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I i I
AEDC-TR-77-7
^%
T7tr
A E R O D Y N A M IC
A I D
T H E R i A L P E R F O R iA N C E
C H A R A C TE R IS T IC S
OF
SUPERSONIC-X TYPE
D E C E L I R A T O R S
AT
MACH l U i B E R
8
V O N K A R M A N GA S D Y N A M IC S F A C I L IT Y
A R N O L D E N G I N E E R I N G D E V E L O P M E N T C E N T E R
A I R F O RC E S YS TE M S C O M M A N D
A R N O L D A I R F O R C E S T A T I O N , T E N N E S SE E 3 7389
February 1977
Final R eport for Period August 4 9, 1976
A p p r o v e d f o r p u b l i c r e l e a s e ;
d i s t r i b u t i o n u n l i m i t e d .
Prepared for
A I R F O RC E F LIG H T D Y N A M I C S L A B O R A T O R Y (A F F D L / F E R )
W R IG H T -P A T T E R S O N A I R F O R C E B A S E , O H I O 4 54 33
11X753
.C67
1977
i f
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When U. S. Gover:
any purpose oth - > >
UNCLASSIF IED
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AEDC-TR-77-7
PREFACE
The work reported herein was conducted by the Arnold Engineering
Development Center
(AEDC),
Air Force Systems Command
(AFSC),
at the
request of the Air Force Flight Dynamics Laboratory (AFFDL/FER) under
Program Element 62201F. The monitor for this project was Mr. Charles A.
Babish III, AFFDL/FER, Wright-Patterson Air Force Base, Ohio. The results
of the test were obtained by
ARO, Inc.
(a subsidiary of SverdrupCorporation),
contract operator of AEDC, AFSC, Arnold Air Force Station, Tennessee, under
ARO Project No. V41B-G2A. The author of this report was J. D. Corce, ARO,
Inc.
The test was conducted from August 4 to August 9, 1976, and data
reduction was completed on September 2, 1976. The manuscript (ARO Control
No.
ARO-VKF-TR-76-137) was submitted for publication on November 19, 1976.
t INDA HALL L IBRAR1
KANSAS CJTY, MO
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A E D C - T R -
C O N T E N T S
Page
1.0 INTRODUCTION . 5
2.0 APPARATUS
2.1 Wind Tunnel , 6
2.2 Test Article 6
2.3 Instrumentation and Precision 7
3.0 PROCEDURE
3.1 Test Conditions 9
3.2 Test Procedure 9
3.3 Data Reduction 10
3.4 Data Precision 12
4.0 RESULTS AND DISCUSSION . 13
5.0 CONCLUDING REMARKS . 16
REFERENCES 17
I L L U S T R A T I O N S
F i g u r e
1. Configuration 580-111 Installed in Tunnel B . . . . . . 19
2.
Forebody Cone, Support Equipment, and Decelerator
Location 20
3. Decelerator Details 21
4.
Wake Survey Rake Details 24
5. Results of Vertical Surveys in the wake of the
Forebody Cone at Y/D = 0 and q = 1 . 0 psia 25
6. Results of Vertical Surveys in the Wake of the Forebody
Cone at Y/D = 0 and Various Dynamic Pressures 28
7. Results of Vertical Surveys in the Wake of the Forebody
Cone at Various Y/D Locations and Dynamic Pressures . . 31
8. Drag and Dynamic Characteristics of Various Kevlar 29
Configurations at X/D = 5 . 0 and T = 860R 34
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Figure Page
9. Effect of X/D on Kevlar 29 Parachute Configuration
250-77 7 at T = 860R 35
o
10.
Effect of T on Kevlar 29 Parachute Configuration
o
250-77 7 at Various X/D's 36
11. Parachute Material Effect on Configuration 250 at
X/D = 4.0 and T = 860R 37
o
12.
Typical Material Failures 38
13. Shadowgraphs of Configuration 250-777 at X/D = 3 . 5
and T = 860R 39
o
TABLE
1. Test Summary - Parachute Data 40
NOMENCLATURE 41
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A E D C - T R - 7 7 - 7
1 . 0 I N T R O D U C T I O N
Supersonic deployable aerodynamic decelerators, such as Supersonic-X
parachutes, operate in the wake of and provide drag and stability for Air
Force re-entry and test vehicles, special and conventional weapons, and
aircraft crew escape modules that are moving through the atmosphere at
supersonic speeds. The aerodynamic and thermal performance characteristics
of trailing supersonic decelerators are influenced by the Mach numbers and
total temperatures of the forebody wake ahead of the decelerators. These
wake flow properties are characterized by Mach numbers from 1.0 to 3.5
and total temperatures from 100 to 700F.
