A Reproduced Copy OF Reproduced for NASA by the NASA Scientific and Technical Information Facility (NASA-TM-X-69441) TEST REPORT FOR N74-11599 120-INCH-DIAMETER SOLID ROCKET BOOSTER (SRB) MODEL TESTS (NASA) -9- p HC $7.00 CSCL 21H Unclas G3/28 22279 FFNo 672 Aug 65
94
Embed
A Reproduced Copy - NASA€¦ · W. C. Jones, DDSED -.. er, DD-SED Space Shuttle Solid Rocket T e nical Director Booster Retrieval Task Team
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
A Reproduced CopyOF
Reproduced for NASA
by the
NASA Scientific and Technical Information Facility
(NASA-TM-X-69441) TEST REPORT FOR N74-11599120-INCH-DIAMETER SOLID ROCKET BOOSTER(SRB) MODEL TESTS (NASA) -9- p HC $7.00
CSCL 21H UnclasG3/28 22279
FFNo 672 Aug 65
5 eTR-1 253
JOHN F. KENNEDYSPACE CENTER
F.EFERENCE COPYX
IOHN F. KENNEDY SPACE CENTENASA LIBRARY
SEP x b 1973
TEST REPORT
FOR
120-INCH-DIAMETERSOLID ROCKET BOOSTER (SRB)
MODEL TESTS
Conducted at theLong Beach Naval Shipyard, California
August 1973
JOHN F. KENNEDY SPACE CENTER, NASA
:%
TEST REPORT
FOR
120-INCH-DIAMETERSOLID ROCKET BOOSTER (SRB)
MODEL TESTS
Prepared by: Approved by:
W. C. Jones, DDSED -.. er, DD-SEDSpace Shuttle Solid Rocket T e nical Director
Booster Retrieval Task Team
TR-1253
ABSTRACT
//The-Space Shuttle Solid Rocket Boosters (SRB's).will be jettisoned toimpact in the ocean within a 200-mile radius of the launch site. Tests wereconducted at Long Beach, Calif.rmi-a-,using a 120-in-ch-diameter Titan 3C modelto simulate the full-scale characteristics of the prototype SRB during re-trieval operations//
The objectives of the towing tests were to investigate and assess thefollowing:
a. floating and towing characteristics of the SRBb. need for plugging the SRB nozzle prior to towc. attach point locations on the SRBd. effects of varying the SRB configuratione. towing hardwaref. difficulty of attaching a tow line to the SRB in the open sea.
The model was towed in various sea states using four different types andvarying lengths of tow line at various speeds. Three attach point locationswere tested.
Test data was recorded on magnetic tape for the tow line loads and formodel pitch, roll, and yaw characteristics and was reduced by computer totabular printouts and X-Y plots. Profile and movie photography provideddocumentary test data.
The free floating characteristics of the model with the nozzle pluggedwere very stable with the nose of the model up at a +1-1/2-degree pitchangle. The model positioned its longitudinal axis in the troughs of the seaand experienced heaving motions from the swell of the sea.
The free floating characteristics of the model with the nozzle unpluggedwere assessed in calm water only. The model ingested water until it stabi-lized at a nose-up attitude of +7-1/2 degrees. At that time it was determinedthat subjecting the unplugged model to a sea state would result in taking onmore water and cause the SRB to rotate to the spar buoy mode.
The model exhibited stable pitch, roll, and yaw characteristics under-tow in all test configurations at tow speeds below 10 knots. Instability inthe roll and yaw axes occurred at speeds of 10 to 14 knots with the heavierand longer lengths of wire tow line. The model pitch angle decreased as towspeed increased, and the model plowed significantly at speeds of 10 knots andabove. Removal of the nozzle exit cone improved model stability at thehigher tow speed.
Analysis of test data indicates that plugging of the nozzle area is neces-sary for model towing due to the exposure of the nozzle throat area at thehigher tow speeds.
All attachment configurations tested provided acceptable towing character-istics with the single center attachment resulting in the smallest tow line load.
PRECEDING PAGE BLANK NOT FILMEDiiiPRECEDING PAGE BLANK NOT FILMED
TR-1253
Tow speeds had the most significant effect on tow line loads and modeltowing characteristics. Using 7-inch-circumference nylon tow line, the towline loads at the tow vessel increased with speed and ranged from 1500 poundsat 6 knots to 13,500 pounds at 14 knots.
Use of the 7-inch-circumference nylon line produced the smallest tow lineloads and produced no increase in line loads as the length was increased. The1-inch-diameter steel wire, 6-inch-circumference nylon line, and 7-inch-circumference nylon line were optimally sized for towing the model while the2-inch-diameter steel wire was oversized. To determine the tow line which isbest suited for towing the actual Shuttle SRB, scaling of the model load datais required.
Scaling of the model data causes the full scale values for speed and towline loads to increase as the square root and cube, respectively, of the scalefactor, .78. The full scale loads were much higher than the model loads witha difference between them of 15,647 pounds at 14 knots for the 7-inch-circumference nylon tow line. The 1-inch-diameter steel wire is undersizedfor full scale model towing, while the 7-inch-circumference nylon line wouldbe acceptable at speeds up to 15 knots without exceeding the maximum workingload.
