Aviation Maintenance Terms beginning with L
L/D ratio
A measure of efficiency of an airfoil. It is the ratio of the lift to the total drag at a specified angle of attack.
Labyrinth seal
A type of air and/or 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 to prevent oil flowing past the seal.
Laminar flow
Airflow in which the air passes over the surface in smooth layers with a minimum of turbulence.
Laminate
A product obtained by bonding two or more laminae of the same material or of different materials.
Laminated wood
A piece of wood built up of plies or laminations that have been joined either with glue or with mechanical fastenings. The term is most frequently applied where the plies are too thick to be classified as veneer and when the grain of all plies is parallel.
Land (piston)
The portion of a piston between the ring grooves.
Land (splined shaft)
The portion of a splined shaft between the grooves.
Landing gear extended speed
The maximum speed at which an aircraft can be safely flown with the landing gear extended.
Landing gear operating speed
The maximum speed at which the landing gear can be safely extended or retracted.
Landing gear warning system
A system of lights used to indicate the condition of the landing gear. A red light illuminates when any of the gears are in an unsafe condition; a green light shows when all of the gears are down and locked, and no light is lit when the gears are all up and locked. An aural warning system is installed that sounds a horn if any of the landing gears are not down and locked when the throttles are retarded for landing.
Large aircraft
Aircraft of more than 12,500 pounds, maximum certificated takeoff weight.
Laser tachometer
A highly accurate tachometer that shines a laser beam on a rotating element that has reflective tape or a contrasting mark. The reflected laser beam is converted into electrical pulses which are counted and displayed on a monitoring instrument.
Last-chance oil filter
A small filter installed in the oil line to the bearing jet in a gas turbine engine. This filter traps any contaminants that have passed the main filter and holds them until the engine is disassembled for overhaul.
Latency
The time incurred between two particular interfaces. Total latency is the delay between the time of a measurement and the time that the measurement is reported at a particular interface (the latter minus the former). Components of the total latency are elements of the total latency allocated between different interfaces. Each latency component will be specified by naming the interfaces between which it applies.
Latent heat
Heat that is added to a material that causes a change in its state without changing its temperature.
Lateral axis
An imaginary line, passing through the center of gravity of an airplane, and extending across it from wing tip to wing tip.
Lateral stability
The stability about the longitudinal axis of an aircraft; the rolling stability, or the ability of an airplane to return to level flight due to a disturbance that causes one of the wings to drop.
Lay-up
The placement of the various layers of resin- impregnated fabric in the mold for a piece of laminated composite material.
Leading edge
The edge of the blade that leads the direction of rotation and first encounters the air.
Leading edge
The thick edge at the front of a propeller blade.
Leakage field
The magnetic field forced out into the air by the distortion of the field within a part, caused by the presence of a discontinuity or change in section configuration.
Lean die-out
A condition in which the fire in a gas turbine engine goes out because the air/fuel mixture ratio is too lean to sustain combustion.
Lean mixture
A air/fuel mixture that contains more than 15 parts of air to 1 part of fuel, by weight.
Lever
The simplest machine. There are three basic parts in all levers: the fulcrum “F,” a force or effort “E,” and a resistance “R.” Load cell. A component in an electronic weighing system that is placed between the jack and the jack pad on the aircraft. The load cell contains strain gauges whose resistance changes with the weight on the cell.
Light-sport aircraft
An aircraft, other than a helicopter or powered-lift that, since its original certification, has continued to meet the following: (1) A maximum takeoff weight of not more than— (i) 1,320 pounds (600 kilograms) for aircraft not intended for operation on water; or (ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water. (2) A maximum airspeed in level flight with maximum continuous power (VH) of not more than 120 knots CAS under standard atmospheric conditions at sea level. (3) A maximum never-exceed speed (VNE) of not more than 120 knots CAS for a glider. (4) A maximum stalling speed or minimum steady flight speed without the use of lift-enhancing devices (VS1) of not more than 45 knots CAS at the aircraft’s maximum certificated takeoff weight and most critical center of gravity. (5) A maximum seating capacity of no more than two persons, including the pilot. (6) A single, reciprocating engine, if powered. (7) A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider. (8) A fixed or feathering propeller system if a powered glider. (9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a gyroplane. (10) A nonpressurized cabin, if equipped with a cabin. (11) Fixed landing gear, except for an aircraft intended for operation on water or a glider. (12) Fixed or retractable landing gear, or a hull, for an aircraft intended for operation on water. (13) Fixed or retractable landing gear for a glider.
