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National Advisory Committee for Aeronautics, Technical Notes - A Method of Estimating the Aerodynamic Effects of Ordinary and Split Flaps of Airfoils Similar to the Clark Y

An .empirical method is given for estimating the aero-
dynamic effect of ordinary and split flaps on airfoils
similar to the glark Y. The method is based on a serIEi
of charts that have been derived from an analysis of ex-
isting wind—tunnel data. Factors are included by which
such variables as flap location, flap span. wing as ect
ratioI and wing taper may be taken into account. K series
of comparisons indicate 'that the method. would be suitable
for use in making preliminary performance calculations and
in structural design.

In order to improve the speed range omeIrplanes it
is customary to use some sort of highrlift device. At"_
present the use for this purpose of either the ordinary"
flap or some modification of the-simple split flap is al-
most universal. Although the results of numeroui"§1peri-
ments for wings with flaps exist, little attempt has been
made to analyze the data as a whole except in a qualita-
tive way. The present note is intended to summarize avail—
able data on the ordinary and split types of flap in such
form that it may be readily used in estimating the charac—
teristics of airfoils equipped with flaps.

As the results have been derived principally from
tests made in the N.A.G.A. 7— by 10-foot wind tunnel on
the clerk Y airfoil. it is expected that the method will
give the best results when applied to similar airfoils.
Results from tests ox‘othsr airfoils have been included
in several cases in order to derive factors by which nod-
ifications of the flap arrangement may be taken into ac-
count.

The analysis given herein-holds only for the range
between maximum negative and maximum positive lift. In
this range the effect of flap displacement on the wing
lift. drag. and pitching-moment coefficients as well as on
the variation of the flap-lift and hinge-moment coeffir
cients is covered. The types of flap considered are the
plain trailing—edge, or ordinary. flap and the split trail-
ing-edge flap. Variations of the latter type of flap oc—
cur as the pivoting point moves along the lower surface of
the wing section.

The sources of the data considered in the.ana1ysis
and the important geometric characteristics of the wings
tested are given in table I. All tests were made with
wings of aspect ratio 6 and without gap or balancing area.
Only these tests in which the ratio of the flap to the
wing chord was constant on the portion of the wing equipped.
with flaps were used in the analysis althoughgfactors for
taking into account other slight variations are given.