Application of one part of Von Karman's two-dimensional transonic similarity law to drag data of NACA 65-series wings Page: 4 of 11
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NACA RM No. LSF24 3
RESULTS AND DISCUSSION
The pressure drag parameter C(t/) was calculated for the various
wings from the continuous curves of CD against Mo of references 3 to 5
at equal increments of the parameter . Because of the lack of
any reliable friction drag data in the transonic range, a friction drag
coefficient of 0.006 was assumed for all wings. The parameters for the
three wings having an aspect ratio of 7.6 are plotted in figure 1. The
data are plotted as individual points rather than as continuous curves
In order to gain a quantitative idea of what the deviations shown
in figure 1 mean in terms of drag coefficient and Mach number, the faired
curve of figure 1 was used to recompute a curve of CDp against Mo for
each wing. In figure 2 these curves are compared with curves of CDp
against Mo computed fran the reference data. The experimental
uncertainty in Mach number is about 10.01. At the highest Mach numbers
tested, the experimental uncertainty in CD is about 0.0025 for the
12-percent-thick wing and about 0.0005 for the 6-percent- and 9-percent-
thick wings. The uncertainties in drag coefficient increase somewhat
as Mo is reduced. The uncertainty in the assumed value of CDf is
probably within about 0.001. Thus, the two curves for the 6-percent-
and 9-percent-thick wings differ in the subsonic range by less than the
maximum possible uncertainties in the experimental data and skin-friction
drag coefficient. The difference between the two curves for the 12-percent-
thick wing exceeds this uncertainty slightly at about Mo = 0.98 because
of the hump in the experimental curve. The difference between the two
curves for each wing in the supersonic range is less than twice the sum of
the experimental uncertainty and the uncertainty in the assumed value
Apparently, in the supersonic range, the similarity law does not
entirely correlate the effect of variations in thickness ratio, and there
is a consistent variation in the drag parameter with thickness ratio. In
figure 3 this trend is compared with the calculated variations in drag
parameter for circular-arc airfoils of the same thickness ratios at higher
Mach numbers where the supersonic type of flow pattern is wholly established.
The circular-aro-airfoil drag coefficients were calculated from the formula
(formula 9.23, reference 6)
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Amer, Kenneth B. Application of one part of Von Karman's two-dimensional transonic similarity law to drag data of NACA 65-series wings, report, August 24, 1948; (digital.library.unt.edu/ark:/67531/metadc57788/m1/4/: accessed November 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.