Nylon Line . . .. . . . . . . . . . . . . . . ... . . . 5225 Tow Speed Versus Model Pitch Angle for 1-Inch-Diameter
Steel Wire .. . . - - -........ ..... . . . . . 5326 Tow Speed Versus Average Model Pitch Angle for all
Test Runs . . . . . .. ..... . . ... . .. 5427 Tow Speed Versus Model Pitch Angle with Exit Cone Attached
and Removed ..... . . . . . . . . . .. . .. . . . 5628 Tow Speed Versus Model Roll Position for Test Nos. 10H1,
iOM1, 1001, and 1OU . . . . . . . . . . . . . . . . . . . - 5729 Instability as Related to Tow Speed and Test Configuration
(3 pages) . . . 58(3 pages) ...... ................ 5830 Free-Floating SRB Model ..... ..... ....... 6131 Attitude Test at Dockside. . . . . . . . . . . . . . .... 6332 Pitch Attitude of Model While Floating .... . . . . . . . 6433 Pitch Angle of Model . . . . . . . . . ....... . . 6634 Type of Attachment Versus Average Tensile Load at the Tug
Using 400 Feet of 1-Inch-Diameter Steel Wire .6735 Type of Attachment Versus Average Tensile Load at the Tug
Using 800 Feet of 1-Inch-Diameter Steel Wire . ....... 6836 Tow Line Attachment Locations . . . . . . . . . . . . . . 6937 Tow Speed Versus Average Load at Tow Vessel Using 800, 1100,
1400, and 1800 Feet of Tow Line. . ............. 71
vii
TR-1253
LIST OF ILLUSTRATIONS (cont'.d)
FigureNo. Title Page
38 Tow Speed Versus Average Load at Model Using800, 1100, and 1400 Feet of Nylon Line ........... 72
39 Tow Speed Versus Average Load at Tow VesselUsing 2-Inch-Diameter Steel Wire . ...... ...... . 73
40 Tensile Load at the Tug as a Function of Waveand SRB Relative Motion . . . . . . . . . . .... . . . . 74
41 Tow Speed Versus Tow Line Loads at Tow Vessel andat Model . ............ ............ 75
42 Tow Speed Versus Maximum Tow Line Load for 1- and2-Inch-Diameter Steel Wire at Tow Vessel and for7-Inch-Circumference Nylon Line at Model . ......... 77
43 Type of Tow Line Versus Average Loads at ModelUsing 1100-Foot Tow Line . . .... . . . . . . . ..... . 78
44 Type of Tow Line Versus Average Loads at ModelUsing 1400-Foot Tow Line . . . . . . . . . . . . . . . . . . 79
45 Tow Line Length Versus Average Loads at Tow VesselUsing 1-Inch-Diameter Steel Wire . . . . . ....... . . 81
46 Tow Line Length Versus Average Load at Tow VesselUsing 2-Inch-Diameter Steel Wire . ............. 82
47 Tow Line Length Versus Average Load at ModelUsing 7-Inch-Circumference Nylon Line . ........ . . 83
48 Model Versus Full Scale Loads ............... . 8749 Model and Full Scale Corresponding Speeds . ........ 8850 Model and Full Scale Tow Line Loads Versus Tow
Speeds Using 7-Inch-Circumference Nylon Line . ....... 89
LIST of TABLES
TableNo. Title Page
I Tow Line Load Data for Load Cells at the TowVessel and at the Model . .............. . . . 38
II Tow Cable Data . . . . . . . ........... . . . . 76III Model Versus Full Scale Loads (Pounds) . ., . .... . 85IV Corresponding Speeds (Knots) ........ . .. . . . . 86
viii
TR-1253
SECTION I
INTRODUCTION
1.1 PURPOSE AND SCOPE
The purpose of this document is to present the test plan and testresults of large scale Solid Rocket Booster (SRB) model tests conducted atLong Beach, California. Testing began on March 26, 1973, and was completedon April 5, 1973. The test program utilized a 120-inch-diameter (Titan 3C)model of .the Space Shuttle SRB as shown in Figure 1. The model simulatedthe 142-inch-diameter baseline dated February 2, 1973, with the exception ofthe flared aft skirt. Tests conducted were: waterborne attitude, waterbornestability, harbor and ocean towing, and attachment at sea.
Figure 1. 120-Inch-Diameter SRB Model
The tests were conducted in two phases:
Phase 1 (March 26 to March 30): Harbor tow tests,stability test, andattitude test
Phase 2 (April 3 to April 5): Ocean tow tests andattachment at sea test
1
TR-1253
The purpose of the in-harbor testing was to establish a calm water baselinefor acquisition of data and to gain the experience and confidence necessary toconduct the ocean tests. Tests were conducted in the ocean to assess theeffects of variable ocean conditions on the SRB.
Test data recorded during the towing tests consisted of tow line loadsat the tow vessel and at the model, and pitch, roll, and yaw characteristicsof the model. The results of attitude, stability, and attachment tests weredocumented also.
1.2 MODEL DESCRIPTION
The model was a previously static fired 120-inch-diameter Titan 3Csolid rocket booster which was obtained from MSFC. The model consisted of anose section, segmented body sections, aft support skirt, a 6-degree cantednozzle, and an exit cone extension. The center of gravity of the model simu-lated the 142-inch-diameter baseline for the Shuttle SRB.
The longitudinal position of the center of gravity (lcg) of the modelfor the MSFC drop tests was located 435 inches from the aft edge of thestructural support skirt and required relocation for the tow tests due to achange in the Shuttle SRB baseline from a 156-inch diameter to a 142-inchdiameter. The 142-inch-diameter baseline required locating the lcg at 415inches (reference aft skirt). This was accomplished by relocating the ballastsystem.
The ballast system consisted of eight I-beams with associated weightswhich were moved further aft in the model. An additional 5200 pounds of leadwas attached to the beams. All weights were attached symmetrically about theroll axis of the model to maintain the original roll axis cg (see Figure 2).
To simulate the Shuttle SRB after parachute descent and water impact,an open nose fairing was welded to the forward handling fixture of the model(see Figure 3). This structure represented the empty parachute compartmentof theShuttle SRB after the parachutes are deployed.
Three different tow line attachment configurations were tested: two-point bridle, single center, and single side. Towing brackets were added tothe model for the two-point bridle and single side configurations; anexisting 2-inch shackle on the nose section was used for the single centerconfiguration (see Figures 4, 5, and 6).
A bulkhead plate with an access hatch was installed as a nozzle plugto prevent the SRB from sinking during the tow tests. The assembly wasplaced between the nozzle and the exit cone extension (see Figure 7).
As part of the data acquisition system, a telemetry package was placedon the model to transmit tow line loads at the model and pitch, roll, and yawdata to the tow vessel. The electronic equipment was placed in waterproofpressurized cannisters which were fastened to gusset plates inside the nosefairing of the model for easy access (see Figure 8). A pitch, roll, and yawmeasuring system in the waterproof container was installed at the lcg of themodel (see Figure 9). Three antennas were placed around the outside skin ofthe model at 120-degree intervals (see Figure 10).
2
TR-1253
1.
-4 _ -i /
44 -- ;j
Fgr 2,. B l S t I- li on
.'I
F 2ae a
,; .-',
/L:;
'i ;j
j>' Z;iQ ~ 1~:a
Figure<4 2.UlatSs;mIsalto
TR-1253
Ilk
GOODu
'50
F3 n I l
Fiu re 3j 0 on In
-1 i
Fir3.Oe IoeFing nsaltn
TR-1253
--
--U t.I
S, .
r
/
SFigure 4. Towing Bracket for Two-Point Bridle Attachment
5
TR-1253
IPA
Figure 5. Towing Bracket for Single Side Attachment
.6
TR-1253
Fir 6
Figure 6. Single Center Attachment
7
TR-1253
j'j
M.
ifdtC-
8.,
a4m \: :
•. • °-,
I-t d "t
jlJ
.. ..- - --lr I -: : - " - .
FoA
~ 4.
Figure 7. Iozzle Plug Assembly
TR-1253
/t I.-
/X
I j
N>
ii
FiguPRO Eri
Figure'8. Electronic Equipment Installation in Nose Fairing
Approximately 200 holes which resulted from the removal of MSFCwater impact test instrumentation on the model were sealed with nuts, bolts,and RTV sealant. Paint patterns were added to the model for photographicdata acquisition.
The dimensions and weight of the modified model were as follows:
Length: 101 feet
Body Diameter: 10 feet
Weight: 93,286 pounds
Longitudinal Postionof Center of Gravity, lcg: 415 inches (reference aft
support skirt)
1.3 VESSELS AND TEST HARDWARE
Two types of tow vessels were used during the testing--a U.S. Navyharbor tug (YTB 807) as shown in Figure 11 and a Fleet Ocean Tug (USS Molala,ATF 106) as shown in Figure 12. The YTB 807 was used for the tow operationsin the harbor phase of the testing. It produced 1500 shaft horsepower, andits towing equipment consisted of an aft-mounted capstan, H-bitts aft, andmiscellaneous securing cleats. Since this vessel does not normally performastern towing operations, 900 feet of 1-inch-diameter steel tow wire, 600feet of 6-inch-circumference nylon line, and a storage reel were added to thevessel.
