Royall, John F

Stoney, William E, Jr

English

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RM L56D16 
MACA 
RESEARCH MEMORANDUM 
ZERO-LIFT DRAG OF A SERIES OF BOMB SHAPES AT MACH 
NUMBERS FROM 0.60 TO 1.10 
By William E. Stoney, Jr., and John F. Royall 
Langley Aer onautical Laborator y 
Langley Field, Va. 
NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
WASHINGTON 
July 26, 1956 
https://ntrs.nasa.gov/search.jsp?R=19930089367 2020-06-17T05:34:15+00:00Z

i 
I . 
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NACA RM L56D16 
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
RESEARCH MEMORANDUM 
ZERO-LIFT DRAG OF A SERIES OF BOMB SHAPES AT MACH 
NUMBERS FRCM 0.60 TO 1.10 
By William E. Stoney, Jr., and John F. Royall 
SUMMARY 
Zero-lift drag data were obtained on a series of six bomb shapes. 
Five configurations had the same body shape, the only difference being 
in the body-surface conditions and the profile and plan form of the fins', 
while the sixth configuration had a different and longer body shape. 
The models were launched from a helium gun (at the Langley Pilotless 
Aircraft Research Station at Wallops Island, Va . ), and data were obtained 
for Mach numbers from 0.60 to 1.10 with corresponding Reynolds numbers 
based on body length of 5 X 106 to 10 X 106 . 
It was found that at subsonic speeds the blunt trailing edge of 
the fins contributed a large share of the drag while the effect of the 
blunt leading edge was negligible. Two models whose roughness did not 
exceed 20 rms microinches had measurably lower subsonic drag coefficients 
than the remaining models whose roughness varied between 100 and 250 rms 
microinches. 
INTRODUCTION 
The Langley Pilotless Aircraft Research Division has conducted zero-
lift drag tests on a series of bomb models . The object of the tests was 
to determine the subsonic drag level of a proposed configuration. When 
this original configuration proved to have too high a subsonic drag, 
attention was turned to determining the means and the efficacy of the 
means to be used to reduce the subsonic drag level. The test program 
is reported herein. The models were launched from a helium gun at the 
Langley Pilotless Aircraft Research Station at Wallops Island, Va. 
2 NACA RM L56D16 
SYMBOLS 
M M9.ch number 
q dynamic pressure 
total drag coefficient, Total drag force 
q X Maximum frontal area 
CDb base drag coefficient 
CDf friction drag coefficient 
L length 
D maximum diameter 
rms root mean square 
R Reynolds number, based on model length or fin mean chord 
MODELS AND TESTS 
The test configuration dimensions are shown in figure 1, photographs 
appear in figure 2, and the drawing ordinates are given in tables I(a) 
and l(b). All of the models were measured and found to be within 
±0.016 inch of the desired dimensions. The maximum diameter, 2.598 inches, 
and the total body length, 14.64 inches, were the same for each of the 
first five configurations, while the sixth configuration had a maximum 
diameter of 3.00 inches, and 20.50 inches was the total body length. 
The models have been divided into six configurations (a to f). 
Two essentially identical models of configurations a and f were flown 
and these are noted simply as models 1 and 2 for both configurations. 
A description of each configuration is shown in table II, together 
with the surface measurements. These measurements were made with a small 
portable profilometer (trade-marked Type Q, Physicists Research Co.). 
j 
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NACA RM L56D16 3 
The models were fired from a helium gun at Wallops Island, Va. 
(The helium gun makes use of the rapid release of compressed helium to 
propel the models into free air at a Mach number of about 1.1.) Velocity 
data were obtained as the models decelerated by the use of a CW Doppler 
velocimeter which was located on the ground next to the helium gun. 
Total drag coefficients were determined from the measured velocity 
t ogether with the variation of density, temperature, and wind velocity 
with altitude obtained by a radiosonde survey made about the time of 
firing. These measurements are estimated from experience with previous 
models to be accurate within ±G.Ol in CD and ±C.Ol in M. 
Data were obtained over a range of Mach numbers from 0.60 to 1.10 
a nd for Reynolds numbers based on body length from 5 X 106 to 10 X 106. 
RESULTS AND DISCUSSION 
The drag coefficients for the test models are presented as functions 
of Mach number in figure 3, with the coefficients based on maximum body 
frontal area (~D2/4). The results are of interest primarily at the Mach 
numbers below 0.90. The various configurations are compared to show the 
effects of the following test variables: leading- and trailing-edge 
