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National Advisory Committee for Aeronautics, Technical Notes - Wind Tunnel Tests of an NACA 23021 Airfoil Equipped with a Slotted Extensible and a Plain Extensible Flap

An investigation has been made in the.NAGA 7— by 10-
foot wind tunnel of a large—chord EACA 23021 airfoil
equipped with two arrangements of a completely extended
lE—pércent—chord extensible flap. One of the flaps had a
faired juncture, without a gap; the other was provided
with a slot between the trailing edge of the airfoil and
the nose of the flap. Complete aerodynamic section char—
acteristics are presented for the various flap deflections
for both flap arrangements in the completely extended po-
sition.

The results showed that the basic airfoil gave the
lowest profile~drag coefficients over the low lift range,
the airfoil with the plain extensible flap zave the lowest
profile~drag coefficients over the moderate lift range,
and the airfoil with the slotted extensible flap_£ave the
lowest profile-drag coefficients over the high lift range.
The airfoil with the slotted extensible flap had the same
maximum lift at a flap deflection of 25° as the airfoil
with the plain extensible flap had at a flap deflection
of 600.’ The results of comparisons of the airfoil pitching—
moment coefficients obtained with the two types of flap
are dependent upon the basis chosen for comparison.

The National Advisory Committee for Aeronautics has
undertaken an extensive investigation of various wing~ ‘
flap combinations to furnish information applicable to the
aerodynamic design of hish~lift devices for improving the
safety and the performance of airplanes. .TWO'characteris-
tics of high—lift devices considered desirable'arE'high
lift with variable drag for landing and high lift with low
2 - HACA Technical Note No. 782

drag for take—off and initial climb. Other desirable
aerodynamic features are: no increase in drug with the
flap neutral; small change in pitching moment with flap
deflection; low forces required to operate the flap;
and freedom from possible hazard duo to icing.

As part of an investigation of a balanced split
flap, tests have been made of an FACA 23021 airfoil
equipped with two arrangements of;e 0.15c chord exten—_
siblo flap. The arrangements were tested only in the
completely extended condition. One of the extensible
flaps hes a slot and is the completely-extended Fowler
flap; the other arrangement has no slot and is somewhat
similar to the new Zap type of flap.