404 5631<. S. A R M Y

TRANSPORTATION RESEARCH COMMANDVVORW EUSTIS, VIRGINIA

SEXPERIMENTAL RESEARCH

D AMIC TEST OF AN AIRCRAFT LITTER INSTALLATION

One of a Series of Reports Pertaining to the7 Dynamic Crash Test of a U.S. Army M-21 Helicopter

9j March 1963

9C ýg tract DA.44.177-AMC.888(T) TRECOM Technical Report 63.3

prepirod by J

AVIATION CRASH INJURY RESEARCHjPHOENIX, ARIZONA

A DIVISION OF

FLIGHT SAFETY FOUNDATION, INC.

NEW YORK, NEW YORK

w m IF

NO OTS A~9

HZAbOUAXtTEU

U. S. ARMY TRANSPORTATION RESEARCH COMMANDFort Eustis, Virginia

This report was prepared by Aviation Crash Injury Research (AvCIR),a division of the Flight Safety Foundation, Inc., under the terms ofContract DA 44-177-AMC-888(T). Views expressed in the reporthave not been reviewed or approved by the Department of the Army;however, conclusions and recommendations contained therein areconcurred in by this Command.

On 12 September 1962, AvCIR, under contract to the U. S. ArmyTransportation Research Command. conducted a dynamic crash testof an H-21 helicopter. Among the several experiments aboard theaircraft was the installation of a standard U. S. Army litter/patientrestraint system. This report, the first in a series of six reportsto be published containing data derived from the crash test, presentsinformation relative to the litter/patient restraint system experiment.

Action is being taken at this time by the Office of the SurgeonGeneral, Department of the Army, and by this Command to implementthe recommendations contained in this report.

FOR THE COMMANDER:

KENETHB. ABELCaptain ''Adjutant

APPROVED BY:

WILLIA3 J. LAN

USATR dyoject Engineer

Task IA024701AI2101(Formerly Task 9R95-ZO-001-01)

Contract DA-44-177-AMC-888(T)TRECOM Technical Report 63-3

March 1963

DYNAMIC TEST OF AN AIRCRAFT UTTER INSTALLATIONOne of a Series of Reports Pertaining to theDynamic Crash Test of a U. S. Army H-21

Helicopter

ByJames Schamadan, M. D.

James W. Turnbow, Ph.D.Langston W. T. Weinberg

Technical ReportAvCIR 62-23

Prepared byAviation Crash Injury Research

a division ofFlight Safety Foundation, Inc.

2871 Sky Harbor Blvd.Phoenix, Arizona

for

U. S. ARMY TRANSPORTATION RESEARCH COMMAND

FORT EUSTIS, VIRGINIA

CONTENTS

LIST OF ILLUSTRATIONS ................ v

CONCLUSION ....... . . . . . . . . . . .. . 2

RECOMMENDATIONS . . . . . . . . . . . . . . . . . 3

INTRODUCTION . . . . . . . . . . . . . . . . o . 5

TEST OBJECTIVE . . . . . .. ......... . . . . 6

DESCRIPTION OF TEST ARTICLE. . . . . . . . . . . . 7

TEST PROCEDURE . . . . . . . . . . . . . . .... 11

TEST RESULTS................. . . . . . . . . . . 15

TEST DATA EVALUATION ............... 21

TEST EVALUATION.......... . . . . . . . . 27

DISTRIBUTION .......................... 28

iii

ILLUSTRATIONS

Figure Pge.