bluntness, fin thickness, and body-surface roughness. Though the models 
were rolling at an unknown rate (note 20 incidence of two fins of con-
figurations a to d and unsymmetrical fin profile of configurations e 
and f), no attempt has been made to evaluate the influence of the rolling 
rate on the drag. It seems reasonable to assume, however, that all the 
models of series a to d and series e and f rolled at approximately equal 
rates, but the two groups may have had somewhat different rates of roll. 
Effect of Blunt Trailing Edge 
The subsonic drag levels of both configuration a models (which had 
blunt-trailing-edge fins) were considerably higher than those of the 
remaining models, all of which, with the exception of configuration e, 
had fins with sharp trailing edges (fig. 3(a)). The trailing edge of the 
configuration e was thin enough (approximately 1/4 of that of config-
uration a) so that it may be taken as sharp for the purposes of this 
report. The drag difference between the a models and the remaining models 
may be attributed directly to the base pressure on the blunt fins. If the 
base pressures of reference 1 and the ratio of the model fin base area to 
body frontal area are used, the resulting eDt is approximately 0.06, 
which is about the difference shown in figure 3(a) between model 2 of 
configuration a and configuration c. The difference between models 1 
and 2 of configuration a may be due partly to differences in fin base area 
(due to construction inaccuracies) and partly to test inaccuracy. 
------- --- ~-~.~-~ 
4 NACA RM L56D16 
Effect of Blunt Leading Edge 
Comparisons of the data (fig. 3) of configurations b (sharp leading 
edge) and c (blunt leading edge) indicate that the drag increase caused 
by the blunt leading edge was small. 
Effect of Fin Thickness 
Although the fins of configuration e are of different plan form 
than those of the other short models, it seems reasonable to assume that 
the major cause of the higher drag-rise Mach number of this model is the 
thinness of its fins, that is, 0.046 inch compared with 0.16 inch. Since 
the drag increases shown by all the configurations are approximately 
equal, it is probably not the increased drag rise of the thicker fins 
themselves that causes the early drag rise of the thick-finned models but 
rather the greater interference of the fins with the body which, in turn, 
causes the early drag rise of the body itself. 
Effect of Body Surface 
All of the models presented in figure 3(a) except configuration d 
were in the original "as cast" condition. Configuration d was sanded to 
approximately 30 to 40 rms microinches over the nose and over scattered 
sections of the remaining parts of the model. A comparison of the data 
for configurations band d indicates that as far as drag is concerned the 
body surfaces are equally rough. That even the smoothest model (configura-
tion d) was far from aerodynamically smooth is indicated by the comparison 
of the data with the two calculated friction-drag points at M = 0.7 
and M = 0.9. These points were calculated by the method of Van Driest 
(ref. 2), with the assumption of turbulent flow over the entire lengths 
of both body and fins. Since at subsonic speeds there is no pressure 
drag other than that caused by separated flow regions, most of this dif-
ference between theoretical and measured subsonic drag may be assumed 
to be due to the effect of the surface roughness on the level of the 
t urbulent-friction-drag coefficient. At least a qualitative idea of 
this effect may be gained from the chart on page 44 of reference 3 which 
shows the dependency of the turbulent skin friction on grain size. 
The presence of this effect in the data of all the models of fig-
ure 3(a) is shown by the better agreement of theoretical and measured drag 
in figure 3(b). The two models of configuration f, while longer J were 
considerably smoother allover than the smaller models. This is shown in 
table II which mentions that configura tion f had a maximum roughness 
of 20 rms microinches, while the smoothest of the short models had con-
siderable areas with roughness of 80 to 160 rms microinches. The effect 
of this surface roughness on the friction drag is shown by comparison 
with the theoretical calculations of reference 2. At M = 0.7, the fin 
I • 
NACA RM L56D16 5 
Reynolds number based on mean aerodynamic chord is about 1 X 106 and 
thus a CDf value based on laminar flow for the fin is also presented. 
CONCLUSIONS 
Tests on a series of bomb shapes flown at Mach numbers from 0.60 
to 1.10 and body length Reynolds numbers of 5 X 106 to 10 X 106 indicate 
the following effects of configuration change on zero-lift drag, 
1. At subsonic speeds the blunt trailing edge contributed a large 