Results from a previous experimental investigation (Ref. 1) conducted
in the von Karman Gas Dynamics Facility (VKF) Hypersonic Wind Tunnel (B)
showed that reasonable approximations of these flow properties could be
achieved in the near wake core of a cone forebody immersed in a Mach
number 8 free stream at wind tunnel total temperatures of 860 and 1,220R.
The present test objectives were to determine the aerodynamic and
thermal performance characteristics of model nylon, Kevlar 29- , and
Bisbenzimidazobenzophenanthroline (BBB) Supersonic-X type parachutes in
four configurations. The decelerators were tested at several axial loca
tions in the wake of a strut-mounted cone forebody. All the configurations
were tested at simulated pressure altitudes from 130,000 to 145,000 ft,
corresponding to free-stream dynamic pressures from 2 to 1 psia. The
free-stream unit Reynolds number was varied from 1.1 to 3.6 million per
foot,
The investigation was made at wind tunnel stagnation temperatures
both above and below that required to prevent air liquefaction in the test
section. The lower temperature was required because of the nylon and
Kevlar 29 material temperature limits. Wake survey data were obtained at
several locations downstream of the forebody to determine local wake condi
tions,
strut effects, and verification of wake survey data obtained in
Ref.
1.
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Wake survey pitot pressure, static pressure, and total temperature
results and selected average drag coefficients of the various configurations
showing the effects of location in the wake and free-stream dynamic pressure
are presented. Decelerator stability performance is presented in the form
of a relative dynamic parameter (RDP).
2 . 0 A P P A R A T U S
2 .1 W IN D T U N N E L
Tunnel B is a closed-circuit hypersonic wind tunnel with a 50-in.-diam
test section. Two axisymmetric contoured nozzles are available to provide
Mach numbers of 6 and 8, and the tunnel may be operated continuously over
a range of pressure levels from 20 to 300 psia at M = 6, and 50 to 900
psia at M = 8 , with air supplied by the VKF main compressor plant. Stagna
tion temperatures sufficient to avoid air liquefaction in the test section
(up to1,350R)are obtained through the use of a natural-gas-fired combus
tion heater. The entire tunnel (throat, nozzle, test section, and diffuser)
is cooled by integral, external water jackets. The tunnel is equipped with
a model injection system, which allows removal of the model from the test
section while the tunnel remains in operation. A description of the tunnel
may be found in Ref. 2.
2 .2 T E S T A R T I C L E
The forebody cone support system and a Supersonic-X type parachute
are shown installed in the tunnel in Fig. 1 and schematically portrayed
in Fig. 2. Two designs of decelerators (designs 2 and 5) were tested
with 5- and 8-in. diameters (see Fig. 3) at various X/D locations down
stream of the forebody base. Three materials, nylon, Kevlar 19, and
Bisbenzimidazobenzophenanthroline (BBB) were investigated. The tempera
ture limits of these materials (the temperature at which only 20 percent
of the strength of the material at room temperature is retained) are
nylon,
860R; Kevlar 29, 1,210R;and BBB, 1,410R.
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The forebody cone and support system for this test entry was the
same as that used in an earlier Tunnel B test (see Ref. 1). The forebody
was a 10-deg, half-angle cone with a 6-in. base diameter. The decelerators
were attached to a six-component moment-type balance mounted in the
forebody. Both the balance and the cone support system were water cooled.
A wake survey rake (see Fig. 4) with pitot pressure, cone static
pressure,
and total temperature probes was used to determine local flow
conditions downstream of the cone.
2.3 INS TRU MEN TAT ION A N D PRECISION
Tunnel B stilling chamber pressure is measured with a 100- or 1,000-psid
transducer referenced to a near vacuum. Based on periodic comparisons with
secondary standards, the uncertainty (a bandwidth which includes 95-percent
of residuals) of the transducers is estimated to be within 0.1 percent of
reading or 0.06 psi, whichever is greater, for the 100-psid range, and
0.1 percent of reading or 0.5 psi, whichever is greater, for the 1,000-psid
range.
