power section (reciprocating engine component). The section of the crankcase of a radial engine to which the cylinders are attached.
powers of ten (mathematics). A handy mathematical tool in which very large and very small numbers are changed to numbers between 1 and 10 with a superscript (exponent) to show the number of places to move the decimal point. Powers of ten is another name for scientific notation. Numbers greater than 1 have a positive exponent, and numbers smaller than 1 have a negative exponent.
100 = 1
101 = 10
102 = 100
103 = 1,000
104 = 10,000
105 = 100,000
106 = 1,000,000
power stroke (reciprocating engine operation). The stroke in the operating cycle of a reciprocating engine in which both of the valves are closed, the fuel-air mixture has been ignited and burned, and the piston is being forced downward by the expanding gases. Work is done in a reciprocating engine only during the power stroke.
power supply (electrical component). A circuit or device that changes alternating current at the power-line voltage into direct current of the required voltage. Many power supplies include a voltage regulator circuit that holds the output voltage constant as the load current changes.
power transformer (electrical component). The transformer in an electrical power supply that changes the line voltage into the voltages needed for the circuits using the power supply.
PPI (plan position indicator). A radar indicator in which the returns from the targets appear as bright spots at the locations they would have on a circular or fan-shaped map of the area being scanned. The range of the target is indicated by the distance of the spot from the center of the scope, and the bearing of the target is indicated by the radial angle between the spot and a vertical reference line.
Some radar antenna rotate, and their PPI scopes are circular. Other antenna oscillate, and their PPI scopes are fan shaped.
practice instrument approach (air traffic control). An instrument approach procedure conducted by a VFR or an IFR aircraft for the purpose of pilot training or proficiency demonstrations.
praseodymium. A soft, silvery, malleable, ductile, rare-earth, metallic chemical element. Praseodymium’s symbol is Pr, its atomic number is 59, and its atomic weight is 140.91. Praseodymium is used in the manufacture of colored glass and as an alloy with other metals.
Pratt truss. A type of truss structure in which the longitudinal members are separated by vertical members that carry only compression loads, and diagonal members that carry only tensile loads.
Most fabric-covered airplane wings are built with a Pratt truss. The wing spars are the main structural members, the compression struts or compression ribs carry only compressive loads, and the drag and anti-drag wires carry only tensile loads.
preamplifier (electronic circuit). An electronic circuit that amplifies an extremely weak input signal to a value strong enough to be used in other amplifiers. Preamplifiers used in some sound systems have provisions for mixing inputs from more than one microphone and for equalizing the sounds by amplifying some frequencies more than others.
|
