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Wind Tunnel Investigation of an NACA 23012 Airfoil with Two Sizes of Balanced Split Flap

An investigation has been made in the NASA 7- by 10—
foot wind tunnel of an NAGA 23012 airfoil with a l5~percentv
chord and a 25—percent-chord balanced split flap of the
Clark Y profile. The investigation was made to determine
the aerodynamic section characteristics of the airfoil as
affected by the size. nose location. and deflection of the
flap. Complete aerodynamic section characteristics were
determined for several nose locations of each flap and are
presented for four typical locations for each flap. A
comparison of the drag and lift characteristics is made
with two other medium-chord flaps previously investigated.

The optimum arrangement of either of the balanced
split flaps. from consideration of maximum lift coeffi-
cients and minimum profile—drag coefficients for take—off
.and climb, was a combination comparable to the Fowler flap.
When compared on a basis of flap deflection for equal max—
imum lift coefficients. there was little difference in the
pitching—moment coefficients for any of the arrangements
tested. Any leak between the nose of the flap and the
lower surface of the ring was harmful from consideration
of maximum lift coefficient. but if the gap was increased
to form a suitable slot the maximum lift coefficient was
increased. The results of this investigation furnish data
suitable for application to the design of any probable
split—flap arrangement.

INTRODUCTION

An investigation of various high—lift devices has been
undertaken by the NAGA to provide designers with aerody-
namic and structural data for the design of wine—flap com-

- binations for improved safety and performance of airplanes.

Aerodynamic data for single-slotted flaps on airfoils of
various thi‘knesses have been made available in references
1 through 6, for Fowler and plain flaps on lE—peroent thick-
airfoils in reference 1. and for split flaps on airfoils

of various thicknesses in reference 7. Structural data

for the single-slotted flaps are presented in references

8 and 9, for the plain flap in reference 8, for the split

flap in reference 9. and for the Fowler-flap in reference
10- I
Since-mast of the flaps in general use today are some
form of split flap. the investigation was extended to
flaps of the-balanced split type and the present report
presents aerodynamic data for two sizes of balanced split
flap on an HAUL 23012 airfoil.

APPARATUS AND TESTS

Models

The basic airfoil was built to the NAGA 23012 profile.
the ordinates of which are given in table I. .It has a span
of 7 feet and a chord of 3 feet. and is the same basic nir-
foil used in reference 2. The rear portion of the airfoil
is removable so that flaps of various sizes can be used.

The lS-percentwchord and the 25~percent~chord flaps
were built of laminated mahozany to the Clark Y profile
(table I). The span of each flap was 7 feet and the chords
were 5.4 inches and 9 inches which are. respectively, 15
and 25 percent of the wing chord. The flaps were rigidly
attached to the main wine by four steel fittings which al-
lowed a wide selection of nose locations for each flap and
permitted deflecting the flaps from 0° to 600 in 10°.incre—
ments at each location (fig. 1). The nose point of the
flap is defined as the point of tansency of the flap
leading—edge arc and a line drawn perpendicular to the
flap chord.