Wind tunnel tests were conducted on a 0.03 scale model of a large wide-body commercial aircraft to determine the effects on the static aerodynamic characteristics resulting from the attachment of a belly pod for the long-range deployment of outsize military equipment. The effectiveness of horizontal-tip fins in augmenting directional stability was investigated. At a test Reynolds number of 1.08 x 1,000,000, the addition of the pod results in an increase in total drag of approximately 20 percent. Trim drag due to the pod is very small. Although the pod produces a significant decrease in directional stability, the addition of the tip fins restores some of the stability, particularly at the lower angles of attack

Croom, D. R.

Jernell, L. S.

English

NASA Technical Reports Server

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3 1176 00133 9853 
NASA Technical Memorandum 80052 
NASA-TM-8005219790011930 
EFFECTS OF A MILITARY CARGO POD 
AND TAIL FINS ON THE AERODYNAMIC 
CHARACTERISTICS OF A LARGE WIDE-BODY 
TRANSPORT MODEL 
Lloyd S. Jernell and Delwin R. Croom 
February 1979 
NI\SI\ 
National Aeronautics and 
Space Administration 
Langley Research Center 
Hampton, Virginia 23665 
Ilnlllll lIn IIII nlll nlll IIIII Ilnl IIII 1111 
NF00543 
https://ntrs.nasa.gov/search.jsp?R=19790011930 2020-03-21T23:06:05+00:00Z
1 Report No I 2 Government AccessIon No 3 RecIpIent's Catalog No 
NASA TM-800S2 
4 TItle and SubtItle 5 Report Date 
EFFECTS OF A MILITARY CARGO POD AND TAIL FINS ON THE February 1979 
AERODYNAMIC CHARACTERISTICS OF A LARGE WIDE-BODY 6 Performong OrganIZatIon Code 
TRAN,PORT MOn~1 
7 Author(s) 8 PerformIng OrganIZatIon Report No 
Ll oyd S. Jerne 11 
Delwin R. Croom 
10 Work Unot No 
9 PerformIng OrganIZatIon Name and Address 791-40-13-01 
NASA Langley Research Center 11 Contract or Grant No Hampton, Vlrglnla 23665 
13 Type of Report and Perood Covered 
12 Sponsorong Agency Name and Address TechnlCal Memorandum 
Natlonal Aeronautics & Space Adml m stratlon 14 Sponsoro n9 Agency Code 
Washlngton, DC 20546 
15 Supplementary Notes 
16 Abstract 
Wlnd tunnel tests have been conducted on a 0.03-scale model of a large 
wlde-body commerclal alrcraft to determlne the effects on the statlc 
aerodynamlc characterlstics resultlng from the attachment of a belly 
pod for the long-range deployment of outslze milltary equipment. Also 
lnvestigated was the effectlveness of horlzontal-tail tip fins In 
augmentlng directional stability. 
At a test Reynolds number of 1.08 x 106, the addltlon of the pod 
results In an lncrease in total drag of approxlmately 20 percent. 
Trim drag due to the pod is very small. Although the pod produces a 
slgnlflcant decrease In directional stablllty, the additlon of the 
tlP flns restores some of the stablllty, partlcularly at the lower 
angles of attack. 
17 Key Words (Suggested by Author(s)) 18 D,strobut,on Statement 
Large mllltary cargo pod Unclasslfled - Unlimlted 
Alrcraft/cargo pod lntegratlon 
SubJect Category 05 
19 Securoty Classlf (of thIS report) 20 Securoty Classlf (of thIS page) 21 No of Pages 22 PrIce" 
UnClaSSlfled UnclasSlfled 19 $4.00 
• For sale by the NatIOnal Technical Information Service Springfield Virginia 22161 
NASA-Langley, 1979 
SUMMARY 
Wind tunnel tests have been conducted on a 0.03-scale model of a large 
wide-body commercial aircraft to determine the effects on the static aerodynamic 
characteristics resulting from the attachment of a belly pod for the long-range 
deployment of outsize military equipment. Also investigated was the effective-
ness of horizontal-tail tip fins in augmenting directional stability. 