1 Litter Installation, H-21 Helicopter - Side View . .

2 Litter Installation, H-21 Helicopter - Front View.. 8

3 Accelerometer Installation in the AnthropomorphicDummy Patients . . . . . . . . . . . . . .0. . . 9

4 Force Tensiometer Installed in the Litter SupportStrap System . . . . . . . .0 . . . . . . 9

5 High-Speed Camera Installation for PhotographingPatient Restraint System. ......... . . . . 10

6 Test Conditions ..... ........... .. 1

7 Instrumentation Data Recording System . . . . . . 12

8 Camera Placement Diagram . . . . . . . . .. 13

9 Litter Side-Attachment Failure . . . . . . . . . 15

10 Failure of the Ceiling Structure at the ForwardLitter Strap Attachment Point. . . . ......... 16

11 Forward Litter Strap Ceiling Attachment - PostcrashView . . . . . . .. . . . . . . . . . . . . .. . 17

12 Litter System - Postcrash View . . . . . . . . .*. 18

13 Permanent Deformation of the Lower Litter . . . .. 18

14 Permanent Deformation of the Upper Litter ..... 19

15 Litter/Patient Floor Area and Side PanelDeformation . . . . . . . . . . . . . . . . . . 20

16 Free-Body Diagram of the Upper Dummy PelvicRegion. . 0 . . . . . ." . . 0 0 22

17 Accelerometer and Force Tensiometer Time HistoryPlots . . . . . . . .. . .. . . . . . . . .0 . .. . 23

18 Kinematic Drawing of Litter Restraint System Duringthe Crash Impact Sequence .......... 25

V

SUMMARY

This report presents an analysis of the crashworthiness characteris-tics of a standard litter/patienit restr&int system as instaUed in ahelicopter which was subjected to a dynamic cr--h test.

On 12 September 1962, Aviation Crash Injury Research conducted adynamic crash test of an H-21 helicopter. Several personnel restraintsystems were installed in the aircraft to permit evaluation of perform-ance under impact conditions. Included was a standard litter installa-tion. Anthropomorphic dummies were placed on the litters. Acceler-ometers were mounted in the pelvic areas of the dummies, andtensiometer links were mounted on the litter support straps. A high-speed camera was positioned in the helicopter to record the action ofthe litter installation during the crash sequence.

Although the crash was considered to be survivable, the litter/patientrestraint system failed completely. The details of the failures arediscussed; and it is concluded that the military specifications coveringlitter/patient restraint systems are not realistic and, therefore,litter/patient restraint systems produced in accordance with thesespecifications do not provide adequate protection for the occupant undermoderately severe, but potentially survivable, crash conditions.

10

CONCLUSION

Based on the information contained in this report, it is concluded thatmilitary specifications pertaining to litter/patient restraint systemsdo not require sufficient strength to provide protection for the occu-pants in certain potentially survivable accidents.

RECOMMENDATIONS

Based on the foregoing conclusion, it is recommended that:

1. A thorough investigation be initiated to develop realisticdesign criteria for litter/patient restraint systems.

2. Additional testing of litter/patient restraint systems consistof tests of the entire assembly as contrasted with the testingof single components.

3. Both static and dynamic tests be conducted on the litter/patient system. Dynamic tests should be conducted atacceleration and energy levels consistent with the conditionsexpected in moderately severe, but potentially survivable,accidents.

3

INTRODUCTION

The problem of litter/patient restraint has never been thoroughlyinvestigated in Army aircraft. The concept of air mobility as relatedto the transportation of sick or wounded personnel was proven duringthe Korean conflict. The state-of-the-art in aeromedical evacuationhas since progressed rapidly with the introduction of newer techniquesand specially designed aircraft. Among the most significant advance-ments is the concept of internal loading of patients in utility and cargohelicopters. Although the external-pod-type helicopter is still in use,the scope of this experiment was limited to the application of internalpatient transport in rotary-wing aircraft. It is anticipated that theprinciples developed here will also have application in all types of air-craft that may be involved in aeromedical evacuation.

An investigation of all available accident records of the internallyloaded helicopter ambulance revealed little data which could be usedin an evaluation of the dynamic crash characteristics of any litter/patient restraint systems. Consequently, plans were made to includea standard litter/patient restraint system in the first dynamic crashtest of an H-21 helicopter. This test was conducted by AvCIR for theU. S. Army Transportation Research Command on 12 September 1962.

5

TEST OBJECTIVE

The objective of this experiment was to evaluate the crashworthinessof a standard, internally loaded litter/patient restraint systeminstalled in a typical helicopter.

DESCRIPTION OF TEST ARTICLE

A standard H-21 litter installation was used as the test article in thisproject. This installation normally consists of three litters, sixlitter handle tiedown brackets attached to the aircraft side structure,and three litter handle tiedown brackets attached to each of two strapssuspended between fittings on the passenger cabin ceiling structureand cargo tiedown fittings on the floor.

