Out-of-Control Flight
Aerodynamic Principles
So far, these characteristics are shared by both conventional and high-speed aircraft configurations. An
important characteristic true only of the conventional aircraft configuration is that the spin is primarily rolling
with a moderate yaw rate.
The modern high-speed aircraft configuration (F-14, F/A-18, etc.) is typified by a low-aspect ratio and a
swept-wing planform with relatively large yaw and pitch inertia. Figure 12 illustrates the aerodynamic
characteristics of this configuration.
The lift curve in Figure 12 is quite shallow at high angles of attack, and maximum lift is not clearly defined.
When this type of aircraft rolls at high angles of attack, relatively small changes in the lift coefficient take
place. The adverse yaw due to roll can be very strong prior to stall. When this effect is combined with a
low roll inertia, it is apparent that the roll moments will be relatively weak and will not predominate. The
drag curve, on the other hand, is increasingly steeper with increasing AOA. Thus, the relatively large
differential in drag with rolling motion creates a predominance of yaw in the spin.
CD
Down-Going
Wing
CL
and
CD
CL
Up-Going
Wing
, Angle of Attack
U
D
Figure 12: AERODYNAMICS OF HIGH-SPEED AIRCRAFT
In addition, aircraft with relatively large, long fuselages (F-14) exhibit a significant moment from the
fuselage which acts to flatten out the spin. This moment is capable of producing prospin moments of
considerable magnitude which contribute to the self-sustaining nature of the spin. The large distributed
mass of the fuselage in rolling-yawing rotation contributes to inertia moments which flatten the spin and
o
place the aircraft at extreme (80-90 ) angles of attack.
(9-98) Original
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