At a test Reynolds number of 1.08 x 106, the addition of the pod results 
in an increase in total drag of approximately 20 percent. Trim drag due to the 
pod 1S very small. Although the pod produces a significant decrease in ' 
directional stability, the addition of the t1P fins restores some of the 
stability, particularly at the lower angles of attack. 
INTRODUCTION 
For several years military strategists of the United States have voiced 
concern about the need for increased airlift capability during a limited-warfare 
conflict, particularly with regard to Western Europe. Until the size of the 
military fleet is significantly increased, utilization of commercial aircraft 
on a temporary basis may be necessary during emergency operations. Although 
currently-operational military and commercial transports can carry most military 
equipment in the airlift inventory, the Lockheed C-5A is the only aircraft 
capable of the deployment of outsize cargo (defined as that too large for the 
Lockheed C-141). However, the present C-5A fleet numbers only about 77 
aircraft; production has ceased, and is very unlikely to be resumed. Hence, 
the most critical shortfall in airlift capability at present is that related 
to the long-range deployment of outsize equipment. 
Various solutions to the outsize-cargo problem have been proposed, each 
involving the extensive modification of commercial wide-body aircraft. These 
suggested alterat10ns include increasing the fuselage upper-lobe diameter, 
lowering the main deck, increasing the size of the loading-door openings, 
swinging the tail cone for rear-end loading, and strengthening the main-deck 
floor. However, the overall systems cost of a fleet incorporating such 
modifications would likely be prohibitively high due to the high modification 
cost, loss of operator revenue during modification, significantly higher 
operating cost, likely decrease in resale value of the less efficient aircraft, 
and the cost of the design and construction of new loading equipment for lifting 
the heavy cargo to the height of the aircraft main deck. 
In order to minimize aircraft modification and the adverse effect on the 
efficiency of commercial operations, a preliminary study was conducted to 
determine the feasibility of mating an outsize-cargo pod to the underside of a 
large wide-body aircraft. The design-mission specifications, descriptions of 
the configurations considered, and the study results are reported in reference 
1. No distinct problems were identified which might render the concept imprac-
ticable. 
Since the concept appeared to be feasible, tests were conducted ln the 
Langley V/STOL wind tunnel using a 0.03-scale model of the carrier aircraft with 
the retractable-gear pod of reference 1. In order to augment directional 
stability, horizontal-tail tip fins similar to those used on the NASA alrcraft 
employed in transporting the Space Shuttle were also tested. The purpose of 
this paper is to present the results of the investigation. 
SYMBOLS 
The longitudinal and lateral-directional characteristlcs are referenced to 
the stability- and body-axis systems, respectively. All moments are referred to 
the quarter-chord point of the wing mean aerodynamic chord (see fig. l(a)). 
b 
2 
wing span, 1. 790 m 
Drag 
drag coefficlent, qS 
Lift 
1 ift coefficient, CiS 
Rolling moment 
rolling-moment coefficient, qSb 
6C 1 
effective-dihedral parameter, __ , per degree 
68 
Pitching moment 
pitching-moment coefficient, qSc 
Yawlng moment 
yawing-moment coefficient, qSb 
6C 
directional-stability parameter, __ n_ , per degree 
Side force 
C side-force coefficient, qS y 
C side-force parameter, ACy , per degree ys ~S 
c 
q 
S 
t 
x 
tip-fin chord 
wing mean aerodynamic chord, 0.250 m 
horizontal-tail incidence angle (positive with trailing edge down), 
deg 
free-stream dynamic pressure 
reference wing area, 0.460 m2 
thlckness 
longitudinal dimension, measured from tip fin leading edge 
angle of attack, referred to fuselage reference line, deg 
angle of sideslip, referred to fuselage reference line, deg 
Model and Apparatus 
Drawings of the 0.03-scale model of the 19rge wide-body aircraft with the 
cargo pod are presented in figure l(a). Details of the horizontal-tail tlP fins 
are shown in figure l(b). Photographs of the model mounted in the Langley V/STOL 
tunnel are presented in fiqure 2. Boundary layer transition strips approximately 
0.30 em wide and composed of No. 60 abrasive grit were placed 2.54 cm rearward 
of the leading edges of the wing, tall surfaces, and the cargo pod. A transltion 
strip also was located on the fuselage 5.08 em rearward of the nose apex. 