The ATF 106 was used for tow operations in the ocean phase of the testingand is specifically designed for all types of ocean towing. Its towing hard-ware consisted of an automatic towing machine which maintained a specifictension on the tow cable, capstan, stern rollers, H-bitts, Norman pins, andmiscellaneous pad eyes and securing cleats. The ATF 106 carried 5000 feet of1-inch-diameter and 2100 feet of 2-inch-diameter steel towing cable and 2400feet of 7-inch-circumference, regular lay nylon tow line.
A 100-foot long, 6-inch circumference braided nylon pendant was attached -to the model for the single center and single side attachment configurations.This pendant provided a quick and safe method for connecting and disconnectingthe tow line during initial hook-up and while at sea. For the two-pointbridle attachment, an 80-foot-long, 3-3/8-inch-circumference nylon pendant wasused as part of the bridle.
1 2'i
TR-1253
Figure 11. USN Harbor Tug (YTB 807)
/--7
Figure 12. USNI Fleet Ocean Tug USS Ilolala (ATF 106)
13
TR-125 3
A combined carpenter stopper/load cell arrangement was used with the
wire tow cables to gather data on tow line loads at the tow vessel
Two 34-foot work boats were used to maneuver the model during dockingoperations. One work boat was also used in the harbor tow testing as acamera boat for profile photography of the model. A torpedo retriever boatwas used in the ocean tow testing as the profile camera boat.
1.4 INSTRUMENTATION AND DATA ACQUISITION SYSTEMS
1.4.1 ..Instrumentation
The measurement and acquisition system for the tow tests was usedto record forces on the tow line at the model and tow vessel and to recordthe model's pitch, roll, and yaw characteristics. This system consisted ofthree load cell transducers, two pendulum potentiometers, a rate gyroscope,a radio frequency telemetry link, a strip-chart recorder, and a taperecorder. Measurement components installed on the SRB were in waterproofenclosures and were battery powered. The components installed on the ATFand YTB tow vessels were rack-mounted and used the ship's electrical power.
One or two 0 to 30,000-pound capacity load cells and their associated50-foot waterproof cables were installed at the model in the tow harness asrequired for the tow attachment configurations. Two waterproof load cellpower supply/signal conditioner containers were installed in the SRB nosefairing. A telemetry transmitter and its separate waterproof enclosed batterycontainer were installed in the nose fairing. The transmitter was connectedby 25-foot coaxial cables to three antennas installed 120 degrees apart on thecircumference of the nose fairing (see Figure 10).
14
TR-1253
A waterproof enclosure containing two pendulum potentiometers, one tomeasure +45-degree pitch and one to measure +45-degree roll, and a rategyroscope to measure yaw rate were installed-in the model nose fairing. Thedata was recorded using the reference system in Figure 14. A 100-foot cableassembly was routed inside the SRB to the forward bulkhead and then routed tointerface with the telemetry input connection.
The transmitted data was received by a rack-mounted telemetry receiveron the tow vessel. The data was simultaneously recorded on a tape recorderand a strip-chart recorder. The strip-chart recorder provided real-timereadout and a permanent paper record with written annotations (see Figure 15).A master time clock was utilized to time correlate all test data.
A 0 to 30,000-pound capacity load cell was installed in the tow cableat the tow vessel when 1-inch-diameter and 2-inch-diameter steel wire wasused for towing. Real-time data from this load cell was available on a meterreadout, while simultaneously being recorded on both the strip-chart recorderand the tape recorder. The overall SRB measurement component installation andthe tow vessel measurement component installation are shown in Figures 16and 17, respectively.
A pit log (speedometer) was mounted on the side of each tow vessel toobtain towing speeds during the testing (see Figure 18).
1.4.2 Photographic System
The photographic system consisted of four 24 frames per second motionpicture cameras which were used for documentary coverage and to gather dataon model pitch, roll, and yaw characteristics. Two engineering cameras, onewide angle and the other telephoto, were located on the tow vessel. Anotherengineering camera was located on a camera boat to provide profile photographyof the model. The engineering data cameras were time syncronized with amaster time clock for correlation of the data.
-1.5 REFERENCE DOCUMENTS
Test Plan for MSFC/KSC Space Shuttle Solid Rocket Booster WaterRecovery Program, 77% Model, December, 1972, DD-SED, JohnF. Kennedy Space Center, NASA
Qualitative Investigation of Booster Recovery in Open Sea, TR-1195,March 1, 1973, DD-SED, John F. Kennedy Space Center, NASA
Measurement Support Plan and Requirements for 77% SRB Tow Testing,January 10, 1973, IN-MSD, John F. Kennedy Space Center, NASA
Preliminary Photographic Support Plan for SRB Tow Test, December27, 1972, IS-DOC, John F. Kennedy Space Center, NASA
Test Procedure for Solid Rocket Booster 77% Model Tow Test,January 30, 1973, SO-ENG, John F. Kennedy Space Center, NASA
15
TR-1253
PITCH, e REFERENCE PLANE:HORIZON
e
ELEVATION VIEW
REFERENCE POSITIONROLL, 12:00 HIGH
ROLL. 90 900o
oi 1 e 3 180e
2700
CROSS SECTION
YAW. Y
DIRECTION - YOF TOW
PLAN VIEW
Figure 14. Mlodel Attitude Reference System
16
TR-1253
--4 I if%4ri
40 - __ _I
1~71
-Ak
iii'
Figure 15. Strip Chart and Magnetic Recorders
17
TR-1253
r- nBATTERY
TELEMETRY ,TRANSMITTER
I IPOWER SUPPLY
LOAD SIGNAL INPUTCELL CONDITIONER SIGNAL
CONDITIONER
I I
POWER SUPPLY
COAD CONDITIONER
L
II ! I I
L JG I I
ROLL
YAW RATE
Lt
18
18 I
TR-1253
TELEMETRYRECEIVER
TIME TELEMETRYGENODER DISCRIMINATOR
GENERATOR
POWER STRIPSUPPLY CHARTSIGNAL RECORDER
CONDITIONER
TAPERECORDER
Figure 17. Tow Vessel Measurement System Installation
19
TR-1253
~ ii
t NN i
I/LoAA
20 -
:t ot
Figure 1. Spedoet r Itllaio
.f-
TR-1253
U.S. Navy Towing Manual, Volumes I and II, NAVSHIPS 0925-000-1000,1971
Principles of Naval Architecture, John P. Comstock, Ed., The Societyof Naval Architects and Marine Engineers, New York, 1967
Water, Air, and Interface Vehicles, Philip Mandel, MIT Press,Camridge, Massachusetts, 1969
Unclassified Excerpt from "Dynamic Scale Modeling Technics forMine Countermeasures," Charles Sieber (D.T.M.B.), Proceedingsof the 16th Naval Mine Countermeasures, January 30, 1973
The primary objective of the SRB model test program was to determinethe characteristics of the SRB floating free and under tow. In addition toassessing the floating and towing characteristics, the following requirementswere included as test objectives:
a. Investigate the need for plugging the SRB nozzle prior to towingb. Assess attach point locations on the SRB for towingc. Assess effects of SRB configuration variations on towingd. Assess various towing hardwaree. Assess difficulty of attachment of tow lines at sea.