Stilling chamber temperature measurements are made wi th Chromel-
Alumel thermocouples which have an uncertainty of (1.5F +0.375percent
of reading) based on repeat calibrations.
Model forces and moments were measured with a six-component, moment-
type,
strain-gage balance (Balance No. 4.06-Y-36-014) supplied and
cali
brated by VKF. Before the test, static loads in each plane and combined
static loads were applied to the balance to simulate the range of loads
and center-of-pressure locations anticipated during the test. The following
uncertainties represent the bands of 95 percent of the measured residuals,
based on differences between the applied loads and the corresponding values
calculated from the balance calibration equations included in the final
data reduction. The range of check loads applied and the measurement
uncertainties follow.
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Component
Normal force, lb
Pitching moment,*in. lb
Side force, lb
Yawing moment,*in. lb
Rolling moment, in. lb
Axial force, lb
Balance
Design
Loads
400
1,386
200
693
50
0+50
Calibration
Load Range
300
1,386
150
693
50
0+50
Range Of
Check Measurement
Loads Uncertainty
15
46
15
46
0
0--50
+
0.50
1.00
0.25
1.00
0.24
0.16
*About balance forward moment bridge.
^Balance was mounted backwards in forebody cone.
No moment calculations were incorporated in the data reduction since
only forces were of interest for this test.
The wake survey temperature measurements were made with a Chromel-
Alumel thermocouple probe, with a precision of measurement estimated to be
0.4 percent of reading. The pitot pressure was measured with a 15-psid
transducer, referenced to a near vacuum, which has an estimated precision
of measurement of 0.003 psi or 0.15 percent of reading, whichever is
greater. The cone static pressure was measured with a5-psidfast-response
transducer, referenced to a near vacuum, and calibrated to
1-psia
full
scale. The precision of this transducer is estimated to be 0.002 psi or
1.0 percent of reading, whichever is greater.
The parachute behavior in the airstream was recorded with two high-speed
16-mm motion-picture cameras and two still cameras for both shadowgraph and
direct photography.
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AEDC-TR-77-7
3.0 PR OC ED UR E
3.1 TEST CONDITIONS
The test was conducted at a nominal Mach number of 8 (variations
listed below are from tunnel calibrations) and free-stream unit Reynolds
numbers from 1.1 to 3.6 million. A summary of the test conditions at
each dynamic pressure is given below.
M p ,psia T , R
7.94 210 860*, 1,220
7.95 265
7.96 320
7.97 370
7.98 425
^Temperature below that required to prevent air liquefaction in the
test section.
A test summary showing all configurations and conditions tested along
with the variables for each is presented in Table 1.
3.2 TEST PR OC ED UR E
Parachutes made of nylon and Kevlar 29 materials would not withstand
the temperatures encountered in the normal operation of Tunnel B. For this
reason, the wind tunnel was often operated at a reduced stilling-chamber
temperature below that required to prevent air liquefaction in the test
section.
q ^ P s i a p ^ . p s i a
1 . 0 0 0 . 0 2 2
1 . 2 5 0 . 0 2 8
1 . 5 0 0 . 0 3 4
1 . 7 5 0 . 0 3 9
2 . 0 0 0 . 0 4 4
Re x 10 ,1/ft
V
R
860 1,220
1.8 1.1
2.2 1.3
2.7 1.6'
3.1 1.9
3.6 2.1
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The first test phase was the captive parachute testing. The
parachute was attached to the balance in the forebody cone by means of a
riser line which positioned the decelerator at a specified X/D distance
from the base of the cone. The test procedure used was to allow the
chute to hang free from the balance whe n injected into the tunnel flow.
Upon inject ion, high-speed mov ie cameras and a visicorder which recorded
the drag input from the balance were run for a designated length of time.
If the parachute had not failed after reaching the centerline of the
tunnel,
several seconds of continuous force data were taken. Still pictures
were taken when the force data were obtained.
Wake survey data were also obtained downstream of the forebody cone
by use of the VKF X-Y-Z overhead probe drive mechanism which permitted the
probe to be moved independently of the forebody and supports. The wake
surveys,
at various X/D locatio ns, were made in four vertical planes
parallel to the forebody axis of symmetry at lateral displacements of 0.0,
1.15, 2.25, and 4.0 in.