The wind tunnel section has a height of 4.42 m, a width of 6.63 m, and a 
length of 14.24 m. The model was sting supported and employed a six-component 
3 
strain-gage balance for the measurement of forces and moments. The angle of 
attack was determined by use of an accelerometer mounted within the model 
fuselage. 
Tests, Drag Accuracy, and Corrections 
All tests without the horizontal-tail tip fins on the model were 
conducted at a free-stream dynamic pressure of 2.394 kPa, which corresponds to 
a velocity of 62.3 m/sec and a Reynolds number, based on the wing mean aerody-
namic chord, of 1.08 x 106. All tests with the tip fins on were performed at 
a dynamic pressure of 479 Pa, a velocity of 28.0 m/sec, and a Reypolds number 
of 0.48 x lOb. The angle-of-attack range was from approximately -40 to 240 . 
The angle of sideslip ranged from about -100 to 100 . 
Mixed laminar and turbulent flow existed over much of the model at the 
lower Reynolds number. Hence, longitudinal data are not presented for this 
portion of the tests since the drag coefficients are not representative of fully-
turbulent-flow conditions. Based on balance calibration and data repeatability, 
the accuracy of the higher Reynolds number drag coefficients presented herein 
is believed to be approxlmately ±0.0006. 
Blockage corrections were applied to the data utillzing the method of 
reference 2. Jet-boundary corrections to angle of attack and drag were applied 
in accordance with the method of reference 3. 
DISCUSSION 
The effects of horizontal-tail incidence on the longitudinal aerodynamic 
characteristics of the carrier aircraft and the aircraft/pod configurations are 
shown in figures 3 and 4, respectively. The effects of tail incidence on drag 
coefficient are small at lift coefficients less that approximately 0.6. From 
preliminary performance studies, it is estimated that the cruise lift 
coefficient for the aircraft/pod configuration would be in the range of 0.3 to 
0.4. For this CL range, the data of figure 4(b) indicate that the conflguration 
would trim at a tail incidence of less than one degree. For this trim position, 
the drag polars of figure 4(a) indicate that trim drag is very small. The 
effects on the longitudinal characteristics of adding the pod to the carrler 
aircraft are shown in figure 5. In the aforementioned lift coefficlent range 
for the composite configuration, the addition of the pod results in an increase 
in drag of approximately 20 percent at the test Reynolds number of 1.08 x 106. 
Although the pod causes a slight decrease in pitching-moment coefficient over 
most of the angle-af-attack range, the decrease is appreciable at angles of 
attack between 18 and 22 degrees. 
Variations of the lateral and directional characteristics with angle of 
sideslip at a = 0 and 100 , and it = 0 are presented in figure 6 for the basic 
aircraft, aircraft/pod, and aircraft/pod/fins configurations. The data are 
relatively linear between S = ~5 degrees. Data at these angles were used to 
compute the lateral- and directional-stability derivatives of figure 7. 
4 
Generally, there is a decrease in CyS as components are added. Although the 
pod produces a significant decrease in directional stability, the addition of 
the tip fins restores some of the stability, particularly at the lower angles 
of attack. The pod has an adverse effect on the effective dihedral at angles 
of attack above approximately 15 degrees; however, these effects are partly 
offset by the addition of the fins. 
CONCLUSIONS 
Wind tunnel tests have been conducted on a O.03-scale model of a large 
wide-body commercial aircraft to determine the effects on the static aerodynamic 
characteristics resulting from the attachment of a belly pod for the long-range 
deployment of outsize military equipment. Also investigated was the effective-
ness of horizontal-tail tip fins in augmenting directional stability. The 
conclusions are summarized as follows: (1) At a test Reynolds number of 1.08 
x 106, the addition of the pod results in an increase in total drag of 
approximately 20 percent. (2) Trim drag due to the pod is very small. (3) 
Although the pod produces a significant decrease in directional stability, the 
addition of the tip fins restores some of the stability, particularly at the 
lower angles of attack. 
5 
REFERENCES 
1. Quartero, C. B.; Washburn, G. E.; and Price, J. E.: Boeing 747 Aircraft 
With External Cargo Pod. NASA CR-158932, 1978. 
2. Herriot, John G.: Blockage Corrections for Three-Dlmenslonal-Flow 
Closed-Throat Wind Tunnels, with Consideration of the Effect of Compressibility. 
