Lamb, M.

Sawyer, W. C.

Thomas, J. L.

English

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THEORETICAL AND EXPERIMENTAL SUPERSONIC LATERAL-DIRECTIONAL
STABILITY CHARACTERISTICS
Milton Lamb, Wallace C. Sawyer, and James L. Thomas
NASA Langley Research Center, Hampton, Virginia
ABSTRACT
	
4/
'A program has been initiated at NASA Langley Research Center to
assess several methods for estimation of lateral-directional stability.
As a basis for comparison, experimental data are presented for a simple
wing-body vertical tail configuration. The methods for estimating the
characteristics include a second-order shock expansion and panel
method (MISLIFT), a slender body and "first-order" panel method
(APAS), and a "higher-order" panel method for linearized supersonic
flow (PAN AIR). The results show that PAN AIR provides accurate
estimates of these characteristics at moderate angles of attack for
Q	 complete configurations with either single or twin vertical tails.
CC	 APAS will provide estimates for complete configurations at zero angle
of attack. However, MISLIFT will only provide estimates for the
simplest body-vertical tail configurations at zero angle of attack.,,
INTRODUCTION
Recent developments in analytical methods have resulted in computer codes
for rapid accurate estimates of the aerodynamic characteristics of aircraft
and missile configurations at supersonic speeds. Much attention has been
given to the development and assessment of these methods for predicting the
lift, drag, and pitching moment of complex configurations. Many of these
methods have the capability of predicting the lateral-directional characteris-
tics of aircraft and missiles, but their utility has not been evaluated by
comparison with experiment.
A program has been initiated at NASA Langley Research Center to provide
^y	 experimental data on simple wing-body-vertical tail configurations for the
purpose of assessing lateral-directional stability estimates at supersonic
speeds. This paper will present these data along with an assessment of
several of the existing methods capable of estimating lateral-directional
parameters. The methods include a second-order shock expansion and panel
method', a slender body and "first order" panel method 2 , and a "higher-order"
panel method for linearized supersonic flow .
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for public release and. sale; its
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SYMBOLS
The lateral-directional characteristics are referred to the body axis
system. The moment reference center was located at 75.6 percent of the body
length.
A	 maximum cross-sectional area of body
C t ^	 effective dihedral parameter (roll stability), aCt	 where
os	 = 00,30
C = rolling moment
t qAd
C n
	directional-stability parameter,
	 ° C n ,	 where
a	 o03 h = 0 0 , 30'
C = yawing moment
n	 q d
4C 	 side force
C 
	 side-force parameter,	 Y	 where C 	 - -
ft	 o5	 ^ = 0° , 30 q
d	 maximum body diameter
I	 body length
M	 free-stream Mach number
q	 free-stream dynamic pressure
a	 angle of attack
angle of sideslip
DISCUSSION
The configuration variables are shown in figure 1. The body had a
fineness ratio of 11.67 consisting of a 3.5 caliber tangent ogive nose
followed by a cylindrical section. The wings were 68 0 swept delta planforms
with sharp leading and trailing edges. Vertical tail planforms are shown for
both the single and twin configurations. The vertical tail series for the
single vertical tail configuration incorporates leading- and trailing-edge
sweep variations as well as taper ratio. The area o^ these vertical tails is
constant and equal to 18 percent of the wing area. For the twin vertical
configuration, two areas were used; one is identical to the single tail and
the other is one-half that of the single tail. The twin verticals were
investigated at lateral spacings of both 2 and 4 body diameters apart.
Experimental investigations were conducted in the Langley Unitary Plan Win
Tunnel at Mach numbers from 1.60 to 2.86 for a Reynolds number of 8.2 x 10
per meter. The nominal angle-of-attack range was from -4 0 to 120.
K
1-118
y
tThe features of computational methods used to predict the lateral-
directional characteristics are discussed in figure 2. MISLIFT 1 , devil lo;ed at
NASA Langley Research Center, is a second-order shock expansion and p6.nel
method. The contribution of the body is obtained from a second-order shock
expansion theory, and tie contribution of the vertical is obtained from a sim-
ple panel method. APAS , developed by Rockwell, is a slender body and first-
order panel method. The body contribution is obtained from a slender bod,
theory which concentrates the surface effects along the centerline of the
body. The wing and vertical contributions are obtained from a first-order
panel method. Skill is required in modeling the geometry even for the Simple
first-order methods. For example, it is important to align the edge of the
wing panel with the vertical, otherwise erroneous estimates may be obtained.
PAN AIR , developed by Boeing for NASA Ames Research Center, is a higher-order
panel method for linearized supersonic flow. As indicated in figure 2, the
entire surface of the configuration is represented by panels. Proper use of
PAN AIR requires careful attention to the way in which these panels are
defined, especially in the area where configuration components join, such as
wing-body or body-vertical junctions.
Figures 3 through 5 present comparisons of the experimental and predicted
lateral-directional characteristics at a = 0° for various configurations. The
comparisons shown in figure 3 are for four body-vertical configurations.
The agreement indicates that all three methods are able to predict the roll
stability (C,,) and the side force parameter (Cy,) quite well; how-
ever, only MISLIFT and PAN AIR predict the directional stability (C,i,)
with any degree of success. In figure 4, comparisons are presented for body-
wing and body-wing-vertical configurations. The code MISLIFT has not been
compared because it can only estimate characteristics for surfaces in their
planform plane. APAS and PAN AIR are capable of predicting the lateral-
directional characteristics of a wing-body-vertical configuration at zero
angle of attack. The agreement ranges from good to excellent for the PAN AIR
code. Figure 5 presents a comparison of the theoretical methods with experi-
ment for twin vertical tail configurations at zero angle of attack. The
PAN AIR code prediction is in better agreement with experiment than the APAS
code, especially for estimation of the directional stability of the configura-
tion with small tails inboard.
Because of the limitations of the methods considered, only PAN AIR will
provide estimates of the lateral-directional stability derivatives at angles
of attack. Figures 6 and 7 present comparisons of the PAN AIR code predic-
tions with experimental lateral-directional characteristics at angles of
attack for Mach numbers 1.60 and 2.86. The agreement for the single and twin
vertical tail configurations shown in figures 6 and 7 is excellent for moder-
ate angles of attack. At higher angles of attack and Mach number, the body
nose slopes violate linear theory assumption and the solution is invalid.
- -1—.-T- - -- - .__
r.
M
t
1-119
0
CONCLUDING REMARKS
A program has been initiated at NASA Langley Research Center to assess
several methods for estimation of lateral-directional stability at supersonic
speeds. The methods fo:- estimating the characteristics include a second-order
shock expansion and panel method (MISLIFT); a slender body and "first-order"
panel method (APAS); and a "higher-order" panel method for linearized super-
sonic flow (PAN AIR). The results lead to the following concluding remarks:
(1) PAN AIR provides accurate predictions at moderate angles of attack
for complete configurations with either single or twin vertical
tails.
(2) APAS will provide fairly accurate predictions at zero angle of
attack for complete configurations with either single or twin
vertical tails.
(3) MISLIFT will only provide estimates for the simplest body-
vertical tail configurations at zero angle of attack.
REFERENCES
1. Jackson, Charlie M. Jr.; and Sawyer, Wallace C.: A Method for Calculating
the Aerodynamic Loading of Wing-Body Combinations at Small Angles of
Attack in Supersonic Flow. NASA TN D-6441, 1971.
2. Bonner, E.; Clever, W.; and Dunn, K.: Aerodynmamic Preliminary Analysis
System. Part I.- Theory. NASA CR-145284, 1978.
3. Ehlers, F. E.; Epton, M. A.; Johnson, F. T.; Magnus, A. E.; and Rubbert,
P. E.: An Improved Higher-Order Panel Method for Linearized Supersonic
Flow. AIAA Paper No. 78-0015, 1978.
z-120
DD
DD
^^7
Figure 1. - Configuration variables.
z
• MISLIFT - A SECOND-ORDER SHOCK EXPANSION	 x
AND PANEL METHOD	 Y
• APAS - A SLENDER BODY AND "FIRST ORDER"
PANEL METHOD
• PAN AIR- A "H IGHER ORDER" PANEL METHOD
FOR LINEARIZED SUPERSONIC FLOW
Figure 2. - Computational methods.
I-121
I
o EXPERIMENT ---- APAS
MISLIFT
	
