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National Advisory Committee for Aeronautics, Technical Notes - Free Spinning Wind Tunnel Tests of a Low Wing Monoplane with Systematic Changes in Wings and Tails - I - Basic Loading

A series of tests was made in the N.A.G.A. free-
spinning tunnel to determine the effect of systematic
changes in wing and tail arrangement upon steady—spinning
and recovery characteristics of a conventional low—wing
monoplane model for a basic loading condition. Eight
wings and three tails, covering a wide range of aerodynam—
ic characteristics, were independently ballasted so as to
be interchangeable with no change in mass distribution.
For each of the 24 wing-tail combinations, observations
were made of steady spins for four control settings and of
recoveries for five control manipulations. The results
are presented in the form of charts comparing the spin
characteristics.

The results showed that, with a poor tail arrangement,
wing plan form and tip shape had considerable effect on
the spinning characteristics. A wing with rectangular
plan form gave noticeably steeper spins and faster recov—
eries than the same wing with Army tips. Poorest recov-
eries were obtained for a wing with 5:2 plan—form taper
and no thickness taper; rapid recoveries were obtained
with a wing having 2:1 taper in both plan form and thick—
ness. For all the wings tested, satisfactory recoveries
could be obtained by the use of a tail with a deepened
fuselage and a raised stabilizer. Holding the elevators
up resulted in the steepest spins from which. by reversal
of both controls, the most rapid recoveries were obtained.
Steepest spins were generally, though not always, associa
ated with most rapid recovery, but there appeared to be no
relation between the sideslip of the steady spin and the
turns required for recovery.

As a result of extensive research performed in recent
years in flight. on spinning balances. and in free—spinning
wind tunnels, a considerable body of data (references 1 to
14 as well as unpublished results from the N.A.C.A. free—
spinning tunnel) has been accumulated regarding the effects
of inertial and dimensional modifications on the spinning
properties of specific airplanes. The information availa-
ble d; resent is not, however. sufficient to predict ac-
curately the spinning characteristics of an untried air—
plane design and actual full-scale or model testing must
be resorted to, unless the design incorporates extreme
features known to be beneficial in the spin.