3.3 DA T A RED UC TIO N
Main balance force data wer e reduced in the body axis system. Drag
was calculated by the equation
Drag
9 2 21
0.
F
N
)
2
+
F
Y
)
2
+
F
A
)
2
J
which is the resultant force along the riser lines of the parachutes
measured by the balance.
A statistical method was used to analyze the decelerator drag data
which were recorded at a rate of approximately 800 samples per second.
The method provides a means of evaluating the drag dynamics of each decele
rator tested by calculating Gaussian distribution parameters from each
group of data ( see Ref . 3 ) . The calculated parameters are average drag
coefficient (C ) , standard deviation
(DEV),
skew ness, and kurtosis.
o
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AEDC-TR-77-7
The average drag coefficient is the most probable value in the drag
coefficient distribution and is determined by the equation
N
C
n
= (1/N) .2 C,
D
'Standard deviation measures the spread of the distribution and is
calculated by
DEV
N 9
(1/N) 2 (C
D
. - C
D
)
i
=
l
i
0.5
Skewness is a measure of the asymmetry of the distribution determined by
3
Skewness
1/N
(DEV)'
N o
s ( c
D i
- c
D o
)
Kurtosis is a measure of the peakedness of the data and was found by the
equation
4
Kur tosi s
1/N (DEV)
l
C
D i - V
The value of N is the total number of drag coefficient data samples in a
group of data. This value decreased from approximately 1,600 to 700
samples per group as the test progressed, and on-line evaluation of the
parachute drag dynamics showed the sample size could be reduced.
To compare drag dynamics of one decelerator with those of another,
it is necessary to determine a relative dynamic parameter (RDP). This
value is calculated by determining a 95-percent probability interval and
dividing this interval by C^ . In equation form, RDP = (Z
1
+ Z) (DEV)/Cj)
where Z and Z- are parameters derived from the skewness and kurtosis
values (see Ref. 3) representing a factor of the 95-percent probability
interval limits (see Appendix II, Ref. 4 for additional information con
cerning this
method).
The significance of the relative dynamics parameter (RDP) can be
readily understood by explaining the drag dynamics of a decelerator
when values of zero, unity, and two are assigned to the RDP. A value of
zero implies no dynamics, a value of unity implies that the magnitude of
dynamics about the average is equal to 50 percent of the average drag
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AEDC-TR-77-7
coefficient, and a value of two implies that the magnitude of dynamics
about the average drag coefficient value is equal to 100 percent of the
average drag coefficient. The relative drag parameters of the various
parachute configurations tested are presented in Table 1.
3.4 D A T A P R E C I S IO N
An evaluation of the influence of random measurement errors is
presented in this section to provide a partial measure of the uncertainty
of the final test results presented in this report.
3.4.1 Test C ondit ions
Uncertainties in the basic tunnel parameters p and T (see Section 2.3)
and the two-sigma deviation in Mach number determined from test section
flow calibrations were used to estimate uncertainties in the other free-
stream properties, using the Taylor series method of error propagation.
Uncertainty (),percent
M
OO
7 . 9 4
7 . 95
7 . 96
7 . 97
7 . 9 8
M
00
0 . 4
0 . 4
0 . 3
0 . 3
0 . 3
P
o
0.1
0 .1
0 .1
0 .1
0 . 1
T
o
0 . 4
0 . 4
0 . 4
0 . 4
0 . 4
P
o
1.7
1.7
1.2
1.2
1.2
Poo
2 . 4
2 . 4
1.6'
1.6
1.6
loo
1.7
1.7
1.1
1.1
1.1
Re
00
1.2
1.2
1.0
1.0
1.0
3.4.2 Test Data
The basic precision of the wake parameter and drag coefficients
was computed using the measurement precision values listed in Section
2.3 with the assumption that the free-stream flow nonuniformity is a
bias type of uncertainty which is constant for all testruns.
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AEDC-TR-77-7
Precision()Measured Values
M
OO
7.94
7.95
7.96
7.97
7.98
P
t
/ p
o
0.017
0.017
0.012
0.012
0.012
P/P
0.122
0.110
0.081
0.076
0.072
T
T
/T
o
0.006
0.006
0.006
0.006
0.006
S
0.008
0.007
0.005
0.005
0.004
The uncertainty
in
forebody angle
of
attack,
as
determined from
tunnel sector calibrations
and
consideration
of the
possible errors
in
model deflection calculations,isestimatedto be 0.1 deg. Noestimate
has been madetotake into account strutandcone deflection attributable
to heating fromthetunnel flow.