---- PAN AIR
-C^
C	 on	 ^.	 o
0	 0	 0	 _ --
0
-. 2
0—
_ 4 ^,	 J
0
C Y 2
-. 4	 d'
1	 2	 3M	 1	 2	 3M	 1	 2 3M	 1	 2	 3M
Figure 3. - Comparison of experimental and predicted
lateral-directional characteristics.
a = 00 ; body-vertical.
.4
.2-
Cnp 0 
o EXPERIMENT
0 0-0 '-0 ---- APAS
Ct	 — — PAN AIR	 O
R -. 2	 ^.r .•
-.4
C
0_^
YR -.2 
-.4
1	 2	 3	 1	 2	 3
M	 M
Figure 4. - Comparison of experimental and predicted
lateral-directional characteristics.
a = 00 ; body-wing, body-wing-vertical.
I-122
r
1
1
1
1
I
,8
.6
C	 ,4
n0 
.2
	
0 	 o EXPERIMENT
	
-.2	 1 -.,J	 --- APAS
	
0	 ---- PAN AIR
C
-.2
•4
0
r Yp -, 2 
4
1 2 3 M
O 0
..0
cr0'•
1 2 3 M
Figure 5. - Comparison of experimental and predicted
lateral-directional characteristics.
a = 00 ; body-wing-twin verticals.
,4	 M=1.60
.2
Cn
a 0
-, 2
M=2.86
00 0
	
',41	 1	 1	 I	 1
0
Ci -.2
4
.61
0
	
C Yp-, 2	 —0o
.4
	
-4	 0 4
	
8 12 16
a, deg
0 EXPERIMENT
PAN AIR
	 o 0 0
00
-4 0	 4	 8 12 16
a, deg
Figure 6. - Comparison of experimental and predicted
lateral-directional characteristics.
a # 00 ; body-wing-vertical.
I-123
i
i
k
X00
1	 1	 1	 1
-A	 0	 4	 8 12 16
a, deg
	
0	 EXPERIMENT
PAN AIR
M=1.60	 M=2,86
Cn(3 0
	
.2	 0	 0 0
	4 	 1 ,._.J	 j
2
0
C1	2
	
L
.4 	 0 0
-.6
0
C 	 2
R-.4
-4	 0	 4	 8 12 16
a, deg
Figure 7. - Comparison of experimental and predicted
lateral-directional characteristics.
a # 00 ; body-wing-twin verticals.
1-124
I


Theoretical and experimental supersonic lateral-directional stability characteristics

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