Only the top and middle litters of the standard three-litter stack wereused in this experiment because of a weight limitation of the testvehicle. Since the bottom litter of a normal three-litter stack attacheswithin a few inches of the floor, it was calculated that the gross effectof this litter/patient combination on the dynamic characteristics of thelitter support system as a whole would be small. Experience gainedfrom previous dynamic crash tests of helicopters of similar construc-tion indicated that the floor structure would deform upward on impactand contact the bottom litter. This deformation and subsequent littercontact would remove any load on the total litter support system whichmight be attributed to the bottom litter/patient combination. Therefore,a valid test of the litter/patient restraint system could be obtained withonly two litters installed.

Three 1/4-inch nylon ropes were suspended from the cabin ceiling tothree cargo tiedown rings in the floor to prevent interaction of thisexperiment with other experiments in the event that the litter supportsystem failed. The addition of these ropes was the only alteration tothe standard litter installation, and their presence had little effectupon the performance of the litter/patient system itself.

An anthropomorphic dummy was placed on each litter in a head-

forward, supine position. The dummy occupying the lower litter wasrestrained by a standard single belt restraint system across the pelvicarea, and the upper dummy was restrained by a standard single beltrestraint system across the chest cavity. The complete precrashlitter installation is shown in Figures 1 and 2.

Accelerometers were installed in the pelvic region of each anthropo-

morphic dummy to measure accelerations in the lateral, longitudinal,and vertical directions on the top litter patient and in the longitudinaland vertical directions on the lower litter patient. A force tensio-meter was installed between the ceiling tie point and the litter supportstrap on both the forward and the rear litter support straps. Theseinstallations are shown in Figures 3 and 4.

Figure 1. Litter Installation, H-21 Helicopter - Side View.

Figure 2. Litter Installation, H-Z1 Helicopter, Front View.

8

Figure 3. Accelerometer Installation in the Anthropo-morphic Dummy Patients..

Figure 4. Force Tensiometer Installed in the U~tterSupport Strap System.

9

A high-speed 16mm motion picture camera and necessary auxiliarylighting were installed in a position to photograph the action of thelitter/patient installation during the impact sequence. A photographof this installation is presented in Figure 5.

Figure 5. High-Speed Camera Installation for Photo-graphing Litter/Patient Restraint System(Camera No. 4).

10

TEST PROCEDURE

DESCRIPTION OF TEST OPERATIONS

A drone control system was irnstalled in the helicopter to allow com-plete remote control of the helicopter through the entire test flight.The actual flight flown during this test followed the profile shown inFigure 6.

MM" LOY AMN ATrM=w AT BE" V

Fiur 6. TetCndMos

A report covering the more detailed mechanics of the test operationis being prepared at this time for release at a later date.

The accelerometers and force tensiometers were connected through

a balance and sensitivity unit to a 50O-foot umbilical cable which wasconnected directly to recording oscillographs located at a stationary

point on the ground. A block diagram of the instrumentation system

is presented in Figure 7.

Just prior to the test, an eight-step resistance calibration was madeon all appropriate channels by connection of a calibration unit to thebalance and sensitivity unit on the helicopter. The bridge batteryvoltage was monitored on one channel to record any change in thebridge voltage during the crash sequence. No voltage change was

recorded.

11

500-FT. UMBILICAL CABLEACCELEROMETER

BALANCEAND JRECORDING

SENSITIVITY OSCILLOGRAPH

FORCETENSIOMETER[

POWERSUPPLY

Figure 7. Instrumentation Data Recording System.

The high-speed camera and associated auxiliary lighting were con-trolled by a switch on the master control panel at the control point.During the descent, the cameras and lights were turned on manuallyby the instrumentation operator, and they were automatically turnedoff after a 10-second period by a time delay circuit.

The area covered by the high-speed camera is shown in Figure 8.

12

.44

70)

13

INSTRUMENTATION

A list of the data acquisition system components related to this experi-ment is presented in the table.

