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National Advisory Committee for Aeronautics, Report - The Effect of Multiple Fixed Slots and a Trailing Edge Flap on the Lift and Drag of a Clark Y Airfoil

Lift and drag tests weremadeona Clark Ywing
equipped with four fired slots and a trailing-edge flap in
the 5-;f00t vertical wind tunnel of the National Advisory
Committee for Aeronautics. All possible combinations of
the four slots were tested with the flap neutral and the
most promising combinations were tested with the flap
down 45°. 00midering both the maximum lift coeflicient
and the speed—range ratio Climax/0min, with the flap
mum drag coefficient of the arrangement was high.
A relatively low-drag fixed slot near the leading edge
of an airfoil has been recently developed by the Na-
tional Advisory Committee for Aeronautics, with which
the maximum lift coefficient of a Clark Y airfoil was
increased from 1.30 to 1.75. (Reference 2.)
The present investigation was made to determine the
effect on its aerodynamic characteristics of equipping
a Clark Y airfoil with several fixed slots similar in
neutral no appreciable improvement was found with the
use of more than the single leading—edge slot. With the
flap down 45° a marimum lift coefficient of 2.60 was
obtained but the particular slot combination used had a
rather large minimum drag coefiioient with the flap neutral.
With the flap down 45° the optimum combination, con-
sidering both the maximum lift coefl’icient and the speed-
range ratio, was obtained with only the two rearmost
slots in use. For this arrangement the marimum lift
coeflicient was 24.4.
As an extension of the investigation of lateral stabil-
ity and control at low speeds, the National Advisory
Committee for Aeronautics has undertaken an investi-
gation of devices intended to increase the maximum
lift coefficient. In an investigation conducted by
Lachmann (reference 1) a large increase in the maxi-
mum lift coeflicient was obtained with a highly cam-
bered airfoil equipped with fixed slots but the mini-
shape to the recently developed low-drag fixed slot. The
tests were made with all possible combinations of the
various slots. In addition, since it was know that a
multislot wing could advantageously have greater
camber than that of the Clark Y, tests were made with
the rear portion deflected downward as a flap.