NSWC TR 89-306
AD-A262 414
FORCE DISTRIBUTION IN THE SUSPENSION LINES OFCROSS PARACHUTES
BY WILUAM P. LUDTKE
UNDERWATER SYSTEMS DEPARTMENT
DECEMBER 1989
OTICIF , ECTE
Approved for public rlease; distribution is unimited. MAR2 3 1993
Reproduced FromBest Available Copy -.
I, $swNAVAL SURFACE WARFARE CENTERDehigren. Virginia 2244-5000 e Silver Spring. Maryland 20903-S000
93-05846
__ '3 19 021
NSWC TR 89-306
FORCE DISTRIBUTION IN THE SUSPENSION LINES OFCROSS PARACHUTES
BY WILLIAM P. LUDTKEUNDERWATER SYSTEMS DEPARTMENT
Accesion For
NTIS CRAl
DTIC TABEUnannounced -
DECEMBER 1989 Justification
By ..DBy....i••i........................
Availability Codes
S "..: 1 Dist Avail and/orSpcciji
IL
Approved for public release; distribution is unlimited..
NAVAL SURFACE WARFARE CENTERDahlgren, Virginia 22448-5000 . Silver Spring, Maryland 20903-5000
NSWC TR 89-306
FOREWORD
uneven forces in the several suspension lines of Crossparachutes cause design problems due to lack of engineering forcedistribution data. A series of Cross parachutes was wind-tunneltested and the forces in individual suspension lines measured forseveral lengths of individual lines to determine the loadvariations.
The pressure distribution adjacent to the canopy center linewas also measured ahead of and within the parachute canopy.
Approved by:
C. A. KALIVRETENOS, Deputy HeadUnderwater Systems Department
NSWC TR 89-306
ABSTRACT
The force distribution in the sevsral suspension linesattached to an arm of a Cross-type parachute is nonuniform. Theouter suspension lines carry the minimum force. The forcesincrease in each suspension line as the line attachment approachesthe center of the arm with the maximum force carried by the mostcentral lines.
This report describes a series of wind tunnel tests tomeasure the forces in individual selected suspension lines ofCross type parachutes with 8, 16, and 24 suspension lines. Thetest results show that lengthening the inner suspension linestends to equalize the suspension line forces. The static pressuredistribution adjacent to the parachute center line was measuredfor each parachute model. Positive pressures were found to existahead of the canopy skirt hem as well as inside of the canopy.The magnitude of the pressures is influenced by the canopy clothpermeability.
NSWC TR 89-306
CONTENTS
Chapter Page
1 INTRODUCTION .I. .. .......... ...... 1
2 APPROACH................ . ............ 7
3 TEST METHOD ....................... . . . . . . . 17
4 RESULTS . . . . .......... . . . . . . . 19
SUSPENSION LINE FORCES ...... ........... . . 19
CANOPY INTERNAL STATIC PRESSUREDISTRIBUTION . . . . . . . . . . . . . . .. 21
5 CONCLUSIONS . . . . . . . . . . . . . . . . . .. 41
REFERENCES . . . . . . . . . . . .. . . . . .. 43
iii/iv
NSWC TR 89-306
ILLUSTRATIONS
Figure page
1 COMPA.RISON OF SUSPENSIOrd LINE ELONGATION CFRIBBON AND CROSS PARACHUTES....................... . . 2
2 TYPICAL FORCE-ELONGATION TEST DATA FOR ATUBULAR BRAIDED NYLON PARACHUTE SUSPENSIONLINE CORD . . . . . . . . . . . . . . . . . . . . . . 3
3 PARACHUTE CONFIGURATIONS FOR MODELS NO. 1THROUGH 7.......................... . . . . . . . . . . 9
4 MODEL PARACHUTE CONSTRUCTION DETAILS FORMODEL PARACHUTES NUMBERED 1 THROUGHs7......... . . . 10
5 41.7 PERCENT SCALE MODEL OF THE PARACHUTEMK 38 MOD 0 . . . . . . . . . . . . . . . . . . . . . 11
6 SUSPENSION LINE FORCE SENSING GAUGEINSTALLED IN THE WIND TUNNEL........... . . . 13
7 LOCATIONS OF ACTIVE LOAD CELL CHANNELS . . .. .. . .14
8 STADIA ROD AND PRESSURE SENSOR LAYOUT .. . . . . . . 15
9 PLAN VIEW OF WIND TUNNEL SUPPORT ANDPHOTOGRAPHIC SYSTEMS .... . . . . . . . . . . . . 16
10 VARIATION OF SUSPENSION LINE FORCE COEFFICIENTFOR THE VARIED SUSPENSION LINE LENGTHS OFTHE 16 SUSPENSION LINE PARACHUTE . . .. .. .. . .20
11 VARIATION OF SUSPENSION LINE FORCE COEFFICIENTFOR THE VARIED SUSPENSION LINE LENGTHS OFTHE 24 SUSPENSION LINE PARACHUTE . . . . . . . . . . 22
