Stivers, Louis S , Jr

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XACA CB NO. L4125
3 l176013623m
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
CONFIDENTIAL BULLETIN
AERODYNAMIC CHARACTERISTICS OF THE NACA 747A315 AND
747A415 AIRFOILS FROM TESTS IN TRE
NACA TWO-DIMENSIONAL LOW-TURBULENCE PRESSURE TUNN31J
By Albert E. von Doenhoff and
SUMMARY
Two low-drag airfoils, the
Louis S. Stivers, Jr.
NACA 747A315 and the
NACA 747A415, designed to have reduced pitching moments
about the quarter-chord point and moderately high values
of the design lift coefficient have been tested in the
NACA two-dimensional low-turbulence pressure tunnel.
Section llft, drag, and pitching-moment qoefficie ts are
Bpresented for Reynolds numbers of 3 x Mlb, 6 x 10 , and
9 x 106, together with section lift and section drag data
for a Reynolds number of 6 X 106 for the same airfoils
with roughened leading edges.
A comparison of the characteristics, at a Reynolds
r.uwber of 9 x 106$ of the NACA 747A315 and NACA 747A415
airfoils with characteristics of the NACA 652-415 airfoil
is riven in the following table:
NACA
airfoil
section
747A315
747A415
652z415
Ibdinimum
seotion
~drag
,ooef-
,fioient
0.0038
.0041
.()(342
Range of
section
liftcoef-
ficient
for low
drag
0.22 to O@?
..9 to .Iz
.08to .56
SectIonpitohing
momentCoeffi-
cientabout
quarterohordat
designsection
lift ooeffioient
-0.017
‘.036
-on
Maximl.ull‘CriticalMach
seothn numberat
lift designseutlm
ooef- liftooeffi-
ficiedwcient
1.43 0.626
1.50 .e12
1.62 .641
I
2 NACA CB No. L4125
INTRODUCTION
The type of mean line usually used to camber the
6-series alrf’oilspresented in reference 1 led to rela-
tively high pitching-moment coefficients about the
quarter-chord point for a given desl~ lift coeffichnt.
rsr examples the measured pitching-moment coefficients
‘or airfoils having a mean line of type a = 1.0
~s.yh~red for a design lift coefficient of 0s4 were
&pproximately -0.070. This moment coefficient is sore-
what higher tham is desirable for many applications.
The NLCA 7-series airfoils were derived in an attempt
ta obtain moderately high values of the design lift coef-
ficient and to retain the low-drag characteristics of the
6-series airfoils, but with reducgd pitching moments.
The NACA 7-series airfoils differ from the 6-series air-
foils in that the 7-series airfoils have a slightly modi-
fied thickness dl~trlbution antiare co~~red with mea
lines in such a manner that more extensive regions of
laminar flow are possible over the lower surface than
over the upper surface. The chordwlse load distribution
is so chosen that the main portion of the lift is carried
by the forward part of the airfoil and the pitching
moments &bout tliequarter-chord point are thus reduced.
The present report gives data for two airfoils of
this type, de~i~ated the NACA 747A315 and the
TACA 747A415 cirfo!ls, from tests in the KACA two-
di.mensional low-turbulence pressure tunnel (TDT). Lift ,
drag, sad pitching moments of these sections were mea -
8cred for a range of Re-ynoldsnurrbers from 3 to 9 X 10 .
The effect of roughness at the leading edge on the lift
and drag characteristics of th
8
sections was determined
at a Reynolds number of 6 x 10 .
x
u~
c
distance from airfoil
along chard line
leading edge measured
section angle of attack
airfoil chord length
ITACACB No. L4125 3
cl
%1
cd
c“%/4
v
v
section lift coefficient
design lift coefficient for mean line
section drag coefficient
section pitching-moment coefficient about
quarter-chord point
local velocity over airfoil surface
free-stream velocity
mean-line designation described In reference 1
Reyzml.dsnumber
critical Mach number
In the derivation of the NACA 74’?A315airfoil, an
attempt was made to have uniform load from the leading
edge to 0.4c back of’the leading ed~e, to have this load
decrease linearly to zero at 0.7cS and to have zero load
from C.7C to the trailing edge. This object was attained
by combining a mean line of type a = 0.4 for a design
lift coefficient of 0.763 with a mean line of type
a = 0.7 for a desi~n lift coefficient ~f -0.463. Ordi-
nates and load distributions for these mean lines may be
derived from data presented In reference 1. ‘
In ~rder to maintain a favorable pressure Cradient
to 0.7c along the lower surface of the NACA 747A315 air-
f~il, the resulting mean llne was combined with a modl-
iication of the lTACA64,2-015 airfoil section. The
64,2-015 airfoil section was modified to reduce the slope
of the pressure gradient from 0.4c to 0.7c. Figure 1
shows the pressure distribution over the modified sym-
metrical NACA 64,2-015 airfoil section, together with
the pressure distribution of t~e NAOA 747A315 airfoil at
the design lift coefficient. Table I gives the ordinates
of the modified 64,2-015 airfoil section. Table II gives
the ordinates of the 747A315 airfoil section.
