Airfoil section data obtained in the NACA variable-density tunnel as affected by support interference and other corrections Page: 7 of 38
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AIRFOIL SECTION DATA AS AFFECTED BY SUPPORT INTERFERENCE
N. A. C. A. 8318 airfoil from the fair curve is only of
the order of the possible experimental error.
The shape of the curve of figure 1 suggests that the
interference may be largely of the nature of a buoyancy
effect, in which case the interference should be primarily
a function of airfoil thickness; and other factors, such
as camber, should ordinarily be minor variables. Ac-
cordingly, because the present tests fail to show sig-
nificant variations with camber and because it is not
considered practicable to make such tests for a large
number of airfoils, the values obtained from the faired
curve of figure 1 will ordinarily be used to correct the
measured minimum profile-drag coefficients. These
values are thought to represent the correction with
sufficient accuracy for most applications of commonly
O~ /2
I
. 012 o / o 3 d - --5 -
M+. A.C.A symmetrical series
s r oNACA. 430 series -
aDNA.CA. 8318
-4-
.0068
004 -
70 /O 20 0 40 S0 60
Air foil thickness, percent chord
FuLooRE I-Variation with airfoil thickness of the increment of minimum profile
drag coefficient caused by support interference for the N. A. C. A. variable-density
tunnel. /
used airfoils. The applicability of these values to
data obtained at other values of the Reynolds Number
is more doubtful, but such application appears to offer
the best approximation possible at this time and,
accordingly, will be made.
The corrected minimum profile-drag coefficients for
the symmetrical airfoils from 9 to 25 percent thick are
given in table I. The second column of this table
gives the C00 values originally pub)lislted in reference 2.
The third column gives the ca values taken from
reference 5, except for the N. A. C. A. 0025. Some of
these cd0 values were obtained b)y correcting the Coo
values for the drag increment (0.0011) to correct to
the effective Reynolds Number and for the tip-drag
increment (reference 4). The rest of the c60 values are
from the results of more recent measurements similarly
corrected. The fourth column gives the support-
interference increments taken from the curve of fig-
ure 1. The finally corrected Cdj values of the fifth
column were obtained front the third column by cor-
recting the data, according to the procedure suggestedin the appendix (equation (1)), for the support inter-
ference and for the revised correction for the effective
Reynolds Number. Corresponding values obtained
from the support-interference tests are presented in
the sixth column. The principal result is presented
in the last column and represents the difference in
minimum profile-drag coefficients between the data
published in references 4 to 6 and those presented
herein. Other published data may be corrected by
the methods presented in the appendix.
TABLE I
DATA ON CORRECTION OF MINIMUM DRAG OF
SYMMETRICAL AIRFOILS
Effective Reynolds Number, approximately 8,00o,OOOjN. A.
C. A.
airfoil
0006
0009
0012
0015
0018
0021
o0025CD
(refer-
ence 2)
0. 0065
.0074
.0083
. 0093
.0108
0120
.0143ii0 (refer-
ence 5)
o0. 0051
0061
0069
.0077
0088
.0100
b. 0119Stil) oprt
inter-
rerenre
(fig. 1)
0 001,5
.00017
.00106
.8013
.0016
.0022te (from
cte (cor- suppot-
inter-
rected) ference
tests)
0,0051 ......
.0058 ----
.0060 0.0060
. 0064 _
.0071 .0073
.0079 ......
. 00oO2 .0091Correc-
t ion
incre-
0. 0003
.0D006
.0009
me
0013
.0017
.0021
0027e Correction increments are sums of increments resulting from support-interference
correction and change in method of correcting for effective Reynolds Number.
Reference 6.
,!.012 ....3- ,
0 N.A.C.A symmetrical series
O NA.CA. A230 series
,.0/ o NA.C. A 430 series
.0/O + NA. CA. 630 series
.008 - .. ...
-4-
S.004
i
. 002 - ---- --
03$
Airfoil thickness, percent chord
FIot R 2.-Variation of minimum profile drag coefficient with airfoil thickness.
F ffectise Reynolds Number, 8,200,000
The application of these corrections results in a
greatly decreased variation of drag within airfoil thick-
ness. This variation is shown for the N. A. C. A.
symmetrical, 230, 430, and 630 series airfoils in figure 2,
which may be considered a correction of figure 53 of
reference 5. It is evident that the smaller increase in
drag with section thickness will affect the choice of
wing sections. The best simple criterion for the selec-
tion of wing sections being considered the speed-range
index cmaxl/cdooM, figure 3 has been prepared from the
corrected data of figure 2 to be used in connection with
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Jacobs, Eastman N. & Abbott, Ira H. Airfoil section data obtained in the NACA variable-density tunnel as affected by support interference and other corrections, report, 1939; (https://digital.library.unt.edu/ark:/67531/metadc66327/m1/7/: accessed February 17, 2025), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.