AERONAUTICAL GLOSSARY : MOMENT - NONDIRECTIONAL RADIO BEACON (NDB)


MOMENT—The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG.

MOMENT ARM—The distance from a datum to the applied force.

MOMENT INDEX (OR INDEX)— A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of airplanes where heavy items and long arms result in large, unmanageable numbers.

MONOCOQUE—A shell-like fuselage design in which the stressed outer skin is used to support the majority of imposed stresses. Monocoque fuselage design may include bulkheads but not stringers.

MONOPLANES—Airplanes with a single set of wings.

MOVABLE SLAT—A movable auxiliary airfoil on the leading edge of a wing. It is closed in normal flight but extends at high angles of attack. This allows air to continue flowing over the top of the wing and delays airflow separation.

N1—Rotational speed of the low pressure compressor in a turbine engine.

N2—Rotational speed of the high pressure compressor in a turbine engine.

NACELLE—A streamlined enclosure on an aircraft in which an engine is mounted. On multiengine propeller-driven airplanes, the nacelle is normally mounted on the leading edge of the wing.

NATIONAL SECURITY AREAS— Airspace that consists of defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities.

NDB—See NONDIRECTIONAL RADIO BEACON.

NEGATIVE STATIC STABILITY—The initial tendency of an aircraft to continue away from the original state of equilibrium after being disturbed.

NEUTRAL STATIC STABILITY— The initial tendency of an aircraft to remain in a new condition after its equilibrium has been disturbed.

NONDIRECTIONAL RADIO BEACON (NDB)—An L/MF or UHF radio beacon transmitting non directional signals whereby the pilot of an aircraft equipped with direction finding equipment can determine the bearing to or from the radio beacon and "home" on or track to or from the station. When the radio beacon is installed in conjunction with the Instrument Landing System marker, it is normally called a Compass Locator.

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