UNCLASSIFIED

AD NUMBER

AD910278

NEW LIMITATION CHANGE

TOApproved for public release, distributionunlimited

FROMDistribution authorized to U.S. Gov't.agencies only; Test and Evaluation; 31 DEC1972. Other requests shall be referred toNaval Air Development Center, Warminster,PA 18974.

AUTHORITY

NADC ltr dtd 31 Oct 1973

THIS PAGE IS UNCLASSIFIED

NAVAL AIR

DEVELOPMENTCENTER

WARMINSTER. PA, 18971

REPORT NO. NADC-72136-VT 31 Dec 1972

DETERMINATION OF THE LUG AND SWAY BRACE REACTIONSFOR THE MAU-9/A BOMB RACK

FINAL REPORT

AIRTASK 532000004Work Unit No. A53213-I

Distribution limited to U. S. Government agencies only;

Test and Evaluation; Report Issue Date. Other requestsfor this document must be referred to COMNAVAI>DEVCENor COHNAVAIRSYSCM.

C

Ir

,,_..,. -OF

Of LOT

Or

DEPARTMENT OF THE NAVYNAVAL AIR DEVELOPMENT CENTER

WARMINSTER. PA 18974

AIR VEHICLE TECHNOLOGY DEPARTMENT

REPORT NO. NADC-72136-VT 31 Dec 1973

DETERMINATION OF THE LUG AND SWAY BRACE REACTIONSFOR THE MAU-9/A BOMB RACK

FINAL REPORT

AIRTASK 532000004Work Unit No. A53213-1

This report summarizes a series of static load tests which wereconducted at NAVAIRDEVCEN (Naval Air Development Center) to develop amethod of calculating the lug and sway brace reactions for the MAU-9/A

Bomb Rack.

Prepared by:_(_/_____E. KENKELEN

W. WIESEMANN

Reviewed by: L"W. J BOLLINGFgHead, Search and Rescue Sec

Approved by: ___ ___ ___L. A. FUCHSSupt, Aircraft Subsystems Div

Distribution limited to U. S. Government agencies only; Test and Evalua-

tion; Report Issue Date. Other requests for this document must bereferred to COMNAVAIRDEVCEN or COMNAVAIRSYSCOM.

NADC-72136-VT

SUMMARY

This report presents the results of a test program designed to deter-mine the distribution of yawing moment and side load reactions between thesway braces and the lugs on the MAU-9/A Bomb Rack. Reference (a) developsthe general design criteria for airborne stores and suspension equipment.Experience with bomb racks, however, has led to the conclusion that someof the assumptions in the specification, particularly the assumption

regarding yawing moment distribution, may be in error. Consequently, itis necessary to identify, analyze, test, and possibly revise some of thebasic assumptions composing the present design standards.

The actual test program involved a MAU-9/A Bomb Rack subjected tosimulated in-flight loads. Known loads were applied by means of hydrau-lic jacks, and the reactions of the rack were determined by means ofstrain gages and piezotron load cells installed at the 30-in. hooks andsway braces, respectively. Tests clearly demonstrate that some of theassumptions specified in reference (a) are not applicable to the MAU-9/ABomb Rack or to other bomb racks with similar hook and sway braceconfigurations. The eva],,'.ion techniques employed and the resultanttest data are presented for the MAU-9/A Bomb Rack. It is recommendedfor the MAU-9/A that for yawing moments less than 60,000 in.-lb, 50percent be reacted by the sway braces 'tnd 50 percent by the lugs. Foryawing moments greater than 60,000 in.-lb, 30,000 in.-lb should be

reacted by the sway braces and the remainder by the lugs. It is alsorecommended that the side load distribution as presented in reference(a) remain unchanged. It is further recommended that effort be under-taken to revise reference (a) so that it will contain a more realistic,but still conservative, yawing moment distribution which will beapplicable to all suspension equipment.

oPECEDIr PACE BLANK-NOT FIMED."1'

iii

mwf

NADC-72136-VT

i

TABLE OF CONTENTSI

Page

SUMMARY ... . . . . . . . . . . . . . i

LIST OF FIGURES ..........................

