Wind tunnel investigation of control surface characteristics 9: some analytical considerations and experimental test results for an internally balanced flap Page: 3 of 28
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cion of control-surface hinge moments Thoud refer-
ably be accomplished in such a manner as to improve and
not to impair the flying qualities of the airplane. In an
effort to solve this problem, the NACA is conducting an
extensive investigation of the aerodynamic characteristics
of control surfaces. The main objectives of this investi-
gation are to arrive at a rational method for the design
of airplane control surfaces, to determine the type of
flap arrangements best suited for use as control surfaces,
and to supply experimental data for design purposes.
Several years ago the NACA made measurements in two-
dimensional flow of the pressure distribution on an NA0A
0009 airfoil with plain tlaps of various chords. The re-
suits of these tests are reported in roforences 1, 2, and
3. The pressure-distribution records of these tests have
been analyzed to determine the possible characteristics of
a flap with an internal balance. The internal balance is
a mechanism by which the pressure difference between two
points on the airfoil is used to act upon a flat plate or
similar device entirely enclosed within the airfoil pro-
file and thus to do ~irorin in deflecting the control surface.
By the proper location of vents on the airfoil surface, it
was found to be theoretically possible to vary independent-
ly the flap hinge-moment parameters to any desired magni-
tude and to provide the control surface with any desirod
initial hinge moment at 0 angle of attack and flap defloc-
The present paper presents a theoretical analysis of
the characteristics of an internal balance and a method
of calcuiating the physical character istcs of such a bal-
ancing device to give any desired section hinge-moment
characteristics to a control surface, In order to check'
the analytical calculations, tests of an internally bal-
anced flap have baeen made in two-dImensIonal flow and the
results of these vests are liscussoed. 'tne application of
internal balance to tabs is briefly treated.
The symbols used in this paper are:
OL airfoil lift coefficient (L/qS)
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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/m1/3/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.