Out-of-Control Flight
Aerodynamic Principles
RECOVERY FROM STEADY-STATE SPINS
To recover the aircraft from a spin, you need to do two things:
1. Reduce the yaw rate
2. Reduce the angle of attack
Reducing the yaw rate involves a number of factors. Principal among these factors are mass distribution,
which is by far the most important single factor, and tail design. You can usually use these two engineering
characteristics to predict the controls required for recovery and whether the aircraft has satisfactory
recovery capabilities.
As explained earlier, mass distribution significantly affects the spin characteristics of an aircraft. A fuse-
lage-loaded aircraft will spin in a flatter attitude, with yaw much more predominant than roll. In these
aircraft, rudder authority may not be sufficient to reduce the yaw rate enough to affect recovery and usually
requires a lateral stick input.
Tail design, or the position of the horizontal stabilizer may disrupt airflow across the rudder, decreasing
rudder effectiveness in the spin. Figure 14 shows examples of the effect that tail design has on rudder
effectiveness.
A parameter used to describe tail design is the tail damping power factor (TDPF) which is a measure of the
damping provided by the unshielded part of the rudder. Generally speaking, the higher the TDPF, the
more likely it is that the rudder will be an effective recovery control surface.
(9-98) Original
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