12 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 4 PARACHUTE MODELNO. 1 WITH 8 EQUAL LENGTH SUSPENSION LINES . . . . . 24
13 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 5. PARACHUTE MODELNO. 2 WITH 16 EQUAL LENGTH SUSPENSION LINES . . . . . 25
NSWC TR 89-306
ILLUSTRATIONS (cont)
Figure Page
14 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 6, PARACHUTE MODELNO. 3 WITH 16 MODIFIED LENGTH SUSPENSION LINES . . . . 26
15 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 7. PARACHUTE MODELNO. 4 WITH 16 MODIFIED LENGTH SUSPENSION LINES . . . . 27
16 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 8. PARACHUTE MODELNO. 5 WITH 24 EQUAL LENGTH SUSPENSION LINES . . . . . 28
17 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 9. PARACHUTE MODELNO. 6 WITH 24 MODIFIED LENGTH SUSPENSION LINES . . . . 29
18 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 10, PARACHUTE MODELNO. 7 WITH 24 MODIFIED LENGTH SUSPENSION LINES . . . . 30
19 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 11, PARACHUTE MODELNO. 8 WITH 16 EQUAL LENGTH SUSPENSION LINES ............ 31
20 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 12, PARACHUTE MODELNO. 9 WITH 16 EQUAL LENGTH SUSPENSION LINES . . . . . 32
21 MEASURED PRESSURE DISTRIBUTION ALONG THE STADIAROD. WIND TUNNEL RUN NO. 13, PARACHUTE MODELNO. 10 WITH 16 EQUAL LENGTH SUSPENSION LINES . . . . . 33
22 EFFnCT or THE NUMBER OF SUSPENSION LINES ON THEMEASURED STATIC PRESSURE DISTRIBUTION ALONGTHE STADIA ROD SHOWING ELEVATED LOCAL STATICPRESSURES AHEAD OF THE CANOPY SKIRT HEM, TESTVELOCITY 200 MPH . . . . . . . . . . . . L. .. .. . .34
23 EFFECTS OF VARYING THE INNER SUSPENSION LINELENGTHS ON THE MEASURED STATIC PRESSUREDISTRIBUTION ALONG THE STADIA ROD SHOWINGELEVATED LOCAL STATIC PRESSURES AHEAD OF THECANOPY SKIRT HEM. TEST VELOCITY 200 MPH . . . . . . . 35
vi
NSWC TR 89-306
ILLUSTRATIONS (cont)
Figure Page
24 EFFECT OF THE NUMBER OF SUSPENSION LINES ON THEMEASURED STATIC PRESSURE DISTRIBUTION ALONGTHE STADIA ROD SHOWING ELEVATED LOCAL STATICPRESSURES AHEAD OF THE CANOPY SKIRT HEM.TEST VELOCITY 200 MPH . . . . . . . . . . . . . . . . 36
25 EFFECT OF CLOTH PERMEABILITY ON THE MEASUREDSTATIC PRESSURE DISTRIBUTION ALONG THE STADIAROD SHOWING ELEVATED LOCAL STATIC PRESSURESAHEAD OF THE CANOPY SKIRT HEM. TEST VELOCITY200 MPH ......... .. . .. . . . . . . . . . . 37
26 EFFECT OF THE CLOTh RATE OF AIRFLOW ON THE DRAGCOEFFICIENT OF THE MK 38 MOD 0 PARACHUTE ........ 39
vii
NSWC TR 89-306
TABLES
Table Page
1 MATERIALS USED IN MODEL PARACHUTE CONSTRUCTION . . . . 8
2 SUMMARY OF SUSPENSION LINE LENGTHS AND MEASURED
WIND TUNNEL SUSPENSION LINE FORCE DATA . . . . . . . 12
v/
//
vii
- - - - - - - - - - - - - - - - - - - --i- -
NSWC TR 89-306
INTRODUCTION
The Cross parachute has been demonstrated to be a reliablaretarder for ordnance and other applications. Characteristica ofthe Cross parachute are low opening shock factor, good parachutestability, good two-body stability, supersonic inflationcapability up to Mach 2.5, and a reduced manufacturing cost. Anengineering problem with the Cross parachute is the occasionalfailure of one or more suspension lines when conventional analysisindicates that they were structurally adequate. The cause of thefailure is due to the unique inflated shape of the Cross canopy.Conventional parachutes are symmetrically constructed and theforces in the several suspension lines are usually assumed to beuniform. This is a reasonable assumption because all of thesuspension lines are of the same design length and elongateequally. The arms of a Cross parachute each have a set ofsuspension lines which are usually of the same design length.Figure 1 shows that the several suspension lines attached to anarm of the canopy elongate in a uniform, but unequal pattern.
