LIFT—One of the four main forces acting on a rotorcraft. It acts perpendicular to the relative wind.
LOAD FACTOR—The ratio of a specified load to the total weight of the aircraft.
MARRIED NEEDLES—A term used when two hands of an instrument are superimposed over each other, as on the engine/rotor tachometer.
MAST—The component that supports the main rotor.
MAST BUMPING—Action of the rotor head striking the mast, occurring on underslung rotors only.
MINIMUM LEVEL FLIGHT SPEED—The speed below which a gyroplane, the propeller of which is producing maximum thrust, loses altitude. 
 

NAVIGATIONAL AID (NAVAID)
—Any visual or electronic device, airborne or on the surface, that provides point-to-point guidance information, or position data, to aircraft in flight.
NIGHT—The time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac.
 
 

NORMALLY ASPIRATED ENGINE
—An engine that does not compensate for decreases in atmospheric pressure through turbocharging or other means.
ONE-TO-ONE VIBRATION—A low frequency vibration having one beat per revolution of the rotor. This vibration can be either lateral, vertical, or horizontal.
OUT OF GROUND EFFECT (OGE) HOVER—Hovering greater than one diameter distance above the surface. Because induced drag is greater while hovering out of ground effect, it takes more power to achieve a hover out of ground effect.
 

PARASITE DRAG—The part of total drag created by the form or shape of helicopter parts.
PAYLOAD—The term used for passengers, baggage, and cargo.
PENDULAR ACTION—The lateral or longitudinal oscillation of the fuselage due to it being suspended from the rotor system.
PITCH ANGLE—The angle between the chord line of the rotor blade and the reference plane of the main rotor hub or the rotor plane of rotation.
PREROTATION—In a gyroplane, it is the spinning of the rotor to a sufficient r.p.m. prior to flight.
PRESSURE ALTITUDE—The height above the standard pressure level of
29.92 in. Hg. It is obtained by setting
29.92 in the barometric pressure window and reading the altimeter.
PROFILE DRAG—Drag incurred from frictional or parasitic resistance of the blades passing through the air. It does not change significantly with the angle of attack of the airfoil section, but it increases moderately as airspeed increases.
RESULTANT RELATIVE WIND— Airflow from rotation that is modified by induced flow.
RETREATING BLADE—Any blade, located in a semicircular part of the rotor disc, where the blade direction is opposite to the direction of flight.