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wing increases. At the same time, the lift produced by the raised wing decreases. This uneven lift, caused
by lateral stability, returns the airplane to level flight.
lateral vibration (helicopter operation). Vibration of a helicopter which causes the rotor to move back
and forth in a lateral plane. Lateral vibration is often caused by an out-of-balance main rotor.
lathe (machine tool). A metalworking or woodworking power tool used to change the shape or size of
cylindrically shaped objects. The material to be shaped is clamped horizontally in a chuck and is rotated.
The unclamped end of the material is steadied by the lathe tail stock. Cutting tools are fed into the material
from the side to remove unwanted material.
latitude. The angular measurement of distance on the surface of the earth, north and south of the equator.
Latitude is measured in degrees, minutes, and seconds, and parallels of latitude cut the earth into imaginary
parallel slices. The equator, which is zero degrees latitude, forms a belt around the center of the earth. The
north pole is 90° north latitude, and the south pole is 90° south latitude.
launching pad (rocket operation). A smooth, debris-free, nonflammable area from which rockets are fired
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 347
to launch them.
law of conservation of energy. One of the basic laws of physics stating that energy can be neither created
nor destroyed, but it can be changed from one form into other forms. Regardless of the form or forms into
which the energy is changed, the total amount of energy always remains the same.
lawrencium. A synthetic, radioactive chemical element. Lawrencium’s symbol is Lr, and its atomic
number is 103. One of the isotopes of lawrencium has a mass number of 257 and a half-life of eight
seconds.
layer (meteorology). With regard to sky cover, layers refer to clouds or other obscuring phenomena whose
bases are at approximately the same level. The layer may be continuous or composed of detached elements.
The term layer does not imply that a clear space exists between the layers or that the clouds or obscuring
phenomena composing them are of the same type.
lay line (flexible hose). A colored line that runs the length of a piece of flexible hose. A lay line is used to
indicate whether or not the hose was twisted during installation. If the lay line spirals around the hose, the
hose is twisted.
lay-up (composite structure). The placement of the various layers of resin-impregnated fabric in a mold in
the process of manufacturing a piece of laminated composite material.
L-band radar. Airborne radar which operates in the frequency range of 0.39 to 1.55 gigahertz. The
wavelength of L-band radar is between 77 and 19 centimeters.
LC circuit (electrical circuit). An alternating current circuit containing both inductance (L) and
capacitance (C). An LC circuit is considered to have no resistance.
In a purely capacitive circuit, changes in current lead changes in voltage by 90°. In a purely
inductive circuit, current changes lag 90° behind voltage changes. Because the effects of capacitance and
inductance are 180° apart, the total opposition to the flow of current in an LC circuit is the difference
between the capacitive and the inductive reactances.
LCD (liquid crystal display). A type of visual display used in digital watches, computers, calculators, and
some of the newer aircraft instruments. An extremely thin layer of a normally transparent liquid crystal
material is sealed between two sheets of glass. The outsides of the two pieces of glass are coated with an
electrically conductive oxide. The oxide coating on one side of the glass is etched to form the segments of
letters and numbers, and each segment is connected by a printed circuit lead to a connector at the edge of
the display.
The back of the display is covered with a reflecting material, and a piece of transparent polarizing
material is placed over the display to polarize the light passing through it. When light is polarized, all its
waves vibrate in the same plane.
When a voltage is placed between the oxide coatings on the two sides of the display, the
molecules in the liquid crystal material arrange themselves in such a way that the polarized light cannot
pass through them. The liquid crystal material under the segment having voltage on it shows up as though it
were black against the reflected background.
LCR circuit (electrical circuit). An alternating current circuit containing inductance (L), capacitance (C),
and resistance (R). The total opposition to the flow of current in an LCR circuit is the circuit impedance (Z),
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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航空术语词典Dictionary of Aeronautical Terms 中(105)
