Wind tunnel investigation of control surface characteristics 9: some analytical considerations and experimental test results for an internally balanced flap Page: 2 of 28
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3 1176 01354 2726
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
ADVANCE RESTRICTED REPORT
WIND-TUNNTEL INVESTI GATION OF
IX - SOi ANALYTICAL CONSIDERATIONS AND EXPERIMENTAL
TEST RESULTS FOR AN INTERNALLY BALANCED FLAP
By Richard I. Sears
An analysis has been made to determine the probable
aerodynamic section characteristics of a plain flap with
various arrangements of an internal balance. Tests in two-
dimensional flow have been made in the IACA 4- by 6-foot
vertical tunnel of an NACA 0009 airfoil with an internally
balanced flap in order to check the validity of the analyt-
ical calculation. The results of these tests, presented
in this paper, indicate that the calculations are in agree-
ment with experiment. The analysis has been extended on
the basis of the lifting-line theory to include an approx-
imate method for the design of an internal balance for a
control surface of finite span.
The present investigation indicates that an internal
balance is an aerodynamically desirable means of control-
ling the magnitude and the direction of the rate of change
of flap hinge moment with angle of attack and with flap
deflection. Because the internal balance is entirely con-
cealed within the airfoil contour, the lift, the drag,
and the pitching-moment characteristics of the control
surface are in no way affected by the presence of the bal-
ancing surface. Analytical considerations indicate that a
full-span balancing tab actuated by an internal balance
should prove to be a feasible method of reducing control
The desirability of reducing the hinge moments of air-
plane control surfaces has long been apparent. The reduc-
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Sears, Richard I. Wind tunnel investigation of control surface characteristics 9: some analytical considerations and experimental test results for an internally balanced flap, report, July 1942; (digital.library.unt.edu/ark:/67531/metadc61526/m1/2/: accessed January 19, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.