance. An
unknown resistance is placed in one arm of the bridge and is compared with a variable, or known,
resistance in an opposite arm.
When the variable resistor is adjusted until no current flows through the indicator, the bridge is
balanced and the unknown resistance is exactly the same as that of the variable resistor.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 629
wheel well (aircraft structural component). A part of an aircraft structure that houses the landing gear
when it is retracted. Wheel wells may be part of the wing, engine nacelle, or fuselage.
“When able” (air traffic control). A phrase used in conjunction with ATC instructions that gives the pilot
latitude to delay compliance until a condition or event has been reconciled. Unlike “pilot discretion,” when
an instruction is prefaced with “when able,” the pilot is expected to seek the first opportunity to comply.
Once a maneuver has been initiated, the pilot is expected to continue until the specifications of the
instructions have been met. “When able,” should not be used when expeditious compliance is required.
whetstone. An abrasive stone used to wear away, or sharpen, the edges of cutting tools.
whiffletree. A pivoted beam used in an aircraft control system to allow more than one force to act on a
common point. For example, two pulling forces may be applied to the ends of a whiffletree, and the device
being pulled is connected to the point between the pulling forces.
whip antenna (radio antenna). A flexible, vertical antenna often used with high-frequency (HF) and
very-high-frequency (VHF) radio equipment. The length of a whip antenna is one-quarter the wavelength
of the frequency to which the antenna is resonant. A whip antenna is nondirectional; it transmits or receives
its signals equally well in all directions.
Whittle, Sir Frank. The British Royal Air Force Flying Officer who in 1929 filed a patent application for
a turbojet engine. Whittle’s engine first flew in a Gloster E.28 on May 15, 1941. The first jet flight in
America was made on October 2, 1942, in a Bell XP-59A that was powered by two Whittle-type General
Electric I-A engines.
wicking (soldering problem). A problem that occurs when solder flows up around the individual wires in
a stranded electrical conductor until it reaches the insulation. When stranded wire is soldered, there should
be a short piece of the bare wire between the end of the solder and the beginning of the insulation. This
bare section allows the wire to flex smoothly so it will not break when it is vibrated.
winch. A machine used for pulling or moving heavy loads. A cable is wound around a drum turned by a
geared hand crank or some type of motor. The load is attached to the cable and is moved by it.
wind (meteorology). Air in motion relative to the surface of the earth. The term wind generally denotes
horizontal movement of the air.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 630
wind chill factor (meteorology). A measure of the cooling effect of the wind. Wind chill factor is based on
both the temperature of the air and the velocity of the wind.
windmilling (aircraft engine operation). An aircraft engine is said to be windmilling when it is turned by
aerodynamic action of air flowing over the propeller or through the compressor in a gas turbine engine. If
an engine fails in flight, air flowing over the propeller or through the compressor produces enough force to
keep the engine turning.
When a propeller windmills, it produces so much drag it can cause difficulty in controlling the
airplane. For this reason, the propellers of most multiengine airplanes are made so that they can be
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航空术语词典Dictionary of Aeronautical Terms 下(123)