23/24
TR-1253
SECTION III
TEST DESCRIPTION
3.1 HARBOR TOW TESTING
The initial towing tests were accomplished within the outer break-water at Long Beach, California, (see Figure 19) to determine calm watercharacteristics and to gain initial test experience in calm water.
Three attachment configurations were used:
a. Two-point bridle
b. Single center
c. Single side
Two types of tow lines were used during the testing: (1) 1-inch-diametersteel cable and (2) 6-inch-circumference nylon line. A nylon pendant of either3-3/8-inch or 6-inch circumference nylon was attached at the model for alltest runs (see Figures 20, 21, and 22). The nozzle remained plugged throughoutall tow tests.
A YTB was used to tow the model. Tow speeds, tow line configurations,and model configurations were varied according to the test profile sheets inparagraph 3.1.1.
3.1.1 Test Profile Sheets, Harbor Tests
3.1.1.1 Two-Point Bridle Attachment (See Figure 20)
Test configurations for the two-point bridle attachment tests (TestNo. 1 and Test No. 2) using 1-inch-diameter steel cable and 6-inch-circumfer-ence nylon line are tabulated below:
1-Inch-Diameter Steel Cable 6-Inch-Circumference Nylon LineTest Tow Vessel Length of Test Tow Vessel Length ofNo. Speed (knots) Cable (feet) No. Speed (knots) Cable (feet)
Test configurations for the single center attachment tests with theexit cone attached (Test No. 3 and Test No. 4) using 1-inch-diameter steelcable and 6-inch-circumference nylon line are tabulated below:
1-Inch-Diameter Steel Cable 6-Inch-Circumference Nylon LineTest Tow Vessel Length of Test Tow Vessel Length ofNo. Speed (knots) Cable (feet) No. Speed (knots) Cable (feet)
Test configurations for the single center attachment tests with theexit cone removed (Test No. 7 and Test No. 8) using 1-inch-diameter steelcable and 6-inch-circumference nylon line are tabulated below:
1-Inch-Diameter Steel Cable 6-Inch-Circumference Nylon LineTest Tow Vessel Length of Test Tow Vessel Length ofNo. Speed (knots) Cable (feet) No. Speed (knots) Cable (feet)
Test configurations for the single side attachment tests (Test No. 5.and Test No. 6) using 1-inch-diameter steel cable and 6-inch-circumferencenylon line are tabulated below:
1-Inch-Diameter Steel Cable 6-Inch-Circumference Nylon LineTest Tow Vessel Length of Test Tow Vessel Length ofNo. Speed (knots) Cable (feet) No. Speed (knots) Cable (feet)
The ocean testing was conducted outside the breakwater at Long Beachin the Pacific Ocean (see Figure 19) to encounter various sea states.
The single center attachment point was utilized throughout the oceantests. Three types of tow line were used: (1) 1-inch-diameter steel cable,(2) 2-inch-diameter steel cable, and (3) 7-inch-circumference nylon line whichwere connected to a 6-inch-circumference nylon pendant.
The tow tests were conducted with the model towed at various headingsrelative to the wave motion. Tests were also performed with the exit coneremoved and attached.
31
TR-1253
An ATF was used to tow the model. Tow speeds, tow line configurations,and model configurations were varied according to the test profile sheets inparagraph 3.2.1.
3.2.1 Test Profile Sheets, Ocean Tests
Test configurations for the single center attachment tests with theexit cone attached (Test Nos. 10, 11, and 13) using 1-inch-diameter steelcable, 2-inch-diameter steel cable, and 7-inch-circumference nylon line,respectively, are tabulated below:
1-Inch-Diameter Steel Cable 1-Inch-Diameter Steel CableTest Tow Vessel Length of Test Tow Vessel Length ofNo. Speed (knots) Cable (feet) No. Speed (knots) Cable (feet)
*The number following the hyphen indicates the direction of sea as coded inFigure 23.
32
TR-1253
LEGEND
( HEADING SEA
( /4 LEFT HEADJNG SEA
( 1/4 RIGHT HEADING SEA
G FOLLOWING SEA
G 1/4 LEFT FOLLOWING SEA
1/4 RIGHT FOLLOWING SEA
52
3
Figure 23. Wave Direction in Relation to SRB
33
TR-1253
7-Inch-Circumference Nylon Line
Test Tow Vessel Length ofNo. Speed (knots) Cable (feet)
13Y-1 14 110013Z-1 14 1400
Test configurations for the single center attachment tests with theexit cone removed (Test No. 15 and Test No. 16) using 1-inch-diameter steelcable are tabulated below:
* The number following the hypen indicates the direction-of sea as coded inFigure 23.
3.3 STABILITY TEST
A stability test was conducted during which the model was released tofloat freely without the tow cable in a sea state 2 condition. The positionthe model assumed relative to the wave motion and wind, as well as the modelpitch, roll, and yaw characteristics were documented by movie cameras.
3.4 ATTITUDE TEST
An attitude test was conducted along dockside in calm water. Themodel was lowered into the water with the nozzle unplugged and permitted to
34
TR-1253
take on water until an equilibrium position was achieved. The exit cone waspointed downward when the model was placed in the water.
3.5 ATTACHMENT TEST
An attachment-at-sea test was performed in the ocean. The modelwas cast adrift with the 100-foot nylon pendant attached to the nose and afloat attached to the free end of the pendant. A small rubber boat with anoutboard motor was deployed from the ATF, and personnel attached a messengerline to the 100-foot nylon pendant. After the messenger line was attached,it was passed to the stern of the ATF where a capstan was used to pull themodel closer. When the free end of the 100-foot pendant reached the ship,the 7-inch-circumference nylon tow line was attached, and the ATF proceededto tow the model at 8 knots.
35/36
TR-1253
SECTION IV
TEST RESULTS
4.1 GENERAL
The tow test data recorded on magnetic tape for tow line loads andmodel pitch, roll, and yaw were reduced by computer to tabular printouts andX-Y plots. Photographi! documentation of selected test runs was reduced toprovide additional pitch, roll and yaw data.
Table I presents a summary of tow line load data from the load cell(s)for each test run with the attachment configuaration, type of tow cable, modelconfiguration, tow speeds, and tow cable lengths.
Test results are presented and discussed in the following paragraphs:
4.2 Towing Characteristics4.3 Floating Characteristics4.4 Nozzle Plugging4.5 Attachment Configurations4.6 Tow Speedc4.7 Tow Lines4.8 Scaling
4.2 TOWING CHARACTERISTICS
The test results indicate that the model exhibited stable pitch,roll, and yaw characteristics for most towing configurations. Instability inthe yaw and roll axes occurred only at the higher tow speeds (10 to 14 knots)and with longer lengths of wire tow line. Removal of the exit cone improvedmodel stability at the higher tow speeds.
