Aerodynamic Center: The point along the wing chord where all changes in lift effectively take place.
Angle of Attack (AOA): The instantaneous angle between a reference line on the airplane (usually the
wing chord line) and the relative wind direction.
Center of Gravity: A point at which the weight of an object may be considered concentrated for weight
and balance purposes.
Departure: The phase of flight during which the airplane goes from controlled to uncontrolled flight.
Incipient Spin: The initial, transitory phase of spin characterized by yawing, rolling, and pitching motions
during which it is possible to begin to identify the spin mode. Rotational motion of an airplane following a
stall, but prior to the equalization of aerodynamic and inertial forces.
Inertia Coupling: Coupling results when some disturbance about one aircraft axis causes a disturbance
about another axis. There are two principal axis systems: (1) the aerodynamic and (2) the inertia. When
the inertia axis is inclined to the aerodynamic axis, rotation about the aerodynamic axis will create centrifu-
gal forces and cause a pitching moment. In this case, a rolling motion of the aircraft induces a pitching
moment through the action of inertia forces. This is inertia coupling. If the inertia axis and the aerody-
namic axis are aligned, no inertia coupling would result from a rolling motion.
Maneuvering (Cornering) Speed: Maximum speed where aerodynamic limit is reached prior to struc-
tural limit--aircraft at this speed cannot be overstressed.
Moment of Inertia
: With respect
to any given axis, the moment
is a measure
of the resistance