WADC TECHNICAL REPORT 52-9B

APP ROVED FO R PUBL TC REEFA S3 p

DITSTUBU OIN U NLIMIT ED

STRUCTURAL AN4D ENVIRONMERALCTSTGOF AERO X61 BOMBRAS

'f 1

PAUL B3. WINTERUALTER

ARMAMENT LABO0RATORY

Reproduced From ARL15

Best Available COPY

'WRIGHT AIR DEVELOPMENT CENTER

AF-WP-(B).O-31 JUL 52 50

WADC TECHNICAL REPORT 52°98

SI I

APPRaVED FOR PUBLIC RELE&' "DIT:T2IUT.IDN UNJLI~f• ] ..

STRUCTURAL AND ENVIRONMENTAL TESTINGSOF AERO X61 BOMB RACKS

Cl1.ai ýFon cancelled in accordance with

ExecuLive OM e,, 1uu, ,cs:ued 5 Nc rverb 1913

PAUL B. WINTERHALTERARMAMENT LABORATORY

Reproduced From APRIL 1952Best Available Copy

WRIGHT AIR DEVELOPMENT CENTER

A&-WP-(B)-O-31 JUL 52 50

UNULAS1

NOTICES

When Government drawings, specifications, or other data areused for any purpose other than in connection with a definitely relatedGovernment procurement operation, the United States Government there-by incurs no responsibility nor any obligation whatsoever; and the factthat the Government may have formulated, furnished, or in any way sup-plied the said drawings, specifications, or other data, is not to be re-gardedby implication or otherwise as in any manner licensing the hold-er or any other person or corporation, or conveying any rights or per-mission to manufacture, use, or sell any patented invention that may inany way be related thereto.

The information furnished herewith is made available for studyupon the understanding that the Government's proprietary interests inand relating thereto shall not be impaired. It is desired that the JudgeAdvocate (WCJ), Wright Air Development Center, Wright-Patterson AirForce Base, Ohio, be promptly notified of any apparent conflict betweenthe Government's proprietary interests and those of others.

The U.S. Government is absolved from any litigation whichmay ensue from the contractor's infringing on the foreign patent rightswhich may be involved.

s-' T i rmen ttih amatiot ctingi Natiog e,•se p th It ta _ hi • ene na •

bti I o n IIn to a••t h°ri • ers pro•

UNCLAS"R

WADC TECHNICAL REPORT 52-98

STRUCTURAL AND ENVIRONMENTAL TESTINGOF AERO X61 BOMB RACKS

Paul B. WinterbalterArmament Laboratory

April 1952

RDO No. 552.659

Wright Air Development CenterAir Research and Development Command

United States Air ForceWright-Patterson Air Force Base, Ohio

UNCLASSIFIED

SMN~ASSIRED

FOREWORD

This report was prepared by the ArmamentLaboratory of Wright Air Development Center. Work wasinitiated and completed under Research and DevelopmentOrder No. 552-659, Bomb Suspension and Related SpecialWeapons Equipment.

project engineer on this work was Mr.Paul B. Winterhalter.

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ABSTRIACT

A program of static and environmental testingwas conducted on the Aero X61A and Aero X61B bomb racksin the Armament Laboratory of Wright Air Development(;enter between August 1951 and February 1952.

The purpose of the tests was to determine thesuitability of the bomb racks to function under adverseclimatic conditions and, in addition, to determine thecapability of the racks to release loads approximating10,000 lbs.

No data on flight tests of a complete bombsuspension and release system incorporating the AeroX61 series of bomb racks has been included in thisreport because of security requirements.

The bomb racks are designed for the releaseof 2000 lb. stores. Lechanical revisions in the rackswere necessitated by the need for a release mechanism

capable of releasing the 10,000 lb. load.

Redesign recommendations were forwarded tothe Douglas Aircraft Company as operational failuresin the bomb racks were encountered and analyzed. Thesefailures usually resulted as attempts were made tooperate the racks under the higher load condition.

It is concluded that the Aero X61B bomb rack,incorporating the design revisions as recommended, isacceptable for Air Force use.

The secritc classification of the title ofthis report is i J NCLSS i

PUBLICATION REVIEW

This report has been reviewed and is approved.

