Usaarl Report No 91-6 Vol 1

7/30/2019 Usaarl Report No 91-6 Vol 1

1/45

USAARL Report No:91 -6Volume I

The Airbag as a Supplementto Standard Restraint Systemsin the AH-1 and AH-64 Attack Helicoptersand Its Ro1.e n Reducing Head Strikesof the %opllot/Gunner

BYNabih M. AlemDennis F. ShanahanJohn V. Barson

Biodynamics Research Divisionsand

William H. Muzzy, IllNaval Biodynamics LaboratoryNew Orleans, Louisiana

January 1991

Approved for public roloaw; distrlbutlon unlimited.

United States Army Aeromedical Research LaboratoryFort Rucker, Alabama 36362-0577


2/45

NoticeQualified reuuestersQualified requesters may obtain copies from the Defense TechnicalInformation Center (DTIC), Cam eron Station, Alexandria, Virginia22314. Orders will be exped ited if placed through the librarianor other person designated to request docum ents from DTIC.Chanae of addressOrganizations receiving reports from the U.S. Army AeromedicalResearch Laboratory on automatic m ailing lists should confirmcorrect address when corresponding about laboratory reports.DisoositionDestroy this docum ent when it is no longer needed. Do not returnit to the originator.DisclaimerThe views, opinions, and/or findings contained in this report arethose of the author(s) and should not be construed as an officialDepartment of the Army position, policy, or decision, unless sodesignated by other official docum entation. Citation of tradenames in this report does not constitute an official Departmentof the Army endorsement or approval of the use of such comm ercialitems.Reviewed:

DENNIS F. SHANKLTC, MC, MFSDirector, BiodynamicsResearch DivisionReleased for publication:

Cherman, ScientificReview Committee Commanding \


3/45

UNCLASSIFIEDSECURITYLASSIFICATION OF THIS PAGEREPORT DOCUMENTATION PAGE Form ApprovedOMB No. 0704-0188

la. REPORT SECURITY CLASSIFICATIONUNCLASSIFIED2a .SECURITY CLASSIFICATION AUTHORITY2b. DECLASSIFICATION /DOWNGRADING SCHED ULE

1b. RESTRICTIVE MARKINGS

3 . DISTRIWTION /AVAIlABILITY OF REPORT, Approved for public release, distributionunlimited

4. PERFORMING ORGANIZATION REPORT NUMBER(S)USAARL Report No. 91-6, Volume I

5. MONITORING ORGANIZATION REPORT NUMBER (S)

I6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONlfORlNG ORGANIZATIONU.S. Army Aeromedical Research (lfapplicabk) U.S. Army Medical Research and DevelopmentLaboratory SGRD-UAD-IE Command6c .ADDRESS (C&y, So&, wd ZIPCot&) 7b. ADDRESS (Qry, State, dd ZIP Co&P.O. Box 577 Fort DetrickFort Rucker, AL 36362-5292 Frederick, MD 21702-5012t3a. AME OF FUNDING /SPONSORING 8b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERORGANIZATION (If applicable~Ec.ADDRESS (City, State, ad ZIP Code)

11. TITLE (mdudc Secudty Chssific~ti~~

10. SOURCE OF FUNDING NUMBERSPROGRAM PROJECT TASKELEMENT NO. NO. NO .0602787A :M162787A878 AG

WORK UNITACCESSION NO.13 1

The airbag as a supplemen t to standard restraint systems in the AH-1 and AH-64 attackhelicopters and its role in reducing head strikes of the copilot/gunner, Volume I12. PERSONAL AUTHOR(S)Nabih M. Alem, Dennis F. Shanahan , John V. Barson, and William 8. Muzzy, III.lk . TYPE OF REPORT 13b. TIME COVEREDFinal16 .SUPPLEMENTARY NOTATION

17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necesety ad identify by Mock numbersFIELD GROUP SUBGROUP , Airbag, restraint, head strikes, sled tests, injuries,helicopter crashes

