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National Advisory Committee for Aeronautics, Technical Notes - Effects of Mach Number Variation Between 0.07 and 0.34 and Reynolds Number Variation on the Maximum Lift Coefficient of a Wing of NACA 64-210 Airfoil Sections

The effects of Mach number and Reynolds number on the maximum lift
coefficient of a wing of NACA 6h-210 airfoil sections are presented.
The wing was tested through the speed range of the Langley 19-foot
pressure tunnel at two values of air pressure. The ranges of Mach
number obtained were from 0.07 to 0.3M at atmospheric pressure and
from 0.08 to 0.26 at a pressure of 33 pounds per square inch absolute.

The corresponding Reynolds number ranges were from 0.97 x 106 to
4. hh x 106 and from 2. 20 x lo6 to 8.10 x 10 , respectively. The tests
were made with and without partial—span and full—span split flaps
deflected 60°. Pressure-distribution measurements were obtained for
all configurations.

The maximum lift coefficient was a function of the two independent
variables, Mach number and Reynolds number, and both parameters had an
important effect on the maximum lift coefficient in the ranges investi-
gated. The stall-progression and, consequently, the shape of the lift-
curve at the stall were influenced by variations in both Mach number
and Reynolds number. Peak maximum lift coefficients were measured at
Mach numbers between 0.12 and 0.20, depending on the Reynolds number
range and flap configuration.

There was very little influence of either Mach number or Reynolds
number on the maximum lift of the wing with leading-edge roughness.

The maximum lift of airfoils as influenced by Reynolds number has
received extensive treatment (for example, ref. 1). Relatively little
consideration, however, has been given to the interrelated influence
of compressibility and Reynolds number on théfmaximum lift. These
interrelated effects were shown to be significant-at—Mach numbers as
low as 0.2 in references 2 and 3. An investigation has been conducted,
therefore, to study qualitatively these interrelated effects of
compressibility and Reynolds number.

Three wings, differing only in airfoil sections, have been tested
in both the Langley'lg-foot pressure tunnel and the Langley 16-foot—
high-speed tunnel. The tests in the 19-foot pressure tunnel were
conducted with the test air at—atmospheric pressure and at a pressure
of 33 pounds per square inch abSolute.' Two variations of Mach number
with Reynolds number were thus obtained.