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atomic number is 36, and its atomic weight is 83.80. Krypton is used to fill fluorescent lamps.
L
LAAS (low altitude alert system). An automated function of the ground radar that alerts the controller
when a Mode C transponder-equipped aircraft on an IFR flight plan is below a predetermined minimum
safe altitude.
labyrinth seal. A type of air and/or oil seal used around the main-shaft bearings in a gas turbine engine.
The seal consists of a series of rotating blades that almost contact the seal land. A small amount of air flows
between the seal and the land and prevents oil flowing past the seal.
lacing cord (aircraft fabric covering material). A strong cotton, linen, or synthetic fiber string used to
lace fabric to an aircraft structure.
Lacing cord is also called rib-stitching cord.
lacquer (finishing material). A material used to decorate and protect a surface. Lacquer is made of a film
base, solvents, plasticizers, and thinners. The film base forms a tough film over the surface when it dries.
The solvents dissolve the film base so it can be applied as a liquid. The plasticizers give the film base the
needed resilience, and the thinners dilute the lacquer so it can be applied with a spray gun.
Lacquer is sprayed on the surface as a liquid, and as soon as the solvents and the thinner evaporate,
the film base remains as a tough, decorative coating.
lagging (lubrication system component). A type of insulation wrapped around some of the lines in an
aircraft engine lubrication system to keep it from losing heat in the oil to the outside air.
lagging current (electrical current). Current flowing in an AC circuit that has more inductive reactance
than capacitive reactance. Voltage changes occur in an inductive circuit before current changes, and the
current is said to lag the voltage.
LAHSO (land-and-hold-short operations) (air traffic control). Operations which include simultaneous
takeoffs and landings and/or simultaneous landings when a landing aircraft is able and is instructed by the
controller to hold short of the intersecting runway/taxiway or designated hold-short point. Pilots are
expected to promptly inform the controller if the hold-short clearance cannot be accepted.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 342
lambert (luminance). The unit of luminance (photometric brightness) that is the same as 1/π (0.3183)
candela per square centimeter.
laminar flow (aerodynamics). A type of airflow over an airfoil in which the air passes over the surface in
smooth layers with a minimum of turbulence. With most airfoils, there is a layer of air adjacent to the
surface that flows in a random fashion, even sometimes reversing its direction of flow. This is called the
boundary layer.
A laminar-flow airfoil is designed in such a way that the boundary layer has a minimum thickness,
and nearly all the air flows in smooth layers. Laminar flow of the air decreases the drag produced by the
airfoil.
laminated core (electrical machinery). The core of an electrical transformer made up of a stack of thin
sheets, or laminations, of soft iron or a special highly permeable steel, insulated from each other by an
oxide or varnish coating.
Eddy currents are induced into the cores of transformers by alternating current flowing in the
windings surrounding them, and these eddy currents produce heat and cause electrical losses. The high
resistance of the laminated core opposes the flow of eddy current and minimizes the losses.
laminated plastic material. A type of reinforced plastic resin made by laminating, or stacking together,
layers of cloth, paper, or wood that are impregnated with plastic resin. The layers of the material are forced
together by pressure, and the resin is cured with heat.
laminated wood. A type of wood product made by gluing together several thin strips of wood. In
laminated wood, the grain of all the pieces runs in the same direction. A wooden propeller is made of
several pieces of hardwood laminated together.
lampblack. A form of almost pure carbon made by burning oil or coal in an atmosphere in which there is
not enough oxygen for complete combustion. Lampblack is used for making brushes for electric motors
and generators, for the graphite in lead pencils, for the pigment in paint, and for mixing with rubber for
making tires.
land (reciprocating engine piston component). The portion of a piston between the ring grooves.
land (splined shaft). The portion of a splined shaft between the grooves.
land-and-hold-short operations. See LAHSO.
land breeze (meteorology). A coastal breeze blowing from land to sea. Land breezes, which normally
blow at night, are caused by a temperature difference when the sea surface is warmer than the adjacent land.
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航空术语词典Dictionary of Aeronautical Terms 中(101)