19. ABSTRACT (Continue an reverse if neceswy and Mcntit) by Mock numbedAccident investigation records of U.S. Army helicopter crashes show injuries of pilots dueto striking a structure inside the cockpit outnum ber those due to excessive accelerationsby a five-to-one ratio. This two-volum e report presents the results of a study of theeffectiveness of airbags in reducing the severity of contact injury to the gunner whenstriking the gunsight. Airbag systems were installed on the gunsights in simulated Cobraand Apache cockpits, then sled tested at 7 and 25 g. The tests indicated airbags reducedhead accelerations by 65 percent, head injury criteria by 77 percent, and head angularacceleration by 76 percent in the Cobra tests. In the Apache tests, the airbags reducedthose same indicators by 68, 52, and 83 percent. An airbag system, the report concludes,is likely to prevent severe or fatal head and chest injuries in an Apache or Cobra crash.Volume 1 of the report describes the tests and discusses the results. Volume 2 consists ofAppend ixes A, B, and C of the report and contains processed signal graphs of all sled tests.Volume II is available upon request from SIC, USAA RL.!O .DISTRIBUTION /AVAILABILITY OF ABSTRAC T 2 1. ABSTRACT S ECURITY CLA SSIFICATION

~~UNCLASSIFIEDNNLIMITED 0 SAME AS RPT. 0 DTIC USERS UNCLASSIFIED2a . NAME OF RESPO NSIBLE INDIVIDUAL 22b. TELEPHON E (/n&de Area Code) 22~. OFFICE SYMBO LD Form 1473, JUN 86 Previous editions we obsolete. SECURITY CLASSIFICATION OF THIS PAGE


4/45

AcknowledumentsThe authors are grateful to Mr. Joseph L. Haley, Jr., for hisadvice in selecting realistic test conditions. The dedication,creativity, hard work, and comm itment to excellence by everymem ber of the sled team at the Naval Biodynam ics Labo ratory

(NBDL ) made this project a success. Special thanks go to thedata processing staff at NBD L for extracting and delivering acomp lete set of the raw and processed data, and to SPC CharlesPaschal and SPC Bradley Erickson, USA ARL , for reviewing andextracting valuable information from most of the high-speedfilms.

i


5/45

-----------~--------------_--p-------_--_ -_-_-_-________-_ _--------______--------~~~~~________----____----------

This page intentionally left blank.


6/45

ContentsPage

List of figures .............................................. 2List of tables ............................................... 3Summary ..................................................... 5Introduction ................................................. 7Objectives ................................................... 7Test methods ........ ..i ...................................... 10Data processing .............................................. 19Test conditions .............................................. 21Test results ................................................. 26Discussion of tests and results .............................. 30Discussion of airbag tests ................................... 34Conclusions .................................................. 36Recommendations .............................................. 38References .................................................. 39


7/45

.of fluuresFigure Page

1.2.3.

4.5.6.7.a.

9.

10.

View of the Cobra TSU 35-degree test set-up............ 12View of the Apach e ORT 35-degree test set-up........... 13Close-up view of the Apache ORT mou nted on thesled test frame and showing its base and thebreakaw ay nylon mo unting screws ...................... 14View of the hydraulic compression test device usedto test the strength of mounting screws.............. 14Com ponents of the manikin frangible face developedby NBD L and used to detect head strikes.............. 16Structure used with the Cobra TSU airbag tests toprovide back supp ort to the inflated airbag.......... 18Structure used with the Apache ORT airbag tests toprovide back support to the inflated airbag.......... 19Deformations to the manikin frangible face producedin test LX6202. These deformations are typical ofthose observed in most head strikes with theOR T and TSU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Deformation to the manikin frangible face producedin test LX6212 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Evidence of severe head strikes with the ORT wasobtained from stroking of the tube and shearingof the nylon mounting screws......................... 31

2


8/45

List of tablesTable Page

1.

2.

3.

4.

5.

6.

7.

