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Effect of Wing Leading Edge Slots on the Spin and Recovery Characteristics of Airplanes

By Anshal I. Neihouse and Marvin Pitkin
SUMMARY

An investigation has been made in the NAGA 15—foot
free-spinning tunnel to determine the effect of wing
leading—edge slots on spin and recovery characteristics.
Results obtained from these tests establish a criterion
from which the adverse or favorable effects of slots may
be predicted from a nondimensional mass-distribution
parameter.

The results indicate that, for single—engine designs
with mass distributed heavily along the wings and for
nultiengine designs, recovery will be slower with slots
open than with slots closed and the spin will be flatter
and at a lower rate of descent. If the mass is distributed
heavily along the fuselage, however, recovery will be more
rapid with slots open than with slots closed.when the 916— J
vator is neutral or down, although there will be little ap— a)
parent effect when the elevator is full up. There will be '
little effect upon the angle of attack or rate of descent
when slots are open and when the mass is distributed
heavily slang the fuselage.

.’

The slots, when open, will depress the inboard wing
of an airplane regardless of loading.

INTRODUCTION_

The use of leading-edge slots on the wings of certain
types of American airplane to improve the stalling charac—
.teristics or to increase the speed range has recently in—
creased. Indications that slots may have a large influ—
ence on the behavior of an airplane in a spin have been
reported in references 1 to 5. These references indicate
that the effect of slots may be either detrimental or
beneficial but do not provide means for predicting the ef-
fect for a particular condition unless the spin character—
istics of the airplane without slots are definitely known.
The investigation in the NAGA 15—foot free-spinning tunnel
reported in the present paper was undertaken in an attempt
to relate the effect of slots on spin and recovery charac—
teristics to the mass distribution of the airplane.

Five models of recent airplanes of widely different
types. all haVing slots. were tested with the slots both
Open and closed. The mass distributions were varied to
cover a wide range of loadings from a single-engine mass
distribution with mass distributed chiefly along the fuse—
lage to a multiengine mass distribution with mass distrib-
uted chiefly along the wings. The effects of the slots on
the steady~spin and recovery characteristics were deter—
mined.