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National Advisory Committee for Aeronautics, Technical Notes - A Flight Investigation of the Reduction of Aileron Operating Force by Means of Fixed Tabs and Differential Linkage, with Notes on Linkage Design

Flight tests were made to demonstrate the practica—
bility of employing fixed tabs in conjunction with a suit—
ably designed differential linkage to reduce the force re—
quired to operate ailerons. The tests showed the system
to be practicable with tabs of the inset type. The relae
tive ineffectiveness of attached tabs for changing the
aileron floating angle rendered them unsuitable. Experi—
enco gained in the investigation has indicated that the
use of the system is limited to maximum deflections of one
aileron relative to the other of less than 30° and that the
differential linkage should always be designed on the basis
of the highest probable floating angle.

Experience with drooped ailerons has drawn attention
to the marked effect upon the stick force that the differ-
ential linkage of the ailerons may exert. When such ailer—
ons are adjusted to the high—lift positionl the upward-
moving aileron may have a fairly large hinge moment tend-
ing to rotate it upward throughout its range of deflection.
Under certain conditions this assisting hinge moment, to-
gether with the relatively large mechanical advantage of
this aileron with respect to the control stick as compared
with that of the downward—moving aileron, may overbalance
the effort on the stick required to rotate the downward—
moving aileron downward, resulting in a reversal of the
stick force.

Jones and Nerken (reference 1) suggested a method, for
the case of the ordinary undrooped ailerons, of utilizing
these characteristics of the differential linkage for the
purpose of reducing the stick forces required for their
operation. It was suggested that_the ailerons be fitted
with narrow—chord full-span tabs deflected downward sever—
al degrees so as to adjust upward the position for zero
hinge moment (floating angle). The results of flight tests
to determine the feasibility of this method of reducing
aileron forces form the subject of the present paper.

The tests were made with a Fairchild 22 airplane. In
the first series of tests, tabs were attached to the ailer—
ons of a wing having a 2:1 taper. Difficulty experienced
in obtaining satisfactory results with the attached tabs
resulted in the second series of tests, which covered
trials of inset tabs. The second series of tests was made
with the standard wing for the Fairchild 22 with the ailer~
ons modified to incorporate inset tabs. Three arrangements
of the differential linkage were tried with these ailerons.
The flight tests consisted primarily of pilots' observa-
tions of the relative control forces with the different ar-
rangements. Measurements of the rolling motion were made
with one linkage'to determine the effect of tab setting on
the aileron effectiveness.