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wash primer (aircraft finishing system component). A type of primer used to prepare an aluminum or
magnesium surface to receive a topcoat of finishing material. Wash primer contains an etchant, a material
that chemically roughens the metal, to prepare the surface to accept the topcoat material.
waste gate (turbosupercharger component). A controllable butterfly valve in the exhaust pipe of a
reciprocating engine equipped with an exhaust-driven turbocharger. When the waste gate is open, the
exhaust gases leave the engine through the exhaust pipe. But when it is closed, the gases must pass through
the turbine that drives the turbocharger compressor.
By controlling the amount the waste gate is open, the speed of the turbocharger can be controlled,
and this speed determines the manifold pressure in the engine.
water equivalent (meteorology). The depth of water that would result from the melting of snow or ice.
water injection (gas turbine engines). Pure water or a mixture of water and alcohol is sprayed into the
compressor inlet or the diffuser inlet. When the water evaporates, it absorbs heat from the air and drops its
temperature making the air more dense. Increasing the density of the air flowing through the engine
increases the mass airflow, and this increases the thrust the engine produces.
water injection (reciprocating engines). A system in which a water and alcohol mixture is injected into
the induction system of a reciprocating engine when it is developing full power. When the water injection
system (or antidetonation [ADI] system, as it is more properly called) is used, the fuel-air mixture being
produced by the carburetor is automatically leaned, or deriched, to allow the engine to develop its
maximum power.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 626
The liquid water-alcohol mixture is injected with the fuel and air into the cylinders where it turns
into vapor. As it evaporates, it absorbs the heat that would otherwise cause detonation.
waterline (reference line). A horizontal reference line used in lofting (laying out the contour of an airplane
fuselage). Waterline zero (WL 0) is used as the reference, and measurements above this line are positive
water lines. Measurements below WL 0 are negative waterlines. An object located on WL 104 is 104
inches above WL 0.
water/methanol injection. See W/M injection.
watt. The basic unit of mechanical power in the metric system and also as a measure of electrical power.
One watt is the amount of power needed to do one joule (0.7376 foot-pound) of work in one second and is
also the equivalent of 1/746 horsepower.
In terms of electrical power, one watt is the amount of electrical power needed to force one
ampere of current to flow under a pressure of one volt.
wattage rating (electrical component rating). The maximum power an electrical component can dissipate
without becoming overheated or otherwise damaged.
watt-hour. The basic unit of electrical work. One watt-hour is the amount of work done when one watt of
power is used for one hour. One watt-hour is equal to 3,600 joules of work.
wattmeter. An indicating instrument that measures electrical power.
watt-second. The amount of work done when one watt of power is used for one second. One watt-second
is equal to one joule.
wave cyclone (meteorology). A cyclone which forms and moves along a front. The circulation about the
cyclone center tends to produce a wavelike deformation of the front.
waveform. The visual or graphic shape of an electromagnetic wave as is seen on a cathode-ray
oscilloscope. Some of the more common waveforms are sine waves, square waves, sawtooth waves, and
random or complex waves.
waveform analyzer. An electronic instrument that measures the frequency and amplitude of the various
components of a complex electromagnetic wave.
wave guide. A hollow transmission line through which high-frequency electromagnetic waves are directed.
wavelength (λ). The distance between a peak or a trough of an electromagnetic wave and the
corresponding peak or trough in the next cycle of the wave. Wavelength is inversely related to the
frequency of the wave.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 627
wave soldering. A method of soldering components to a printed circuit (PC) board. All the components are
assembled on the PC board, and the side of the board on which the copper strips are formed is treated with
flux.
A tank of molten solder is vibrated so waves form on the surface of the solder, and the board is
passed over the solder so the tip of the waves touch the fluxed copper strips. All the component leads
protruding through the board are soldered to the copper strips.
　
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