GLOSSARY ABSOLUTE ALTITUDE —The act- ual distance an object is above the ground. ANGLE OF ATTACK —The angle between the airfoil’s chord line and the relative wind. BLADE FLAP —The ability of the rotor blade to move in a vertical direc- tion. Blades may flap independently or in unison. BLADE GRIP —The part of the hub assembly to which the rotor blades are attached, sometimes referred to as blade forks. ANTITORQUE PEDAL —The pedal used to control the pitch of the tail rotor or air diffuser in a NOTAR ® system. ADVANCING BLADE —The blade moving in the same direction as the helicopter or gyroplane. In rotorcraft that have counterclockwise main rotor blade rotation as viewed from above, the advancing blade is in the right half of the rotor disc area during forward movement.  ANTITORQUE ROTOR —See tail rotor. BLADE LEAD OR LAG —The fore and aft movement of the blade in the plane of rotation. It is sometimes called hunting or dragging. BLADE LOADING —The load imposed on rotor blades, determined by dividing the total weight of the hel- icopter by the combined area of all the rotor blades. ARTICULATED ROTOR —A rotor system in which each of the blades is connected to the rotor hub in such a way that it is free to change its pitch angle, and move up and down and fore and aft in its plane of rotation. AIRFOIL —Any surface designed to obtain a useful reaction of lift, or neg- ative lift, as it moves through the air. AGONIC LINE —A line along which there is no magnetic variation. BLADE ROOT —The part of the blade that attaches to the blade grip. AUTOPILOT —Those units and components that furnish a means of automatically controlling the aircraft. AIR DENSITY —The density of the air in terms of mass per unit volume. Dense air has more molecules per unit volume than less dense air. The densi- ty of air decreases with altitude above the surface of the earth and with increasing temperature. BLADE SPAN —The length of a blade from its tip to its root. AUTOROTATION —The condition of flight during which the main rotor is driven only by aerodynamic forces with no power from the engine. AIRCRAFT PITCH —When refer- enced to an aircraft, it is the move- ment about its lateral, or pitch axis. Movement of the cyclic forward or aft causes the nose of the helicopter or gyroplane to pitch up or down. AXIS-OF-ROTATION —The imagi- nary line about which the rotor rotates. It is represented by a line drawn through the center of, and per- pendicular to, the tip-path plane. BLADE STALL —The condition of the rotor blade when it is operating at an angle of attack greater than the maximum angle of lift. BLADE TIP —The further most part of the blade from the hub of the rotor. BLADE TRACK —The relationship of the blade tips in the plane of rota- tion. Blades that are in track will move through the same plane of rotation. BASIC EMPTY WEIGHT —The weight of the standard rotorcraft, operational equipment, unusable fuel, and full operating fluids, including full engine oil. AIRCRAFT ROLL —Is the move- ment of longitudinal axis. Movement of the cyclic right or left causes the helicop- ter or gyroplane to tilt in that direction. BLADE TRACKING —The mechan- ical procedure used to bring the blades of the rotor into a satisfactory relation- ship with each other under dynamic conditions so that all blades rotate on a common plane. BLADE CONING —An upward sweep of rotor blades as a result of lift and centrifugal force. AIRWORTHINESS DIRECTIVE —When an unsafe condition exists with an aircraft, the FAA issues an air- worthiness directive to notify con- cerned parties of the condition and to describe the appropriate corrective action. BLADE DAMPER —A device attached to the drag hinge to restrain the fore and aft movement of the rotor blade. BLADE TWIST —The variation in the angle of incidence of a blade between the root and the tip.  BLOWBACK —The tendency of the rotor disc to tilt aft in forward flight as a result of flapping. BLADE FEATHER OR FEATH- ERING —The rotation of the blade around the spanwise (pitch change) axis. ALTIMETER —An instrument that indicates flight altitude by sensing pressure changes and displaying alti- tude in feet or meters. G-1