LIST OF TABLES . . . . . . . ................. vi

LIST OF SYMBOLS .... . . . . . .. ........... . vii

SECTION I. INTRODUCTION ..... .. .... ....... I

SECTION II. TEST CONFIGURATION. . ... . .......... 2

SECTION III. OBJECTIVE. ........... . ......

SECTION IV. DISTRIBUTION TEST RESULTS . . . . 9

SECTION V. COMBINED LOADS TESTING ....... . . . . . 15

SECTION VI. CONCLUSIONS AND RECOMMENDATIONS . . . . . 29

SECTIO" VII. ADDITIONAL INFORMATION ... . . . . .. . 31

SECTION VIII. REFERENCES. o o . . o o o . . . . o . 31

iv

U-

NADC-72136-VT

LIST OF FIGURES

Figure No. Description Page

I MAU-9/A Bomb Rack Test Setup Showing Instrumentation. 3

2 MAU-9/A Bomb Rack Test Setup Showing Detail ofInstrumentation . . . . . . * . . . .. . . . . . . 4

3 MAU-9/A Bomb Rack Test Setup ...... ............. 5

4 MAU-9/A Bomb Rack Test Setup Showing Deflection Dueto Yawing Moment. . . . . . . .. .. ... 6

5 MAU-9/A Bomb Rack Test Setup (Side View) ShowingStrain Gage Instrumentation . . . . . . . .. . 7

6 MAU-9/A Bowb Rack Test Setup Showing Detail of aLoad Cell .... ............... . . .

7 Average Yawing Moment Reaction at the Sway Braces U)

8 Average Yawing Moment Reaction at the 30-In. Lugs . 1!

9 Average Percentage Side Load Reaction .... ........ 14

10 Combined Loads Test No. I - Forward Left Brace 18

11 Combined Loads Test No. I - Aft Left Brace ........ . 19

12 Combined Loads Test No. 2 - Forward Left Brace . 20

13 Combined Loads rest No. 2 - Aft Left Brace. . .... 21

14 Combined Loads Test No. 2 - Aft Right Brace .. . 22

15 Combined Loads Test No. 3 - Forward Left Brace. . . . 23

16 Combined Loads Test No. 3 - Forward Right Brace . . . 24

17 Combined Loads Test No. 3 - Aft Right Brace . . . . . 25

18 Combined Loads Test No. 4 - Forward Left Brace. . . . 26

19 Combined Loadb T( t No. 4 - Forward Right Brace . . . 27

20 Combined Loads Test No. 4 - Aft Left Brace. . .. . 27

21 Combined Loads Test No. 4 - Aft Right Brace ..... 28

V

NADC-72136-VT

4

LIST OF TABLES

Table No. Page

I Derivation of Yaw Trap and Sway Brace DesignReactions . . . . .. . . . . . . . . . . . . 13

II Loads Appliee in Combined Loads Testing . . . . . . 16

III Combined Loads Test Results ....... . . . . 17

Vi

L4L

NADC-72136-VT

LIST OF SYMBOLS

Fy Total side load applied at store C.G. lb

Total yawing moment applied (about the store's C.G.) in.-lb

Fore-and-aft distance from store C.G. to lug in.

Fore-and-aft distance from store C.G. to sway brace in.

b Aagle between vertical plane and the line-of-actionof sway braces in a fore-and-aft view deg

Lug reaction lb

Vertical Component of each sway brace reaction lb

a Indicates that the quantity pertains to an aft lug

or sway brace

f Indicates that the quantity pertains to a forward lugor sway brace

zYz Subscript indicating that the reaction "R" is acomponent acting in the direction indicated by thesubscript

vii

NADC-72136-VT

I. INTRODUCTION

A. The test evaluation presented in this report investigates the

validity of three basic assumptions stated in the appendix of reference (a).According to the specification, the assumptions are as follows:

I. The sway braces take compressive loads only. Lugs take onlytensile loads in the vertical direction.

2. The two diagonally opposed sway braces react the torqueinduced by the yawing moment, Mz, or it may be reacted by differentialaction of the forward and aft sway braces on the same side.