FOR THE CaCL1ANDING G•ERAL:

,..'CBigadier General, U14 Chief, Weapons Components Division

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TABLE OF CCQTENTS

Page

I Static Load Tests . ...... ... .... 1II Time of Release Tests. . . . .* ........ 2III Cold Tests . . . . . . ... ........ *

IV Frost Test,. . . .* *...... 9V Life Test . . . . .. . . ......... 10VI L.iinimum Voltage Test .. .. .. . . .. .. . 12VII X3 Rack Rework .. . . . . . ..... . . . . 12VIII Comparison Cold and Frost Tests . . . . . . . . . 13IX High Voltage Tests . . . . . . ....... 14X Natural Vibration Frequency Survey . . . . . . . . . 15XI Minimum Impulse Test . . .. .. .. .. .. . 15XII Sand and Dust Test . . . . .. .. . . . . . . 16XIII Heat Test s * .. . ... & . .. 17XIV Salt Spray Test . .. . .. . .. .. . . .. 17XV Humidity Tests . .. . . . . . ...... 17Conclusions . . . ... .* 0 * 0 * 0 * 4 18Recommendations .. . .. .. .. . . ...... 20

LIST OF ILLUSTRATIONS

Figure Page

1 Aero X61A Bomb Rack After Structural Testing . .... 212 Close-Up of Aero X61A Bomb Rack After Structural Testing . . 213 Channel No. 2267266 After Structural Testing . . . . . . 224 Channel No. 2267266 After Structural Testing . . . . . . 225 Aero X61B Bomb Rack After Life Test . . . . . . .* 226 Aero X61B Bomb Rack S6top No. 2254177 After Life Test . . . 227 Close-Up of Aero X61B Bomb Rack After Life Test . .o . 238 Graph Showing Angular Displacement, Velocity, and Accelera-

tion of Cocking Arm As a Function of Time. . . . . . . 249 Graph Showing Angular Displacement, Velocity, and Accelera-

tion of Cockcing Arm As a Function of Time . o 2510 Graph Showing Linear Displacement, Velocity, and Accelera-

tion of Suspended Weight As a Function of Time . . . . . 2611 Aero X61B Bomb Rack After Sand and Dust Test ...... 2712 Close-Up of Aero X61B Bomb Rack After Sand and Dust Test . . 2713 Drawing of Aero X61B Bomb Rack Outlining Parts Referred to in

Report .. .. . . . . . . . . . . . . . . 29

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INTRODUCTION

The Aero X61A bomb rack, commonly referredto as the "Three-Hook Bomb Rack", is an external storecarrying unit with built-in sway braces, hoist attachingfitting, and electrical release mechanism. Essentially, therack consists of a housing containing two carrying hooks(with three point suspension, one forward and two aft);spring loaded cocking levers; and a solenoid for electricalactuation of the release mechanism. Weight of the externalstore rack is 22.3 lbs.

The salient feature of the Aero X61B bombrack is the incorporation of a dual solenoid in the electricalrelease mechanism. By contrast, the Aero X61A bomb rackutilizes a single solenoid.

The bomb racks were manufactured by theDouglas Aircraft Company, El Segundo, California. Two racksof the B type and one of the A type were delivered to theAir Force for test and evaluation. Douglas part number ofthe A rack was 5258077-500; serial number 2H. Correspondingnumbers of the B racks were 5432515-501, serial number X3;and 5432515-501, serial number X4. For the purpose of brevity,The Aero X61A bomb rack is referred to throughout the bodyof the report as the 2H rack. By the same token, the AeroX61B bomb racks are referred to as the X3 and X4 racks,respectively.

The sole test to which the Aero X61A bombrack was subjected was the static load test. All other testsincluding time of release, cold, heat, frost, humidity, sandand dust, salt spray, natural vibration frequency survey,high voltage, minimum voltage, minimum impulse, and the lifetest vere parfczrmed on the Aero X61B bomb racks.

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Static Load Tests:

The 2H bomb rack was subjected to structuraltests in accordance with the load factor requirementsoutlined below.

The rack satisfactorily supported 100 percent ultimate load for all required loading conditions.The rack was tested to destruction for the down loadcondition. As 215 per cent ultimate load was beingapplied, (59,lOOlbs.), the rack release mechanism failed.

The load factor requirements under which the

rack was tested are as follows:

Condition A - Straight pull-out

11 G down

Condition B - Rolling pull-out

Bl -7.938 G down and 0.939 G out-board combined with

(1) left yaw 1557 lbs. at bombstation 92,78 outboard and333 lbs. at bomb station176.00 up.

or (2) right yaw 3199 lbs. at bombstation 75.39 inboard and333 lbs. at bomb station176.00 up.

B2 3.831 G down and 1.665 G outboardcombined with

(1) left yaw 1769 lbs. at bombstation 81.50 outboard and303 lbs. at bomb station182.60 up.

or (2) right yaw 1769 lbs. at bombstation 78.10 inboard and303 lbs. at bomb station182.60 up.

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Conditon G - S L't

1.0 G down combined with

(1) left yaw 3156 lbs. at bombstation 98.8 outboard and383 lbs. at bomb station-285.5 up.

or (2) right yaw 5160 lbs. at bombstation 77.7 inboard and383 lbs. at bomb station-285.5 up.

