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National Advisory Committee for Aeronautics, Report - The Development of Cambered Airfoil Sections Having Favorable Lift Characteristics at Supercritical Mach Numbers

Several groups of new airfoil sections, designated as the
erCL-l S-series, are derired analytically to hare lift character-
istics at supercr-itical JIach numbers which are favorable in the
sense that the abrupt loss of lift, characteristic of the usual airfoil
section at Elfach numbers above the critical, is avoided. Aero-
dynamic characteristics determined from two-dimensional
wind-tunnel tests at Ellach numbers up to approximately 0.9
are presented for each of the dericed airfails. Comparisons
are made between. the characteristics of these airfoils and the
corresponding characteristics of representatire M—IC‘A 6-series
airfoils.

The experimental results confirm the design expectations in
demonstrating for the NACA 8-series airfoils either no varia-
tion, or an increase from the lampeed design calue, in the lift
coqflicient at a constant angle of attack with increasing bfach
number above the critical. It was not found possible to im-
prore the variation with hfach number of the slope of the lift
curve for these airfoils above that for the NAC‘A 6-series
airfoils. The drag characteristics of the new airfoils are some-
what inferior to those of the NAC’A 6-series with respect to
divergence with ZlIach number, but the pitching-moment
characteristics are more favorable for the thinner new sections
in. demonstrating somewhat smaller oariations of moment
coejicient with both angle of attack and M’ach number.

The effect on the aerodynamic characteristics at high flfach
numbers of removing the cusp from the trailing-edge regions
of two IO—percent-chord-thiclc NACA 8—series airfoils is de—
termined to be negligible.

The use of a negat-icely deflected plain flap at supercritical
llIach numbers on an NACA 6-series airfoil is indicated to
be a feasible and promising means for obtaining on demand the
favorable mm’ation with hIach number of the lift coefficient
at a given angle of attach, characteristic of the NACA 8-series
airfoils, while retaining at all other times the superior drag
characteristics of the NAC‘A 6-series type of airfoil.