4
~
NACA CB No. L4125
The NACA 747A41.5 airfoil was obtained by combining
the modified 64,2-015 airfoil section with the following
mean-line conibination: a = 0.4, cl~ = 0.763; a = 0.7,
%i = -0.463; and a = 1.0, Czi = 0.100. Figure 2
shows the theoretical pressure dlstrlbutlon of the
NACA 747A415 airfoil at the design llft coefficient,
together with that of the basic symmetrical section (the
modified NACA 64,2-015 airfoil.). Ordinates for the
NACA 747A415 airfoil section are given in table III.
AIRFOIL DESIGNATION
The significance of the numbering system for these
airfoils is explained by the following exam le:
R71! in&c%gSdesignation NACA 747A415, the first number
the new series number; the second number “41’indicates
the extent over the upper surface, in tenths of the
chord from the leading ewe, of the region of favorable
pressure gradient at the design lift caefficlent; the
third number “7” indicates the extent over the lower
surface,in tenths of the chord from the leading edge,
of the region of favorable pressure gradient at the
design lift coefficient. The significance of the last
group of three numbers is the same as for the previous
6-series airfoils (reference 1); tkat is, the first
number followlng the letter gives the design lift coef-
ficient in tenths, and the last two numbers give the
airfoil thickness in percent of the chord. The letter
I?Air,which follows the first three numbers, is a serial
letter to distinguish different airfoils having parame-
ters that would correspond to the same numerical desig-
nation. For example, a second airfoil having the same
extent of favorable pressure gradient over the upper and
lower surfaces, the same design lift coefficient, and
the same maximum thiclmess as the original airfoil but
having a different mean-line combination and thickness
distribution would have the serial letter l’B;[’
TEST PRGCT3DURE
The models of the NACA”747A315 and
sections had a chord of 24 inches and a
The methods of constructing and testing
~.
747A415 airfoil
span of 35.5inches.
these models were
NACA CB NO. L4125 5
the same as those described in reference 1. The nozmal
corrections for wind-tunnel wall Interference were made
to the data obtained In the TDT according to the fol-
lowlng formulas, in which the primed quantities refer
to the values measured in the wind tunnel:
a. = 1.015 ao?
cd = 0.990 Udt
cl = 0.975 Ctf
cmc/4 = 0.990 cme/4 ‘
Tn addition to tests at Reynolds numbers of 3, 6, and
9 X 106 in the Smooth cond~tlon, tests were made at a
Reynolds number of 6 x 106 with the leading edges of
the airfoils roughened. The roughness consisted of
Carborundum grains with a maximum diameter or about
C.OIC to 0.015 inch. These grains were thinly sprinkled
cvsr the leading-edge phrtion of the wing section
covering a region of 1= inches from the leading edge
o.ntP.eupper and lower s-m?facesacross the span of the
wode1. A thin coat of shellac was used to hold the
grains on the surface.
Since the presentation of the data in reference 1,
certain changes have been made in the method of com-
puting lift coefficients from tunnel data. More accurate
factors have been derived, which give the proportion of
lift actually transferred to the floor and the ceiling
of the tunnel in the finite length covered by the floor
and ceili~ orifices. The revised factors result in a
decrease in the slope of the lift curve and a decrease
in the values of the maximum lift coefficient of approxi-
mately 4 percent. In addition to the change in these
factors, a correction for increased blocking effect at
angles of attack in the neighborhood of maximum lift has
been applied to the data presented herein. For the
present data, this additional blocklng correction derived
from pressure measurements along the floor and ceiling of
the tunnel resulted in a further reduction of the maximum
lift coefficient by between 1 and 2 percent.
* NACA CB No. L4125
RESULTS AND DISCUSSION
Sectisn lift, drag, an~pitchhg-moment data obtained
‘“:-.”:l;!the TIM?tests are presented for the NACA 747A315 and
T4’7A415alrfolls In figures 3 and 4, respectively. Fo1’
each atrfoil, the extent of the low-drag range Is nearly
as large as would be expected from the tests of a 15-
percent thick 6-series airfoil. Th8 center cf the 10W-
dmg range for both airfoils, however, Is about O.lcz
higher than the design lift coefficient given from the
combination of mean lines used for each airfoil. Thin
flifference iS probably aue to the approximations involved
in the mean-line theory in which the increments in
velocity over the upper and lower surfaces are assur,ed to
he sr,allcompared with the free-otrea;~ velocity.
A comparison of the oharacterlstics of the NACA747A31.5
and the NACA 747A415 alrfolls with those of the NACA652-415
airfoil at a Re-~olds numiber of 9 x 105 is given in the
table that follows. The dats i?cm the NACA 652-415 alrfoll
given in the table were obtafned fram test~ In the T9T and
have been reduced in the sarcemanner as for the 7-series
airfails. The values of critical Kach rxuiaer Mc were
ottalned from tinetheoretical low-speed pressure distri-
hutlsns by usina the chart presented on page 20 of tho
~ur~llemer~tto reference 10
1A(7A Range of
‘%/4/.at
~ &t
airfoil cd~n ox for 0$llaX de8ign
seotion low drag designc1 Cz
747A~15 0.J038 0.22 too.& -0:017 1.L3 0.626
7b7AU5 .C@l .32 tO .72 -.c136 1.50 .612
65#5 .oo&2 .99 to .58 -.071 1.62 l@
Langley b!emorial Aeronautical Laboratory
National Advisory Comaittee for Aeronautics
Langley Field, Va.