The pitch angle of the model at zero tow speed was +1-1/2 degrees,and as two speeds increased, the pitch angle decreased. Figure 24 representsthe relationship between tow speed and pitch angle for 7-inch-circumference -nylon tow line. These data points were selected because the 7-inch-circum-ference nylon tow line has a specific gravity of 1.14, and the effects of towline weight were reduced. The pitch angle decreases as a linear function ofspeed to 12 knots where the pitch rate increases significantly and the plotbecomes curvilinear. A plot of the same relationship shown in Figure 25 for1-inch-diameter steel wire tow line indicates the same result with the pitchrate increasing above 12 knots.
The change in the pitch rate above 12 knots is a result of the modelnose plowing at the higher tow speeds which increases the drag at the noseof the model. In both the 7-inch-circumference nylon line and the 1-inch-diameter steel wire plots the pitch rate began to increase when the model hada pitch angle between -0.80 and -1.0 degree. Figure 26 represents the re-lationship between model tow speed and average model pitch angle computedfrom all test runs. Model pitch attitude decreases as tow speed increases witha greater decrease in pitch angle between a tow speed of 12 and 14 knots.
37
K -4I
STable . Tow Line Load Data for Load Cells atthe Tow Vessel and at the Model
* Number following the hyphen indicates direction of sea as coded in Figure 23.
** Value was less than 300 pounds.
-I
(5n-J
-aw
TR-1253
+3
HELD CONSTANT:SINGLE CENTER ATTACHMENTEXIT CONE ATTACHED
12
I0z
7 to 12 14
SPEED (KNOTS)
52
-3
52
TR-1 253
+3
HELD CONSTANT:SINGLE CENTER ATTACHMENTEXIT CONE ATTACHED
+2
w +1
SPEED (KNOTS)
Figure 25. Tow Speed Versus Model Pitch Angle for l-lnch-Diameter Steel Wire
-53
-i
-2
-3w 0 21
-53
TR-1253
+3
HELD CONSTANT:SINGLE CENTER ATTACHMENTEXIT CONE ATTACHED
+2
+1
54
-l0
4C-xU-
-2
-31
4 ~~SPEED (KNOTS) 1 21
Figure 26. Tow Speed Versus Average Model Pitch Angle for All Test Runs
54
TR-1253
Removal of the nozzle exit cone decreased the model pitch angleslightly as shown in Figure 27 which represents data recorded during TestNo. 15. This reduction was attributed to the loss of the upward planingforces on the aft of the model from the exit cone.
The model was extremely stable in the roll and yaw axes for all testsconducted at tow speeds below 10 knots. The model floated with the exit conepointed down and the #3 position up at zero tow speed, and as speed increased,water pressure on the exit cone forced the model to roll clockwise or counter-clockwise and stabilize. Figure 28 represents tow speed versus model rollposition for the conditions stated. As speed was increased, the model rolledfrom the 180-degree position high to 360-degree position high with the exitcone pointed upward. The exit cone created a "rudder effect," which causedthe model to yaw in the same direction as the exit cone cant.
Model instability was primarily a function of tow speed. The typeand length tow line also influenced model towing characteristics to a lesserextent. As the speed was increased, the model increased its yaw angle andstarted rolling due to skin friction, similar to a water wheel. The rollingoccurredwhen the model had yawed about 7 degrees from the direction oftow. The speed at which the instability occurred varied with the test configu-rations as shown in Figure 29. Using 1-inch-diameter steel wire, the modelstarted rolling at 13 knots with 1100 feet of tow cable and at 10 knots with1400 feet of tow cable. The 2-inch-diameter steel wire produced the worstunstable conditions with yaw angles up to 17 to 18 degrees and roll rates upto 13 rev/min. Using 7-inch-circumference nylon tow line (1100 and 1400 feetlong), the model did not begin rolling until the tow speed was increased to14 knots.
To further investigate the effects of the exit cone on towingstability, the exit cone was removed during Test Nos. 7, 8, 15, and 16. Themodel stability at the higher tow speeds and longer line lengths was signifi-cantly improved; no roll was experienced and a maximum yaw angle of 4 degreeswas recorded.
4.3 FLOATING CHARACTERISTICS
To determine the floating characteristics of the model, tests wereperformed with the nozzle plugged and unplugged. With no water in the casingand the nozzle plugged, the model floated at a +1-1/2-degree pitch angle. The#3 position was up and the canted nozzle was down in the water (see Figure 30).
During the stability test, the model was cast afloat in a sea state2 condition and gusting winds. The model aligned itself in the trough of thewaves, perpendicular to the direction of the wind. In this position the modelwas very stable with no erratic pitch and no roll or yaw. The model heavedabout I to 2 feet as it rode the swells, but the movement was smooth with noerratic motion.
55
TR-1253
HELD CONSTANT:SINGLE CENTER ATTACHMENT1100 FEET 1-INCH STEEL CABLE
1
S KOC -TEST NO. 15
EXIT CONEan -REMOVED
TEST NO. 10EXIT CONE
> ATTACHEDC,
Lu
-31 1
SPEED (KNOTS)
Figure 27. Tow Speed Versus Model Pitch Angle with Exit Cone Attachedand Removed
56
360
270 OSFRONT VIEW
OF MODEL
S180
PLANING EFFECT ON THE EXIT CONE AS SPEED INCREASES
6 8 10 12 14
SPEED (KNOTS)
-I
Figure 28. Tow Speed Versus Model Roll Position for Test Nos. 10H1,10M1, 10Q1, and 10U1
\ IIU-4
U,
TEST NO. 10I.INCH-DIAMETERSTEEL WIRE
ROLL
1800
Uiw
u
.- ROLL
1400ui.0-
t-
ROLL
1100
8006 8 10 12 14
SPEED (KNOTS)
Figure 29. Instability as Related to Tow Speed and Test Configuration(sheet 1 of 3)
TEST NO. 112-INCH-DIAMETERSTEEL WIRE
ROLL
1800
U-
- LROLL
IA.1400
0
600
6 8 10 12 14
SPEED (KNOTS)
-4I
-,
Figure 29. Instability as Related to Tow Speed and Test Configuration(sheet 2 of 3)
00o
TEST NO. 13 NOTE: THE 1800-FOOT TOW7-INCH-CIRCUM- LINE WAS NOT USEDFERENCE NYLON DURING THIS TEST.LINE
1800
I-ww
_-_ ROLL1400U
0
000
6 8 10 12 14
SPEED (KNOTS)
Figure 29. Instability as Related to Tow Speed and Test Configuration(sheet 3 of 3)
TR-1253
NASA/KSC i.
Figure 30. Free-Floating SRB Model
61
TR-1253
The attachment at sea test, which was conducted in a sea state 1condition, resulted in a model floating attitude similar to the stabilitytest, except for reduced model heave. A time span of 30 minutes was requiredto approach the free-floating model, attach the tow line, and commence towing.The use of a nylon pendant and float provided a good method for attachingthe tow line while keeping a safe distance between the model and the towvessel.
