excessive angles of attack. Of course, a low 
speed airplane could be: designed to be spin- 
proof by making it stallproof. By limiting 
the amount of control deflection, the airplane 
may not have the longitudinal control power 
to trim to maximum lift angle of attack. Such 
a provision may be possible for certain light 
planes and commercial aircraft but would 
create an unrealistic and impractical limita- 
tion on the utility of a military airplane. 
The modern high speed airplane configura- 
tion is typified by low aspect ratio, swept wing 
planforms with relatively large yaw and pitch 
inertia. The aerodynamic characteristics of 
such a configuration are shown in figure 4.32. 
The lift curve (C, versus U) is quite shallow at 
high angles of attack and maximum lift is not 
clearly defined. When this type of airplane is 
provided a rolling motion at high angles of 
attack, relatively small changes in C, take 
place. When this effect is combined with the 
relatively short span of this type airplane, it is 
apparent that the wing autorotation contribu- 
tion will be quite weak and will not be a pre- 
dominating pro-spin moment. The relatively 
large changes in drag coefficient with rolling 
motion imply .a predominance of yaw for the 
spin of the high speed airplane configuration. 
Actually, various other factors contribute 
to the predominating yaw tendency for the 
spin of the modern airplane configuration. 
The static directional stability deteriorates at 
high angles of attack and may be so weak that 
extemely large yaw displacements result. In 
certain instances, very high angles of attack 
may bring such a decay in directional stability 
that a “slice” or extreme yaw displacement 
takes place before a true spin is apparent. At 
these high angles of attack, the adverse yaw 
due to roll and aileron deflection can be very 
strong and create large yaw displacements of 
the airplane prior to realizing a stall. 
The aircraft with the relatively large, long 
fuselage can exhibit a significant moment con- 
tribution from the fuselage alone. The cross 
flow pattern on the fuselage at high angles of 
NAWWEPS DO-BOT-BO 
STABILITY AND CONTROL 
attack is capable of producing pro-spin mo- 
ments of considerable magnitude which con- 
tribute to the self-sustaining nature of the 
spin. Also, the large distributed mass of the 
fuselage in rolling-yawing rotation contributes 
to inertia moments which flatten the spin and 
place the aircraft at extreme angles of attack. 
The spin recovery of the modern high speed 
airplane involves principles which are similar 
to those of the spin recovery of the conven- 
tional airplane. However, the nature of the 
spin for the modern configuration may involve 
specific differences in technique necessary to 
reduce the sideslip and angle of attack. The 
use of opposite rudder to control the sideslip 
and effect recovery will depend on the effective- 
ness of the rudder when the airplane is in the 
spin. At high positive angles of attack and 
high sideslip the rudder effectiveness may be 
reduced and additional anti-spin moments must 
be provided for rapid recovery. The deflection 
of ailerons into the spin reduces the autorota- 
tion rolling moment and can produce adverse 
yaw to aid the rudder yawing moment in 
effecting recovery. 
There may be many other specific differences 
in the technique necessary to effect spin re- 
covery . The effectiveness of the rudder during 
recovery may be altered by the position of 
elevators or horizontal tail. Generally, full 
aft stick may be necessary during the initial 
phase of recovery to increase the effectiveness 
of the rudder. The use of power during the 
spin recovery of a propeller powered airplane 
may or may not aid recovery depending on the 
specific airplane and the particular nature of 
the slipstream effects. The use of power during 
the spin recovery of a jet powered airplane 
induces no significant or helpful flow but does