Figure 2 is a typical load elongation test result of tubularbraided nylon cord of the type used by the Naval Surface WarfareCenter in parachute designs. The samples witness to th'3repeatability of the cord's performance. The obvious conclusionto be drawn from Figures 1 and 2 is that the tensile force in theCross parachute's suspension linas varies, and this forcedvariation manifests itself by the different elongations of thelines. The equal elongation of the ring-slot parachute suspensionlines indicates uniform suspension line loading. The suspensionline forces can be modified to a uniform distribution byselectively lengthening the inner suspension lines. If thesuspension lines were lengthened so that they hang loosely theywould not transmit any force.
Several approaches are available as solutions to the brokensuspension line problem. Each approach has some advantage anddisadvantage.
-APPROACH ------------ ADVANTAGE --------- DISADVANTAGE----
1. All suspension lines No production line Some increase insame length. Design misassembly suspension linestrength related to problems. cost and requiredmaximum suspension packing volume.line force.
1
NSWC TR 89-306
R1NG LOT ARA HUT WI H E UALL EL NGA ED USP l~.~oN Do 37' INCH DIA
LONGT16% POROSSIONTy
CROSS PARACHUTE WITH UNEQUALLY ELONGATED SUbPENSION L -40 INCH DIALINES AT 200 MPH W/L a 0.264
FIGURE 1. COMPARISON OF SUSPENSION LINE ELONGATION OF RIBBONAND CROSS PARACHUTES
NSWC TR 89-306
CORD SAMPLES AS PER MIL-C-17183, TYPE VI
SAMPLE 1 SAMPLE 2
8 00o- 800
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FIGURE 2. TYPICAL FORCE-ELONGATION TEST D)ATA FOR A TUBULAR BRAIDEDNYLON PARACHUTE SUSPENSION LINE CORD
NSWC TR 89-306
2. All suspension lines Less weight and Possible productionsame length. Design packing volume line problems withstrengths tailored than approach suspension lineto various maximum No. 1 misassemblysuspension lineforces
-APPROACH ------------ ADVANTAGE --------- DISADVANTAGE----
3. Suspension line Less weight and Possible productionlengths varied, packing volume line problems withDesign strength of than approach suspension lineall lines constant No. 1 misassembly
4. All suspension Best possibility Less likelylines are the same fcr a minimum production linelength and strength. weight system. problems.Respace reinforcementtapes on the canopyto vary pressurizedcanopy area toproduce uniformsuspension lineforces.
From *he standpoint of potential production problems,approach number one is best. Any suspension line may be correctlyassembled to any attachment point on the arm. This is also trueof approach number four. The possibility of misassembly of thecanopy reinforcements to the canopy in approach number four can becontrolled in the layout and marking of the canopy cloth. Spotinspections of the reinforcement to canopy assembly are easilyaccomplished. Misassemblies should be obvious. Approache3 twoand three have the possibility of assembling either the wronglength or wrong strength suspension line to the attachment point.This possibility exists for each line attached and may not beobvious. Approach number four appears to be the best candidatefor achieving a minimum weight system.
The first step in the analysis of the problem of unequalloading was to conduct a 200-mile-per-hour wind-tunnel test wherethe tension force was measured in individual Cross parachutesuspension lines. A series of parachutes were constructed withsuspension line lengths predetermined from existing data. Themodels were attached to the force measuring instrumentation. Astadia rod was attached to the wind-tunnel mount and extendedalong the wind-tunnel center line into the inflated canopy. Thestadia rod was marked to provide a reference for measurements andwas also rigged to measure static pressures at various pointswithin the canopy and immediately ahead of the skirt hem.
4
NSWC TR 89-306
A second objective of the wind tunnel tests is to examine thestatic pressure distribution along the canopy center line withinthe canopy and in the zone immediately ahead of the skirt hem.
* Figure 23 of Appendix A of Reference 1 presents photographs ofairflow patterns around parachute profiles. The volume of airassociated with an inflated parachute is shown to extend ahead of
* the canopy skirt hem. This volume of air must also be collectedduring the inflation time interval in order to have a fullyinflated parachute. As a demonstration that this air massactually exists a stadia rod with ten pressure taps was mountedalorng the parachute center line to measure the static localpressure distribution ahead of and inside of the canopy. Elevatedstatic pressures are indicative of air masses with less than freest'ream velocity.