3. In general, the lug and associated suspension structure areassumed to be very rigid with respect to the sway brace and strong-areastructure.

B. By considering only the reactions to purely compressive loads,assumption (i) effectively ignores the tendency of a store to slip underthe sway brace pad's surface. This tendency, however, is always presentas a result of elastic deformations developed in both the rack (suspensionstructure) and the store, and the wedge-like effect provided by the swaybrace pads. Any normal compressive force acting on the sway brace padalso generates a proportionate frictional shear force acting parallel tothe surface of the pad. Assumption (1) completely eliminates such fric-tional effects in the load analysis. Assumption (1) also states that thelugs withstand only vertical tensile loads. However, experience in bombrack testing has indicated that the hooks may be required to withstand sideloads as well as down loads. Thus, any hooks designed to the present stand-ard could prove to be structurally inadequate. The sway braces in theMAU-9/A Bomb Rack have been machined to provide an indentation which fitsclosely around the lug on the store. The purpose of this device, whichhas been designated a 'yaw trap" is to relieve the hooks of the side loadwhich would normally be imposed by the yawing moment.

C. Assumption (2) assumes that the sway braces alone react the entireapplied yawing moment. This theory is questionable since definite lateralcontact is likely to occur between the lugs and the side walls of the yawtraps due to the application of yawing moment. Therefore, it is highlyprobable that the yaw traps react a portion of the yawing moment. It isalso expected that this portion is much greater than that reacted by the

sway braces. Assumption (2) is conservative in regard to the sway braces,since it is unlikely that they react 100 percent of the applied yawingmoment. Consequently, if the lugs and bomb rack are not designed for sideload at their interface, the effects of a substantial yawing moment couldbe catastrophic.

D. According to assumption (3), the suspension structure is rigidwith respect to the sway brac3 and strongback structure. Practical experi-ence, however, does not seem to justify this theory. When subjected to

ka1

NADC-72136-VT

high flight loads, suspension structures may undergo large deflections.At the same time the sway braces are displaced by the action of the sup-porting structure and deflected by the action of the applied load. Itis reasonable to assume that neither of these influences is negligible.Therefore, the relative rigidities of both the suspension structure andthe sway brace structure should be equally considered.

II. TEST CONFIGURATION

A. The test setup (figures I and 2) was designed to accurately applythe forces and moments necessary for evaluating the validity of the pre-viously stated assumptions. The MAU-9/A Bomb Rack (figure 3) was selectedbecause of its relatively high sway brace strength and stiffness, andoverall structural rigidity. This rack was expected to indicate a com-paratively large sway brace reaction which would 1-nd t-- conservativedesign criteria for the sway braces of less rigid bomb racks. Hydraulicjacks were employed for applying side 3oad, vertical load, drag load,yawing moment and pitching moment direcLiy to a simulated store. Straingages were applied to the internal side walls of both 30-in. lugs in orderto indicate the reactions at the yaw traps. These gages -=ere calibratedfor yawlig moment (figure 4). The bomb rack 30-in. hc'ks were straingaged a.d calibrated to read the hook reactions to vertical tension loads(figure 5). Semiconductor load cells were fitted on the sway brace pads(figure 6) and calibrated to read the normal reactions of the pads. Thus,with this test setup, the three reaction points in the rack (braces, yawtraps, and hooks) could be monitored for any ty'e of loading.

B. Instrumentation

rat t Type

4 Kistler Instrument Corp Load Wa3hers - Model Number 905AS/N 20175 S/N 20177SIN 20176 S/N 20178

4 Kistler Instrument Corp. Universal Dial-Gain ChargeAmplifiers - Model 504

S/N 129 S/N 458S/N 130 S/N 1401

1 DC Micro-Volt-AmmeterMV-07C62269 - USN019383

I Budd Instruments Div - Datran Digital Strain Indicator62269 - USN A

[I 019136

4 Baldwin-Lima-Hamilton CorpSR-4 Strain Gages

'1 2_ _ _ _ _ _

-i

NADC-72136-VTI

4-4

4J

a-)

