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landing/takeoff area is not required to have facilities for shelter, servicing, and receiving or discharging
passengers or cargo.
landing weight (aircraft specification). The maximum weight an aircraft is allowed to have for landing.
Landings put far more stress into an aircraft structure than takeoffs, and therefore large aircraft that fly for
long distances are allowed to have a greater weight for takeoff than for landing.
Airplanes approved for a greater takeoff weight than landing weight must have some method of
jettisoning enough fuel to bring the weight down to the allowable landing weight if the aircraft should have
to land before enough fuel has been consumed by the engines.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 344
landing wires (airplane structural components). Brace wires used to support the weight of the wings
during landing and when they are not producing lift. The landing wires of a biplane run from the center
section of the upper wing to the interplane strut on the lower wing.
landplane. An airplane with a wheeled landing gear that enables it to operate from a hard surface, rather
than from water or snow.
lanthanum. A soft, silvery-white, malleable, ductile, metallic, rare-earth chemical element. Lanthanum’s
symbol is La, its atomic number is 57, and its atomic weight is 138.91. Lanthanum is used as an element in
making glass for special lights.
lap belt. A name sometimes given to a seat belt or safety belt used to hold a person seated in an aircraft. A
lap belt passes across a person’s lap.
lap joint. A type of joint made between two pieces of material in which one piece is lapped over the other
and the two fastened together. Lap joints are used to join sheets of metal by welding, riveting, or bolting.
Lap joints are also used for joining sheets of wood, paper, or cloth with adhesives.
lapping (machining operation). A method of producing a close fit between two metal parts by rubbing
them together with a very fine abrasive lapping compound between them. The fit of a lapped joint is
checked by removing all the lapping compound and lightly coating one of the surfaces with Prussian blue
transfer dye. The parts are reassembled and rubbed together. If the parts fit as they should, the Prussian blue
will transfer evenly to the part that was not covered. If not enough blue transfers, more lapping is required.
lapping compound. A very fine abrasive paste used to wear away a metal surface to make it smooth, and
to assure a perfect fit between two machined surfaces. Lapping compound is similar to valve-grinding
compound.
laps (metal defects). A type of metal defect produced in the rolling mill. Ridges or bulges on the surface of
the metal are folded over and forced down into the metal as it is being rolled. Laps decrease the strength of
the metal.
lapse rate (meteorology). The rate of decrease of an atmospheric variable with height. Lapse rates often
refer to a decrease in temperature with height.
lap winding (electrical armature). A method of connecting the armature coils in a DC generator or motor.
The ends of each coil on the armature are connected to the next adjacent commutator segment, and the coils
lap over each other. Lap winding differs from wave winding in which the ends of the coils are attached to
segments on the opposite side of the commutator.
large aircraft. 14 CFR Part 1: “Aircraft of more than 12,500 pounds, maximum certificated takeoff
weight.”
large calorie (C). A unit of heat energy. One large calorie, also called a kilocalorie, is the amount of heat
energy needed to raise the temperature of one kilogram of water one degree Celsius. One large calorie is
equal to 1,000 small calories.
LASCR (light-activated silicon controlled rectifier). A semiconductor device having two P-sections and
two N-sections. Light falling on the LASCR produces gate current that triggers it into a state of conduction.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 345
laser. A coined word meaning Light Amplification by Stimulated Emission of Radiation. A laser changes
incoherent light, light whose vibrations do not have any consistent phase relationship, into coherent light,
light whose vibrations are all in phase.
The light beam from a laser is highly concentrated, very narrow, and has an extremely high
intensity. High-power lasers produce a great deal of heat in an extremely small area, and laser technology is
opening new doors in all aspects of science.
laser memory (computer memory). A method of storing a large amount of digital information
permanently and inexpensively on a disk similar to but smaller than a phonograph record. A high-power
　
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