In the attitude test, the model was placed in the water at docksidewith the nozzle unplugged and the #3 position up (see Figure 31). Waterfilled the casing until the nozzle area became submerged, and the air remaininginside the model was trapped. The model stabilized in 1 minute and 15 secondsat a +7-1/2-degree pitch angle with the #3 position up. The air escapingfrom the model prior to stabilization imparted a small forward velocityto the model. The preliminary results from the MSFC drop tests indicated thatafter the model impacted the water and stabilized, it achieved a 5- to 7-degreepositive pitch angle. These values compare closely with the attitude testresults with the variation resulting from the different lcg location anddifferent water entry conditions. The MSFC model (156-inch baseline) lcgwas 20 inches farther forward than on the tow test model. The lcg beinglocated farther forward would reduce the model pitch angle.
Figure 32 represents a cross-section of the model floating in thewater with the nozzle plugged and unplugged.
4.4 NOZZLE PLUGGING
To determine the requirement for a nozzle plugging system, thepitch characteristics of the model were analyzed. From the section on towingcharacteristics, it was determined that pitch angle was a function of towspeed, tow line, model configuration, and sea state. The pitch angledecreased as the tow speed and tow line length and weight increased; whilethe sea state caused the model pitch angle to oscillate.
The average pitch angle for each test run was determined by the towspeed and tow line and model configurations, and the range of pitch valueswas determined by the sea state conditions during the test run. The tabula-tion below lists the greatest average negative pitch values and range basedon the data reduced for three types of tow line used in the testing.
Type of Maximum Average Sea Maximum DecreaseTest No. Tow Line Negative Angle State Range in Pitch Angle
10 1-inch- -1.20 3 6.40 5.50diameter ,steel
11 2-inch- -2.750 1 2.30 5.40diametersteel
13 2-inch-cir- -3.60 1 2.20 6.20cumferencenylon
62
TR-1253
I r'
ago-
Figure 31. Attitude Test at Dockside
63
TR-1253
-1
NOZZLE PLUGGED-ATTITUDE Ig NOSE UPPITCH ATTITUDE AT 0 VELOCITY, CALM WATER
1 o
10NOZZLE UNPLUGGED-ATTITUDE 7f NOSE UP
PITCH ATTITUDE AT 0 VELOCITY, CALM WATER
Figure 32. Pitch Attitude of Model While Floating
64
TR-1253
Since the nozzle was plugged during all tow tests, some assumptionsmust be made concerning model pitch characteristics when the model isfloating with the nozzle unplugged. Hypothetically, the model pitch charac-teristics for the plugged and unplugged nozzle configurations will be con-sidered relatively close. The model with the unplugged nozzle floated at apitch angle of +7-1/2 degrees. If the model pitch decreases by 4 degrees dueto a high tow speed, the model with the unplugged nozzle would float at a+3-1/2-degree pitch angle as shown in Figure 33. The nozzle area would be atthe water/air interface and water could enter the model. If a pitch oscillationof +2 degrees is added for the sea state effects, then the nozzle area wouldcome out of the water, and the model would start to take on water. This condi-tion would either result in the model sinking, or tow line tensile loadingwould increase to the point which would cause the model to assume a "sparbouy" mode thereby making towing operations very difficult.
Another factor which must be considered is the potential changes insea state during towing operations which could produce even greater SRB pitchangles than those experienced during the testing. The highest sea state exper-ienced during the testing was a sea state 3 (3- to 5-foot waves) during TestNo. 10, and the criteria for SRB recovery is that it shall be accomplished ina sea state 5.
4.5 ATTACHMENT CONFIGURATIONS
The three attachment configurations for towing the SRB were:(1) two-point bridle, (2) single center, and (3) single side. All testconfigurations were used in the harbor testing; however, only the single centerattachment was used in the ocean testing. Originally, all attachment config-urations were to be used in both harbor and ocean phases of the testing, butduring the harbor phase, sea conditions reached sea state 3 and providedsufficient data for attachment configurations relative to sea states.
Use of the same attachment point for the ocean testing also providedmore data points under constant conditions for analysis of other factors, i.e.,types of tow line and lengths, which affected tow line loads and model towingcharacteristics.
Figures 34 and 35 present the relationship between attachmentconfigurations and tow line loads at the tow vessel for equivalent speedranges. The line loads using the single center attachment were significantly-smaller than the other attachment configurations. Loads experienced usingthe two-point bridle and single side attachments were approximately the same.
The lower line loads with the single center attachment could haveresulted from the tow cable attachment for the single center being located atthe forward tip of the model while the other attachments were located 11 feetaft, creating a larger drag profile. This is especially true for the wiretow lines whose direction of pull was not parallel to the direction motionbut at a downward angle determined by catenary of the wire (see Figure 36).
65
TR-1253
NOZZLE UNPLUGGED - ATTITUDE 7 NOSE UP
NOZZLE UNPLUGGED - ATTITUDE 3- NOSE UP2
PITCH ATTITUDE AT HIGH TOW VELOCITY, CALM WATER
NOZZLE UNPLUGGED - MAXIMUM AND MINIMUM PITCH ATTITUDE
PITCH ATTITUDE AT HIGH TOW VELOCITY, ROUGH WATER
Figure 33. Pitch Angle of Model
66
15 _ SINGLE SIDE ATTACHMENT
_ _ _ _ _ _ _ _ TWO-POINT BRIDLE14 : ATTACHMENT
13_ SINGLE CENTER
13 ATTACHMENT
HELD CONSTANT:12 CABLE LENGTH = 400 FEET
NOZZLE EXTENSION ATTACHED
z 6 KNOTS 8 KNOTS 10 KNOTSa.U-o 10
9
N N
5
-r
TESTT5 NO.
NO. NO.Q EST T 3U
NO.
TEST ESTNO. TEST 30N
33U
0 . .......
TYPE OF ATTACHMENT
C-I
u- Figure,34. Type of Attachment Versus Average Tensile Load at theTug Using 400 Feet of 1-Inch-Diameter Steel Wire
I
rUT
15 SINGLE SIDE ATTACHMENT15
TWO-POINT BRIDLE
14 _ATTACHMENT
V7 SINGLE CENTER13 ATTACHMENT
HELD CONSTANT:CABLE LENGTH = 800 FEETNOZZLE EXTENSION ATTACHED
12
6 KNOTS 8 KNOTS 10 KNOTS11o 10
o9
TEST
LU 1Wex TEST5 .... NO.TEST' 5W . :I-I
NO. :TEST
4 1S 7 NO.
3 0.0___
T S ;;.TEST NO
2 NO - NO. ___7__ _ ___
030
TYPE OF ATTACHMENT
Figure 35. Type of Attachment Versus Average Tensile Load at theTug Using 800 Feet of 1-Inch-Diameter Steel Wire
WATER
LIN
L
'\3
F-t
Figure 36. Tow Line Attachment Locations
TR-1253
4.6 TOW SPEEDS
Tow speed had the most significant effect on tow line loading and modeltowing characteristics. Figure 37 represents the relationship between towspeeds and average line load at the tow vessel for Test No. 10 using 800, 1100,1400, and 1800 feet of tow line. Tow line loads increased as an exponentialfunction of the tow speed up to 8 knots with an essentially linear region from8 knots to 14 knots. A linear regression line developed to describe thisrelationship is presented below:
Y = -4186.5 + 1330.9X
where
X = tow speed, knotsY = load at tow vessel, pounds
which has a correlation coefficient of 96 percent with the range of 6 to 14knots. In Figure 38 the tow speed versus average load at the model is shownfor 7-inch-circumferance nylon line. Again the load increases exponentiallyup to 10 knots and then becomes essentially linear up to 14 knots.