5/6
NSWC TR 89-306
APPROACH
The best way to investigate the Cross parachute suspensionline variable force problem is to conduct a wind-tunnel testwherein the forces in designated suspension lines can be measuredsimultaneousiy under controlled test conditions. Seven,40-inch-diameter model parachutes were designed and manufactured.The seven models built with the materials of Table 1, consisted ofone parachute with two suspension lines per arm, three parachuteswith four suspension lines per arm, and three parachutes with sixsuspension lines per arm. The models were built as per, Figures 3and 4 with uniform suspension line spacing on the canopy as abaseline force distribution which is representative of our currentdesign technique. Each of the parachutes had different suspensionline length distributions which were derived from existing data.Three 41.7 percent scale models of the parachute MK 38 MOD 0 werealso constructed as per Figure 5. These parachutes, numbered 8,9, and 10, were tested to determine the effects of the rate ofairflow of the production canopy cloth on the drag coefficient ofthe parachute. Parachute materials are listed in Table 1. Theparticular suspension line lengths for every model parachute testare listed in the te~st data summary of Table 2.,
The 200 mph test was conducted at the University of MarylandSubsonic Wind Tunnel at College Park, Maryland. Win-s1 'unnelengineering personnel designed and constructed the 24 attachmentpoint suspension line force measuring device of Figure 6. Twelveof the sensing elements were instrumented to measure force data.The instrumented active load cell channels were located asindicated in Figure 7. Each parachute was attached to the loadcell with two complete sets of adjacent lines connected to act-ivechannels. The active channels were continuously recorded byinstrumentation which determined the average value of the tensileforce and the one sigma variation.
The stadia rod of Figure 8 was attached to the aft end of theforce sensing gauge. The stadia rod was marked with contrastingstripes to permit measurements of the inflated models, and alsofitted with ten static pressure sensing taps to measure the staticpressures within the inflated canopy and the zone directly aheadof the canopy skirt hem. Orthogonal photographs of the severalparachutes under test were obtained by still cameras positioned asshown in Figure 9.
7
NSWC TR 9-306
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NSWC TR 89-306
5 " SEE TABLE 1 FOR MATERIALS IDENTIFICATIONAND TABLE 2 FOR SUSPENSION LINE LENGTHS
IIt
S2 TYPICAL TAPE - CANOPY CROSS SECTION
I--- 5
SKIRT HEM - SUSPENSION LINE ASS'Y
FIGURE 4. MODEL PARACHUTE CONSTRUCTION DETAILS FOR MODEL PARACHUTESNUMBERED 1 THROUGH 7
10
NSWC TR 89-306
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"CONSTRUCTION DETAILS FOR MODEL PARACHUTES NUMBERED 8, 9. AND 10
FIGURE 5.41.7 PERCENT SCALE MODEL OF THE PARACHUTE MK 38 MOD 0
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NSWC TR 89-306
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NSWC TR 89-306
12 6
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ACTIVE LOAD CELL CHANNELS .
LOOKING UPSTREAM
RNN. LINES PER PARACHUTE CONNECTEDRUNNO. ARM TO ACTIVE CHANNELS NO.
4 2 2,5, 8,11
5, 6, 7 4 2.3, 4, 5, 8, 9,10, 11 ÷
8, 9, 10 6 1, 2. 3, 4,5, 6,7,8, 9,10, 11, 12"
11, 12, 13 4 2.3, 4,5, 8, 9,10. 11
FIGURE 7. LOCATIONS OF ACTIVE LOAD CELL CHANNELS •,_
14
NSWC TR 89-306
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NSWC TR 89-306
TEST METHOD
The suspe~nsion line force and static pressure instrumentationwere mounted on the support and aligned with the center line ofthe wind tunnel. A 20-mph run was conducted without a parachuteinstalled to obtain the system aerodynamic tare and a referencestatic pressure distribution along the stadia rod. A parachutewas then installed on the force sensor with the parachutesuspension lines connected to active channels as listed inFiguro 7. The wind tunnel was accelerated to 200-mph and thesuspension line forces were recorded. The steady state drag forceof the parachute was also recorded by the wind tunnel balancesystem. The static pressure distribution together with front andside view still photographs of the test configuration completedthe data. This procedure was followed for each parachute. Someparachutes had the inner line lengths modified and the test wasrepeated to measure changes in the suspension line forcedistribution.
17/18
NSWC TR 89-306
RESULTS
SUSPENSION LINE FORCES
Test results confirm that selectively lengthening the Crossparachute inner suspension lines redistributes the forces andimproves the uniformity of the force distribution. The test dataand calculations are summarized in Table 2. Note that thesuspension lines are attached and distributed around thecircumference of a 3-1/4-inch-diameter circle. The length of thesuspensiin lines in this study is taken to be the actual length ofthe cord and not the projected effective length of all thesuspension lines to a single confluence point.
