High-speed tests of an airfoil section cambered to have critical Mach numbers higher than those attainable with a uniform-load mean line Page: 2 of 25
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
TECHNICAL NOTE NO. 1396
HIGH-SEED TESTS OF AN AIRFOIL SECTION CAMBERED TO
HAVE CRITICAL MACH NUMBERS HIGHER THAN TEOSE
ATTAINABLE WIT A UNIFORM-LOAD MEAN LINE
By Donald J. Graham
SUMMARY
High-speed wind--tunnel tests have been made to determine the
aerodynamic characteristics of an NACA 6-series airfoil section
especially cambered to have critical Mach numbers higher than those
for an airfoil having the some design lift coefficient with a
uniform-load type of mean camber line. Section coefficients of
lift, drag, and pitching moment for the airfoil, designated as a
modified NACA 66.(109)-210 section with a modified mean camber line,
are presented for angles of attack throu g the lift stall at Mach
numbers up to approximately 0.9. Comparisons are made between the
characteristics of the modified airfoil and those of the NACA 66-210
airfoil with a uniform-load type of mean camber line.
The test results indicate most of the characteristics of the
modified NACA 66(109)-g10 airf6il to be essentially the same as
those Qf-the..NACA 66-210 (a = 1.) airfoil. The-especially cambered
airfoil exhibits slightly more favorable lift-- and drag-divergence
characteristics, however, than the NACA 66-2210 (a = 1.0) airfoil,
the former having divergence Mach numbQrs approximately 0.01 higher
than those of the latter over most of the useful lift-coefficient
range.- This -ssmall difference roughly corresponds to the difference
in the critical sppeds of the two airfoil sections.
INTRODUCTION
The principal objective in the design of airfoil sections for
high-speed applications is the realization of high force-divergence
Mach numbers. For design purposes, however, the airfoil critical
Mach itmber is a more useful parameter than the force-divergence
Mach number because it is directly under the control of the designer.
There being a qualitative correspondence between the critical Mach
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Graham, Donald J. High-speed tests of an airfoil section cambered to have critical Mach numbers higher than those attainable with a uniform-load mean line, report, July 1947; (https://digital.library.unt.edu/ark:/67531/metadc55477/m1/2/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.