INSTRUMENTATION

Device To Provide Location Specification

High-Speed Motion Displacement/ 4 on ground PhotosoniciPicture Camera time for heli- 1 on air- lB high G

copter and dummy craft tolerancekinematics data 500 fpa 16mm

EktachromeER 430

Normal-Speed General photo- 4 on 2 Kodak 16mm

Motion Picture graphic coverage g'round 64 fpsCamera 2 Bolex 16mm

24 fpsKodachrome H

Electrical Accel- Acceleration 5 in Statham ASA-

erometers sensing dummies 50-350 and3 on cabin ASA-100-350floor

Tensiometer Force sensing 2 each in AvCIR 2500 lblitter strap load link

Recording Amplitude-time 4 each at CEC Model

Oscillograph records of trans- ground 5-114-26ducer outputs control Channel rs-

point cording oscillo-graph with re-lated powersupplies

Photographic/ Zero time for 2 each Photo flashOscillographic camera film and bulbs mountedData Correlation oscillograph in field of viewDevice record of cameras.

Firing pulseto bulbs re-corded on

oscillographrecord forcorrelation

Voltage Generator Timing for Ground 115 Volt AC

high-speed control generator,cameras point 60 cps timing

pulse

Fairchild Flight Horizontal and 500 feet FDFA-044Analyzer vertical speed perpen-

of the heli- dicular tocopter center of

flight path

14

TEST RESULTS

LITTER SIDE ATTACHMENTS

All four of the litter-fuselage attachment brackets failed in themanner illustrated in Figure 9. The bracket assembly consists of aclip device to hold the litter pole. The clip is bolted to a formedaluminum bracket which is, in turn, attached by screws to a castingon the bulkhead.

Figure 9. Litter Side Attachment Failure.

The application of a downward load on the clip places both shear andbending moment on the aluminum bracket. The moment puts the lowerface of the bracket in compression with a tension load on the upperscrews and upper portions of the bracket. The brackets all failed bya tension-type fracture in the area of the upper screws.

The casting on the bulkhead in no case showed evidence of failure.

15

LITTER STRAPS

The aisle support for the litters is provided by the same type of clipas used on the wall. These clips are attached at appropriate points to1-inch-wide by 1/8-inch-thick nylon straps, which, in turn, areattached to both the floor and the ceiling of the aircraft cabin as shownin Figure 2.

This test points out two weaknesses of the strap restraint system.The first, pertinent to the H-21 installation only, is the failure of theceiling attachment for the forward strap. The strap passes through acasting which is bolted to a thin metal bulkhead near a lightening hole(no doubler is provided). The casting is connected by two bolts in linewith the axis of the strap so that all force in the strap acts on the sameportion of the bulkhead. The failure of this strap connection is shownin Figures 10 and 11.

Figure 10. Failure of the Ceiling Structure at the ForwardLitter Strap Attachment Point.

16

Figure 11. Forward Litter Strap Ceiling Attachment -

Postcrash View.

The second weakness concerns the longitudinal restraint value of theclip. The litter handle is placed in the clip and secured by a nylonweb hooked over the handle. This arrangement provides good verticaland lateral restraint to the capacity of the system, but gives verylittle restraint longitudinally. This is the principal reason why therear strap did not fail like the front, since the litter handles at therear slipped forward and out of the clip, thus unloading the strap. Theforward handles push against the clip in a forward deceleration, whichin this experiment prevented the pullout, but caused the upper fittinginstallation to be overloaded to failure.

LITTERS

A postcrash photograph of the litters is presented as Figure 12. Th-lower litter* retained its basic shape; however, permanent deforma-tion of the litter poles occurred. The floor beneath the litters wasnot badly deformed; thus, the litter and occupant impacted upon arelatively flat surface. The left rear stirrup hooked onto one of thenylon ropes, which tended to hold it in the same relative position.The outboard forward handle also caught in the unused bottom litterbracket (see Figure 9), causing the fabric to tear along the outboard

*Note that this litter would have been the center litter of the normalthree-litter installation. (See Figure 2.)

17

pole. This greatly helped to check the forward motion of this litterafter the failure of its restraint system. A permanent set of about 5inches was retained in the litter poles, as shown in Figure 13.