Condition D - Ejector Loads

10,000 lbs. at bomb station61.0 down and 1000 lbs. at bombstation 101.0 down.

Note: These ejector loads are tobe combined with loads for conditionsA, B and C, above.

These loading conditions were based upon externalcarriage of a 1700 lb. store on a F-84G airplane on a pylonequipped with bomb ejectors which apply preload to the storeuntil the store is released.

The results of all structural tests are containedin Tables I through IV. A sketch showing the arrangement ofstructural members during the tests is shown following TableIV.

Illustrations 1 through 4 indicate the conditionof the 2H rack subsequent to the destruction test. As isvisibly evident, breakage occured in the channel, Douglaspart number 2267266.

II Time of Release Tests:

In order to determine the time of release character-istics of the bomb rack under various loading conditions,a series of loads wad applied to the X3 rack, and each loadin turn was released by the application of 28 volts to the

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TABLE fIII

Equipment Tested: Ty~pe of Test: Test Data:Aero X61A Bomb Rack Ultimate Load Tests Deflection Data in Inches

FTest No. 1 Tes No. 3N*4Load 1L 2L 1R 2 L 2R 2R I 2Lt~. Tet R. 1L' 2L

0 .1432C.3905 .48251 0 515cý.4130 .3885 t.4635 .5025>14175j.4,0001 . 4520 .493Q0.41701,4000;

20 ý,46C.865.4565" .4961;*4210O!.4115:.4140:'.46,451.4230 1.4230 039101 .4.40.4310 !.4235140 1.91q.345.43251 .481!,.41001.4200 .3710 .4380.4240;.4360 .3495!.4169. 4375i.44001

60o 38Q32 .4090.469q.4100;*42800*425 .4180 .42801.4500i.304 1386q.43551.4510'

80 ,*343Q.3510 .3840! .456, .4040,:.4320 .3015 1.3975;.4240 .4580K.2495 3530.4355 .4635-100 001..49440.7700 i.4345 j.25

-. 3210.3400 .360 904 '3977434 .48'46-44!.1142 .4690ý

0 1.4115.3870 1.45951.4994.4190 .4025 .*4500 1649001.4200 ,.40601 ... _ .486N.4220 .4080.

TABLE IV

Equipment Tested: TLype of Test: Test Data:Aero X61A Bomb Rack Ultimate Load Tests Deflection Data in Inches

% -o--4Test No.-5 -- Tes -t No.- 6 Test No. 7Load IR2 R 2 L 2 R 2 L 2 R 2R

I T--0 .4510.4910.1.4210' .40704.44651.48801'.4215 14070145 1.80

20 .-4080-4510 ;.4345 .2045 .4470 ;4490 ý64200 .4230 65 430.2'47 ý2840 415 2-11 .44 5 456 .3 450 0460.6 05 28

4 !0 729 4170ý i415.4460.3680 415475435370.4025'.4830;.4385!.3850.90

60 .3445.3925 4.4430'.460d33034 .4910 .460 36550 3530-36 . -" .41-'--- -- F 60.90.5033 .5O

80 .3120.36 .44~41.3020 .3365 -.5040 ý4510 3480 .33851.5135 .4580.3425 .3140L -1 4- --

,100 !!.2915 3250 ý044351.4815..2760:,.2950 :.5140 *4560 03255 03020;i.5270 .4670.3205

i;.45ý450'.4230;.42115..4425 ý.4845 ':4 ý00ý 41 1775ý.35ý42.3 47:

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14

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release solenoid. The time of release was defined to be theelapsed time from the beginning of the electrical impulsethrough the release circuit to the moment when the carry-ing hooks begin to open.

Summarized results for selected loads are asfollows:

Load Time of ReleaseLbs. Milliseconds

0 171000 172500 255000 177500 21

10000 1712500 1515000 16

Additional tests of a similar nature were con-ducted on the X3 rack in order to investigate the effectof a variable voltage upon the time of release of therack under various high load conditions.

Summarized results:

Voltage Load Time of ReleaseVolts Lbs. Milliseconds

20 7500 2520 7500 1720 7500 2020 10000 3620 10000 2720 10000 2520 10000 3220 12500 No Release20 12500 No Release22 12500 No Release24 12500 No Release26 12500 No Release26 10000 25020 12500 6220 12500 4926 12500 Released26 12500 Released26 12500 Released

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RESTRIC

u-n - fixe 't :LA '- above, the AN 392-25pin was sheared. This 1/8 inch diameter pin is a partof the toggle shaft assembly, which in turn is a partof the release mechanism. The AN 392-25 pin was replacedby a pin having the same physical characteristics asto its diameter and tensile strength.