09

3

NADC- 72136-VT

4.4

'4

I4-

444

04

60

4

4"

dL.4

NADC-72 136-VT

414

R .4

t-r,

AV

50

dL -A

NyADc,72l36-VT

7 .774

~1Figure 4. MUI-9/A Bomab Rack Test Setup ShowingDeflection Due to Yawing Mom"ent

6

NADC-72136-VT

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NADC- 72136-VT

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NADC-72136-VT

III. OBJECTIVE

A. The primary objective of the test evaluation described in thisreport is to determine the distribution of yawing moment between the yawtraps and sway braces. The sway braces are expected to indicate an increasein reaction with an increase in yawing moment up to a certain level. Atthis level the braces should cease to exert any further increase in reaction,while the yaw traps provide the required increase in moment reaction. Thiscould be the result of the structure's geometry and differential rigiditiesof the braces, yaw traps, and supporting structure. A second objective isto evaluate the loads experienced by the sway braces during the applica-tion of side load. In these tests, side load is applied at the center lineof the store. Thus, there is an induced rolling moment (about the contactpoints of the sway brace pads) which will always accompany side load. Itis expected that this rolling moment will increase the sway brace loads.Having calibrated the reaction points for each individual load, a reason-able prediction of the structure's reactions to a simultaneous applicationof all loads should be possible.

IV. DISTRIBUTION TEST RESULTS

A. The test program was initiated to establish a load distribution

for all suspension equipment which would reveal the inherent deficienciesof the assumptions made in reference (a). The MAU-9/A Bomb Rack was util-ized as the suspension structure throughout the testing. The sway braceson this bomb rack were felt to be relatively strong and rigid compared toother racks. Thus, it was expected that the reactions provided by thesesway braces would be greater than those provided by the braces of mostother suspension equipment. Since the loads in these tests were relativelyhigh, the resulting sway brace design criteria were considered to be con-servative for most in-service racks. The yaw trap or lug reactions alsoproved to be of major significance during the test program. Consequently,the percentage load distribution between the braces and 30-in. lugsdeveloped from this test data should affect any future suspension equipmentdesign.

B. Yawing Moment Tests

1. Figures 7 and 8 depict results of the yawing moment and initialpreload tests which were conducted on the MAU-9/A Bomb Rack. Since theyawing moment test data provides sufficient information to develop tworeaction curves for every preload yawing moment combination only averagevalues of all the data recorded are considered in all cases. Pure yawingmoment tests with zero preload reveal that more than 90 percent of theapplied moment is accounted for by gauges monitoring the yaw traps and swaybrace reactions. The remaining 10 percent could easily be attributed tofrictional effects between the store and sway brace pads and/or between thestore lugs and bomb rack hooks.

NADC-72136-VT

PRELOAD ,LB)0 oo 5,0000 Io,000

15,00020,000

S30

co 25 -

020 0Lu

-- 15- /10>

z

u 0 400 12 0_ 16 200

LA1

010

00 40 80 120 160 200ii APPLIED YAW (IN-LB x 10-3)

.IFIGUE 7 AVEAGEYAWNG MMEN RECTIO ATTHESWAYBRAES/

NADC-72136-VT

160"

PRELOAD (LB) ) >0

140 - 0 0 - i0 5,000 ] a0e

c I10,000 1/£~ 15,000 k ,7 20,000 /

4

1201

0 0c

00 100

,0

z 0

wz _ _0 _ _

2 60o0

0- 801010 0

ui

60~ ... I

o>20o0©

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40 40 80 12 60d

APPLIED YAW (IN-LB x 10-)

