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of square-wave pulses of energy.
pulse counter. An electronic circuit that measures the number of pulses of electrical energy it receives in a
given interval of time.
pulse-echo method of ultrasonic inspection. A form of nondestructive inspection used to detect the
presence of internal damage or faults in a piece of aircraft structure. Pulses of ultrasonic energy are
introduced into the material being inspected, and the time required for these pulses to travel through the
material and return to the transducer is measured.
If there is a fault in the material, the pulses will bounce off it, rather than traveling all the way to
the rear surface of the material. This short travel time indicates the presence of a fault.
pulse generator (electronic test equipment). An electronic device that produces a series of pulses of
electrical energy. These pulses have an accurately controlled pulse width, pulse spacing, pulse amplitude,
and pulse repetition rate.
pulse-jet engine. A type of air-breathing reaction engine that was used during World War II to power
jet-propelled missiles. Fuel is sprayed into the combustion chamber and ignited. The air is thus heated, and
as it expands, it closes the one-way shutter valve in the front of the engine and exits the engine through the
nozzle at the rear. As soon as the pressure inside the combustion chamber decreases, air enters through the
shutter valve and more fuel is ignited. The thrust is produced in a series of pulses.
pulse length (radar technology). The dimension of a radar pulse. It may be expressed as the time duration
or the length in linear units. The linear dimension of a pulse is equal to time duration multiplied by the
speed of propagation, which is approximately the speed of light.
pumice. A very fine abrasive powder used to polish metal surfaces.
pump control valve (hydraulic system component). A control valve in a hydraulic system that allows the
pilot to manually direct the output of the hydraulic pump back to the reservoir when no unit is being
actuated.
punch test (aircraft fabric). A test of the strength of aircraft fabric that can be performed on the aircraft
with a minimum of damage to the fabric. A special tester with a sharp-pointed, spring-loaded punch is
pressed into the fabric, and the amount of force needed for the punch to penetrate the fabric is measured.
A punch test does not give a truly accurate indication of the strength of the fabric, but it is
sufficiently accurate to tell whether or not the fabric strength is above a minimum value.
Pureclad. A registered trade name for clad aluminum alloy sheets.
purge (air conditioning system maintenance). The maintenance procedure in which all of the moisture
and air is removed from a cooling system by flushing the system with a dry gaseous refrigerant.
push-button switch (electrical switch). A type of electrical switch actuated by a push button. The button
must be pushed each time the switch is to be opened or closed.
pusher powerplant. A powerplant whose propeller is mounted at the rear of the airplane and pushes, rather
than pulls, the airplane through the air.
pusher propeller (aircraft propeller). A propeller installed on an aircraft engine whose propeller shaft
faces the rear of the aircraft. Thrust produced by the propeller pushes the aircraft, rather than pulling it.
push fit. A fit between pieces in a mechanical assembly that is close enough to require the parts to be
pushed together. A push fit is looser than a press fit, but closer than a free fit.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 466
push-pull amplifier (electronic circuit). A type of electronic amplifier with two output circuits whose
output voltages are equal but 180° out of phase with each other. A push-pull amplifier is also called a
balanced amplifier.
push-pull rod (aircraft control system component). A stiff rod in an aircraft control system that moves a
control surface by either pushing or pulling on it.
pushrod (reciprocating engine component). A stiff rod or hollow tube used to open the intake and
exhaust valves of a reciprocating engine. One end of the pushrod rides in the cam follower, and the other
end fits in a socket on one end of a rocker arm. When the cam follower rides up on the cam lobe, the
pushrod transmits this movement to the rocker arm, and the rocker arm pushes the valve off its seat.
PVC (polyvinylchloride). A thermoplastic resin used to make transparent tubing for insulating electrical
wires.
PV diagram (reciprocating engine relationship). A diagram showing the relationship between the
volume of a cylinder and the pressure during a cycle of engine operation.
pylon (jet aircraft component). The structure which holds an engine nacelle or pod to the wing or
　
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