The relationship between tow speed and line loads at the tow vesselare shown in Figure 39 for 2-inch-diameter steel wire. Tensile load data fortow line lengths of 1100, 1400, and 1800 feet are shown to reflect the effectof the heavy weight of the tow line on the tow line loads. The plots have asteeper slope at the longer tow line lengths. For the speed range of 8 to 12knots, the 1100-foot plot shows line loads in essentially a linear relation-ship with tow speed. The 1400-foot plot indicates an exponential increase inload versus speed from 10 knots up to 12 knots which is probably a result ofthe extreme roll and yaw at 11 knots which became more severe as speed wasincreased.
The 1800-foot plot has approximately the same slope as the 1400-footplot, but higher load values from 3000 to 6000 pounds were experienced. Againextreme roll and yaw occurred when the tow speed reached 9 knots which couldhave caused the exponential increase in the speed versus load plot.
Figure 40 represents a typical relationship between tow line loadsand speeds for a tow relative to a heading sea and a following sea. Theheading sea produced the highest loads with an average difference betweenheading and following seas of 2070 pounds.
In Figure 41 the difference in the tow line loading at the towvessel and model are shown for 1-inch-diameter steel wire. The loads at thetow vessel were the highest with the average difference between the two of 2543pounds. As speed increased, the difference between the loading at the towvessel and at the model increased. The range of tow line loads is alsoshown with the variation increasing as the tow speed increases.
70
14000
HELD CONSTANTiI.INCH.DIAMETER STEEL WIRESINGLE CENTER ATTACHMENT
Sy 1 -4186.5 * 1330.9X
0
TOW SPEED (KNOTS)
-4
-JI
* Figure 37. Tow Speed Versus Average Load at Tow Vessel Using 800,1100, 1400, and 1800 Feet of Tow Line
/ -rI
r'UHELD CONSTANT: w7-INCH-CIRCUMFERENCE NYLON LINESINGLE CENTER ATTACHMENT
1200O
10000
az
00
2 4 a 10 12 14 16 1
JOW SPEED (KNOTS)
- /
I and 1400 Feet of Nylon Line
TR-1253
HELD CONSTANT:3.4MC.DIAMETER STEEL WIRESINLE CENTE ATTACHMENT
1400 FEET
4 1 IS I 14 16 Is
OW SPEED (KNOTS)
Figure 39., Tow Speed Versus Average Load at Tow Vessel Using 2-Inch-Diameter Steel Wire
73
-I
11
15 -
TITAN III14 - S D NSRBRLC-3 4626LCI 4625
I A L-- 1 31100 FT 1 IN STEEL CABLE 100 FT
z CX WAVES FOLLOWING SRB
2 aI
0
3 5 6 7 10 11 12 13 14
SPEED (KNOTS)
Figure, 40. Tensle Load at the Tug as a Function of Wave and SRB
Relative Motion
3-
2-
Relative Motion
14000 I / MAXIMUM LC.3
HELD CONSTANTs1IINCH.DIAMETER STEEL WIRE /1100.FOOT TOW LINESINGLE CENTER ATTACHMENT /
12000 I _AVERAGE LC.3
NOTE: /LC.1 AT MODELLC.3 AT TOW VESSEL
/ MINIMUM LCI3
/ / AVERAGE LC1
z 8000
Z 6000
L
0I0
-4i(000
6 10 12I 14 16 1
TOW SPEED (KNOTS)
-Fn
FIgure 41. Tow Speed Versus Tow Line Loads at Tow Vessel and at Model
TR-1253
4.7 TOW LINES
Four types of tow lines were used during the tow tests: (l) 1-inch-diameter steel wire, (2) 2-inch-diameter steel wire, (3) 6-inch-circumferencebraided nylon line, and (4) 7-inch-circumference twisted nylon line. Table IIpresents the specification data for the tow lines and the maximum allowableload for each which was calculated using the following equation and a 4 to 1safety factor:
Maximum Allowable Load -Tensile Breaking Force, Pounds
The maximum allowable load limit was not exceeded for any of the tow linesused in ocean testing as shown in Figure 42. Eighty-two percent of themaximum allowable load was the highest value achieved in Test No. 10 whileusing 1100 feet of 1-inch-diameter steel wire and towing at 14 knots. The1-inch-diameter steel wire and 7-inch-circumference nylon line were optimallysized for towing a model of the size used in this test program, but it isnecessary to consider scaling factors in considering the use of these towlines for the full scale SRB. The 2-inch-diameter steel wire was oversizedfor its application in towing the model because the maximum load recordedduring the tests was only 32 percent of its maximum allowable working load.
Average tow line load at the model versus tow speed was plotted forthe 1-inch-diameter steel wire, 2-inch diameter steel wire, and 7-inch-circumference nylon line (Figures 43 and 44) to study the effect of the towline itself on tow line loads. Tow line length was held constant at 1100feet in Figure 43 and 1400 feet in Figure 44.
Table II
Tow Cable Data
MaximumForce to AllowableBreak Load
Size Material Type (pounds) (pounds) Weight (Ib/ft)
1-inch-diameter Steel 6 x 37 85,600 21,400 1.5(in water)IWRC*
2-inch-diameter Steel 6 x 37 330,000 82,500 5.8(in water)IWRC*
28 -4 .4 - 447.INCH-CIRCUMFERENCE NYLON LINE MAXIMUM ALLOWABLE LOAD
I-INCH-DIAMETER STEEL WIRE MAXIMUM ALLOWABLE LOAD
0I -INCH-DIAMETER
I2-NCHDIAMETER STEEL WIRE
o STEEL WIRE
z4 _ _ _ _ _1 0 1 2 1 :
Figure 42. Tow Speed Versus Maximum Tow Line Load for 1- and 2-Inch-Diameter Steel Hire at Tow Vessel and for 7-Inch-CircumferenceNylon Line at Model
77
-I00O
I I I --20
HELD CONSTANT: TEST NO. 11: 2-INCH-DIAMETER STEEL A)
1100-FOOT TOW LINESINGLE CENTER ATTACHMENT
10000
TEST NO. 10: I-INCH-DIAMETER STEEL
TEST NO. 13: 7-INCH-CIRCUMFERENCE NYLON
8000
0
a
a
w
2000
2 4 6 8 10 12 14 16 18
TOW SPEED (KNOTS)
Figure 43. Type of Tow Line Versus Average Loads at Model UsingI 1100-Foot Tow Line
30000
HELD CONSTANT:1400-FOOT TOW LINESINGLE CENTER ATTACHMENT
25000
20000
a
15000
2-INCH-DIAMETERSTEEL WIRE
14NCH-DIAMETER
10000
7-INCH-CIRCUMFERENCENYLON LINE
5000
2 4 6 8 10 12 14 16 18
TOW SPEED (KNOTS)
Figure 44. Type of Tow Line Versus Average Loads at Model Using1400-Foot Tow Line
TR-1253
The 2-inch-diameter steel wire plot in Figures 43 and 44 produced towline loads at equivalent speeds significantly greater than the other lines.The 2-inch-diameter steel wire plot in Figure 44 became extremely divergentat 8 knots with the tow line 100 percent greater than that exhibited by theother lines at 12 knots. This extreme increase in tow line load for the 2-inch-diameter steel wire at 1400 feet can be attributed to the increased down-ward (negative) pitch angle of the model produced by the longer, heavier towline. The 1-inch-diameter steel wire and the 7-inch-circumference nylon plotsare very close for both the 1100-foot and 1400-foot lines with the 7-inch-circumference nylon producing the smallest effect on the tow line loads.