FIGURE 8. AVERAGE YAWING MOMENT REACTION AT THE 30 INCH LUGS

11

;,t0 r

NADC-72136-VT

2. The tests involving 5000-, 10,000-, 15,000- and 20,000-lb pre-loads indicated a. steady decrease of accountable reaction from the appliedyawing moment as the initial preload was increased. The increase in pre-load apparently caused a corresponding increase in frictional effectswhich could not be monitored during the tests. At the maximum preload(20,000 lb) a&?proximately 73 percent of the applied yawing moment was

recorded on the instrumentation. It was possible to analytically demon-strate that the difference could be accounted for by friction at the hookand brace interfaces. Consequently, it can be conzluded that frictionforces can be quite significant at high preloads. !owever, the preloadrange selected for these tests, to demonstrate the influence of friction,was of a much higher mangitude than that normally encountered in service.Since more representative values of preload are cn the order of 5000 ib,at which level frictional forces are not as significant, the interpreca-tion of data will be limited to preloads at and below :his magnitude.

3. The general trend in the range of 0 to 60,000 in.-lb of appliedyawing moment, as can be observed from the curves, is for the sway braces,at a given preload, to increase unifoimly in reaction while the yaw trapreactions remain in the relatively low range. In the upper applied momentrange the converse occurs, and the yaw trap reactions steadily increasewhile the sway brace reactions remain relatively constant. This lattereffect is a definite indication of the inability of the sway braces toprovide reactions to significant yawing moments. When the lugs make con-tact with the side walls of the yaw traps, the sway braces essentiallycease to resist any further increase in yawing moment.

4. A conservative design curve, independent of preload, wasderived from the data by assuming that friction between the brace/storeand the lug/yaw trap interface imposed a moment equal to the differencebetween the applied and measured moments. As indicated in Table I, themaximum recorded sway brace and yaw trap reactions selected from theacccptable preload range, were summed and subtracted from the appliedmoment to yield the nximent induced by friction. This friction moment wasthen divided equally between the sway brace and yaw trap reactions toidentify coordinates of the design curves. Figures 7 and 8 show the respec-L.LV dcsign curves and illustrate the magnitude of reaction attributableto friction. Several oLher distributions were assigned to fit the testdata, but the best correlation with the combiaed load tests (Section V)was obtained using the recommended values.

C. Side Load Test

S. Figure 9, illustrating data from side load tests (10,000 '6bmax at zero preload), indicates that the sway brace readings account foressentially all of the reaction to the applied side load and accompany- Aing rolling moment. Consequently, little frictional effect is experienced.The percentage reaction of the braces is scattered in the low load range

12

k ;(_

NADC-72136-VT

u r. 00 0 C

U 4~ -r '0~

~~ 40

+11

41 0au 00 440 Z

Q I 0 .4 a c ,Lr1cN mtr Ca lq MtnC4 O) IJ4 (n -44-4v--4-4C' -4'Je

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U-4 Z tr% 14 r4 r-4 4 o 4'-r0 00 0 0 00 0 0

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to 0 13W

NADC-72136-VT

PRELOAD (LB)

o Oo 5,000

0 I,000

120

0

80 r __ 1__ _ _

00

w -08

60

"'0

w

z 0 _ _ _ _ _ _ _

o I]

20

w

20-0 - - - --- --

0 2 4 6 8 10

APPLIED SIDE LOAD ( LB x 10-3

FIGURE 9. AVERAGE PERCENTAGE SIDE LOAD REACTION

14

4_

NADC-72136-VT

(0 - 2000 Ib), but rapidly levels off to a value between 100-110 percentof applied load in the high side load range (2000-10,000 lb).

2. The finsl side load tests involving 5000- and 10,000-lb pre-loads provide less satisfactory, but acceptable, data. With an increasein initial preload, less side load reaction is accounted for by the swaybraces. This is caused by the fact that the increasing side load relievesthe preload on the opposite side braces. However, in each case, the samegeneral trend of sway brace reaction is observed. The percentage bracereactions in the respective trials are found to be scattered in the lowside load range, but approach a magnitude of approximately 80-100 percentof applied load in the upper range.

