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Wind Tunnel Investigation an NACA 23012 Airfoil with a 0.30 Airfoil Chord Double Slotted Flap

By Paul I. Purser. Jack Iischel, and John H. Eiebe
SUMMARY

Tests to determine the effect of flap position and
deflection on the aerodynamic characteristics of an NAGL
23012 airfoil with a double slotted flap having a chord
30 percent of the airfoil chord (0.300) were conducted
in the LMAL 7— by 10—foot tunnel. In addition, a few
tests were made to determine the aerodynamic section
characteristics as affected by the size and shape of the
fore flap, by movement of the fore flap and rear flap as
a unit, and by variation in the airfoil lower lip. Gena
tours of rear—flap—nose position for various values of
minimum section lift coefficient, section profile~drag
coefficient, and section pitching—moment coefficient are
presented at three selected fore—flap positions for vari—
ous rear—flap deflections. The complete aerodynamic sec—
tion characteristics are given at the three selected fore-
flap positions for the optimum—lift and optimum—drag po—
sitions of the rear flap at several deflections. Polars
of the section profile—drag coefficient at the flap po-
sitions and deflections for optimum lift and optimum
drag are shown. A discussion is given of the relative
merits of the present arrangement as compared with a
0.2566c and a 0.40c slotted flap, a 9.30c Fowler flapI
and a 0.40c double slotted flap on the same airfoil.

The optimum deflection of the rear flap within the.
range investigated at each position of the 0.1170 fore
flap was 600 in almost all cases and the maximum lift of
the airfoil was obtained with the fore flap deflected
25° in the rearmost of the three selected positions.

The use of the 0.14670 fore flap provided a slightly
higher maximum section lift coefficient than was obtained
with the smaller fore flap. The 0130c.doub1e slotted
flap (0.117c fore flap) gave a maximum section lift coef—

‘Iicient'(3.30) that was higher than that 6: the 0.25660

or 0.m&:single slotted flaps, approximately equal to
that of the 0.30c Fowler flap, but about 0.16 less than
that of the 0,40c double slotted flap. The profile—drag
coefficients of the 0.50c double slotted flap were higher
than those of the 0,300 Fowler'and the 0.40c double -
slotted flaps over the entire lift range and higher than
those of the two single slotted flaps in the range of
section lift coefficients below 2.7. The negative sec-
tion pitching—mement coefficients at maximum section
lift coefficient produced by the 0.30c double slotted
flaps were equal to those of the 0.30c Fowler flap and
were greater than those produced by other slotted flaps
on the same airfoil.

INTRODUCTION

An extensive investigation of various high—lift
devices has been undertaken by the Rica to furnish in—
formation applicable to the aerodynamic design of wing—
flap combinations for improved safety and performance of
airplanes, A high—lift device capable of producing high
lift with variable drag for landing and high lift with
low drag for take—off and initial climb is believed to
be desirable° Other desirable characteristics are: no
increase in drag with the flap neutral, small change in
pitching moment with flap deflection, low forces required
to operate the flap, and freedom from possible hazard due
to icing,

aerodynamic data on the HAUL 23012 airfoil have been
made available for single slotted flaps in references 1
and 2, for a Fowler flap having a chord 30 percent of the
airfoil chord (O, 30c) in reference 3, and for a 0.400
double slotted flap in reference 4.

The data presented in reference 4 indicated that the
double slotted flap gave higher lift than the single
slotted flap and had lower drag at high section lift coef-
ficients. The double slotted flap also had higher lift
than the Fowler flap.

Although an investigation essentially the same as
that reported herein had been planned at LMAL several
years ago, no tests were made at that time because of
other proJects of greater interest. Renewed interest
of designers and manufacturers in devices capable of
L—h69

.producing-very.high lift on combat airplanes. however,

led to the present investigation, in'which'tests were
made of a 0.30c double slotted flap on the HAUL 23012
airfoil (fig. 1). It was believed that this device
would combine the advantageous aerodynamic character-
istics of the 0.400 doublerlotted flap (reference 4)
with the structural advantages of the small single
slotted flap (reference 1). The small size of the

fore flap would also allow the use of simpler doors for
sealing the break in the airfoil lower surface with the
flaps retracted,