Estimates
of
precision
of
measurement
as
given above
are
normally
considered
a
measure
of the
repeatability
to be
expected
in the
test
results. Forthese parachute data, however, twofactors whichcangreatly
influencetheresultsandhencethedata repeatability shouldbenoted.
Theseare (1) thedegreeofsimilitude achievedin theparachute models
each
of
which
is
individually hand made
and (2) the
initial behavior
(dynamics)of themodel duringtheinjection sequence which could have an
unobservable effect uponthematerial propertiesandstructural integrity
before data taking begins.
4.0RESULTSAMDDISCUSSION
Surveysof theforebody wake were madetodeterminethelocal flow-
field conditionsinwhichtheparachutes were tested. These vertical
surveys consistedofpitotandstatic pressureandtotal temperature
profiles,andthesearepresentedinFigs.5through7. Allwake survey
data were obtainedat T =1,220R.
o
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The present data obtained along the vertical plane of symmetry of
the forebody (Y/D = 0) at q * 1.0 psia are compared with similar data
from a previous test (Ref. 1) in Fig. 5. The data in Ref. 1 were
obtained at T = 1,220 and 860R using the same forebody and support
system; the data for both temperatures are presented in the figure.
The pitot and static pressure profiles were in good agreement with the
previous data (Fig. 5a and b , and the total temperature profiles
agreed well at X/D = 3 . 0 and 4.0 (Fig. 5c). At X/D = 2.0, the temperature
profiles were in good agreement outside the wake shock (Z/D > 0 .3), but
differences were evident at Z/D < 0.3 for all three sets of data. These
differences were attributed to the effects of Reynolds number on the
temperature probe recovery characteristics (probes were not calibrated)
which were not evaluated in either test; furthermore a different probe was
used in the present tests.
The effects of varying dynamic pressure on the wake survey profiles
are illustrated in Fig. 6 for Y/D = 0. The pressure profiles were
unaffected as shown inFigs.6a and b. Slight changes in level of the
temperature profile inside the wake shock were observed (Fig. 6c). These
levels increased with q^, which again is an indication of Reynolds number
effect on the probe response.
Pressure and temperature profiles obtained at various lateral survey
stations are presented in Fig. 7. The pressure profiles (Figs. 7a and b)
at Y/D = 0.3 8 and X/D = 3 . 0 showed a disturbance near Z/D = 0, which
indicates the wake shock location in the horizontal plane. The disturbances
at Y/D = 0.67, X/D 2.0 and 3.0, and Z/D - 0 . 5 were caused by flowdis
turbances from the top right strut (view looking upstream) supporting the
forebody.
Selected results of the parachute tests are presented inFigs.8
through 11 in terms of average drag coefficient (C
D
) and relative dynamic
o
parameter
(RDP).
A complete summary of these data is presented in Table 1.
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AEDC-TR-77-7
The drag and dynamic characteristics of various Kevlar 29 parachute
configurations at X/D =5 . 0 are presented inFigs.8a and b, respectively.
Data are shown for two decelerator designs with two canopy diameters.
Generally, the smaller parachutes developed a higher drag coefficient over
the dynamic pressure and axial location ranges, and the drag coefficients
did not vary as much with q as did the results for the 8-in. parachutes.
All configurations approached similar drag coefficient levels at the higher
dynamic pressures. Figure 8b shows the high dynamic instabilities en
countered on the 8-in. parachutes near q^ = 1.25 psia.
The drag and dynamic characteristics of Kevlar 29 parachute configu
ration 250-77 7 at several X/D locations are illustrated in Fig. 9 for
T = 860R. In general, the drag coefficient (Fig. 9a) was maximum at
o
the most aft trailing distances (X/D >_
4.5),
where the effects of q
were also minimal. At all X/D locations, increasing q generally increased
C Q . The dynamic characteristics tended to decrease with increasing X/D
o
and q as shown in Fig. 9b.