Elongation of the spacer hole through whichthe above-mentioned pin is positioned was also noticed.Modification of the spacer was effected to the extentthat the outer diameter of the spacer was increasedfrom its original dimension of 5/8 inch to 11/16 inch,thus enlarging the wall thickness of the spacer by1/32 inch. Douglas part number of the spacer is 2267547.

The X3 rack was again subjected to time ofrelease tests under various loads and voltages.

Voltage Load Time of ReleaseVolts Lbs. Milliseconds

20 0 2420 2000 2420 2000 2220 5000 41

27.5 2000 1627.5 2000 1827.5 5000 17

20 5000 No Release20 5000 No Release

27.5 5000 1420 5000 33

On the final release, above, the AN 392-25pin once again sheared. The pin was replaced by a pinhaving the same dimensions but heat treated to a tensilestrength of approximately 130,000 p.s.i.

The X3 rack was again subjected to time of re-lease tests under various loads and voltages in order todetermine the stitability cf the revised pin to withstandthe high loads.

Voltage Load Time of ReleaseVolts Lbs. Milliseconds

27.5 5000 1720 5000 26

27.5 7500 18

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Volage P Ta of ReleaseVolts Lbs. Milliseconds

20 7500 37

27.5 10000 2620 10000 No Release20 10000 33

27.5 12500 1820 12500 No Release20 12500 No Release22 12500 No Release24 12500 36

27.5 15000 1620 15000 33

The revised AN 392-25 pin did not shear through-out the series of releases outlined above.

It is not readily apparent from the data accumu-lated throughout the timing tests Just what combinationof load and voltage rating could be considered criticalas to whether or not the rack would consistently release.Subsequent inspection of the rack interior, however,revealed a brinelling of the K6AR48 bearing surface. Itwas theorized that failure to release would be encounteredshould the sear assembly, Douglas part number 2386807,which is linked to the release solenoid, engage theK6AR48 bearing at a point where indentation of the bearingsurface has occured.

III Cold Tests:

The X3 rack was placed in a chamber whoseambient temperature was maintained at -65 degrees Fahren-heit. After a period of twenty-four hours had elapsedat this temperature, various loads and release voltageswere applied to the rack in order to inve3tigate therelease characteristics.

Summary of Results:

Voltage Load Time of ReleaseVolts Lbs. Milliseconds

20 7000 3420 10000 /4720 lcoOo 127

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Vo(Itage Load Time of Release

Volts Lbs. Lilliseconds

20 lCOflO No lelegse20 1C000 No Release

27.5 10000 19

The A-J 392-25 pin (!.'0,1000 p.s.i. tensilestrength) again sheared on the final release, above. Thepin was replaced by a Dir of chrcrie-moly1xienuLu alloy steel,which was heat treated to anproxuo ately 160,000 p.s.i.tensi]le strength.

IV Frost Test:

The X2, rkl not. previously tested, ro.iedthe 73 r 1-•h ]•, t,}:e iol chamber. The X4 rack .as modifiedto the extent that, the AN 392-25 pin was replaced by apin of chrome-mnoybdenun alloy steel baving a tensil- strenpthof 160,000 p.9.1. Twenty-fouir hours in an ambient temperatureof - 65 degrees Fahrenheit oreceded thPe iithdrawal of theX4 rack from the chamber and its placement in a chamberwhose interior was maintained at a temperature of ý 76degrees Fahrenheit and a relative humidity of 98 per cent.The X4 rack remained in this environment until all theaccumulated frost had disappeared and moisture had collectedover the entire rack. The rack was then returned to thecocld chamber and a tempera-ture of - '5 degrees Fahrenheit.The temperature was then raised to zero degrees Fahrenheitafter ei~ht hours at the lover temperature and the racksubjected to time of release investigation under veril-sloads and voltages. The results are as follows:

Voltage Load Time of ReleaseVolts Lbs. Milliseconds

20 2000 2520 10000 530

27.5 10000 2920 10000 4420 15000 No Release22 15000 No Release24 15000 No Release26 15000 No Release

27.5 15000 307

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, t~d t a. relativehumidity condiAoit of 98 par cent at / 50 degrees Fahr-enheit while still in the cold chamber. The temperaturewas subsequently lowered to - 40 degrees Fahrenheit andkept in that state for seventeen hours. A load of 2000lbs. was then applied to the rack. Upon the applicationof 28 volts to the release solenoid the rack released intwenty milliseconds.

The above cycle was then repeated to the extentthat the ambient temperature and relative humidity wereraised to , 50 degrees Fahrenheit and 98 per cent, respect-ively. The release portion of the test, however, was moredemanding of the rack from a performance standpoint.In• •ead of maintaining a temperature of - 40 degreesFahrenheit for a period of seventeen hours and then apply-ing a 2000 lb. load, a temperature of - 65 degrees Fahr-enheit was maintained for a similar period and a 10,000lb. load applied. Two consecutive releases of the heavierload with a voltage of twenty volts resulted in releasesof 53 and 65 milliseconds respectively.

