NAVWEPS OO-BOY-BO  STABIUTY AND CoMml  damping in roll is generally referred to as  “autorotation.”  warning, and preserves lateral control effec-  tiveness at high angles of attack. Also, the  airplane must maintain positive static longi-  tudinal stability at high lift coe&ients and  should demonstrate satisfactory stall recovery  characteristics.  When the conventional airplane is stalk4  and some rolling-yawing displacement takes  place, the resulting autotiotation rolling mo-  ments and yawing moments start the airplane  into a self-sustaining rolling-yawing motion.  The autorotation rolling and yawing tenden-  cies of the airplane at high angles of attack  are the principal prospin moments of the  conventional airplane configuration and these  tendencies accelerate the airplane into the  spin until  some limiting  condition exists.  The stabilized spin is not necessaray  a simple  steady vertical spiral but may involve some  coupled unsteady oscillatory motion.  In order to visualize the principal effects of  an airplane entering a spin, suppose the air-  plane is subjected to the rolling and yawing  velocities shown in figure 4.32. The yawing  velocity to the right tends to produce higher  local velocities on the left wing than on the  right wing.  The rolling  velocity tends to  increase  the angle of attack for the downgoing  right wing (a,) and. decrease the angle of  attack for the upgoing left wing (al).  At  airplane angles of attack below the stall this  relationship produces  roll due to yaw, damping  in roll, etc., and some related motion of the  airplane in unstalled flight.  However, at  angles of attack above the stall, important  changes take place in the aerodynamic char-  acteristics.  An important characteristic of the mote  conventional airplane configuration is that the  spin shows a predominating contribution of  the autorotation tendency. Generally, the  conventional configuration has a spin motion  which is primarily rolling with moderate yaw.  High directional stability is favorable since it  will limit or minimize the yaw displacement  of the spinning airplane.  Figure 4.32 illustrates the aerodynamic  characteristics typical of a conventional air-  plane configuration, i.e., moderate or high  aspect ratio and little-if  any-sweepback.  Ifs this airplane is provided a rolling displace-  ment when at some angle of attack above  the stall, the upgoing wing experiences a  decrease  in angle of attack with a correspond-  ing increase  in C, and decrease  in C,,. In other  words, the upgoing wing becomes  less stalled.  Similarly, the downgoing wing experiences  an increase in angle of attack with a corre-  sponding decrease  in CL and increase  in CD. Es-  sentially, the downgoing wing becomes more  stalled.  Thus, the rolling motion is aided  rather than resisted and a yawing moment is  produced in the direction of roll.  At angles  of attack below stall the rolling motion is  resisted by damping in roll and adverse yaw  is usually present. At angles of attack above  the stall, the damping in roll is negative and  a rolling motion produces a rolling moment  in the direction of the roll.  This negative  The fundamental requirement of the spin is  that the airplane be placed at an excessive  angle of attack to produce the autorotation  rolling  and yawing  tendencies. Generally  speaking, the conventional airplane must be  stalled .before a spin can take place. This  relationship establishes a fundamental p&r-  ciple of recovery-the airplane must be un-  stalled by decreasing  the wing angle of attack.  The most dfective procedure for the conven-  tional configuration is to use opposite rudder  to stop the sideslip, then lower the angle of  attack with  the elevators. With  sufficient  rudder power this procedure will produce a  positive recovery with  a minimum loss of  altitude.  Care should be taken during pullout  from the ensuing dive to prevent excessive  angle of attack and entry into another spin.  It should be appreciated  that a spin is always  a possible corollary of a stall and the self-  sustaining motion of a spin will take place at 