Free flight telemetry testing in hypersonic wind tunnel for obtaining interference-free base pressure dat

Welton, J. T.

English

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N A T I O N A L  A E R O N A U T I C S  A N D  S P A C E  A D M I N I S T R A T I O N  
Technical Report No. 32- 775 
Free- Flight Telemetry Testing in tbe 
Jet Propulsion Laboratory Wind Tunnels 
John 7: Welton 
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J E T  P R O P U L S I O N  L A B O R A T O R Y  
PASADENA, CALIFORNIA 
C A L I F O R N I A  I N S T I T U T E  O F  TECHNOLOGY 
September 15,1965 
https://ntrs.nasa.gov/search.jsp?R=19650024803 2020-03-17T01:17:27+00:00Z
I 
N A T I O N A L  A E R O N A U T I C S  A N D  S P A C E  A D M I N I S T R A T I O N  
Technical Report No. 32- 775 
Free-Flight Telemetry Testing in the 
Jet Propulsion La bora tory Wind Tunnels 
John T. Welfon 
. .  
E. A. Laumann, Manager 
Aerodynamic Facilities Section 
J E T  P R O P U L S I O N  L A B O R A T O R Y  
C A L I F O R N I A  I N S T I T U T E  O F  T E C H N O L O G Y  
PA s A D E  N A, CALI  F o R N I A 
September 15, 1965 
Copyright 0 1965 
Jet Propulsion Laboratory 
California Institute of Technology 
Prepared Under Contract No. NAS 7-100 
National Aeronautics & Space Administration 
I JPL TECHNICAL REPORT NO . 32-775 
CONTENTS 
1 . Introduction . . . . . . . . . . . . . . . . . .  1 
II . Model Design and Construction . . . . . . . . . . .  1 
111 . Telemetry Package Design and Construction . . . . . . .  2 
IV . Model launch Mechanism and launch Technique . . . . . .  3 
VI . Results and Conclusions . . . . . . . . . . . . . .  6 
Nomenclature . . . . . . . . . . . . . . . . . . .  8 
References . . . . . . . . . . . . . . . . . . . .  9 
TABLE 
1 . Data summary . . . . . . . . . . . . . . . . . .  5 
FIGURES 
1 . Model dimensions . . . . . . . . . . . . . . . . .  1 
2 . Model and telemetry package . . . . . . . . . . . . .  2 
3 . launch gun-cooling shield assembly . . . . . . . . . . .  3 
4 . Model mounted on launch gun . . . . . . . . . . . . .  4 
5 . Sample oscilloscope traces . . . . . . . . . . . . . .  5 
6 . Telemetry data curve with corresponding model flight position . . . .  6 
7 . Examples of erroneous base pressure telemetry signals . . . . . .  7 
8 . Base pressure ratio versus Reynolds number . . . . . . . . .  8 
JPL TECHNICAL REPORT NO. 32-775 
4 
ABSTRACT 
w404 
A program was conducted in the Jet Propulsion Laboratory Hyper- 
sonic Wind Tunnel to develop an operational technique for obtaining 
interference-free base pressure data. The technique developed utilizes 
a pneumatic launch mechanism to project the models into free flight 
and an electronic transmitter and receiver system to obtain base pres- 
sure data from the model. Both 10" and 15" half-angle cone configu- 
rations were tested. 
JPL TECHNICAL REPORT NO. 32-775 
6 
&-' 
1. INTRODUCTION 
It is often desirable in wind tunnel testing to obtain tions and other pressures, e.g., model surface pressures. 
model pressure data that are free of model-support inter- Other methods of obtaining support-free wind tunnel data 
ference. Therefore, a program was conducted in the have been investigated at JPL (Refs. 1 through 3) with em- 
JPL Hypersonic Wind Tunnel for the purpose of de- phasis on development of an operational method. Although 
veloping an operational technique for obtaining the free-flight telemetry technique developed is con- 
interference-free base pressure data. The technique sidered operational, more sophisticated data reduction 
developed is easily adaptable to other model configura- techniques are being developed for this type of testing. 