V Life Test:

The X4 rack was subjected to a life test, theobject of which was to determine the capability of therack to release high loads consistently *nd to cycle thebomb rack until mechanical failure occured within the rack.Each cycle consisted of loading the rack to 10,000 lbs.and then releasing the rack electrically with a ratedvoltage of 28 volts.

During the first 120 cycles of the life test14 failures to release were encountered before the AN 392-25 pin again sheared.

In order to alleviate the intermittent failurecondition, three changes were made in the release mechanismof the rack. These changes were:

(1) A Nice bearing, AN 201-KP8A, with a higherradial load characteristic was substitutedfor the Fafnir bearing, part number K6AR4P.The Fafnir bearing maximum radial load was600 lbs., while the Nice bearing would sup-port 1950 lbs. It was hoped that this changewould eliminate the brinelling situationwhich the higher loads were imposing on theK6AR48 bearing.

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(2) The substitute AN 392-25 pin was replacedby a pin having a diameter enlarged by 1/32inch. The physical characteristics of thispin were a material of chrome-molybdenumalloy steel heat treated to 160,000 p.s.i.and having a diameter of 5/32 inch.

(3) Douglas spacer number 2267547 was replacedby a spacer of steel material. The Douglasspacer, being made of aluminum, was exhibit-ing elongation of the hole through which theAN 392-25 pin was positioned. The new steelspacer was also machined to accommodate thelarger diamaeter pin mentioned above.

Following the above changes, the X4 rack, undera 10,000 lb. load condition released 2523 consecutivetimes before rack failure was noted. Disassembly of theX4 rack revealed the following conditions:

(1) Breakage of spring number 2267936

(2) Severe deformation of stop number 2254177

(3) Excessive wear on the housing assemblycaused by the lateral movement of linknumber 2267255 against housing bosses.

(4) Rough movement of the dual solenoid asevidenced by manual operation.

(5) Indentation of channel number 2267266 ata point where it contacts clip number2432871.

Illustrations 5 through 7 indicate the conditionof the bomb rack and stop after the life test had beencompleted.

This rack failure imist not be construed as afailure to release. The presence of the load in this casewould be sufficient to cause the carrying hooks to openwhen the solenoid was electrically activated.

It was tbhoiht advisable to ascertain certainphysical aspects to which the bomb rack was being subjectedunder a high load as applied by the test jig. To attainthis information, high speed motion pictures were made ofthe X4 rack in operation. Attention was focused on thedisplacements,velocities and accelerations imparted to thecarrying hooks, and the cocking handle as it revolved,upon release.

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Illustrations 8 through 10 indicate a comparisonbetween the physical aspects imparted to the rack whilereleasing loads of 2000 and 15,000 lbs. The weight referredto in illustration number 10 is a 65 lb. metal slab ofdimensions 30 inches by 5 inches by 1+ inches. The loadsreferred to were hydraulically applied through this itemwhich incorporated three carrying lugs. Essentially, thisarticle simulated an actual bomb of three point suspension.

VI Minimum Voltage Test:

A minimum voltage test was conducted on boththe X3 and the X4 racks simultaneously. It was establishedthat the lowest no load release voltage at this time nec-essary to trip the rack was 13.8 volts on each rack.

VII X3 Rack Rework:

At the suggestion of the Douglas Aircraft Company,the X3 rack was returned to the Douglas organization inorder to introduce an anti-icing feature into the bomb rack.This additional feature was the outgrowth of tests conductedby Douglas Aircraft on the use of Dow Corning DC4a waterrepellent compound at critical points throughout the rack.Satisfactory performance under cold conditions without theuse of internal heaters was the objective of the use ofDow Corning water repellent compound.

When the X3 rack was returned by Douglas Aircraftit embodied seven fittings through which the DC4a compoundwas to be inserted into the rack. These fittings were pos-itioned at the following places:

(1) At both ends of the aft pin around which theaft hooks pivot.

(2) At both ends of the cocking shaft.

(3) At both ends of the manual release shaft.

(4) On the left hand side, looking aft, of thefront pin, around which the forward hookpivots.

In addition, at the request of the Air Force, therack hoist bracket was discarded and replaced by a simplecover assembly consisting of two discs 3-15/32 inches indiameter connected by a NAS 42DD-106 spacer. The cockinghandle was also changed to the extent that it no longerrotated when the rack was released.

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VIII Comparison Cold aid Lst Tests

Upon receipt of the modified X3 rack, it wasimpregnated with tihe DC4a compound as specified. A seriesof comparison frost and cold tests between the X3 rack(with the water repellent compound) and the X4 rack wasbegun. A chronological sequence of events is outlinedbelow.

