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The Subsonic Aerodynamic Characteristics of Two Double-Wedge Airfoil Sections Suitable for Supersonic Flight

High—speed wind-tunnel tests have been made to investigate the aero-
dynamic characteristics at subsonic Speeds of two symmetrical double—
wedge airfoil sections of h-and 6—percent—chord thickness suitable for
application to supersonic aircraft. Section coefficients of lift, drag,
and quarter»chord pitching moment are presented for a moderate range of
angles of attack at Mach numbers up to approximately 0.93. Comparisons
are made between the significant characteristics of the double—wedge
airfoils and those of the NADA 65w206 airfoil as an.index of the merit
of the former at subsonic speeds.

The doubleswadge airfoil exhibits no characteristics other than
these common to the usual subsonic profile which would contribute to unr
steady or uncontrollable flight at subsonic speeds of aircraft employing
such a section for lifting surfaces. The liftwcurve slope varies with
Mach number in a manner similar to that for NACA 65-series airfoils of
small thickness. The maximum lift coefficients at low Mach numbers for
the double—wedge type of airfoil are comparable to those of uncambered
6—percent—chord-thick NACA airfoils. The drag characteristics of the
doubledwedge airfoil, while definitely inferior to those of more conven—
ional airfoils at all but the highest test speeds, are such as to per-
mit reasonably satisfactory airplane performance at subsonic speeds. In
summary, the test results indicate the definite practicability of the
flight at subsonic speeds of aircraft with wings composed of thin airfoil
sections of the doubledwedge type.

The present widespread acceptance of the concept of practical flight
at supersonic speeds has focused increasing attention upon the develop—
ment of airfoil shapes which will permit sustained flight of aircraft at
these speeds. The shapes, and hence the aerodynamic characteristics, of
airfoils designed for use at supersonic speeds differ basically from
those employed at subsonic speeds. The supersonic airfoil, in practical
application, however, must traverse the subsonic speed range in accelere
ating to supersonic velocities. Any airfoil section suitable for super—
sonic application must in addition, therefore, permit steady and con-
trollable flight at subsonic and transonic speeds.