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utility, acrobatic, or commuter category.
normal heptane. A hydrocarbon, C7H16, that has a very low critical pressure and temperature. Normal
heptane is used as the low reference in measuring the anti-detonation characteristics of aviation gasoline.
normalize (steel heat treatment). A process of strain-relieving steel that has been machined, welded, or
worked in any way that leaves it in a strained condition. The steel is heated to a specified temperature,
usually red-hot, and then allowed to cool in still air to room temperature.
normally aspirated engine (reciprocating engine). See naturally aspirated engine.
normally closed (NC) relay. A relay whose contacts are held closed by a spring. The contacts are opened
by the magnetic pull of an electromagnet.
normally open (NO) relay. A relay whose contacts are held open by a spring.
The contacts are closed by the magnetic pull of an electromagnet.
normal operating speed (aircraft performance specification). The level-flight speed of an aircraft at its
design altitude, with the engine operating at no more than 75% of its rated horsepower.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 406
normal operating zone. See NOZ.
normal refraction (radar technology). Refraction of a radar beam under normal atmospheric conditions.
The normal radius of curvature of the beam is about four times the radius of the curvature of the earth.
normal shock wave (aerodynamics). A shock wave that forms ahead of a blunt object moving through the
air at the speed of sound. The shock wave is perpendicular (normal) to the air approaching the object. Air
passing through a normal shock wave is slowed to a subsonic speed, and its static pressure is increased. See
shock wave.
northerly turning error (magnetic compass error). An error inherent in an aircraft magnetic compass.
The float on which the compass magnets are mounted is unbalanced to compensate for the vertical
component of the earth’s magnetic field, and it is this unbalanced condition that causes northerly turning
error.
When a turn is made from either an easterly or westerly heading toward the north, the heavy end
of the float causes the compass to overshoot the heading, and when turning toward the south, to lag behind
the turn. Northerly turning error is also called dip error.
north pole of a magnet. The pole of a magnet from which the lines of magnetic flux are considered to
leave. The north pole is actually the north-seeking pole. When a magnet is suspended so it is free to rotate,
it will turn until its north pole points to the magnetic north pole of the earth.
nose gear (aircraft landing gear). The wheel under the forward end of the fuselage of an aircraft equipped
with a tricycle landing gear.
nose-gear centering cam. A cam in the shock strut that causes the wheel of a retractable nose gear to
straighten fore-and-aft when the strut is fully extended. When the aircraft takes off and the strut extends,
the wheel straightens so it can be retracted into the wheel well.
nose rib (airplane wing component). A partial wing rib that extends back only to the front spar. Nose ribs,
also called false ribs, are installed between each full rib to support the leading edge and give the wing its
correct aerodynamic shape.
nose section (aircraft reciprocating engine component). The forward section of an aircraft reciprocating
engine crankcase that contains the thrust bearing and propeller reduction gears.
NOTAM (Notice to Airmen). A notice containing information (not known sufficiently in advance to
publicize by other means) concerning the establishment, condition, or change in any component (facility,
service, or procedure of, or hazard in the National Airspace System), the timely knowledge of which is
essential to personnel concerned with flight operations.
notch sensitivity. A measure of the loss of strength of a material caused by the presence of a notch, or
V-shaped cut.
NOT gate (logic gate). A NOT gate is an inverter. A NOT gate has one input and one output, and the logic
condition at the output is always opposite the logic condition at the input. The symbol for a NOT gate is a
triangle (the symbol for a buffer), followed by a small circle to show that the output is inverted. See
inverter.
Notice to Airmen. See NOTAM.
Notice to Airmen Publication. See NTAP.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 407
no transgression zone. See NTZ.
NOZ (normal operating zone) (air traffic control). The operating zone within which aircraft flight
remains during normal independent simultaneous parallel ILS approaches.
nozzle. A tapered end of a duct through which fluid flows. The area of a converging nozzle decreases in the
　
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