With reference to the list of suspension line forcecoefficients in Table 2 the following conclusions may be drawn.
1. The force distribution in the eight suspension lineparachute of run number 4 is uniform.
2. The addition of four more evenly spaced suspension lines(16 lines total) of equal length as in run number 5 Cenerallyreduces the force distribution in the outer lines by 50 percent.However, the force distribution is not uniform. The inner pair ofsuspension lines are bearing tensile forces which exceed the outersuspension line forces by 1.47.
3. As the inner suspension lines are lengthened, as in runsnumber 6 and 7, the susnension line loads in the several lines areredistributed with an incrcsq in the outer line forces and adecrease in the inner line forces which results in a more uniformforce cistribution among the lines.As the inner lines were extended the ratio of suspension linetension to outer suspension line tension decreases linearly asshown in Figure 10.
4. The 24 suspension line parachutes of runs number 8, 9,and 10 show the same force distrJbution trends as the 16 lineparachute. The linearity is not as easily seen with theadditional two suspension lines per arm. It is obvious that asthe number of suspension lines increase the evaluation of the mostefficient suspension line length distribution becomes increasinglydifficult.
19
NSWC TR 89-306
"Fin• - 12.475 fin+ 13.944Four tout
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C, GavFOR RUNS 5.6, & 7 0.611a .
O'S 1.0376
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tout Outer Line Length
FIGURE 10. VARIATION OF SUSPENSION LINE FORCE COEFFICIENT FOR THE VARIEDSUSPENSION LINE LENGTHS OF THE 16 SUSPENSION LINE PARACHUTE
"20/" \
/
NSWC TR 89-306
5. The equal suspension line length MK 38 MOD 0 parachutehas similar load distri~butions as run 4. Lengthening thesuspension lines, run 12, did not improve the drag coefficient dueto the hem tape limiting the canopy diameter. The partialcollapse of the 4 momme silk cloth parachute of run 13 isreflected in the reduced suspension line force readings. The loaddistribution shows the same trends even when only partiallyinflated.
The load cell channel suspension line force coefficients havebeen added up for each run, multiplied by 2, and compared to thewind tunnel balance reading. The sum of the suspension line forcecoefficients generally exceeds the balance reading because theload cells measure the tensile force in the suspension lines andthe balance measured the parachute axial aerodynamic force.
For each run the ratio of suspension line length to lenc~th ofthe outer suspension line was calculated. The suspension li.-ieforce coefficients for each set of lines were averaged to m~riimizetest variations and ratioed to the line force coefficients cf theouter lines. These data are plotted in Figures 10 and 11. Thesuspension line length variation of Figure 10 is a linearvariation of force ratio since all of the inner lines weremodified by the same amount. Equation (1) was fitted to thq dataand shows that the force distribution in all lines should beuniform when the inner line l~engths are 1.0376 times the ot~terline length.
As the number of suspension lines in the parachute increasethe effects of varying the lengths of the inner lines complicatesthe data analysis. The interaction of the inner sets .of linescauses a scatter in the data. For each set of lines the data hasbeen averaged for runs 9 and 10 and plotted on Figure 11. Auniform suspension line load distribution in a 24 suspension linerequires that the first inner set of lines be 1.020 times th~e -
length of the outer suspension line and that the lengths of thecentral set of lines be 1.0386 times the length of the outersuspension line.
* CANOPY INTERNAL STATIC PRESSURE DISTRIBUTION
Most inflation time calculation approaches assume that the* volume of air that is to be collected lies inside of the inflated
canopy between the skirt hem and the vent. There is evidence inAppendix A of Reference 1 that the total volume of air associatedwith a fully inflated canopy extends ahead of the canopy skirthem. This additional volume of air was derived in References 2and 3 which presented a method for estimating the total volume ofair, v,, to be collected. Utilization of the V, air volume insubsequent inflation reference time, t , calculations showsexcellent agreement with inflation times calculated using acceptedempirical methods.
21
NSWC TR 89-306
A F12 =-10.484 Lin + 11.697Fout eout
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22
7 .\ I II I I I I I
NSWC TR 89-306
As the flow enters the mouth of an uninflated parachute thevelocity head of the flow is reduced and transformed into apressure head. If the flow were at a complete stagnation thecanopy internal pressure coefficient, AP/q, would be a maximum.As the rate of canopy outflow increases the internal pressure isreduced. Eventually, the internal pressure is too weak to supportfull inflation and inflation instability develops.