Lightening hole
A hole cut in a piece of structural material to get rid of weight 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, and the edges of the hole are flanged to give it rigidity. A piece of metal with properly flanged lightening holes is more rigid than the metal before the holes were cut.
Lighter-than-air aircraft
Aircraft that can rise and remain suspended by using contained gas weighing less than the air that is displaced by the gas.
Lightning strikes
Damage to blades caused by lightning usually manifested by localized burning, discoloration, melted metal, and/or pits.
Line boring
A method of assuring concentricity of bored holes. A boring bar extends through all of the holes and cuts the inside diameters so they all have the same center.
Linear actuator
A fluid power actuator that uses a piston moving inside a cylinder to change pressure into linear, or Lacquer. A finishing material made of a film base, solvents, straight-line, motion. plasticizers, and thinners. The film base forms a tough film over the surface when it dries. The solvents dissolve the film Linear change. A change in which the output is directly base so it can be applied as a liquid. The plasticizers give proportional to the input, 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 when the solvents and thinners evaporate, the film base remains as a tough decorative and protective coating.
Link rod
The rod in a radial engine that connects one of the piston wrist pins to a knuckle pin on the master rod. Also called articulating rods.
Linter
The short fiber left on the cotton seed after ginning.
Liquid cooling
The removal of unwanted heat from an aircraft engine by transferring the heat into a liquid and then passing the heated liquid through a liquid-to-air heat exchanger (radiator) to transfer the heat into the ambient air.
Load factor
The ratio of a specified load to the total weight of the aircraft. The specified load is expressed in terms of any of the following: aerodynamic forces, inertia forces, or ground or water reactions.
Loaded Radius
The distance from the axle centerline to a flat surface for a tire initially inflated to the rated inflation pressure and then loaded to its rated load against the flat surface.
Loadmeter
A current meter used in some aircraft electrical systems to show the amount of current the generator or alternator is producing. Loadmeters are calibrated in percent of the generator rated output.
Localizer
That section of an ILS that produces the directional reference beam.
Localizer
The portion of an ILS (Instrument Landing System) that directs the pilot along the center line of the instrument runway.
Lodestone
A magnetized piece of natural iron oxide.
Logic flow chart
A type of graphic chart that can be made up for a specific process or procedure to help follow the process through all of its logical steps.
Long-range communication system (LRCS)
A system that uses satellite relay, data link, high frequency, or another approved communication system which extends beyond line of sight.
Long-range navigation system (LRNS)
An electronic navigation unit that is approved for use under instrument flight rules as a primary means of navigation, and has at least one source of navigational input, such as inertial navigation system or global positioning system.
Longitudinal axis
An imaginary line, passing through the center of gravity of an airplane, and extending lengthwise Laminated wood. A type of wood made by gluing several through it from nose to tail.
Longitudinal magnetism
A method of magnetizing through a solenoid, or coil, that encircles the part so the lines of magnetic flux pass lengthwise through the part. Longitudinal magnetism makes it possible to detect faults that extend across the part.
Longitudinal magnetization
The magnetic field is produced in a direction parallel to the long axis of the part. This is accomplished by placing the part in a solenoid excited by electric current.
Longitudinal stability
Stability of an aircraft along its longitudinal axis and about its lateral axis. Longitudinal stability is also called pitch stability.
Longitudinal stability
The tendency for an aircraft nose to pitch up or pitch down, rotating around the lateral axis (wingtip to wingtip)
Low bypass ratio engine
A turbofan engine whose bypass ratio is less than 2:1.
Low unmetered fuel pressure
Pressure in a Teledyne- Continental fuel injector pump that is adjusted by the relief valve.
Low-pressure compressor
The first-stage compressor in a dual-spool gas turbine engine. The low-pressure compressor is called the N1 compressor and its speed is not governed. It seeks its own best speed as the atmospheric conditions change so it can furnish a relatively constant mass of air to the inlet of the second-stage compressor.
Lubber line
A reference on a magnetic compass and directional gyro that represents the nose of the aircraft. The heading of the aircraft is shown on the compass card opposite Left-right indicator. The course-deviation indicator used the lubber line with a VOR navigation system.
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