II. MODEL DESIGN AND CONSTRUCTION 
For this development program, the model configura- The model noses were constructed of steel to prevent 
tions were limited to 10" and 15" half-angle cones (Fig. 1) melting during flight, and to provide a proper center-of- 
launched at zero angle of attack. These were chosen for gravity location. The bodies were constructed of injection 
their simplicity of form and construction, and because molded styrene plastic (Fig. 2) ,  and provided an inter- 
comparable sting-mounted base pressure data were ference-free signal path from the telemetry package to 
available. the antenna. The telemetry packages were supported 
I 
I 
I V2 In 
-MODEL A 
2 in. 
NOTE: 
MODEL BODY IS PLASTIC 
MODEL NOSE IS METAL 
Fig. 1.  Model dimensions 
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JPL TECHNICAL REPORT NO. 32-775 
-c 
CKA RING7 
PRESSURE 
OR1 FICE- 
..--. . 
TELEMETRY PACKAGE TELEMETRY PACKAGE HOLDER 
Fig. 2. Model and telemetry package 
in the model by a Lucite holder (Fig. 2), whose design 
allowed the telemetry package to be easily installed or 
removed. Four symmetrically located wooden pins pro- 
jected from the base of the model to provide support on 
the launch piston. These wooden pins, sometimes broken 
or damaged during flight, were easily replaced as were 
the plastic cone bodies and metal noses. The Lucite 
telemetry package holder, thodgh sometimes broken dur- 
ing flight, usually provided sufficient protection to save 
the telemetry package from complete destruction. The 
model, however, was usually damaged or destroyed. A 
total of 134 runs was made with 12 telemetry packages. 
111. TELEMETRY PACKAGE DESIGN AND CONSTRUCTION 
The pressure telemetry package is 0.80 in. long, 0.80 in. 
in diameter at the inductor-antenna end, and 0.50 in. in 
diameter at the battery end. Total weight is 'h oz (Fig. 2 
and Ref. 4). 
The electronic circuit used is a Colpitts oscillator, con- 
sisting of a printed circuit inductor, a pressure sensitive 
capacitor, two small mercury cells, and other circuit com- 
ponents of the micro-miniature pellet type construction. 
The inductor also serves as the transmitter antenna. 
Two sensitivity ranges have been used: 70-kc and 
25-kc changes in frequency for a AP, of 1 mm Hg. The 
package is insensitive to acceleration and thermal shock, 
and can be exposed to an ambient temperature of 
800°F for at least 10 sec before an appreciable fre- 
quency shift occurs. 
2 
JPL TECHNICAL REPORT NO. 32-775 
s 
A- 
IV. MODEL LAUNCH MECHANISM AND LAUNCH TECHNIQUE 
The model launch mechanism (Fig. 3 )  is similar to a 
configuration constructed for use in the JPL 20-in. Super- 
sonic Tunnel (Ref, 5) .  The most outstanding difference is 
the addition of surface cooling for the higher temperature 
requirements of the Hypersonic Wind Tunnel. The com- 
plete launch mechanism consists of a pneumatic launch- 
ing piston, and a model support and cooling shield 
assembly (Fig. 4). A constant model temperature of 150°F 
was maintained to the time of launch by discharging 
gaseous nitrogen over the model surface. Two thermo- 
couples, one near the model surface and one near the 
model base, were monitored while the model was being 
cooled. The model surface temperature thermocouple is 
shown in Fig. 4. A reference pressure at the base of the 
model was sampled just prior to launch. 
Launch sequence: 
1. Model was mounted on the launch gun piston with 
the cooling shield in place (Fig. 3 ) .  
2. Test conditions were established in the tunnel test 
section. 
3. Model support was retracted. 
4. Base reference pressure was recorded. 
5. Cooling shield was raised. 
6. Launch piston retaining pin was released. 
7 .  Launch piston moved forward and injec 
model into free flight. 
