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 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, generally smooth lenses or almonds. Lenticular clouds most often appear in formations on the lee side of a mountain peak as a result of lee waves, and they remain nearly stationary with respect to the terrain.