(1) Th• X3 rack was subjected to a - 65 degreeFahrenheit temperature for seven hours;withdrawn from the chamber and placed inan ambient temperature of $ 76 degreesFahrenheit until the accumulated frost hadmelted.

(2) A weight of sixty-five lbs. was loaded tothe X3 rack; the rack was reinserted intothe cold chamber at - 65 degrees Fahrenheitand successfully electrically operatedafter twenty hours at this temperature.

(3) The X4 rack was subjected to the same con-ditions outlined in 1 and 2, above, terminatinpin successful electrical operation.

(/Q) The X4 rack was again defrosted and reinser-ted into the cold chamber with the accompany-ing temperature of - 65 degrees Fahrenheit.

(5) Seven hours after being returned to the coldchamber the X4 rack would not release, eitherelectrically or manually.

(6) The X3 rack, loaded to sixty-five lbs., wasagain subjected to a - 65 degree temperaturefor a period of sixteen hours; withdrawn forfrosting and defrosting; reinserted into thecold chamber at - 65 degrees Fahrenheit; andsuccessfully operated by electrical actuationafter seven hours at the low temperature.

(7) The X3 rack was again subjected to the aboveprocedure with the above exception that aperiod of sixteen hours after reinsertionelapsed before a successful electrical opera-tion was attempted.

(8) Two additional successful electrical releaseswere made on the 33 raok after being frostcycled; i.e., removal from the cold chamber

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after twenty-four hours at - 65 degrees Fahr-enheit; placement in a chamber maintained at, 76 degrees Fahrenheit and 98 per cent relativehumidity until moisture covers the rack; re-insertion into the cold chamber at - 65 degreesFahrenheit for a period of eighteen hours.

(9) When the X4 rack (without water repellentcompound) underwent the procedure outlinedin 6, above, failure to release the rack eitherelectrically or manually was encountered.

The evidence indicates that the presence of theDC4a compound was advantageous to the successful operationof the rack under frost and cold conditions while carryinga small load.

IX High Voltage Tests:

The dual solenoid of the X3 rach underwent a testto determine .,ihother the electromagnetic unit would withstanda voltage of 30 volts d.c. for a period of thirty secondswithout incurring damage. Although no temperature or in-sulation readings were made, current variations throughthe solenoid are indicated. Several test runs were madeat selected intervals.

Summary of Results:

(1) Time in Seconds Current in Amperes

0 13.310 12.320 11.630 10.9

One minute interval

(2) 0 12.010 11.420 10.830 10.4

Three minute interval

(3) 0 11.810 11.220 10.730 10.3

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X Natural Vibration Frequency Survey:

A natural frequency survey was conducted on theX3 rack throughout the frequency range of zero to 300cycles per second on the three major axes of the rackassembly.

A natural frequency of a component part with-in the rack was noted at a frequency of 103 cycles persecond while the rack was being vibrated in a verticalplane. Evidence to support the claim that a componentwas being vibrated at its natural frequency was presentin the form of noise emanating from the rack interiorand the sudden increase in vibratory acceleration indi-cated through instrumentation.

A fatigue test was performed on the X3 rackat a frequency of 103 cycles per second. The rack wasvibrated at an acceleration of 4 G's along the verticalaxis.

in order to facilitate stroboscopic investigationof the rack interior under a vibrating condition, one halfof the X3 housing was removed and replaced by a remachinedhousing of the 2H rack which was previously rendered in-operative as a result of structural testing.

The X3 rack was vibrated continously at a frequencyof 103 cycles per second for a period of time necessary toaccomplish 10 million cycles. Throughout the fatigue testthe rack was cocked with no applied load.

With the aid of a stroboscope it was apparentthat considerable lateral movement, both in a fore and aftand sideways direction was occuring in link number 2267255which connects the fore and aft carrying hooks. The extentof the damage which this lateral movement was causing wasnot perceptible until the fatigue test was completed andthe housing was removed. Inspection of the interior thenrevealed the presence of minute metal filings in areasimmediately around the points where the aforementioned linkis joined to the fore and aft hooks. It was concluded thatthe lateral movement and resulting wear was not sufficientt6 impair the operational qualities of the bomb rack.

I Yinimum Impulse Test:

The X3 rack was subjected to a release impulsetest to insure that the release mechanism would operate

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on an 100etrical impulse of dutation not exceeding 20milliseconds. As is evident from the following data, therack operates well within the impulse limit of 20 milliseconds,with an impulse of 8 milliseconds appearing to be th eiitie&llength of impulse.

