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beneficial. Such a situation exists for airplanes fitted with wing tip tanks. Once
again, the smal.ler the numerical value of the ratio Iyllx, the greater will be the
effect of out-spin ailerons in aiding the recovery process.
    Application of the opposite rudder slows down the spin rate and steepens the
spin attitude. While the spin rate is decreasing because of the opposite rudder,
the elevator becomes increasingly effective in assisting the recovery. However, an
opposite sequence of operation,i.e., one in which the elevator movement preceeds
the rudder movement,is decidedly objectionable and may result in an aggravated
spin, often resulting in higher rate of rotation and, for some configurations, it may
even result in the development of fiat spin.
     For some airplanes, it may be difficult to recover from a flat spin using normal
recover)r techniques. Such airplanes often make use of a spin-chute to effect a
recovery from flat spin (Fig. 7.23). The opening of the spin-chute generates a nose-
down pitching moment in addition to slowing the yaw rate. When the yaw rate
decreases, application offorward stick (elevator up) results in a successful rjecovery.
   A typical trme history of a spin entry, developed spin, and recovery is shown
in Fig. 7.24,23 The prospin controls for this aircraft consist of fulI-aft stick, full-
rudder deflection in the direction of spin, and full-aileron deflection against the
spin. As shown in Fig. 7.24, full-aft stick is gradually applied from 10 to 17 s. At
about 17 s, full right rudder (8r  < O) for right spin and antispin aileron (8a  >  o,
right aileron to roll to left) are applied. For the next 5-6 s, the angle of attack and
yaw rate build up. Around 25 s, the airplane has entered into a right spin, but it
takes about two turns to establish a steady~state spin as indicated by a steady value
of angle of attack around 52 to 55 deg and a steady value of yaw rate around  110
deg/s. After six complete turns, recover)t controls (opposite rudder, stick forward,
o-} //
o /t
-
   .l -
     -
t //
-
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PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
Fig.7.23   Parachute deployment for spin recovery.
and ailerons neulral) are apphed. The aircraft recovers successfully and retums to
normal steady-level fiight within next 5-10 s.
7.7   Geometrical Modifications to Improve Spin Resistance
7.7.1   Modification to Wing
      ~e autorotational characteristics of the wing have a large impact on the stall-
 spin behavior of the airplane. Eliminating or reducing the autorotative tendency of
the wings can greatly improve the spin resistance of the airplane.
    One modification to the wing that has been successfully tested by NASA on a
number of general aviation airplanes is the reshaping of the wing leading edge of
 the outer wing panels* The modification consists of a chord extension of about 3o/o,
 a drooped-nose airfoil design, and an abrupt discontinuity between the undrooped
 inner wing and drooped outer wing.23-25 An application of this method to a general
aviation airj[,lane is shown in Fig. 7.25. The basic airplane (Fig. 7.25a) had an
 untwisted wing with a NACA 642415 airfoil section. The modification extended
from 57-95% semispan locations as shown in Fig. 7.25b. The variation of the
 resultant force coefficient of the basic airplane and that with the modification are
 shown in Fig. 7.25c. We observe that the basic airplane exlubits the usual drop in
 the resultant force coefficient at stall (around u - 20 deg) thatleads to instabilitjr
v.
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 ..
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 r.
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INERTIA COUPLING AND SPIN
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