:d the 
8. Model traveled to approximately the upstream edge 
of the test section viewing windows, then dropped 
to the floor and slid back into a catch basket at the 
rear of the test section. 
9. Wind tunnel flow was then bypassed, and another 
run was initiated. 
~ ~~ ~ 
Fig. 3. Launch gun-cooling shield assembly 
3 
JPL TECHNICAL REPORT N O .  32-775 
, 
‘4 
Fig. 4. Model mounted on launch gun 
V. DATA ACQUISITION 
The telemetry signal was received by a standard 
McIntosh FM tuner Model MR71. The receiving antenna 
was a half-wave loop attached to the test section window. 
In order to prevent interference from local FM stations, 
the tuner was realigned to receive the telemetry package 
signal (110 to 115 Mc). The output of the tuner was fed 
to an oscilloscope which was triggered by an event timer. 
The scope trace was photographed for each flight (Fig. 5); 
also shown in Fig. 5 is a sample antenna effect tare run. 
When the antenna effect could not be eliminated, these 
tares were applied as corrections to the pressure data. 
Tuner signal was simultaneously recorded on a CEC Visi- 
corder (recording oscillograph). Prior to launch, tuner 
output was compared with model base reference pressure. 
The base reference pressure was obtained with a 5-psia 
Statham transducer and was recorded by the wind tunnel 
central data system. 
4 
~ ~~ 
I JPL TECHNICAL REPORT NO. 32-775 . 
2 
Mach 
No. 
MODEL AT 
REST ON 
LAUNCH GUN, 
COOLING 
SHIELD IN 
PLACE COOLING 7 GAS 06 
REFERENCE 
LEVEL 
Pr, Tr, 
cmHg O F  
MODEL IN FREE - FLIGHT, 
WAKE AND BASE PRESSURE 
AFFECTED BY PROXIMITY 
OF LAUNCH GUN PISTON 
1 
PRESSURE 
MODEL HITS TUNNEL 
SIGNAL LOST 
MODEL IN FREE-FLIGHT 
~ 
VACUUM - T I M E  
FREE FLIGHT DATA 
ANTENNA TARE ( PRESSURE SENSOR PLUGGED 
I f 1 
I t  I I f I 
I I 
c 
I I 
I I 1  I I  
I 1  
1 1  
I 1  
Fig. 5. Sample oscilloscope traces 
High-speed motion pictures of each flight were taken 
with a Fastax movie camera at approximately 5,000 
frames/sec. These optical data were used to determine 
model attitude during flight. Significant model oscillation 
was present in only two of the runs presented as data 
(Table 1). 
Table 1.  Data summary 
Run 
37 
77 
130 
131 
132 
133 
104 
107 
108 
109 
112 
8 
8 
8 ! 8 452 300 300 405 560 400 560 1000 670 
401 
15 
10 0 
10 
10 <5 
15 <2 
0.319 
0.237 
0.264 
0.21 0 
0.230 
0.209 
0.21 5 
0.1 74 
0.1 65 
0.246 L0.340 f 0.047 k0.028 f0.048 f 0.071 k 0.058 f 0.057 k 0.055 k 0.09 1 fO.100 k 0.038 kO.100 12 120 0 0 0 0 0 0 0 60 0 0 0 0 0 0 0 0 0 0 2 0.5 0.069 0.237 0.314 0.316 0.31 6 0.31 4 0.086 0.063 0.063 0.1 35 0.084 1400 1600 960 910 1000 1250 1400 2300 2300 1550 2100 
5 
JPL TECHNICAL REPORT NO. 32-775 
w 
VI. RESULTS AND CONCLUSIONS 
The data curve shape with respect to model flight 
position is shown in Fig. 6; in Fig. 7, several erroneous 
data curves are compared with a typical usable curve. The 
data spread is caused by the linear or sometimes sinus- 
oidal variation of the base pressure during the usable 
portion of the flight (Fig. 5). It is felt that this pressure 
variation is not due to model oscillation, since there was 
no oscillation for the majority of the flights. For the flights 
in which the model did oscillate, model oscillation and 
pressure oscillation did not coincide. The majority of the 
runs indicates a linear change in base pressure rather than 
a pressure oscillation. The limited amount of usable data 
obtained is plotted in Fig. 8 and tabulated in Table 1. 
