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Wind Tunnel Investigation of Control Surface Characteristics -XX - Plain and Balanced Flaps on an NACA 0009 Rectangular Semispan Tail Surface

Force— test measurements have been made in the Langley h-
by 6— foot vertical tunnel to determine the aerodynamic
characteristics of an NACA 0009 semispan tail surface of
rectangular plan form-equipped with flaps of various nose
shapes and overhangs. The flap chord was 50 percent of '
the airfoil chord. -A few tests were made to determine
the effectiveness of a balancing tab on various flap
arrangements.

The test results indicated that the slope of the
lift curve was affected little by the amount of overhang
and the balance nose shape but was increased by sealing
the gap at the flap nose. At zero angle of attack, the
variation of lift with flap deflection for the sealed-gap
condition was the same as or slightly greater than for
the unsealed—gap condition. The change in the hinge—
moment coefficient with angle of attack or with flap
deflection generally was made more negative with sealing
the gap. The effectiveness of the balancing tab in
reducing the flap hinge-moment ocefficients was approxi—
mately the same for both the sealed plain flap and the
unsealed 55— percent— flap- -ohord elliptical overhang; also,
the variation of lift coefficient with tab deflection was
about equal for the plain flap and for the flap with aero—
dynamic balance.

In three—dimensional flow, the measured values of
the lift—curve slope were slightly lower and the measured
values of the hinge-moment parameters were more positive
than the values of the parameters calculated from the
data of previous investigations in two~dimensional flow
by lifting-line theory, modified by the edge-velocity
correction. Application of aspect-ratio corrections
determined from a lifting-surface—theory solution for an
elliptical wing made the computed values of the variation
of the hinge-moment coefficient with angle of attack very
closely approach the measured values.