To determine the relationship between tow line lengths and tow lineloads, Figures 45, 46, and 47 were developed. These graphs indicate that towline loads increase as line length is increased for the wire tow lines, buttow line loads were not affected by line length for the nylon line. The2-inch-diameter steel wire produced the greatest increase in line load perunit length which was to be expected since the 2-inch-diameter steel wireweight is four times as great as the 1-inch-diameter steel wire (see Table II).This is also illustrated in Figures 43 and 44 which show a significant increasein line loads for the 2-inch-diameter steel wire for only a 300-foot increasein tow line length. Instability in the roll and yaw axes occurred at a lowerspeed with 1400 feet of tow line which also added to the increased loadingon the 2-inch-diameter steel wire tow line (see Figure 29).
4.8 SCALING
Model scaling techniques allow the use of small models to predict theperformance of full scale vessels which are costly and often unavailable fortesting. The 120-inch-diameter model used in this test program simulated the142-inch-diameter baseline dated February 2, 1973, except for configurationdifferences in the nose and tail sections. The model had an empty nosefrustum while the SRB baseline reflects removal of the entire nose cone,leaving a blunt front section. The model had a short, straight support skirtwith a 6-degree canted nozzle while the SRB baseline has a full flared supportskirt. The length over diameter (L/D) ratios for the model and SRB are 10.1and 10.9, respectively.
The scale factors for the model and SRB baseline are as follows:
Model/SRBLength: 1212 Tn./1553 in. = 0.7804
Diameter: 120 in./142 in. = 0.845
Weight: 93,286 b1/147,384 lb = 0.6329
The length scale factor is most important in determining the fullscale values of tow line loads since both frictional drag and residuary dragare a function of vessel length. A scale factor of 78 percent or its reciprocal1.282 ( x ) will be used for the tow line calculations. The tow line load atthe model is a combination of both frictional (viscous) forces and residuary(wave-making and eddy currents) forces or in equation form:
RT - RF + RR
80
140004
HELD CONSTANT:I.-INCH-DIAMETER STEEL WIRESINGLE CENTER ATTACHMENT 12 KNOTS
12000
10000
S10 KNOTS
1000
6000
4000
0 400 60 80 00 1000 1200 1400 1600 1800
LENGTH OF TOW LINE (FEET)
-I
-J
Figure 45. Tow Line Length Versus Average Load at Tow Vessel Using1-Inch-Diameter Steel Wire
00f-4
30000
HELD CONSTANT:2-INCH-DIAMETER STEEL WIRESINGLE CENTER ATTACHMENT
12 KNOTS
tO KNOTS
10000
5000
0 1 ,ot 1600 11100
400 600 0 100 120 140 16
LENGTH OF TOW LINE (FEET)
Figure, 46. Tow Line Length Versus Average Load at Tow Vessel Using2-Inch-Diameter Steel Wire
12000
HELD CONSTANTs7-INCN TWISTED NYLON TOW LINESINGLE CENTER ATTACHMENT
12 KNOTS
o 6000
1000
S2 KNOTS
1000
0
-5-
400 600 80 100 1200 14 400 1600 1800
LENGTH OF TOW LINE (FEET)
Figure 47. Tow Line Length Versus Average Load at Model
TR-1253
The frictional force (RF) is a function of Reynold's number,R = L , where
Rn = Reynold's number
v (sneed in knots)(6080)(3600)
L = length of vessel
u = kinematic viscosity of sea water at 680F = 1.14 x 10-5ft2/s.ec
and for this test orogram the Reynold's numbers for the model are in the 1l7
to 108 range which means that the frictional force (RF) is very small ascompared with the total load measured on the tow line. This is true for thefull scale SRB also; therefore, frictional forces will not be considered in thescaling of tow line loads, and RT = RR.
The residuary forces, RR, are a function of the Froude number,
Fn= v
where:
v = velocity of towg = gravitation constantL = length of vessel
At corresponding speeds of
)model SRB
or
VSRB = (X)1/2Vmodel
the residuary forces are proportional to the cube of the scale factor:
RRS = Ls 3 3
Using these equations, speed and load values were calculated for the modeland the SRB prototype as listed in Tables III and IV and plotted in Figures48 and 49.
84
TR-1253
Table III
Model Versus Full Scale Loads (Pounds)
RM x 3 = RSRB
2 x 103 pounds x 2.107 4.214 x 103 pounds
4 8.429
6 12.643
8 16.858
10 21.072
12 25.287
14 29.501
16 33.716
18 37.930
20 42.145
22 46.359
24 50.574
26 54.788
28 59.003
30 63.217
85
TR-1253
, Table IV
Corresonding Speeds (Knots)
Vmodel VSRB
2.0 knots x 1.132 2.264 knots
4.0 4.529
6.0 6.794
8.0 9.052
10.0 11.323
12.0. 13.587
14.0 15.851
To further examine~Lt a'1ing and tow line loads, the model and fullscale values were plotted in r-i are 50 for average tow line loads at the modelversus tow speed using 7-inch i .-cumference nylon line. Full scale tow loadswere plotted for the corresponding full scale tow speed as determined in TablesIII and IV. The full scale loads were much higher than the model loads atequivalent speeds with the differencd between them of approximately 15,647pounds at 14 knots using 7-inch-circumference nylon tow line. Test No. 13 wasselected for scaling purposes because nylon tow line has the least effect ontow line loads, and the use of wire tow lines would have scaled up loadscaused by the tow line itself which is already at full scale. Examination ofFigure 50 with respect to the sizing of tow lines reveals that the 7-inch-circumference nylon line would be acceptable for towing the full scale SRB atspeeds to 15 knots without exceeding the maximum working load.
86
TR-1253
30
20
-
10 O •
0
10 20 30 40 50 60 70
RSRB
Figure 48. Model Versus Full Scale Loads
87
00
00 5
10
0
5 10 15 20
V SRB
Figure 49. Model and Full Scale Corresponding Speeds
TR-1253
32500
30000
MAXIMUM ALLOWABLE LOAD 27.500 LB.27500--------
25000
22500
20000
17500
1500
12500
ow sPEE (KNOT)
Figure 50, Model and Full Scale Tow Line Loads Versus Tow SpeedsUsing 7-1nch-Circumference Nylon Line