Minimum Impulse Results:

Seconds

.006 No Release

.006 No Release

.008 No Release

.008 No Release,008 No Release.008 Release.010 Release.010 Release•,012 Release.012 Release.012 Release.014 Release

.014 Release

XII Sand and Dust Test:

The X3 bomb rack, thoroughly impregnated with theDC4a compound, underwent a sand and dust test in accordancewith the following procedure.

The equipment was placed in a test chamber wherethe sand and dust density was maintained at 0.1 to 0.5 gramsper cubic foot within the test space. The relative humiditydid not exceed 30 per cent at any time during the test. Theinternal temperature of the test chamber was maintained at$ 77 degrees Fahrenheit for a period of twelve hours with airvelocity through the test area of approximately 800 feet perminute; then raised to a temperature of / 160 degrees Fahr-enheit for an additional period of twelve hours with thesame air velocity. At the expiration of this twenty-fourhour period the bomb rack was permitted to cool. The X3rack was then subjected to time of release investigation.Under a no-load condition, the bomb rack mean release timeof six releases was found to be seventeen milliseconds.Condition of the bomb rack interior after test may be seenin illustrations 11 and 12.

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XIII Heat Tests

The X3 bomb rack, incorporating the DG4a compound,was placed in a heat chamber and subjected to a temperatureof s165 degrees Fahrenheit for a period of four hours. Thetime of release characteristics of the bomb rack were in-vestigated at the end of this period. The bomb rack meantime of three releases was found to approximate eighteenmilliseconds.

XIV Salt Spray Test:

The X3 bomb rack was then placed in a salt fogchamber whose temperature was maintained at + 95 degreesFahrenheit. Atomizing equipment, designed to produce a finelydivided, wet, dense salt fog was present inside the chamber.At the end of the salt spray test which lasted fifty-two hours,the bomb rack was examined and satisfactorily operated. Visualinspection revealed very little corrosion, either on the bombrack interior or exterior.

XV Humidity Tests:

The X4 bomb rack was subjected to a humidity testin accordance with the following procedure.

The rack was placed in a test chamber capable ofbeing sealed and maintained at a temperature of $ 160 degreesFahrenheit and a relative humidity of 95 per cent for a periodof 6 hours. At the conclusion of the 6-hour period the heatwas turned off. During the following 18-hour period the temp-erature was permitted to drop at a uniform rate. The cyclewas then repeated a sufficient number of times to extend thetotal time of the test to 360 hours or 15 cycles. Two hoursafter the 15 cycles were completed and the bomb rack had beenremoved from the test chamber, two consecutive electricallyactivated releases were effected. Four days later, however,neither electrical or manual releases on the X4 rack couldbe made. Subsequent inspection of the rack interior revealeda considerable amount of rust on spring number 2267936,bearing number AN 201-KP8A, and on areas adjacent to :andlinkages coupled to the double solenoid.

It was thought that at least two factors contributedto the rusting of the aforementioned partst

(1) The X4 rack had previously been subjected to alife test and the relatively great number ofhigh load releases could have possibly removedsome of the protective plating.

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(2) The humidity condition inside the test chamberwas maintained through the use of ordinary tapwater rather than distilled water as specified.This tap water contained a certain amount ofmineral matter which was probably a factor inthe producing of the rust.

In order to remedy the previous invalid humiditytest the X3 bomb rack, which had been subjected to a rela-tively small number of releases, was placed in a test cham-ber whose humidity condition was obtained from the use ofdistilled water.

In addition, a bomb rack of the A type, Douglaspart number 5258077 ; serial number 127 F, was obtainecfrom the Special Weapons Command, Kirtland Air Force Base,on a loan basis. This rack had never been subjected to testor frequent releases. The A rack was also placed in thetest chamber along with the X3 rack in order to serve as abasis of comparison.

The previously mentioned humidity cycling pro-cedure was repeated until fifteen cycles had been completedon both racks.

Two days after the racks had been removed fromthe test chamber and the humidity test, electrical releaseof each rack was accomplished. Inspection of the rackinteriors, however, revealed a pronounced contrast. Whilethe A type of rack interior remained free of a rustingcondition, the X3 rack interior was heavily corroded muchin the same manner that the X4 rack interior was corrodedafter a humidity test.

CONCLUSIONS

Structurally and operationally, the Aero X61series of bomb racks are acceptable mechanisms for thecarriage and release of 2000 lb. external stores in thesubsonic speed range.

No data on flight tests of a complete bomb sus-pension and release system incorporating the Aero X61series of bomb racks has been included in this reportbecause of security requirements.

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Redesign emphasis was placed upon modificationof the B type of rack. The type of rack found acceptablefor Air Force use evolved, through engineering changes,into a rack defined by Douglas part number 5432515-509.

A recapitulation of changes made on the originaltype. of rack presented for test and evaluation follows.

(1) Elimination of the internal heaters andcontrolling thermostat.