Figure 12. Litter System - Postcrash View.

Figure 13. Permanent Deformation of the Lower Litter.

(Litter shown here inverted.)

18

The upper litter sustained considerably greater damage. After failureof its restraint system, its forward and downward motion was un-checked until it contacted the lower litter and occupant.

One litter pole was bent with a permanent set of 6 inches, as shownin Figure 14. The other pole had a permanent set of 3 inches. Therear spreader bar was collapsed and the left rear stirrup was brokenfree. (See Figure 12. ) This action was due to the shearing deforma-tions induced in the litter because of the absence of longitudinal re-straint on the inboard poles.

Figure 14. Permanent Deformation of the Upper Litter.(Litter shown here inverted.)

LITTER PATIENTS

Failure of the litter support system allowed the dummy patients tomove headfirst toward the forward part of the cabin. The upper litterpatient's buttocks were at about the position of the lower patient'shead, as shown in Figure 12. The upper dummy was also rotated andwas essentially clear of the litter itself. The lower dummy remainedin its litter but shifted forward about 24 inches with respect to thelitter.

19

FUSELAGE STRUCTURE DEFORMATIONS

The entire lower structure of the forward fuselage section, includingfuselage skin, floor support structure, and lower sections of bodyframes, was crushed in the primary impact of the helicopter on therunway. The left side of this lower structure was crushed moreseverely than the right side, since the impact occurred with approxi-mately 4 degrees of left roll. The floor was distorted throughout thecargo compartment, but it maintained an essentially continuous sur-face except in localized areas.

Generally, the fuselage structure above the normal troop seat attach-ment points (approximately 17 inches above the floor line) remainedintact on both sides of the aircraft, while the structure below this linewas crushed extensively.

Although this impact was severe, the crash is classified as potentiallysurvivable because the occupiable areas of the fuselage remainedessentially intact. The shock loads imposed upon the aircraft by theimpact were attenuated by the crushing of the fuselage structure belowthe occupiable space. A postcrash view of the litter/patient area inthe helicopter is presented as Figure 15.

Figure 15. Litter/Patient Floor Area and SidePanel Deformation.

20

TEST DATA EVALUATION

The accelerometer and force tensiometer time-history plots recordedduring the test are presented in Figure 17. A kinematic drawing,taken from the high-speed 16mm film, is presented in Figure 18. Thisdrawing shows the sequence of events occurring at the litter stationduring the test.

The following observations have been made and may be followed throughreference to Figures 17 and 18:

1. No appreciable deceleration (horizontal or vertical) wasimposed upon either dummy from the time of impact of thenose gear of the H-Z1 (time zero) to about 0. 19 second, atwhich time the bottom dummy contacted the floor due todeformation in both the airframe and in the litter supportsystem. A 50G vertical acceleration of over 10 millisecondsduration was recorded in the pelvic region of the lower dummyfollowing contact with the floor.

2. The maximum loads in the litter straps were recorded atapproximately 900 pounds per strap. Assuming that the litterbrackets supported an equal load, the total load would then be4 x 900 = 3, 600 pounds on the complete system. This loadwould produce 9G on the 400-pound mass of the two dummies.The vertical acceleration records (Figures 17-4 and 17-6)indicated accelerations of this order of magnitude up to contactof the lower dummy with the floor.

3. Both the upper and lower litters slipped out of the bracketsattached to the rear support strap with subsequent reductionin load in the strap. The rear strap and its support systemdid not fail.

4. The forward litter strap reached a load of over 900 pounds atthe time of separation of the rear litter handles from the rearstrap. This load dropped to about 800 pounds at 0. 21 secondand then immediately dropped to zero as the support at thecabin ceiling failed.

5. The contact of the bottom dummy with the floor of the aircraftresulted in oscillatory "longitudinal" acceleration as measuredin the pelvic region of the dummy. A positive (forward) longi-tudinal acceleration of 5OG is seen to have occurred at 0. 21

21

second (Figure 17-5) in conjunction with the 50 (plus) Gvertical acceleration. This positive acceleration was dueto the orientation of the dummy and thus of the accelerometerat contact, allowing a negative "vertical" acceleration to berecorded as a positive "longitudinal" acceleration. A similarsituation existed for the upper dummy, as seen in Figure 17-3.This action is illustrated in Figure 16.