V. COMBINED LOADS TESTING

A. Combined loads tests under simulated flight load conditions wereconducted at NAVAIRDEVCEN to investigate the validity of a proposed dis-tribution of yawing moment reaction different from that given in refer-ence (a). The loads applied in the combined loads tests are shown intable II. The results of these combined loads tests are presented intable III and in figures 10 to 21, inclusive. These plots showthe sway brace loads taken from the average test results and those calcu-lated from unmodified reference (a) calculations. Also shown are swaybrace reaction predictions of two modified yawing moment distributionsconsidered for recommendation. It can be seen that all of the sway bracepredictions were affected significantly by redistributing the yawingmoment. It should be noted that in some cases the modified predictionswere higher on certain sway braces than the unmodified predictions. Thisis due to the absen,e of the subtracting efbct of yawing moment and sideload. In every test, however, the maximum sway brace load determined bydistributing the yawing moment is i. er than the maximum sway brace loadcalculated by the method in reference (a).

B. Figure 11 is an extreme example of this phenomenon. The loadingon the aft sway braces of Test No. I is due only to side load and yawingmoment, with side load tending to load the left brace and yawing momentloading the right-hand brace. By assuming that all of the yaw is reactedat the sway braces, the yawing moment dominates the side load in this caseand the aft right sway brace loads, while the aft left brace feels zeroload. With the revised prediction, however, only a small percentage ofthe yawing momenL reacts at the sway braces. In this particular case theside load actually dofiinates, and the aft left sway brace should feel loadrather than the aft right. The actual testing verified the fact that theaft left brace is loaded and not the aft right. Figure 19 is another suchcase where the reference (a) prediction errs in the same manner.

C. The combined loads tests were chosen so that with the revised yaw-ing moment distribution there would be one test for each of the four pos-.

sible loading cases in reference (a). Figures 10, 14, 15, 17, and 21

15

_AJ

NADC--72 136-VT

-4 N 0 r~- r.cn 0 rcn -I 0 r- CY) P-4 0 r- c

x ~ ~~~ . * *** 4 * * 4 -4 -4 4

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NADC-72136-VT

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NADC-72136-VT

0 SPEC MIL-A-8591 (CALCULATED) -

o 25% UP TO 80,000 IN-LBo 50/o UP TO 60,000 :N-LB

12 " AVERAGE TEST RESULTS -

10 1 -70

m 8

z0

L)

0

2

0-10 20 40 60 80 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 10. COMBINED LOADS TEST NO. I FORWARD LEFT BRACE

18

NADC-72 136-V1T

C~SPEC MIL-A-8591 D (CALCULATED)S250/ UP TO 80,000 IN-LBS5 0% UP TO 60,000 IN-LB

L AVERAGE TEST RESULTS

6 --o--

4

0 204 6080 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 11. COMBINED LOADS TEScT NO.1 AFT LEFT BRACE

19

NADC- 72136-VT

/I

14 4

0 SPEC MIL-A-8591D (CALCULATED)o 25% UP TO 80,000 IN-LB

12 C 50% UP TO 60,000 IN-LBL AVERAGE TEFT RESULTS

0

x 8

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o /w

w-

u

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00 ?0 40 60 80 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 12. COMBINED LOADS TEST NO. 2 FORWARD LEFT BRACE

20

-:

NADC-72136-VT

o SPEC MIL-A-8591 D ( CALCULATED)o 250/ UP TO 80,000 IN-LBo 50%/ UP TO 60,000 IN-LB

L AVERAGE TEST RESULTS

10T

_ 8

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NADC-72136-VTJ

o SPEC MIL-A-85911D (CALCULA7ED)o 25%/ UP TO 80,000 IN-LBo 50% UP TO 60,000 IN-LB

£~AVERAGE TEST RESULTS

8

- 6

z0

w

w

0

O 20 40 60 80 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 14. COMBINED LOADS TEST NO. 2 AFT RIGHT BRACE

22

NADC-72136-VT

o SPEC MIL-A-8591 D (CALCULATED)o 250/ UP TO 80,000 IN-LBo 500/ UP TO 60,000 INLB-1-s AVERAGE TEST RESULTS

10

8__ _ _

0

x-J

- 62

z

w4

co

00 20 40 60 80 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 15. COMBINED LOADS TEST NO. 3 FORWARD LEFT BRACE