share of the drag. 
2. The effect of a blunt leading edge was relatively small in com-
parison with drag caused by the blunt trailing edge . 
3 . The subsonic drag showed no change attributable 
the range of roughnesses of 100 to 250 rIDS microinches. 
maximum roughness did not exceed 20 rillS microinches had 
subsonic drag levels. 
Langley Aeronautical Laboratory, 
National Advisory Committee for Aeronautics, 
Langley Field, Va., March 30, 1956 . 
REFERENCES 
to roughness in 
Two models whose 
measurably lower 
1. Morrow, John D., and Katz, Ellis: Flight Investigation at Mach 
Numbers From 0.6 to 1.7 To Determine Drag and Base Pressures on 
a Blunt-Trai1ing-Edge Airfoil and Drag of Diamond and Circular-Arc 
Airfoils at Zero Lift. NACA TN 3548, 1955. (Supersedes NACA 
RM L50E19a .) 
2 . Van Driest, E. R.: Turbulent Boundary Layer in Compressible Fluids. 
Jour. Aero. Sci., vol. 18, no. 3, Mar. 1951, pp. 145-160, 216. 
3 . Hoerner, Sighard F.: Aerodynamic Drag. Publ. by the author 
(148 Busteed, Midland Park, N. J.), 1951. 
6 NACA RM L56D16 
TABLE I. - DRAWING ORDlliATES OF CONFIGURATIONS 
(a) Configurations a, b, 
c, d, and e 
Station, in. Radius, in. 
0 0 
.12 
·315 
.28 .476 
.44 .585 
.70 .787 
.935 .833 
1.170 .914 
1.400 .981 
1.640 1.046 
2.440 1.190 
2.840 1.235 
3.240 1.271 
3.640 1.287 
4.040 1.299 
6.200 1.299 
6.90 1.289 
7.60 1.259 
8.31 1.210 
9.02 1.142 
10.42 .947 
11.134 . 836 
11.839 .706 
12.160 .642 
12.544 .563 
13.249 .417 
13.954 .271 
14.521 .153 
14.640 0 
(b) Configuration f 
Station, in. Radius, in. 
0 0.529 
.100 .608 
.165 .656 
·300 .736 
.600 .886 
.665 .916 
1.100 1.071 
1.165 1.093 
1.600 1.208 
1.665 1.225 
2.040 1.300 
2.165 1.325 
2·520 1.378 
2.665 1.393 
2.980 1.432 
3.165 1.453 
3·440 1.470 
3.665 1.486 
4.165 1.498 
4.240 1.499 
4.365 1.500 
10.762 1.500 
11.576 1.488 
12.388 1.454 
13·201 1·397 
14.015 1.319 
14.829 1.200 
15.642 1.095 
16.454 .966 
17.638 .742 
18.895 .481 
19·709 .313 
20.363 .176 
20.500 0 
- - - - - -- ""- --- ~~~. ---- - .--~----- ~ ~~ -.......- ----~-......-- -- ---------.~ ----
NACA RM L56D16 7 
TABLE II. - CONFIGURATION DETAILS 
Fin leading Fin trailing Body_ Body-surface Configuration 
edge edge surface measurements, 
condition rIDS microinches 
a (models 1 Blunt Blunt Rough Nose - 80 to 130 
and 2) Body - 140 to 250 
Fins - 40 to 60 
b Sharp Sharp Rough Same as 
configuration a 
c Blunt Sharp Rough Same as 
configuration a 
d Sharp Sharp Smooth Nose - 30 to 40 
Body - 40 to 50 
(smooth sections) 
80 to 160 
(rough sections) 
Fins - 30 to 35 
e Blunt Blunt Rough Same as 
configuration a 
f (models 1 Blunt Blunt Smooth Body and fins -
and 2) 16 to 20 
I 
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f 
! 
L 
I " LID = 5· 61 : I 
I • LID = 1.55 , I !,ID = .83, I ' LID = 3.2 3 
'" ,-~ 
-It ~ 4 
, , ,1 
------------- cr- l-
D = 2.598 
2.75 
i-c' 14. 64 ~ I 
Config. 
a. 
b, d 
c 
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L .16 L.07 
! II III/LIfT /1/11 I ! __ 
1I I I I II I nT r 1 Tl 7 7 I I I I -
Section A-A 
(N ot to scale) 
Note- 2 fins set at about 
2 0 incidence. 
(a) Dimensions of configurations a , b , c , and d . 
Figure 1 .- Test configurat ions. (All dimensions are in inches.) 
"-
-----------~-.------ ,---'-------
co 
~ () 
~ 
~ 
t:-i 
\J1 
0\ 
t:1 
f-' 
0\ 
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NACA RM L56D16 9 
T 
---c:r- 4 . 00 
~ 
-L -L .o.;;)~ ~ 1/11 1/12111 /I IJ,) II pol L . 020 
lNote- Fin section tapered on 
Se ction A-A one side only. 
( No t to scale) 
(b) DLmensions of configuration e (body dimensions same as for configu-
r ations a , b, c , and d) . 
T 
~-----L/D = 6 .84-----~:1 
= 2.13 --I LID = 3 .25----;>-i 
LID = 1 .46 
-------r- 4 .75 
D = 3.00 ~ 
~------------------2 0 ·5 0--------------------~~ 
~ -L L:~4~111777777771'I I'Dl t= .020 
- Note- Fin section tap ered on 
Secti on A- A 
(Not to scale) 
one si d e only. 
(c) Dimensions of configuration f. 
Figure 1 .- Concluded . 
10 NACA RM L56D16 
(a) Configurations a , b, c, and d. 
(b) Configuration e. 
(c) Configuration f. L-92473 
Figure 2.- Photographs of models. 
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.. . . .... . .... . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . 
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CD 
.2 
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a 
.5 .6 
·7 .8 ·9 1.0 1.1 1.2 1.3 
M 
(a) Configurations a , b, c , d, and e. 
Figure 3.- Drag coefficients as a function of Mach number for test f-' 
configurations. f-' 
L 
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12 NACA RM L56D16 
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Zero-lift Drag of a Series of Bomb Shapes at Mach Numbers from 0.60 to 1.10

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