The amount and accuracy of these data are considered 
sufficient to establish the advantages of this data gather- 
ing technique. 
I 
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I 
I 
I 
I 
I 
I 
1 
I 
I I 
A .  PISTON ACCELERATING MODEL 
8 .  MODEL IN FREE FLIGHT; 
WAKE SEPARATED BY PISTON 
C .  MODEL IN FREE FLIGHT. 
D . MODEL ENTERS BOUNDARY 
WAKE UNINFLUENCED’ B Y  PISTON 
LAYER AND STRIKES FLOOR 
Fig. 6. Telemetry data curve with corresponding model flight position 
JPL TECHNICAL REPORT NO. 32-775 
9 
P 
UNAFFECTED FREE FLIGHT- 
BASE PRESSURE AREA 
I 
LOSS OF SIGNAL- I 
CAUSE UNKNOWN - 
I 
I 
I 
I 
I 
I 
I 
I 
I 
-Ivlc- 
I 
LOSS OF SIGNAL- - ,..a,..- I l . I V . l n k . , . l  
C.cI”JC “I”nl”””l. 
LOSS OF SIGNAL- 
BATTERY POWER 
FAILURE 
Fig. 7. Examples of erroneous base pressure telemetry signals 
7 
J P L  TECHNICAL REPORT NO. 32-775 
0.5 
0.4 
0.3 < 
0.2 
0. I 
0 
0 0.1 0.2 0.3 0.4 
Ro, x 10-6 
Fig. 8. Base pressure ratio versus Reynolds number 
NOMENCLATURE 
a,, 
P, supply pressure 
Pb model base pressure 
P ,  free stream static pressure 
maximum model angle of attack during flight 
ppm parts per million water vapor by volume 
8 , 
r b  model base radius 
R,), Reynolds number based on model diameter 
T,, model nose radius 
u cone half angle 
AP,  model base pressure variation 
JPL TECHNICAL REPORT NO. 32-775 
. 
REFERENCES 
! 
1. Dayman, B. Jr., “Simplified Free-Flight Testing in a Conventional Wind Tunnel,” 
Technical Report No. 32-346, Jet Propulsion Laboratory, Pasadena, California, 
October 1, 1962. 
2. Dayman, B. Jr., “Optical Free-Flight Wake Studies,” Technical Report No. 32-364, 
Jet Propulsion Laboratory, Pasadena, California, November 1, 1962. 
3. Jaffe, P., “Obtaining Free-Flight Dynamic Damping of an Axially Symmetric Body 
(At All Angles of Attack) in a Conventional Wind Tunnel,” Technical Report 
No. 32-544, Jet Propulsion Laboratory, Pasadena, California, January 15, 1964. 
4. Harrison, R. G. Jr., “A Pressure Telemeter for Wind Tunnel Free-Flight Pressure 
Measurement,” Technical Report No. 32-763, Jet Propulsion Laboratory, Pasa- 
dena, California (to be published). 
5. Holway, H. P., Herrera, J. G., and Dayman, B. Jr., “A Pneumatic Model Launcher 
for Free-Flight Testing in a Conventional Wind Tunnel,” Technical Memorandum 
No. 33-1 77, Jet Propulsion Laboratory, Pasadena, California, July 30, 1964. 
ACKNOWLEDGMENT 
The author wishes to express his appreciation to Royal G. Harrison, Jr., Instru- 
mentation Section, whose efforts on the design and perfection of the telemetry 
system made this program possible. 
9 


Free-flight telemetry testing in the jet propulsion laboratory wind tunnels

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