23

NADC-72136-VT

0 SPEC MIL-A-8591 D (CALCULATED)o 25% UP TO 80,000 IN-LB0 50% UP TO 60,000 IN-LBL AVERAGE TEST RESULTS

I

I

8

6

-J00

0

n. 4 •_

0 20 40 60 80 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 16. COMBINED LOADS TEST NO. 3 FORWARD. RIGHT BRACE

24

,' 1I

NADC-72136-VT

12 0 SPEC MIL-A-8591 D (CALCULATED)

o 25%/ UP TO 80,000 IN-LBo50%/ UP TO 60,000 IN- LB

10~ AVERAGE TEST RESULTS

r 8 -

x

-J

z0 6

4-

0

r FGUE07 20 40 LIITAPLE 80 100

FIGUE 1. CMBIND LADSTEST NO. 3 AFT RIGHT BRACE

25

NaDC-72136-VT

14

12 0 SPEC MIL-A-8591 D (CALCULATED)

o 250/ UP TO 80,000 IN-LBo 50%/ UP TO 60,000 IN-LBL AVERAGE TEST RESULTS

ID-

-j 6

0

I-

0

22

A08 0

NADC- 72136-VT

0 SPEC MIL-A-8591D (CALCULATED)

0 25 UP TO 80,000 IN-LB I40 50%/ UP TO 60,000 IN-LB

' AVERAGE TEST RESULTS

z0

u

-

ci) 00 20 40 60 so 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 19. COMBINED LOADS TEST NO 4. FORWARD RIGHT BRACE

6

0_ 0 SPEC MIL-A-8591 D (CALCULATED)-

x 0] 25%1 UP TO 80,000 IN'LB

4 0 50% UP TO 60,000 IN-LB r_4

4

P AVERAGE TEST RESULTS APPIE

., j....0 20 40 60 80 100

PERCENTAGE OF LIMIT LOADS APPLIED

FIGURE 20. COMBINED LOADS TEST NO. 4 AFT LEFT BRACEi 27

NlADC- 72136-VT

o SPEC MIb-A-8591 D (CALCULATED)o 25% UP TO 80,000 IN-LBo 50%/ UP TO 60,000 IN-LBn AVERAGE TEST RESULTS

8

0

6

z

0 _ __ _ _ _ _ _ _ __ _0:

w

0 20 PECNTG LII 0 PLE 80 1OO

FIGURE 21. COMBINED LOADS TEST NO. 4 AFT RIGHT BRACE

28

_________ - -- 7 - - ~

NADC-72136-VT

indicate that the reference (a) predictions are at least twice the testvalues. On each graph the reference (a) predictions are conservative, butexcessive when compared to the test values. The two modified predictionsconsidered are still conservative in every case, but much more realistic.In these five sway brace loadings the reference (a) predictions deviateconsiderably from test data, while the modified predictions show an excel-lent correlation.

D. Figures Il and 19 show that the unmodified predictions are zero,while the test results indicated load. Figures 13, 16, and 20 illustratethe same phenomenon to a lesser degree. In each of these graphs the ori-ginal reference (a) predictions are less than half the experimental values.Both modified predictions again are a significant improvement in each case.

E. Figures 12 and 18 show the reference (a) predictions to be up to40 percent above the test values. The revised predictions are a maximumof 2000 lbs unconservative on these plots. Thus, in these two examplesthe modified predictions are more accurate than the original predictions,but less conservative. Consequently, in the particular cases noted abovefor these sway braces, another yawing moment assumption would be advis-able in order to avoid insubstantial designs. During the preparation ofthis report a number of distribution assumptions were evaluated. However,the one recommended in this report proved to be the best modification fromthe overall standpoint, considering both conservatism and realism.

VI. CONCLUSIONS AND RECOMMENDATIONS

A. it has been concluded from the results of this program that modi-fications are required in the load analysis given in reference (a) to pro-duce an acceptable correlation with the loads derived by extensive test-ing of an instrumented MAU-9/A Bomb Rack. It is assumed that this correla-tion will prove conservative in the design of other bomb racks because ofthe relative rigidity of the MAU-9/A Rack and the attendant high sway braceloads which were used to establish the recommended design criteria.

