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National Advisory Committee for Aeronautics, Technical Notes - The Aerodynamic Characteristics of a Model Wing Having a Split Flap Deflected Downward and Moved to the Rear

Tests were made on a model wing with three different
sized split trailingfiedged flaps, in the N.A.C.A. 7 by 10
foot wind tunnel. The flaps were formed of the lower rear
portion of the wing and were rotated downward about axes
at their front edges. The lift, drag, and center of pres—
sure were measured with the axis in its original position
and also with it moved back in even steps to the trailing
edge of the main wing. giving in effect an increase in
area. The split flaps when deflected about their original
axis locations gave slightly higher maximum lift coeffi—
cients than conventional trailing-edge f1aps,_and the lift
coefficients were increased still further by moving the
axes toward the rear. -The highest value of CL max' which
was obtained with the largest'flap_hinged at 90 per cent
of the chord frOm the leading edge, was 2.52 as compared
with 1.27 fer the basic wing.

Among the devices for increasing the maximum lift co~
efficient over that obtained with a conventional wing, the
one most cOmmonly used has probably been the trailing~edgs
flap, which is deflected downward to increase the camber of
the wing. A few tests have been made on airfoils with
flaps in which the rear portion of the airfoil is split in—
to upper and lower sections.and the lower section-deflected
downward. (References l and 2.) In at least two cases the
flap has been moved to the rear as well as deflected down-
ward in angle, giving in effect an increase in area as well
as in camber. A flap of this nature was incorporated in
the Alfaro airplane entered in the Guggenheim Safe Aircraft
Competition. (Reference 3.) The most recent developments
along this line are the results.of the work of Mr. E. F.
Zap. who has carried on many wind-tunnel tests on model
wings and also flight tests On an airplane equipped with
the Zap flap-.' In flight the flap was effective not. only
in givi.ng. a lower minimum speed but also, by virtue of
its increase in drag, in making possible steeper glides
and shorter landings over obstacles.