The effect of lateral controls in producing motion of an airplane as computed from wind-tunnel data Page: 1 of 26
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REPORT No. 570
THE EFFECT OF LATERAL CONTROLS IN PRODUCING MOTION OF AN AIRPLANE
AS COMPUTED FROM WIND-TUNNEL DATA
By FRae E. WmEic and _RoBERT T. JONESSUMMARY
An analytical study of the lateral controllability of an
airplane has been made in which both the static rolling
and yawing moments supplied by the controls and the reac-
tions due to the inherent stability of the airplane have
been taken into account. The investigation was under-
taken partly for the purpose of coordinating the results of
a long series of wind-tunnel investigations with phenom-
ena observed in flight tests; for this reason a hypothetical
average airplane, embodying the essential characteristics
of both the wind-tunnel models and the full-size test air-
planes, was assumed for the study.
Stability derivatives for the average airplane and for
several of the actual flight-test airplanes were computed,
and computations were made in an attempt to reproduce
by the theory the conditions of several actual flight tests.
Computations made of forced rolling and yawing motions
of an F-YS airplane caused by a sudden deflection of the
ailerons were found to agree well with actual measure-
ments of these motions.
The conditions following instantaneous full deflections
of the lateral control have been studied, and some attention
has been devoted to the controlling of complete turn maneu-
vers. A portion of the work was devoted to a study of con-,
trollability at stalling angles, and the results of this appli-
cation of theory were found to agree qualitatively with fight-
testing experience.
The angle of bank produced in 1 second, <ps,by a defec-
tion of the rolling control may be taken as a relative meas-
ure of the control effectiveness. In the analysis of con-
trollability below the stall, it was found that a simple
measure of the rolling effectiveness of a control is given by
the sum of a constant times the rolling moment and a con-stant times the yawing moment. Thus a relative weight or
importance is given to the secondary yawing moment pro-
duced by the rolling control. It was concluded that the
importance of such secondary moments can be minimized
by alteration of the moments of inertia of the airplane.
Increasing the yawing moment of inertia reduces the
effectiveness of a given yawing control in producing either
yawing or rolling motion. Changes of rolling moment
of inertia have little direct effect on either the rolling or
yawing motion produced by a given rolling-control moment.
The study of conditions above the stall indicated that
satisfactory control could not be expected without some
provision to maintain the damping in rolling and that a
dangerous type of instability would arise if the damping
were insufficient. The quantity L, N,-L, N,<O was
found to give a good measure of this type of instability.
INTRODUCTION
For some time the N. A. C. A. has been conducting
a program of research on lateral control for the specific
purpose of obtaining information that would lead to
improvement of control at the low speeds and high
angles of attack above the stall, a region in which
present conventional ailerons are known to be unsatis-
factory. Several series of wind-tunnel investigations
have been completed and an attempt has been made to
compare a number of widely different lateral-control
devices on the basis of what has been considered their
primary function-the provision of rolling moment.
Some of the secondary characteristics, such as the
yawing moments given by the controls and their effect
on the damping in rolling, were considered but only
by comparing the various values separately. Flight
465
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Weick, Fred E. & Jones, Robert T. The effect of lateral controls in producing motion of an airplane as computed from wind-tunnel data, report, April 20, 1936; (https://digital.library.unt.edu/ark:/67531/metadc66228/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.