NACA Rep. 995, 1950. (Supersedes NACA RM A7B28). 
3. Gillis, Clarance L.; Polhamus, Edward C.; and Gray, Joseph L., Jr.: 
Charts for Determining Jet-Boundary Corrections for Complete Models in 7-
by la-Foot Closed Rectangular Wind Tunnels. NACA WR L-123, 1945. (Formerly 
NACA ARR L5G31). 
6 
-A 
-t 
I ~ ~ 
": -0 
I 
1 
i 
L 
.-
~ 
_t 
-
Fuselage 
1 
1l73J 
954 - ,- - -- / 
- - I. 645 ---
C 
4 
2060 -----
~-t--.--
(al Aircraft/pod configuration. 
Figure I. - Model geometry. DimenSions are In meters. 
I 
- -- ~ 
~ 
-> 
Fin airfoil thickness 
distribution 
x t 
Cf Cf 
0.0000 0.0000 
.0050 .0140 
.0125 .0210 
.0250 .0279 
.0500 .0396 
.0750 .0477 
.1000 .0547 
.2000 .0745 
.3000 .0850 
.4000 .0896 
.5000 .0885 
.6000 .0780 
.7000 .0605 
.8000 .0407 
.9000 .0221 
1.0000 .0035 
/ 
--~ 
.004 ~ 
o 
t 
, ~ .087 ---~ 
I 
~ .069 ~ : .006 
I I ' I 
r -J-- --! - --
I--l 
I I 
.1--1_ 
---==-=-
t 
N 
2: 
t 
.0I4~ ~ I 
~ ~.024 
(b) Horizontal-tail tip fins. 
Figure I. - Concluded. 
(a) Aircraft/pod configuration without horizontal-tail tip fins. 
Figure 2. - Model installed in tunnel. 
til 
C 
'r-
'+-
D. 
+-' 
n::s 
+-' 
I 
r-
n::s 
+-' 
c 
0 
N 
'r-
>- "0 0 OJ 
..c:: 
"0 
::l 
..c:: r-
+-' U 
C 3: 0 
c u 
0 
+-' 
n::s N 
>-
::l OJ Ol >-
'r- ::l 
'+- Ol C 
0 
U 
I..L. 
"0 
0 
D. 
........ 
+-' 
'+-
n::s 
>-
u 
>-
0::( 
.0 
.7 
It. deg 
0 Off 
.6 0 -5 
<> 0 b. 5 
.5 
3 
.2 
.1 
o 
25 
20 
15 
a,deg 10 
5 
o 
-5 
-.4 -.2 o .2 .4 .6 .8 1.0 12 1.4 
(a) lift and drag ooefftclents 
Flgure 3.- Effect of homontal-talllncidence on the longitudinal aerodynamic characteristics of the carrier aircraft model. 
.6 
:-
.4 
2 
It. deg 
0 0 Off 0 
-5 
Cm 0 0 6. 5 
-2 
-.4 
-.6 
-.8 
-5 0 5 10 15 20 25 
a,deg 
.6 
.4 
.2 
0 
Cm 
-2 
-.4 
-.6 
-8 
-4 -2 o 2 4 6 8 1.0 12 1.4 
(b) Pite/ling-moment coefficient 
Figure 3. - Concluded. 
.7 
It· deg 
o Off 
.6 8 .~ 
!::. 5 
5 
.4 
Co 
3 
2 
25 
20 
15 
a,deg 10 
5 
o 
-5 
-4 
- 2 o .2 4 .6 8 1.0 
(a) lift and drag ooefflclents 
Figure 4.- Effect of honzontal-talllncidence on the longitudinal aerodynamic characterIStiCS 
of the carner aircraft model With the cargo pod attached. 
1.2 14 
.6 
.4 
.2 
0 
Cm 
-2 
-.4 
-.6 
- 8-
4 -2 0 2 4 6 8 10 12 1.4 
CL 
(b) Pltchng-moment ooefflclent 
F1gu re 4. - Conci udf'd. 
.6 
5 
.4 
3 
2 
.1 
o 
25 
20 
15 
a,deg 10 
5 
o 
-5-
-.2 .2 
cargo 
pod 
o Off 
o On 
.4 .6 
CL 
.8 
(a) lift and drag coefficients. 