Summary of conditions and results of the inertiareel tests with the AH-l (Cobra) telescopicsighting unit (TSU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Summary of conditions and results of the inertiareel tests with the AH-64 (Apache) opticalrelay tube (ORT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Summary of conditions and results of G-triggeredairbag sled tests simulating 35-degree impact........ 24Restraint system action and manikin interaction withthe TSU in the Cobra tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Restraint system action and manikin interaction withthe ORT in the Apache tests . . . . . . . . . . . . . . . . . . . . . . . . . . 28Restraint system action and manikin interaction withthe ORT and TSU in the airbag tests.................. 29Comparison of means of head response parameters ofinertia reel tests with and withoug airbags.......... ,37

3


9/45

--------_-----_-----------me --------------___---------------------_-_-__----------m- PI=-------------__-------------

This page intentionally left blank.

4


10/45

A recent review of Army accident investigation records todocum ent injuries sustained in Army helicopter crashes showedinjuries due to excessive accelerations have been reduced inApache (AH-64) and Black Hawk (UH-60) crashes compared to otherhelicopters. This injury reduction may be attributed to currentArmy design standards which feature energy-absorbing landing gearand seats, and increased h igh mass item retention. Significant-ly, contact injuries of pilots outnu mbered acceleration injuriesby a five-to-one ratio. Contact injuries occur when the pilotstrikes a structure inside the cockpit because of inadequ aterestraint or becau se of collapse or intrusion of the structure.

The Apache optical relay tube (ORT) and the telescopicsighting unit (TSU) in the Cobra (AH-l) are used by the gunner(front-seat copilot) for target sighting, ranging , and designa-tion. Since the TSU and ORT present potential contact hazards tothe gunner, this investigation focused on Apache and Cobracrashes.

Accident investigation records at the U.S. Army Safety Center(USASC) were examined to determine the frequency of gunner in-juries incurred from striking the TSU and ORT during survivablemishaps. Gunn er injuries were attributed to the TSU in 20 of the105 survivable Cobra crashes during the 1972-1980 period.Gunners in nine of these cases received minor injuries while fivesustained major ones. The remaining six gunners received fatalinjuries. The Apache had eight su rvivable mishaps since itsfielding in 1985. Of these, only one gunner sustained a concus-sion and skull fractures as a result of his head striking theORT. In this Apache mishap and in the 11 Cobra cases where majoror fatal injuries occurred, it was theorized an airbag would haveprevented serious injuries.

To explore this theory, 32 sled tests were conducted at theNaval Biodynam ics Laboratory (NBDL) in New Orleans, Louisiana.Eleven of the tests simulated a 25 g impact of the C obra/TSU, asevere but survivable crash. An additional 12 tests of 7 gsimulations of the Apache/ORT were designed to simulate the earlyportion of the deceleration pulse produced by the collapse ofApache landing gear. The test manikin (dumm y) which w as used torepresent the gunner was restrained by the standard 5-point beltsystem and inertia reel an d wore the appropriate flight helmet.Com ponents of the Cob ra or Apache cockpits essential for realis-tic simulations were incorporated in the test hardw are. Theremaining 9 tests were intended to duplicate the conditions ofthe first 23 tests, except that an airbag was installed below thesighting system in an attempt to cushion the head and reduce theseverity of its strike.

5


11/45

Head strikes did occur in most tests despite the properfunctioning of the restraint system s and inertia reels. In alltests without airbags, dummyhead accelerations indicated headstrikes w ere sufficiently severe to cause facial fractures, butnot necessarily irreversible brain damage . Airbags provedextremely e ffective in reducing the severity of head strikesagainst sighting system s regardless of inertia reel function.For example,severity, using mean values of several indicators of injuryairbags reduced head accelerations by 65 percent, headinjury criteria by 77 percen t, and head angular accelerationpeak-to-peak swings by 76 percent in the Cobra/TSU tests. In theApache/ORT tests, the airbags reduced those same indicators by68, 52, an d 83 percent, respectively.

