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lean flameout (gas turbine engine operation). A condition in which the flame inside a gas turbine engine
goes out because there is not enough fuel for the amount of air flowing through the engine. Turbine engine
fuel controls are designed to measure the air flowing through the engine and adjust the fuel flow so a lean
flameout, or lean die-out, cannot occur. A lean flameout is also called a lean die-out.
lean mixture. A fuel-air mixture that contains more than 15 parts of air to 1 part of fuel, by weight.
least significant bit. See LSB.
least significant digit. See LSD.
Leclanche cell (batteries). Another name for a carbon-zinc cell. An ordinary carbon-zinc flashlight battery
is an example of a Leclanche cell. The negative terminal is the zinc can that forms the outside shell, and the
positive terminal is a carbon rod supported inside the can by the electrolyte.
The electrolyte is a moist paste of sal ammoniac (ammonium chloride), with manganese dioxide
mixed in it to absorb the hydrogen bubbles which form on the carbon rod as the battery is used.
LED (light emitting diode). An optoelectronic device that emits visible light when electrons pass through
it. P and N impurities are mixed with such chemical compounds as indium phosphide, gallium arsenide,
and zinc selenide to form a P-N junction.
When the P-N junction is reverse-biased (the negative terminal of the voltage source is connected
to the P-material), no electrons flow, and the LED remains dark. But when the diode is forward-biased (the
negative terminal of the voltage source connected to the N-material), electrons flow through the LED, and
it emits light.
lee side. The side of an island or mountain away from the direction from which the wind is blowing. The
lee side is the side sheltered from the wind.
lee wave (meteorology). Any stationary wave disturbance caused by a barrier in a fluid flow. In the
atmosphere, when sufficient moisture is present, lee waves are evidenced by lenticular clouds on the lee
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 350
side of mountain barriers. Lee waves are also called mountain waves or standing waves.
left-hand rule for electric motors. The rule for determining the direction of movement of a
current-carrying conductor in a magnetic field. Hold the left hand with the thumb, first finger, and second
finger extended so they are at right angles to each other. When the first finger points in the direction of the
lines of magnetic flux (from the north pole to the south pole), and the second finger points in the direction
of conventional current flow (from positive to negative), the thumb points in the direction the conductor
will move. This is also known as Fleming’s rule for electric motors.
left-hand rule for generators. Arrange the fingers of your left hand in such a way that the thumb,
forefinger, and second finger are at right angles to each other. The thumb points in the direction the
conductor in the armature is moving, the first finger points in the direction the magnetic flux passes over
the conductors (the flux leaves the north pole and enters the south pole), and the second finger points in the
direction the electrons are flowing in the armature conductors (from negative to positive).
left-hand rule for the direction of magnetic flux. Grasp a conductor with your left hand in such a way
that the thumb points in the direction electrons are moving (from the negative terminal of the power source
to the positive terminal). Your fingers encircle the conductor in the same direction as the lines of magnetic
flux.
left-hand rule for the polarity of an electromagnet. Grasp the coil of an electromagnet in such a way that
the fingers encircle the coil in the same direction electrons are flowing (from the negative terminal of the
power supply to the positive terminal). The thumb points to the north pole of the electromagnet formed by
the coil.
left-hand thread. The threads on a bolt or screw which are cut in such a direction that they wind in a
counterclockwise direction. A left-hand thread is turned to the left, to screw it in.
left-right indicator (navigation instrument). The course-deviation indicator used with a VOR navigation
system. See VOR.
legs of a right triangle. The two sides of a right triangle which are joined by the right angle.
LEMAC (leading edge of the mean aerodynamic chord). A reference for many of the aerodynamic
measurements used in aircraft design and operation. When the CG of an airplane is given in % MAC,
LEMAC is specified in inches from the datum to allow weight and balance computations to relate % MAC
to the datum. See MAC.
lenticular cloud (meteorology). A species of cloud whose elements have the form of more or less isolated,
　
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