Figures 12 through 21 are profile views of the testparachutes with the pressure coefficient distributionssuperimposed at the particular pressure tap locations along thethe stadia rod. In each of the tests elevated static pressure,ahead of the parachute skirt hem, was detected as well as withinthe canopy. These partial stagnation pressures increase inintensity as the flow approaches the parachute skirt hem and reacha maximum value inside of the canopy. The elevated pressureprofile ahead of the canopy skirt hem is indicative of anadditional mass of air associated with the inflat6d canopy.
Figures 22 through 25 present the effects of the number ofparachute suspension lines and canopy cloth rate of airflow on themeasured pressure distributions. Due to the various parachutesuspension line lengths in the tests, pressure distributionscannot be compared by orienting the pressure taps. For each testthe plane containing the locations of the joint of the canopyskirt hem and the outer most suspension lines on each arm wasestablished. The pressure distributions were shifted to align thecanopy hem planes which compares the canopy pressure distributionsrelative to the hem of the canopies.
The pressure profiles of Figure 22 indicate a rise inpressure distribution with an increase in the number of suspensionlines in the assembly. The dominant change occurs between theeight and 16 suspension line configurations with a smallerpressure increase between 16 and 24 lines. The pattern ofincrease indicates that the effects of increasing the number ofsuspension lines approacýhes a limiting value. This is similar tothe known effects of the number of suspension lines on the Crossparachute drag coefficient. Comparing the pressure levels ofFigures 23 and 24 generally shows the same effects as Figure 22.
Figures 23 and 24 show the pressure distributions for 16 and24 suspension line configurations respectively for lines of equallength and two different distributions of inner suspension linelengths. Lengthening the inner suspension lines appears to causea small reduction in the pressure distribution.
23
NSWC TR 89-306
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33
NSWC TR 89-306
RUN PARACHUTE NO.* PERMEABILITYNO. NO. LINES CANOPY CLOTH (CFM/FT 2 )
0 4 1 8 MIL-C-7020, TYPE I 90X 5 2 16 MIL-C-7020, TYPE I 900 8 5 24 MIL-C-7020, TYPE I 90
0 15 STRUT AND FIXTURE TARE RUN WITH SHORT STADIA ROD
1.o0II
0.8
I xO
0.6 -, .
z,0
0LA. X
00- 0V• ALL OUTER SUSPENSION
M0° LINE-CANOPY SKIRT HEM
0 JOINTS LIE IN THIS PLANE
S0.2 --
0.0 -_
u
-0.2 - 1 I -I I I16 24 32 40 48 56 64
DISTANCE ALONG STADIA ROD (INCHES)
ALL SUSPENSION LINES ARE 34 INCHES LONG.
FIGURE 22. EFFECT OF THE NUMBER OF SUSPENSION UNES ON THE MEASUREDSTATIC PRESSURE DISTRIBUTION ALONG THE STADIA ROD SHOWINGELEVATED LOCAL STATIC PRESSURES AHEAD OF THE CANOPY SKIRTHEM. TEST VELOCITY 200 MPH.
34
NSWC TR 89-306
RUN PARACHUTE NO. PERMEABILITYNO. NO. LINES (CFMIFT 2 )
X 5 2 16 MIL-C-7020, TYPE I 90
A 6 3 16 MIL-C-7020, TYPE I 90
Q 7 4 16 MIL-C-7020, TYPE I 90
o 15 STRUT AND FIXTURE TARE RUN WITH SHORT STADIA ROD
1.0 RUN' ' ' I , ISUSPENSION LINE LENGTH
NC0. 1 2 3 45 34 34 34 34
0.8 6 34 35.2 35.2 34
7 34 35.51 35.51 34
0.6
z
. 0.4UJ.
uJO
ALL OUTER SUSPENSION"LINE-CANOPY SKIRT HEMJOINTS LIE IN THIS PLANE
a. 0.2
0.0 -_ _ _ _
-0.2 1
16 24 32 40 48 56 64
DISTANCE ALONG STADIA ROD (INCHES)
FIGURE 23. EFFECTS OF VARYING THE INNER SUSPENSION LINE LENGTHS ON THEMEASURED STATIC PRESSURE DISTRIBUTION ALONG THE STADIA RODSHOWING ELEVATED LOCAL STATIC PRESSURES AHEAD OF THE CANOPYSKIRT HEM. TEST VELOCITY 200 MPH.
35
K\
" -" " .
