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Wind Tunnel Investigation of Control Surface Characteristics - XI - Various Large Overhang and Internal-Type Aerodynamic Balances for a Straight-Contour Flap on the NACA 0015 Airfoil

SUMMARY

Force~test measurements in two—dimensional flow have
been made in the NACA 4- by 6-foot vertical tunnel to deter~
mine the oharacteristics.of several different shaped
overhang—type aerodynamic balances applied to a straight~
contour flap mounted on an NACA 0015 airfoil. The chord
of the flap was 50 percent of the airfoil chord and the
chord of the overhang was 50 percent of the flap chord.
Cover plates of several widths were used to cover partly
the break in airfoil contour caused by the sharp—nose over~
hang.

The flap with blunt—nose overhang was overbalanced
throughout certain ranges of flap deflection. The hinge-
moment characteristics were improved at the expense of-in-
creased drag by sharply tapering the nose profile of the
overhang. The hinge—moment characteristics of a flap with
a loug sharp—nose overhang can be nearly reproduced by
using a somewhat shorter blunt—nose overhang.

The addition of cover plates over the nose of the flap
having a long overhang of sharp profile materially reduced
the drag of the airfoil with uncovered flap overhang. Unless
the gap at the flap nose was sealed, the addition of cover
plates caused the lift available for control to be less than
for the same flap without cover plates. The addition of
cover plates adversely affected the hinge~moment character~
istics of the flap with sharp~nose overhang unless the air
leak through the gap at the flap nose was sealed. This
fact is particularly evident for the widest cover plates.

INTRODUCTION

The NACA has instituted an extensive investigation of
the section aerodynamic characteristics of various flap
arrangements in an effort to determine the types best suited
for control surfaces and to supply experimental data for de-
sign purposes. The results of this investigation that re—
late to the present report are given in the references.

This paper presents the aerodynamic characteristics of
an NAGA 0015 airfoil with a straight~contour flap having a
chord 30 percent of the airfoil chord (0.300) and an over-
hang of various nose shapes that is 50 percent of the flap
chord (0.500f). Cover plates of three widths and gaps of
four sizes at the flap nose were tested with the sharp-nose
balance.

A blunt-nose balance was first investigated and gave
values of flap hinge—moment coefficient that showed over—
balance at negative angles of attack. Several balances of
more tapered profile were then tested and found to have
improved flap hinge-moment characteristics. The increased
drag, due to the break in the airfoil contour caused by.the
taperedeprofile balance, was, however, excessive and led to
the use of cover plates in an effort to reduce the drag by
partially covering the break in the airfoil contour° Cover-
plates of several widths and gaps of several sizes at the
flap nose were tested to determine the aerodynamic character-
istics of these airfoil—flap combinations.