DIRECTION OF DIRECTION OF NEGATIVEPOSITIVE VERTICAL ACCELERATION

LONGITUDINALACCELERATION

3 ORIENTATION OFDUMMY PELVIC AREA

FORCE

Figure 16. Free-Body Diagram of the Upper DummyPelvic Region.

6. The top litter patient impacted the lower dummy at 0.23second, as shown in Figure 18. A "vertical" accelerationof 125G (see Figure 17-4) and a simultaneous longitudinalacceleration of 70G (Figure 17-3) were recorded. Apositive vertical acceleration of 150G (Figure 17-6) wasalso recorded in the lower dummy. A positive accelerationin this instance implies that downward load has been appliedas was obviously the case here.

22

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TEST EVALUATION

The litter/patient restraint system used in the crash test was astandard military system. All of the components met individualmilitary specifications. As shown by the tensiometer readings, theentire system began to fail under moderate loads.

Litter installation requirements, MIL-A-8865(ASG), provide thatsupports and attachment fittings for litters shall be designed so thatthey will carry to the primary structure a 250-pound litter loadmultiplied by the following ultimate load factors.

Forward 8G

Lateral 1. 5G

Vertical 4.5G down, 2. OG up

The specifications, however, require only static testing of com-ponents. Static tests do not account for combined forces that arecharacteristic of dynamic situations. When the litter/patient re-straint system is assembled in actual use, the conditions are nolonger ideal. There is no way to ensure that the straps are tightenedto the same tensions. The clips that hold the litter handles in theinstallation described in this report are awkward and difficult totighten, leading to loss of restraint under the longitudinal loads whichwill often exist in actual crashes.

The results of this test of a litter/patient restraint system are con-sidered to be typical for all recent litter installations for internallyloaded helicopters. It is apparent that the system as a whole is notcapable of maintaining survivable conditions for the occupants inpotentially survivable crashes of the severity demonstrated.

27

DISTRIBUTION

USGONAROUSAIG 2USACGSG 1USAW IVUSAATBDIUSAARMBD 1USAAVNBD 1USATMC (FT ZAT),ATO0 1DGSLOG 4ARO, Durham 2OGRD,DA 2USATMO Nay Goord Ofc 1NATG 2ARO, OCRD 2CRD, Earth Scn Div 1CG, USAAVNG 2USAAVNS, CDO 1DGSOPS 1QMFSA 1USAT CDA 1USATB 1USATMC 20USATC&FE 4USATSCH 5USATRECOM 22USA Tri Svc Proj Off 1TCLO, USAABELCTBD 1USATRECOM LO, USARDG(EUR) 2TCLO, USAAVNS 1USATDS 5AFSC (SCS-3) 1Air Univ Lib 1ASD (ASRMPT) 1CNO 1ONR 5BUWEPS, DN 5GMC 1MCLFDC 1MCEC IUSCG 1Canadian LO, USATSCH 3

28

BRAS, DAO.MG(Mov & Tn) 4NAFEC 3Langley Rsch Cen, NASA 4MSC, NASA1Lewis Rsch Cen, NASA 1Sci & Tech Info Fac 2USGPO 1ASTIA 10USA MRDG 2HumRRO 2DAA 3ODOSOPS, ASD 2ODCSPER, DS IUSAMCAFO 2EMS, AMSFTB 2BMS, AMTD ISG, AvnB 5AFIP 2USMG, Arlington IUSAFDFSR, Norton AFB IUSABAAR 5USAAHRU 1US Army Rep, USNASC 1USNASC, NAS 2NavAMC 3NADC 1WADD 2ASML 2CARI, FAA 2NLM 2AF,FTC 2HUSTWO 2ARDS, FAA 2BFS, FAA 2DAM, FAA 2BUS, CAB 2APD, USPHS 2APR55, DRG 2FSFI 5AvCIR 100USSTRICOM 1USAMOCOM 3USAMC 8NLM, Bethesda I

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