NSWC TR 89-306
RUN PARACHUTE NO. PERMEABILITY
NO NO. LINES CANOPY CLOTH (CFM/FT 2 )
0 8 5 24 MIL-C-7020, TYPE I 90o 9 6 24 MIL-C-7020o TYPE I 90
L 10 7 24 MIL-C-7020, TYPE I 90
0 15 STRUT AND FIXTURE TARE RUN WITH SHORT STADIA ROD
1.0-i I i I I I I IRUN SUSPENSION LINE LENGTHNO. 1 2 3 4 5 6
8 34 34 34 34 34 34
0.8 9 34 35.02 35.53 35.53 35.02 34
10 34 35.08 35.63 35.63 35.02 34
0.6-
Lu
Lu a:O 0.4-
Lu 6 • ALL OUTER SUSPENSION-_ LINE-CANOPY SKIRT HEM
U, JOINTS LIE IN THIS PLANEU)
a. 0.2
0.0 -Q^
0
-0.2 -III
16 24 32 40 48 56 64
DISTANCE ALONG STADIA ROD (INCHES)
FIGURE 24. EFFECT OF THE NUMBER OF SUSPENSION LINES ON THE MEASUREDSTATIC PRESSURE DISTRIBUTION ALONG THE STADIA ROD SHOWINGELEVATED LOCAL STATIC PRESSURES AHEAD OF THE CANOPY SKIRTHEM. TEST VELOCITY 200 MPH.
36
I•J • - -. . . ,? ": ' "
NSWC TR 89-306 / /
RUN PARACHUTE NO. PERMEABILITYNO. NO. LINES CANOPY CLOTH (CFM/FT 2 )
X 5 2 16 MIL-C.7020, TYPE I 90
o 11 8 16 MIL-C-17208, TYPE I, CLASS B 325
0 12 9 16 MIL-C-17208, TYPE I, CLASS B 325
O 13 10 16 3 MOMME SILK 428
ci 14 STRJT AND FIXIURE TARE RUN WITH LONG STADIA RO "
1.0 1.I-I I I I II
RUNS 11, 12, & 13 ARE 41.7% SCALE MODELSOF THE CROSS PARACHUTk: MK 38 MOD 0.
0.8
ALL OUTER SUSPENSION---,,,,,LINE-CANOPY SKIRT HEMJOINTS LIE IN THIS PLANE xS0.6 -
2 xLL
LL
Lu00
-0.4
o. 0.2 -
0.0
-0.2 - I - -
16 24 32 40 48 56 64A,
DISTANCE ALONG STADIA ROD (INCHES)
FIGURE 25. EFFECT OF CLOTH PERMEABILITY ON THE MEASURED STATIC PRESSUREDISTRIBUTION ALONG THE STADIA ROD SHOWING ELEVATED LOCALSTATIC PRESSURES AHEAD OF THE CANOPY SKIRT HEM. TEST VELOCITY200 MPH.
37
/ , o
NSWC TR 89-306
Figure 25 presents the effects of canopy cloth rate ofairflow on the pressure distribution of 41.7 percent scale modelof the Parachute MK 38 MOD 0. Runs 11 and 12 which had suspensionline lengths of 40 inches and 50 inches, respectively, indicatedessentially identical pressure variations. The three momme silkmodel of run 13 was included to evaluate canopy cloth permeabilityon canopy full inflation. The silk model of the MK 38 parachuteinflated to 75 percent of the design drag area at the testvelocity of 200 mph. The wind tunnel onset of Inflationinstability is somewhere between the 325 CFM/FT production MIL 2C-17208, Type I, Class B cloth rate of airflow and the 428 CFM/FTsilk cloth rate of airflow, see Figures 18, 19, and 20. Thegreater rate of airflow of the silk cloth used in run 13 of Figure25 has reduced the internal canopy pressure to a degree that fullinflation of the parachute cannot be maintained. It is consistentthat the lower cloth rate of airflow of run 5 results in a slightincrease in the pressure distribution. The effects of canopy rateof airflow on the Parachute MK 38 MOD 0 drag coefficient are shownin Figure 26.
38
- - - - -- J
NSWC TR 89-306
LU
W coiz0~o
UL
0
occ 0 .. jO~ LL.(No C2 ' Z
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0
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4i I
3/4
NSWC TR 89-306
CONCLUSIONS
1. Conventional round parachutes have a uniform steady staitesuspension line force distribution in the several equal lengthsuspension lines because all lines elongate equally under load.
2. Equal length suspension lines attached to an arm of a Crossparachute elongate nonuniformly in steady state. This indicates anonuniform force distribution in the lines with the maximum forceoccurring in the longest line(s).
3. The suspension line forces can be reduced by progressivelylengthening the several lines. The longer lines modify the forcedistribution in the suspension line system.
4. The optimum way to make the suspension line force distributionuniform is to adjust the spacing of the suspension lines on thecanopy. This approach will permit use of a single strength andlength of suspension line and minimize inspection duringmanufacture.