B. Figures 7 and 8 graphically illustrate the conclusion that theapplied yawing moment is only partially, rather than totally, reacted bythe sway braces as assumed in reference (a). The yawing moment also pro-duces a very significant reaction in the lateral (Y) direction at the yawtraps, which is not considered in the specification. The conservativecorrelation with test data derived in Table I shows on figure 7 that thesway brace reactions vary linearly from 0 to 30,000 in.-lb over a yawingmoment range of 60,000 in.-lb, which is equivalent to a 50 percent slope.For higher yawing moments a constant 30,000 in.-lb sway brace reaction isshown. In each case the 30-in. yaw traps simultaneously react the absolutevalue of the applied yawing moment minus the portion attributed to the swaybraces. This is showtu in figure 8.

29

. . .... ... .... ... .. - ... - , 'i < ; ..... ,AZ

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C. Figure 9 illustrates the conclusion that side load applied at thecenter of gravity of the store, and consequently accompanied by a rollingmoment, is totally reacted by the sway braces. This conclusion is inagreement with the parallel assumption employed in reference (a).

D. The validity of these correlations, as demonstrated by results ofthe combined loads tests, "s concladed to be sufficiently accurate tojustify revision of current loads analysis techniques. Consequently, itis recommended that the loads analysis published in reference (a), Section20.5.2.2 be revised by introducing the following equations to be used forstores carried on the 30-in. hooks of the MAU-9/A Bomb Rack:

If IMzj < 60,000 in.-lbr~ -Mz

vf _ ya + 0.5MZ1Py'M1z - tan Sf (Za + Tf)-

f 0.5 Mz fyrepresents the fore or aft)

P7 4a + ?f k. lateral yaw trap reaction)

a 0.5 MzRy a + -,f

If IM7l 60,000 in.-lb

fI Py La + 30,000]

yMz tan f (ta + tf)

a FPy.. f - 30,000]

Py, Mz 'tan 8f (Ta + "Tf)

f ~IM - 30,000".: + I

NADC-72136-VT

VII. ADDITIONAL INFOR14ATION

The material presented in this report represents a considerable effortin time and test preparation and voluminous conduct of testing. The testvalues recorded were obtained by repeated testing at each of 25 differentyawing moment and side load test conditions, but only the average valuesare given herein. Likewise, the combined load verification tests wererepeated to establish consistency with the average values shown in thereport. Complete and detailed test data and additional details of thetest program are available at this Center.

VIII. REFERENCES

,a) M!L-A-8591D, Airborne Stores and Associated Suspension Equipment;-oneral Design Criteria for

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Air Vehicle Technology Department UNCLASSIFIEDNaval Air Development Center 2 . GRouPWarminster, Pennsylvania 18974

DETERMINATION OF THE LUG AND SWAY BRACE REACTIONS FOR THE MAU-9/A BOMB RACK

4 .V Cw.PF r'ivC qO'rcES (7y pe of report and jnclu,,e dates)Final Report

SA Y.OR, ' IFt nO e. (uddle Initial, la st name)

Edward Kenkelen and William Wiesemann

REPORT a rt 70. TOTAL NO OF PAGES 176 NO OF REFS

31 Dec 1973 40 1rCO:NTRAC OR GRANT NO 9.. ORIGINATOR'S REPORT NUMBER(S)

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I' OSTRICUTION STATEMtNT

Distribution limited to U. S. Government agencies only; Test and Eva!i.ation; ReportIssue Date. Other requests for this document must be referred to COMNAVAIRDEVCEN orCOMNAVAIRSYSCOM.

11 JP-L,-VIN ANRY NOTEi 12 SPONSORING MILITARY ACTIVVT'

Naval Air Systems CommandHeadquartersWashington, D. C. 20360

1S AC,, TRACT

This report summarizes a series of static load tests which were conducted atNAVAIRDEVCEN (Naval Air Development Center) to develop a method of calculating thelug and sway brace reactions for the MAU-9/A Bomb Rack.

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