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National Advisory Committee for Aeronautics, Report - Wind Tunnel Investigation of an NACA 23021 Airfoil with Various Arrangements of Slotted Flaps

The National Advisory Committee for Aeronautics
is undertaking an extensive investigation of various
wing-flap combinations to furnish information appli-
cable to the aerodynamic design of high-lift devices for
improving the safety and the 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 aerodynamic features 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.

A very promising arrangement of a simple slotted flap
developed for the N. A. C. A. 23012 airfoil is reported
in reference 1. Further improvement, from a consider-
ation of high lift coefficients and low drag at high and
intermediate lift coefficients, was obtained by the addi-
tion of an auxiliary slotted flap to the main flap (ref-
erence 2). Another type of slotted flap, aerodynami-
cally superior but structiu‘ally more complicated, is the
venetian-blind flap reported in reference 3. All these
flap arrangements were tested on the N. A. C. A. 23012
airfoil.

In the present report, the results are given of the
tests of a relatively thick airfoil, the N. A. C. A. 23021,
with several arrangements of 25.66-percent—chord
slotted flaps. This investigation included two flap
shapes, each of which was tested with several slot shapes.