(2) Placement of NAS 497 fittings on bothends of the aft hook pin assembly inorder to accommodate Dow Corning waterrepellent compound.

(3) Placement of the same type fitting onboth ends of the cocking toggle shaftassembly, on 1oth ends of the manualrelease shaft, and on one end of theforward hook pin assembly; all fittingsto accommodate the water repellent compound.In addition, access holes to enable thecompound to spread freely over the outerportion of the shafts and pins were pos-itioned at selected Intervals on the shaftsand pins.

(4) The hoisting bracket was discarded andreplaced by a simple cover assembly con-sisting of two discs connected by a spacer.

(5) The AN 392-25 1/8 inch diameter stop pinwas replaced by a pin of 5/32 inch diameterand heat treated to a tensile strength of160,000 - 180,000 p.s.i.

(6) The preceding change thereby necessitated.corresponding diameter changes in the spacerand channel through which the stop pin ispositioned.

(7) The Fafnir bearing, number K6AR48, was re-placed by bearing AN 201KP-SA.

A bomb rack of the B type which encompassed allof the above changes successfully underwent the testingnoted in this report.

Although no dielectric breakdown tests wereconducted, no apparent damage to the electromechanical

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unit was noticed and the dual solenoid operated satis-factorily many times after the high voltage tbet was per-formed.

The humidity test disclosed that a substantialamount of intermal corrosion may be expected after severalreleases should the bomb rack remain in a humid environ-ment.

RECOMMENDATIONS

Occasions may arise where a type of releasemechanism of three point suspension capable of thecarriage and release of external stores not exceeding10,000 lbs. in weight is desired for use.

When this situation exists, and the lateraldistance between the fore and aft suspension pointsis of the order of twenty inches, then the Aero X61Bexternal stores rack defined by Douglas part number5432515-509 is recommended for use.

Maintenance operations on the Aero X61Bexternal stores rack should include provisions forperiodic inspection of the rack interior to invest-igate for the possible presence of corrosion.

Where corrosion exists, disassembly of therack and replacement of affected parts should beaccomplished.

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Figure 1. Aero X61A Bomb Rack After Structural Testing

Figure 2. Close-lip of Aero X61A Bomb Rack After Structural Testing

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Figure 4. Channel No. 2267266 AfterStructural Testing

Figure 3. Channel No. 2267266 After Structural Testing

Figure 5. Aero X61B Bomb Rack After Life Test

Figure 6. Aero X61B Bomb RackStop No. 2254177 After

Life Test

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Figure 7. Close-Up of' Aero X61B Bomb Rack After Life Test

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Figure 11. Aero X61B3 Bomb Rack After Sand and Dust Test

Figure 12. Close-Up of Aero X61B Bomb Rack After Sand and Dust Test

WADO TR 52-98 27

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Figure 13. Drawing of Aero X61B Bomb Rack Outlining Parts Referred to in Report

WADC TR 52-98 29

UN•iSIAL

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ONCLASUm

DISTRIBUTION LIST

CYS ACTIVITIES AT W-PAFB CYS ACTIVITIES

5 WCWEG I Commanding GeneralSpecial Weapons Center

1 VWCNSO ATfls: ARDC RepresentativeKirtland AF Base, New Mexico2 ,•CZGH

1 Commanding General1 WOSIB Air -roving Ground Command

ATTN: Class. Data Br., D/OI1 dCSS Eglin Air Force Base, Florida

1 d(CSWF 1 Commanding GeneralArmament Test Center

1 iJCPPAA Eglin Air Force Base, Florida

1 1C?1AE 1 DirectorAir University Library

1 MCI&TF-4l ATTN: Req. CR-3998Maxwell AF Base, Alabama

4 BAGR-CD, Lirs. D. Martin1 Commanding General

2 DSC-SA Tactical Air CommandLangley AF Base, VirginiaDEF~T. OF DEFEKSE ACTIVITIES

OTHER THAN THOSE AT 0-PAFB 1 Commanding GeneralStrategic Air Command

Air Force Offutt AF Base, Nebraska

1 Director of Research and Development Special ProjectHeadquarters, USAFWashington 25, D.C. 1 Document Room

Project LINCOLN1 Commanding G eneral Massachusetts Institute of

Air Research and Development Command TechnologyATTIJ& RDON .?.O. Box 390P.O. Box 1395 Cambridge, MassachusettsBaltimore 3, Maryland ATTh: Lthel R. Branz

4 Commanding General OTHERSSpecial 4eapons CenterKirtland AF Base, New Mexico 1 Aepublic Aviation Corporation

A.TTi,: &r. R.G. MelroseFarmingdale, Long Island, iNew York

1 Douglas Aircraft Company, Inc.ATThz Lr. E.H. HleinemanEl Segundo, California

WADC TR 52-98 30