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lift that varies with the shape of the airfoil and the angle of attack. The lift coefficient (CL) is obtained from
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wind tunnel data and is plotted on a set of airfoil characteristic curves.
lift fan. A special type of turbofan engine installed on an aircraft in such a way that it can be pivoted to
direct its thrust in a vertical direction. Lift fans are used on some types of V/STOL (vertical, or short
takeoff and landing) aircraft.
lifting body (aerodynamic shape). The shape of the fuselage of an aircraft that produces lift. Such a
device can fly without wings.
lifting condensation level (meteorology). The level at which a parcel of unsaturated air lifted
dry-adiabatically becomes saturated.
lift wires (airplane structural components). Wires installed between the wings of a biplane to support the
wings against the forces of lift. Lift wires run from the inboard end of the lower wing to the interplane
struts on the upper wing. Lift wires are also called flying wires.
light. The portion of the electromagnetic spectrum that produces waves visible to the naked eye. The
wavelengths of visible light range from 3,800 to 7,800 Angstroms.
light aircraft. As defined by the Federal Aviation Administration, a light aircraft is one having a maximum
certificated takeoff weight of less than 12,500 pounds.
light chopper (optoelectronic device). An optoelectronic device that interrupts a beam of light being
shone on a photoelectric cell. The chopper changes the steady DC output of the photoelectric cell into
pulsating DC that can be easily amplified.
lighted airport. An airport with runway and obstruction lighting available.
light-emitting diode. See LED.
light ends (petroleum products). The portions of a petroleum product that boil off first in the process of
fractional distillation. Butane is an example of one of the light ends of petroleum fuel.
lightening hole (aircraft structure). A hole cut in a piece of structural material to get rid of weight, or
lighten the structure, without losing any strength. A hole several inches in diameter may be cut in a piece of
metal at a point where the metal is not needed for strength; for example, in the web of a wing rib. The
edges of the hole are flanged (bent outward) to give the metal rigidity. A piece of metal with flanged
lightening holes is more rigid than the metal before the lightening holes were cut.
lighter-than-air aircraft. A device sustained in the air by aerostatic lift. Balloons and dirigibles are
examples of lighter-than-air aircraft made of materials that are heavier than air, but are filled with a gas (or
with hot air) that is less dense than the surrounding air.
When a gas-filled aircraft displaces a greater weight of air than it weighs, aerostatic lift is
produced, and the aircraft rises into the air. 14 CFR Part 1: “Aircraft that can rise and remain suspended by
using contained gas weighing less than the air that is displaced by the gas.”
light gun (air traffic control). A hand-held directional light signaling device, which emits a brilliant
narrow beam of white, green, or red light as selected by the tower controller. The color and type of light
transmitted is used to approve or disapprove anticipated pilot action when radio communication is not
available.
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lightning (atmospheric condition). A bright flash of light in the atmosphere caused by a discharge of
electricity from one cloud to another or between a cloud and the earth. Lightning is actually an extremely
large spark.
lightplane (type of airplane). A simple, single-engine airplane, used for training or noncommercial flying.
light sensitive diode (semiconductor device). A semiconductor diode whose ability to conduct in a
forward direction is determined by the amount of light falling on the PN junction.
light year. The distance traveled by light in one year. The light year is a unit of measurement commonly
used in discussing astronomy and is equal to 5.879 trillion (5.879 x 1012 miles).
lime grease. A semisolid lubricant made by mixing oil with calcium carbonate. Lime grease is more
suitable for use around water than grease having a sodium carbonate base.
limit switch (electrical switch). A precision electrical switch, used to turn a mechanism on or off when
some part of the mechanism reaches a specific position or location. Limit switches are actuated by a very
short movement of the actuating control, and they actuate at exactly the same position of the control each
time.
Lindberg fire detection system. A type of aircraft fire detection system that detects either a fire or a
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航空术语词典Dictionary of Aeronautical Terms 中(109)