This U.S. Army Aeromedical Research Laboratory (USAAR L) studydemons trated that airbags reduced head injury severity assessmen tindicators. Since this was a preliminary study, the researchefforts were limited to off-the-shelf autom otive airbags withminimal hardware modification. An airbag system , specificallydesigned for Apache or Cobra, likely would prevent severe orfatal head and chest injuries. It is recommende d that U.S. ArmyAviation Systems Comm and AVSC OM) initiate R&D efforts to furtherdevelop the airbag concept for use in Army helicopter cockpits tosupplement standard restraint systems.

6


12/45

IntroductionThe AH-l Cobra was first introduced into comb at service bythe U.S. Army in 1967 to serve as an attack and antiarmor heli-copter. Since its introduction , it has undergone a numb er ofupgrades to improve its performance and weapons capability. In1985, the AH-64 Apache was fielded as a new generation attackhelicopter offering marked improvemen ts in performance andarmamen ts, and an ability to operate at night and in poor weatherconditions. The AH-l and AH-64 function as attack helicoptersoperating in a high threat environment. Even in peacetime, thetraining missions for these aircraft subject their p ilots to highrisks of injury. Flying nap-of-the-earth (NOE) and having to"high hover I) during bore sightings and firings frequently placesthese aircraft in the "dead man" zone of altitude versus airspeedwhere recovery is-difficult in the event of an emergency.A comm on eature of both aircraft is the presence of a

gunsight in the front cockpit used for target sighting, ranging,and designation of the TOW or Hellfire missiles. In the AH-l,the gunsight is referred to as a telescopic sighting unit (TSU)and in the AH-64, it is an optical relay tube (ORT ). From acrash injury perspective, there are two major differences betweenthe TSU and the ORT. The ORT is located physically closer to thecrewmember, and it has a breakaway system that allows it to yieldto excessive forces generated by the striking of the crewmem ber'sbody during a crash. Because of the p resence of the respectivesighting systems, the copilot/gunner in both types of helicoptercan sustain serious or fatal injuries if his upper body strikesthe gunsight during a crash. Of particular concern is thepotential for serious head injury from head strikes on the TSU orORT.

Accident historyInjuries occurring in U.S. Army helicopter crashes have beendocum ented by num erous studies over the past 25 years (Adams andHicks, 1979; Bezreh, 1963; Haley, 1971; Hicks, Adam s, and Shana-han, 1982; Mattox, 1968; Sand, 1978; and Shanahan and Shanahan,1989a). From these studies, we know most potentially survivable

helicopter crashes involve near vertical impacts with terrain andmost injuries arise from forces generated along the verticalaxis. Consequently, new design standards for crash resistanthelicopters emph asize reducing crash forces along the helicop-ter's vertical axis. Current Army design standards requireforces to remain within tolerable limits at all o ccupiablepositions for vertical impacts of up to 12.8 m/s (42 ft/s) on a

7


13/45

hard surface (Shanahan and Shanahan , 1989b). The generallyaccepted vertical acceleration tolerance limit for service ageindividuals is 20-25 g (1 g = 9.80665 m/s') for approximately 100ms. To achieve this desired design goal requires some ingenuitysince stopping distance in a vertical crash usually is small.This is due to the relative lack of crushable structure on thebottom of standard fuselages and the poor deformation predic-tability of most impacted surfaces. Meeting the standard re-quires energy-attenuating capability be provided in the landinggear, fuselage floor, aircraft seating, or any comb ination of thethree. Both the Apache and Black Hawk helicopters incorporateenergy-attenuating landing gear and stroking seats. As we willdiscuss below, the addition of these features mod ifies the crashpulse of these helicopters in comp arison to other n oncrashwo rthyhelicopters.

