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• November 25, 2016 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - Effect of the Surface Condition of a Wing on the Aerodynamic Characteristics of an Airplane

In order to determine the effect of the surface con—'
ditions of a wing on the aerodynamic characteristics of an
airplane, tests were conducted in the N.A.C.A. full—scale
wind tunnel on the Eairchild F—22 airplane first with nor—
mal commercial finish of wing surface and later with the _
same wing polished. Comparison of the chara§teri§tics_ of
the airplane with the two surface conditions shows _th_at_the
polish caused a negligible change in the lift cu.rve, but _
reduced the minimum drag coefficient.by 0.001, @his reduc—
tion in drag if applied to an airplane with_a given speed_
of 200 miles per hour and a minimum drag coefficient of
0. 025 would increase the speed only 2_ _9 miles per hour, but
if the speed remained. the same, the power would be reduced
4 percent.

With the speed of military and_commercial airplanes_
increasing rapidly, many of the problems of racing airplanes
are being encount_ered in 'service types,_ among these _problems
is the one of surface condition of the wings. _As large in—
crea.ses in speed have been claimed for racing airplanes as
a result of polishi_ng the surfaces,_ and also because it has
been thought that poli.shing the surfa.ces a.ffected the
min lift, tests were conducted. to determine the effect of
polishing the wing Surfaces upon the aerodynamic character—
istics of a small monoplane. The tests were conducted first
with the surface of the wing in normal condition and later
with the surface highly polished.

The airplane used for the tests was a Feirchild 3—22
parasol monopla.ne with" a wing of CYH_airfoil section. The
principal dimensions of the airplane are given on the plan
and elevation views shown in figure 1. The wing was made
of the customary wood and féhtic'honstruction and the sur-
face of the covering was finished in accordance with stand—
ard commercial practice. Figure 2 is a photomicroaraph of
the original surface.