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National Advisory Committee for Aeronautics, Report - Wind Tunnel Investigation of Ordinary and Split Flaps on Airfoils of Different Profile

The Clark Y, the N. A. C. A. 23019, and the N. A. C.
A. 23021 ai1foils equipped with full-span ordinary flaps
and with full-span simple split flaps were tested in the
N. A. 0. A. 7- by 10-foot wind tunnel. The principal
object of the tests was to determine the characteristics of the
airfoils with ordinary flaps and, in addition, to determine
the relative merits of the various airfoils when equipped
with either ordinaryflaps or with simple split flaps -The
Clark Y airfoil was tested with 3 widths of ordinary flap,
10, 20, and 30 percent of the airfoil chord. The optimum
width of the ordinary and the simple split flap based on
the maximum lift attained with the Clark Y airfoil was
then tested on each of the other two airfoils.

The optimum width of ordinary flap for maximum lift
attainable was found to be the same as that of the split
flap, 20 percent of the airfoil chord. The split flap
produced somewhat greater increases in CI,” on the
airfoils tested than did the ordinary flap of” the same
width, but the L/D at maximum lift was practically the
same for the two types of flap. Any gap between the
airfoil and the leading edge of ordinary flaps had a very
detrimental eject on the sz attainable. Based prin-
cipally on factors afiecting airplane performance, the
relative order of merit of the air-foils tested with either
ordinary or split flaps is N. A. C. A. 23012, Clark Y,
and N. A. C. A. 23021. The hinge-moment coeflicients
(based on flap chord and area) of the full-span ordinary
flaps were practically independent of flap chord; the actual
hinge moments varied approximately as the square of the
chord. In addition, the hinge-moment coezficients of the
split flaps were practically the same as those of full-span
ordinaryflaps of corresponding widths.