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laser (see laser) burns extremely small pits into the reflective surface of a disk to write, or record, digital
data on the disk. The information stored on the disk is read by the reflection or the lack of reflection of a
low-power laser shone on the surface. A reflection is read as a logic one, and a space where there is no
reflection, an area caused by a pit, is read as a logic zero.
The fact that billions of bits can be stored on a relatively small disk makes laser memory an
inexpensive method of storing video programs.
laser printer. A type of printer used to produce a hard copy of the information being processed by a
computer. A laser (see laser) shines a series of dots of light in a matrix pattern onto the surface of the paper
as it moves in front of the print head, and each dot of light leaves the paper with an electrostatic charge.
A dust of metallic powder, called toner, is blown across the paper, and some of it sticks to the
charged areas. None, however, sticks to the uncharged portion of the paper. The paper with the powder
sticking to the charged areas passes over a heater, which fuses, or melts, the powder into the paper to form
a permanent image.
laser tachometer. A highly accurate tachometer that shines a laser beam on the rotating element and senses
the reflection from a reflective tape or contrasting mark. The reflected laser beam is converted into
electrical pulses which are counted and displayed on a monitoring instrument.
laser welding. A method of welding by the heat produced by a laser beam. The high-intensity,
concentrated heat allows the welding of exotic alloys that cannot be welded by other methods.
last-chance filter (gas turbine engine component). An oil filter installed in the lubricating system of a gas
turbine engine just ahead of the jets that spray oil onto the bearings. These filters trap any contaminants that
get past the main system filters and prevent the oil jets becoming clogged.
Last-chance filters cannot be serviced during normal engine maintenance. They are cleaned only
when the engine is disassembled for overhaul.
latching relay (locking relay). A relay that, once energized, remains in its energized condition after the
current stops flowing in its coil. When the relay is energized, the contacts are locked in the energized
position by a mechanical latch. A mechanical release must be actuated to allow the relay to return to its
de-energized condition.
Latching relays are being replaced to a great extent by solid-state flip-flop circuits.
latent heat. Heat added to a material which changes its physical state, but does not change its temperature.
When a pan of water is put on a hot stove and heat is added to it, its temperature rises — but in standard
conditions, only until it reaches 100°C. Heat which changes the temperature of water is called sensible heat.
If additional heat is added to the water, it will boil away, or change from liquid water into water
vapor, but its temperature will not change. Heat added to water after it begins to boil is called latent heat —
more correctly, latent heat of evaporation, or latent heat of vaporization. When water vapor is cooled until
it condenses into liquid water, the latent heat which caused the evaporation is given up by the water and
absorbed by the surrounding air.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 346
latent heat of condensation. Heat released during the change of state that occurs when water vapor
changes into liquid water.
latent heat of fusion. Heat absorbed during the change of state that occurs when solid water (ice) changes
into liquid water.
latent heat of sublimation. Heat absorbed during the change of state that occurs when ice changes directly
into water vapor without passing through the liquid state.
latent heat of vaporization. Heat absorbed during the change of state in which liquid water is changed into
water vapor.
lateral axis of an airplane. An imaginary line passing through the center of gravity of an airplane and
extending across the airplane parallel to a line joining the wing tips. The lateral axis is also called the pitch
axis, and movement of the elevators rotates an airplane about its lateral axis.
lateral separation (air traffic control). The lateral spacing of aircraft at the same altitude by requiring
operation on different routes or in different geographic locations.
lateral stability (aircraft stability). The stability of an airplane about its longitudinal axis, the axis passing
through an airplane from nose to tail. If an airplane is disturbed from level flight so that one wing drops,
lateral stability returns it to a level-flight attitude.
When a wing drops, the airplane begins to slip to that side, and the lift produced by the lowered
　
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