NACA CB No. L4125 ‘7
REFERENCE
1“ JQ~~:&*~t- N“D Abbott, Ira H., and Davidson,Preliminary Low-Drag-Airfoil and Flap
Data f~om Tests at Large Reynolds Numbers and Low
Turbulence, and Supplement. NACA ACR, March 1942.
!?ACAC13No. L4125 a
TABLE I.- MCDIFHD NACA 64,2-015 AIRFOIL ORDINATZ3
lstation~ and ordinates given il~percent of airfoil chor;l
Station Ordinate
o 0
.5 1.199
.75 1.435lo~5 1.801
2.5 2.462
5.0 5.419
7.5 4.143
10 4.743
15 5.684
20 6 .S84
,.,L5 6.~98
30 7=2X5
35 7.454:
40 7.494
45 ‘7.S16
50 7 .G03
.55 6.584
60 6.064
65 5.449
70 4.’738
75 3.921
80 3.020
85 2.086go 1.193
95 l443
100 0
L.E. radius: 1.544
NATIONAL ADVT30RY COMMITTEE FOR AERONAUTICS
.7 9H4.CACR No. L4125
TABLE II.- NACA 747A315 AIRF’OIL ORDINATES
~tatlons and ordinates given in percent of airfoil chor~
Upper surface I Lower surface
Station I Ordinate I Station I Ordinate
o
.229
.449
.911
2 l 109
4.564
7.053
9.558
14.5’09
19.668
24.758
29.867
35.CO1
40.200
45.375
50.447
55.463
60.435
65.366
70.241
75.130
80.073
85.038
90.016
95.G04
100
0
1.305
1.599
2.065
2.935
4.264
5.286
6.140
7.497
8 l 503
9.242
9.731
9.982
9.962
9.572
8.964
8.206
7.Z24
6.365
5.354
4.336
3 ;295
2.257
1.299
.481
0
0
.771
1.051
1 l 589
2.891
5.436
7 l 947
10.442
1!5.401
20.352
25.242
30 l 13:”
34.399
39.800
44.605
49.553
54.537
E9.565
64.634
69.7’59
74.m’o
79.927
e4.962
89.984
94 l 996
100
0
-1.031
-1.207
-1.473
-1.927
-2.518
-2.952
-3.304
-3.843
-4.247
-4.546
-4.773
-4.926
-5.020
-5.040
-5.@14
-4.930
-4.’?72
-4.509
-4.110
-3.5G2
-2.743
-1.915
-1.097
-.405
0
L.E. radius: 1 l 544
Slope of radius through L.E.: 0.232
NATICNAL ADVISORY COMMITTEE FOR AERONAUTICS
.NACA CB NO. L4125 10
TABLE III.- NACA 747A415 AIRFOIL ORDINATES
1F+atlOns ~d Ordinates given in percent Of airfoil chord~.,
Upper surface Lower surface
Station Ordinate StatIon Ordinate
o 0 0
l 183 1.318 .817 .:.994
.398 1.622 1 l 102 -1.160
.852 2.106 1 l 648 -1.406
2.041 3.016 2 l 959 -1.822
4.487 4.411 5.513 -2.349
6 l 9?2 5.488 8.028 -2.7Z0
9.4ri6 6.390 10.524 -3.038
14.521 7.827 15.479 -3.501
19.598 El.897 20.402 -3.045
24.698 9 l 607 25.3(22 -4.095
29.818 10.216 30,182 -4.286
34.964 10.497 35.(X56 -4.411
40.176 10.499 39mi324 -4.485
45.364 lC.121 44.636 -4.493
50 l 447 9.516 49 l 553 -4.462
55.474 8.753 54.526 -4.381
60.454 7.859 59.546 -4.235
65.393 6.870 64.607 -3.992
7!).273 5.83&3 69.727 -3.622
75.164 4.783 74.836 -3.C53
80.107 3.692 79.893 -2.344
85.066 Z .592 84.934 -1.578
90.037 1.546 89.963 -.838
95.015 .639 94 l 985 -.247
100 0 100 0
L.i%.radius: 1 l 544
Slope of radius through L.c.: 0.274
NATIONAL ADVISORY COMMITTEZ FOR AERONAUTICS
—
. -—
NACA CB No. L4125
.—
Fig. 1
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EAOA 6k,2d15 dFfOlh.
NACA CB No. IJ4125 Fig. 2
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Aerodynamic characteristics of the NACA 747A315 and 747A415 airfoils from tests in the NACA two-dimensional low-turbulence pressure tunnel

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