1.0 1.2 1.4 
Figure 5.- Effed of the cargo pod on the longitudinal aerodynamiC charaderrshcs of the carner aircraft model, It· 0°. 
o 5 
fR±t t I J-c , ,-T~;~~ , -1~ r-'-.2 
I 
f---T+-I I ::!-++ ' 
'-+--rH- -t-+-H~+ 
:1+:- -++ J I +-o 
" +tT r--0-+---
I 
I 
H- I"""" H- ~, --t -.2 
H~++ 
r 
I 
I 
-.4 
I 
I 
I 
f--I-T l+--l-j- L 
L;+: f-i--.- ~j....L t+ :~+-+ . --
-.6 
~~+ 
--f::t+-+- j--+-r ++ 
, ' ~T ~j- ~~ f+++ -·~.2 o .2 
FIgure 5.- Concluded. 
10 
a,deg 
-+ ~ - h-++ 
~,~- ~+ 
I 
-l-
I 
I 
I 
I 
t-l-
.4 
15 
_ +-"-- :. f+ 
~-
,--.--: I 
I 
" 
f--t-Lti= 
.6 
CL 
-r-
o 
o 
+J-- -- 4+ h-+ jt-
20 25 
~ ... -+--
. ri:-l .L-+-~ C++-~-~\:-t+ 
t+: -+ 4- H- f-+1-
~i..i-
-t 
I 
, ' 
I I 
if I f-t~~ f-
. 
I 
, 
I 
I 
, 
I I 
I ~H~4-
.8 1.0 
(b) Pitch lng-moment coefficient. 
Cargo 
pod 
Off 
On 
-J.-I-t· 
+ t' 
I 
4-
-'-
~ 
I 
~t-l 
++~ 1--L 
.-
"T,....,... 
tF:::: 
~ 
~+t 
tt-
I 
f-+ 
, '--+--
~+-
~ 
f f+t1-i}F-
1.2 1.4 
C y 
3 
l" I ~' 
-/ ~ ' 1 I ! rLl,W 
2 ~ fnN~ 
t tr !iH~ 
t- jJ t I, I I ' 
0 
I 
7 
3 
02 
-02 
-04 
04 
.0.:: 
-02 
p ~ ,1 'f J + q ~ 8' rtfl i! ff :~'~)~' !~ 
, 
ft 
j 
r 
+ t4' 
I rl f f +,ittHI-Htlli1 
• It :+ It l~ ~1 ~~ 
It 
1 
et ii 1 j t ~ H 'F f -04.~t~'~~~1 uu~l~r~~141r4:~,~r~-~, ~'~[~I_~J~,I~I~tll,~l~Tl~t~~~~~~~~llll~~~~ 
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 
/3,deg 
(ala .00 
Figure 6.- Effect of the cargo pod and cargo pod plus horrzontai-tail tip fins on the lateral-directional characterrslres of the carner aircraft model. It· ao. 
" C 
n 
Cl 
0 4 
0 2 
-0 2 
-0 4 
0 4 
0 2 
0 
Flgu re 6. - Concluded 
,a,deg 
(b)a • 10° 
-' 
~ , ~ I 
o ; II ~\ 1I ! 
4 j 1++ 
~l } ! 
-0 I t I 
-0 2 
H 3 It -0 
L 
,/I 00 
00 2 -
0 
-00 2 
00 2 
0 
2 
-00 4 
- 00 e:: 
-5 o 
-\1 J i r ! l If I i i 11 \ Iii I i f-! i 1 
- I ~ 1 iii i I t I fl ft, 11 
H qru-n 1 I 1 _ tI} ~V ~ t~ I 
tFt! H 1 
t I 
~lf_l-f II 
, 
-
cargo Horizontal-
pod 
0 Off 
0 On 
<> On 
5 
talj 
tIP fins 
Off 
Off 
On 
10 
a,deg 
15 20 
-~ it t 
+ 
~ I j 
-
25 
Flgu re 7. - Effects of the cargo pod and cargo pod plus horizontal-tail tip finS on the 
lateral-directional stabIlIty derivatives of the carrier aircraft model; It .0°. 
End of Document 


Effects of a military cargo pod and tail fins on the aerodynamic characteristics of a large wide-body transport model

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