The crash experiences of both the Apache and the B lack H awkhave shown the energy-absorbing features work extremely wellsince impacts with vertical velocities in excess of 12.8 m/s (42ft/s) are survivab le in both helicopters . Nevertheless, asignificant num ber of injuries still are occurring in survivab lecrashes of these helicopters. A recent review of injuriessustained in Army helicopter crashes demo nstrated injuries due toexcessive acceleration are, in fact, reduced in Apache and BlackHawk crashes co mpared to other helicopters (Shanahan and Shana-han, 1989a). Significantly, for all helicopters , contactinjuries outnumb ered acceleration injuries by a ratio of approx-imately five to one. Contact injuries arise from secondary col-lisions that occur when an individual strikes or is struck byan object. These contact injuries are due to inadequaterestraint, collapsing structure, or a comb ination of both mechan -isms. Since the TSU and ORT represent a significant potentialcontact hazard in spite of the use of five-point restraintsystems, the Cobra and Apache represented an excellent mod el forexploring the efficacy of the use of airbags in preventingcontact injury in helicopter crashes. The testing project whichis reported here also provided an opportunity to comp are a dual-sensing inertia reel with the standard MA -6 inertia reel u singtwo different lock activation settings.

As part of this project, USA SC accident records of the C obraand Apache were reviewed to do cumen t the frequency of injuriesincurred from striking the TSU or ORT . All survivable groundimpact m ishaps of the AH-1 from 1 January 1972 to 30 June 1990were reviewed. During this 18.5 year period, there w ere 105crashes of the Cobra classified as survivable or partiallysurvivable and for which the vertical velocity at terrain impactwas greater than zero. Of these crashes, 20 (19 percent) re-sulted in injury to the copilot/gun ner as a result of strikingthe TSU. Six individua ls (6 percen t of all c rashes ) received

8


14/45

fatal injuries, another five received major injuries, and ninereceived minor injuries.It should be noted, in the six fatal crashes, the copilot/gunne r (front seat) died as a result of striking the TSU (fivehead strikes and one chest impact) wh ile the pilot (rear seat)sustained only relatively minor injuries. Even though theacciden t reports suggested two of the six individuals failed to

properly tighten their upper torso harnesses, we concluded thefatalities would not have occurred in the absence of the TSU. Inall acc idents resulting in major or fatal injuries from strikingthe TSU (a total of ll), it was felt an airbag wou ld have pre-vented serious injury.When velocities at ground impact for those accidents result-ing in major or fatal injury were com pared to other accidents ofthe AH-l, there was no significant difference (student T-test,.05) in the vertical velocity between the two groups:Z\Z versus 3 .47 m/s (17.5 ft/s versus 11 .4 ft/s). 5.33However, themean longitudinal velocity at impact for crashes resulting in

major injury from TSU strikes was more than twice that of thosethat did not involve TSU strikes: 20.6 m/s versus 8.72 m/s (67.7ft/s versus 28.6 ft/s). All fatal injuries occurred at impactvelocities over 10.3 m/s (33.8 ft]s) excep t for one case of 2.1m/s (6.8 ft/s) where the individual reportedly failed to tightenhis upper torso restraint. Furthermore, only one chest or headinjury occurred at a longitudinal impact velocity of less than5.2 m/s (16.9 ft/s), except for the one case described above.These data suggest TSU strike injuries, unlike most helicoptercrash injuries, are relatively independent of vertical velocityat impact and highly dependent on longitudinal velocity.Mishap records of the AH-64 covering the period since itsfielding in 1985 to 30 June 1990 also were reviewed. There wereeight survivable ground impact mishaps of the Apache. Only oneresulted in injury to the copilot/gunner as a result of strikingthe ORT. In this case, the crewm ember received a concussion andfacial fractures. The estimated vertical velocity was 9.44 m/s(31 ft/s) and the longitudinal velocity was 2.56 m/s (8.4 ft/s).Also, there was a nonsurvivable crash of an Apache where thecopilot/gunner sustained a forehead laceration when he struck theORT. The vertical velocity at impact was estimated to be 15.5m/s (51 ft/s) and the longitudinal velocity was less than 1.1 m/s(3.5 ft/s).Although there is very little experience w ith crashes of theApache, it seems clear the ORT is a significant hazard to thefront seat occupant in spite of its breakaway design. Further-more, the combination of energy-attenuating landing gear and astroking seat in this helicopter, as well as the closer proximityof the ORT compared to the TSU, makes contact with the ORT less