5. Measurements of the axial steady state static pressuredistribution adjacent to the parachute center line indicate thatthe associated air mass of the inflated parachute extends ahead ofthe canopy skirt hem.
6. As the canopy cloth permeability is increased the pressure-----distribution is similar in form but the magnitude is reduced.
This also applies to partially inflated canopies.
* 7. Excessive canopy cloth rate of airflow results in incompletecanopy inflation.
41/42
NSWC TR 89-306
REFERENCES
1. NSWC TR 86-142, Notes on a Generic Parachute Opening ForceAnalysis, 1 March 1986
2. NOLTR 69-159, A New Approach to the Determination of theSteady-State Inflated Shape and Included Volume of SeveralParachute Types, 11 September 1969
3. NOLTR 70-178, A New Approach to the Determination of theSteady-State Inflated Shape and Included Volume of SeveralParachute Types in-24-gore a-nd 3-0 gore configurat-ions, 3 September1970
43/44
NSWC TR 89-306
I)ISTRIIBUTION
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NSWC TR 89-306
IDISTRI'BUTION (Cont.)
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D)ISTRIlBUTION (Cont.)
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NSWC TR 89-306
D)ISTRIIBUTION (Cont.)
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D)ISTRl'IIBUT'ION (Cont.)
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I)ISTIRIBUTION (Cont.)
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Form ApprovedREPORT DOCUMENTATION PAGE oMB No.0704-0188
?.u.•",. "t~h~iit.4
0 tl J in tnt,% ET wde•'t, t tiiia ,4|t. Aoii eitrate.1d toa ~era.e I ho.u pW, respo'nse. iriludng the time foT rivelinng instructions, searching tstting datat*.,ns ,jamt o, and ma n t"i . 141 nita n dted a.1n mpitrng and te•¢wie lng the collction of information end commrents uegarding this burden estimate or any othera=*i•ett, t fi,. .i.AIt• ti .1 ,ltLirJt,Ofl il�lu•.�.�,•iqqestlon$ for toed- y this budfion. to Wasthington Headtlaog ners Wlrs•es. Directorate for Information Operations and
QI D %..i21 .eeii.c 0....s na .. ite t 2I 4 Alnr1 toi . VA 220.1 4302, arid to t•e Office of Management and Budget. Paperwork Reduction Ptoject (0704.0188),
I AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORTTYPE AND DATES COVERED
I)ccemlrhc 1989
4. TITLE AND SUBTITLE S. FUNDING NUMBERS
Futwc I)i trihutitin in hit Suspens•on lifnes of Cross Parachutes
6 AUTHOR(S)
W I' Ludike
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) B. PERFORMING ORGANIZATIONREPORT NUMBER
N Ii. ,d Surface Warfare Cernter119o)I Nvw I lakmp~hirc A% Cenut'e NSWCTR 89-306
Si)•er Sprin1g, M1) 20190)3 50100)
9. SPONSORING MONITORING AGENCY NAME(S) AND ADDRESSUES) 10. SPONSORINGYMONITORING
AGENCY REPORT NUMBER
11. SUPPLEMENTARY NOTES -
12a DISTRIBUTION AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE
Apprii-'.d fior l'uIhI , lea.,e, l)istrihutin, is Unlimited
13 ABSTRACT (Maoimum 200 words)
The force distribution in the se'. eral suspension lines attached to an arm ora Cross-type parachuteis nonuniforni. The outer suspension lines carry the minimum force. The forces increase in eachsuspension line a.,, tile line attachment approaches (he center of the arm with the maximum force carriedb> the mofit central lines.
This repofrt describes a series of wind tunnel tests to measure tile force in individual selectedsuspension line. of Cross-type parachutes with 8, 16, and 24 suspension lines. The test results show thatlengthening the inner suspension lines tend to equalize the suspension line forces. The static pressuredistribution adjacent to the parachute center line was measured for each parachute model. Positivepressures were found to exist ahead of the canopy skirt heni as well as inside the canopy. The magnitudeof the pressures is influenced by the canopy cloth permeability.
14. SUBJECT TERMS 1S. NUMBER OF PAGESParachute Technolfgy Suspension Line Force D)istribution 59Effect ofSuspension Line Length on Force Canopy Internal Center-Line 16. PRICE CODE
Pressure D)istribution
17. SECURITY CLASSiFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF
OF REPORT OF THIS PAGE OF ABSTRACT ABSTRACT
t;N C I.ASSI I.' :) U NCi.ASSI I, E1) I NCIASSI FIEI) SARS$N 7S40 01-280-5500 Standard Form 298 (Rev. 2-89)
Pte. ,ribt. by ANSI ý1Ii IJ9 18298 102
S... . .. . / -- ,
EN
DATE:
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