Results at the two free-stream temperature conditions for a Kevlar 29
configuration are given in Fig. 10. The limited wake survey data available
(see Fig. 5) showed little effect of temperature (increase in Re at
reduced T ) on the pressure profiles, and the differences obtained in the
parachute characteristics may have been caused by temperature effects on
the parachute material properties.
The effects of varying the material, and hence the stiffness and
porosity, of a configuration 250 parachute at X/D =4 . 0 and T = 860R are
shown in Fig. 11. For these conditions, the Kevlar parachute had the
highest drag coefficient and slightly higher dynamics. The BBB parachute
had the most uniform variation of Cn and RDP with q and produced about
o
the same drag level as nylon at the higher q values. This figure also
shows a comparison between the present drag data and corresponding dafa
from Ref. 1 for the nylon parachutes. These data were in good agreement
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In trend, and although the Cp was lower for the present data at the
o
higher q values, the agreement was within the data repeatability
observed in Ref. 1.
It should be noted that 26 parachutes were used in this test and
that only five of these survived. Photographs of two typical parachute
failures (280 configurations) are presented in Fig. 12. Some models were
lost during the injection sequence because of initially high dynamics.
The larger (8-in.-diam) parachutes were particularly vulnerable, and
testing on these was restricted to the more aft trailing distances (X/D >
4.0). Typical shadowgraphs with parachutes in the forebody wake are shown
in Fig. 13.
5.0 CONC LUDI NG R EM AR KS
The results of the wake survey and decelerator investigation may be
summarized as follows:
1. For the most part, the wake survey pressure and
temperature profiles agreed with the previous data
obtained in Ref. 1 using the same forebody cone and
support system.
2.
Generally, decelerator drag increased with increasing
axial location and/or increasing free-stream dynamic
pressure.
3. Typically, parachute design 2 developed slightly
more drag than design 5, over the X/D and q ranges.
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REFERENCES
Lutz,R. G. and Rhudy, R. W. "Drag and Performance of Several
Aerodynamic Decelerators at Mach Number 8." AEDC-TR-70-143
(AD873000),August 1970.
Test Facilities Handbook (TenthEdition)."von Karman Gas Dynamics
Facility, Vol. 4." Arnold Engineering Development Center,
May 1974.
Hahn, Gerald J. and Shapiro, Samuel S. Statistical Models in
Engineeering. John Wiley andSons, Inc., New York, 1967.
Galigher, L. L. "Aerodynamic Characteristics of Ballutes and Disk-Gap-
Band Parachutes at Mach Numbers from 1.8 to 3.7." AEDC-TR-69-245
(AD861437), November 1969.
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AEDC TR 77 7
, * 1
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R - 7 7 - 7
Sym Configuration
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conf igura tions a t X /D = 5 .0 and T = 860 R.
34
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A E D C - T R - 7 7 - 7
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A E D C - T R - 7 7 - 7
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A E D C - T R -
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37
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A E D C - T R - 7 7 - 7
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38
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7/25/2019 Aerodynamic and Thermal Performance Characteristics of Supersonic X Type Decelerators at Mach Number 8
45/46
AEDC-TR-77-7
NOMENCLATURE
Drag coefficient; drag force/q (S)
Each individual C
n
in a group of data
Average drag coefficient
Forebody cone base diameter (6 in.)
Total axial force, lb
Normal force, lb
Side force, lb
Free-stream Mach number
Total number of drag coefficient data samples in a group
Free-stream stagnation pressure, psia
Calculated total pressure behind a normal shock, psia
Measured cone static pressure, psia
Measured pitot pressure, psia
Free-stream static pressure, psia
Free-stream dynamic pressure, psia
41
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7/25/2019 Aerodynamic and Thermal Performance Characteristics of Supersonic X Type Decelerators at Mach Number 8
46/46
Relative dynamic parameter
Free-stream unit Reynolds number, 1/ft
2
Parachute reference area, in. ; for 5-in.-diam canopy,
2 2
S = 19.635 in. ; for8-in.-diamcanopy, S = 50.265 in.
Free-stream stagnation temperature, R
Measured probe temperature, R
Probe position in axial direction divided by forebody
cone base diameter (6 in.)
Probe position in lateral direction divided by forebody
cone base diameter (6 in.)
Probe position in vertical direction divided by forebody
cone base diameter (6 in.)
Parameters derived from skewness and kurtosis values