Out-of-Control Flight
Aerodynamic Principles
INSTRUMENT INDICATIONS
Three instruments provide all the information necessary for recognition and recovery; the fourth is for
obvious safety considerations:
1. AOA indicator
2. Airspeed indicator
3. Turn needle
4. Altimeter
AOA Indicator
AOA primarily determines post-stall gyration, whether the spin mode is upright or inverted, and spin
recovery.
Airspeed Indicator
The airspeed in a steady-state spin will be stable, or oscillating about a constant airspeed. An airspeed
above or below a characteristic range for the type of aircraft, or a steadily increasing airspeed, indicates
that the aircraft is not in a steady-state spin.
Turn Needle
The turn needle will be fully pegged in the direction of the spin. It does not provide other information about
the phase of flight; the needle may also be fully pegged during a post-stall gyration or a high-speed spiral,
for example. The turn needle, however, must be relied on to indicate the direction of the rotation, since
you can misinterpret visual cues during the extreme disorientation that often accompanies out-of-control
flight.
Altimeter
You must reference the altimeter to determine how much time is available for recovery. If you have not
seen indications of recovery by 10,000 ft AGL, eject.
THE ERECT SPIN
The motion of an aircraft in a spin can involve many complex aerodynamic and inertial moments and
forces. However, there are certain fundamental relationships regarding spins with which you must be
familiar. The two primary factors which must be present for an aircraft to spin:
1. Stalled AOA
2. Sideslip or yaw rate
Figure 10 illustrates the rotational velocities experienced by an aircraft in a spin. Notice that the increased
AOA on the down-going wing produces decreased lift and increased drag relative to the up-going wing.
(Remember, up-going and down-going are in the context of rolling moments which are in relation to the
longitudinal axis of the aircraft, not the surface of the planet.) The increased drag on the down-going wing
perpetuates yaw of the spin while the decreased lift on the down- going wing perpetuates the roll of the
spin. With sustained yaw and roll rate, the aircraft is on the way to a steady-state spin in which there is no
overall increase in spin velocity. It is true that velocity may increase and decrease in an oscillatory spin,
but these oscillations are cyclical.
(9-98) Original
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