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666 PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
SPIN RECOVERY
PARACtfUIE SYSIEM
Test atrplane A (Dimenslons given tn
feet).
a)
flg.7 25 An example ofwingleading-edge modification.n.z4
in roll and autorotation, whereas the modrfied configuration does not exhibit such
tendency for the range of angle of attack included in Fig. 7.25c.
The basic aircraft exhibited two spin modes, one at a = 46 deg and another at
ce = 61 deg. However,the modified airplane was highly resistant to enter the spin.25
The aerodynamic phenomenon responsible for tlus beneficial effect is a strong
vortex-type flow that originates at the leading edge discontinuity and tails over
the upper surface of the wing functiorung like an aerodynamic fence that prevents
the spreading of the stalled inboard flow towards the wingtips. As a result, the
drooped outboard wing panels remain effective and generate lift to very high
angles of attack.ll
7.7.2 Fuselage Modifications
The aft sections of the fuselage have a relatively strongerinfluence on the autoro-
tationaVspin behavior of the airplane. Hence, modifications to aft fuselage sections
will be more effectivein controlling the spin behavior. Examples of such modifica-
tions tested by NASAI9 include rounding ofthe bottom surface of the aft fuselage
and installation of strakes on the underside of the aft fiiselage as schematically
depicted in Fig. 7.26. Modifications similar to those shown in Fig.'7.26 result
INERTIA COUPLING AND SPIN
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┃'~ ┃k_ ┃
┃ ┃ I ┃
┃ ┣━┳━━━━━━━━━━━━━━━━━━━━┫
┃ ┃ ┃ ┃
┃ ┃ ┃ ┃
┃ ┃ ┃l . ) ┃
┃ ┃/ ┃ ┃
┃ ┣━┻━━━━━━┳━━━━━━━━━━┳━━┫
┃~ ┃ ┃ ┃ ┃
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