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National Advisory Committee for Aeronautics, Technical Notes - A Study of Factors Affecting the Steady Spin of an Airplane

Data from wind—tunnel tests on a model of the HY—l
airplane were used in a study of the effect on the steady_
spin of a number of factors considered to be important.
The factors were of two classes. mass distribution effects
and aerodynamic effects.

The study indicated that mass extended along the lone
gitudinal axis has no detrimental effect or is even slight—
ly beneficial, mass extended along the lateral axis_is det-
rimental if the airplane spins with the inner wing tip far
down, and mass extended along the normal axis, if of con—
siderable magnitude, has a strong favorable effect. The
aerodynamic effects considered in terms of rolling. pitch—
ing, and yawing moments added to those for a conventional
airplane showed that added stable rolling moment could con-
tribute favorable effect on the spin only in decreasing
the amount of inward sideslip required for equilibrium;
negative_pitohing moment of moderate magnitude has unfavor—
able effect-on a high—ang1e~of—attaok spina and stable
yawing moment has pronounced beneficial effect on the spin.
Experimental- data from various sources were available to
verify nearly all the deductions resulting from the study
of the curves.

When these results were considered for the purpose of
deciding upon the best means to be developed for control-.
ling the spin, the yawing-moment equilibrium was found to
offer the most promising field for research. The wing—cel—
lule yawing moment, of which the shape of the chord—force
curve is an approximate measure, should be made as small
as possible in the unstable sense and the damping yawing
moment of the tail should be made as large as possible.
The most serious unfavorable effect on the damping yawing
moment of the tail is the blanketing of the vertical sur—
faces by the other parts of. the tail.

In a previous study of the steady spin (reference 1),
it was found that wind-tunnel data obtained in simple force
and moment tests with a stationary model could be utilized
with fair success in an analysis of the conditions for e—
quilibrium in a steady spin. The wind—tunnel data used in
that case were obtained on a model of the NY—l airplane
tested at angles of attack up to 90°. The data were used
to predict the angles of attack at which spinning equilib-
rium would occur in flight by utilizing the method of anal
ysis—outlined by Fuchs and Schmidt (reference 2). A com—
parison of these results with flight measurements for the
NY—l airplane showed the agr eement.to be reasonably satis—
factory.