9


15/45

dependent on longitudinal velocity than in the case of the AH-l.If this hypothesis is correct, we can anticipate a higher rate ofgunsight strikes in the Apache than we have experienced in theCobra.An additional factor to cons ider is in the AH-64: The impactenergy-attenuating design of the airframe mod ifies the impactforces so the impact duration is longer. The longer duration

results in lower torso accelerations that m ay not generate the2 g to 3 g upper torso acceleration required to lock sho ulderharness inertia reels su fficiently early to prevent a head strikeon the ORT. Therefore, the standard 2-3 g setting of the shoul-der harness inertia reel may not provide an appropriate degree ofprotection for the front seat occupants in the AH-64.One approach to rem edy the head strike problem in the Apacheand Cobra would be to ch ange the locking parameters of theshou lder harness inertia reel so the reel locks earlier in theimpact sequence, thus reducing the forward movem ent of the torsoand head. Another approach would be the addition of an energy-

attenuating device between the head and the sighting system. Onesuch device is the rapidly inflating airbag currently installedin several mod els of automobiles. The passive airbag can beplaced in the cockp it and tailored so as not to interfere withthe normal operation of the controls, but can be deployed rapidlyby means of a sensor an d diagnostic system sensing the impactaccelerations of the aircraft striking the groun d.Obiectives

The objectives of this two-phase investigation were:a. To analyze data from accident investigations of AH-1 andAH-64 mishaps in which injuries were produced by the gunner(copilot) striking the TSU or ORT.b. To docum ent the m ovement of the helmeted head withrespect to the sighting systems during simulated crashes in theAH-l and AH-64 front seats.C. To exam ine the capability of the inertia reel andshoulder harness restraint system to prevent head strikes on thegunsight system during simulated crashes.d.cushions TO explore the con cept o f using rapidly inflating airand to assess the potential usefulness of this technol-ogy in reducing the severity of head strikes on the gunsightsystem during actual crashes.

10


16/45

Test methodsThe testing to accom plish the objectives of the project wereperformed in two phases. The first took place in October 1988and the second in October-Novem ber 1989. The tests were con-ducted at NBDL using a sled driven by a horizontal linear accel-erator to generate the simulated impact forces.To perform multiple simulated impacts and observe the inter-action of the test manikin in the front seat environment of theCobra and Apache, test devices were fabricated using a comb ina-tion of the actual aircraft hardware and an adjustable attitudesupport structure. The aircraft hardware used for the Cobratests included the distal section of the TSU, the Cobra restraintsystem with the inertia reel, and the Cobra armored seat andbottom seat cushion. The back seat cushion also was included inthe simulated structure. An overall view of the setup for testswith the Cobra and TSU is shown in Figure 1. .The hardware used

in the Apache tests included the full SimulaT" Apache energy-absorbing crew seat* and seat cushions*, the AR-64 restraintsystem with the inertia reel, and the distal direct viewingsection of the ORT. The bottom section of the ORT that containsthe ORT control box and a CRT were simulated using a speciallyfabricated box with lead weights to duplicate the actual struc-tural weight. An overall view of the Apache test setup is show nin Figure 2 with the ORT installed in the front portion of thetest fixture.The mount of the ORT was designed to collapse when the impactforce exceeded 400 pounds. A closeup of the mounted ORT is shown

in Figure 3. To retain the frangibility of the ORT in the testfixture while providing a reusab le test apparatus , the originalmounting bolts that held the upper portion of the relay tube toits base were substituted with nylon screws selected to fail inshear and to be easily replaced. The 4000lb collapse thresholdwas verified by testing the new assem bly in static comp ression asshown in F igure 4.

11


17/45


18/45

Figure 2. View of the Apache ORT 35-degree test setup.


19/45


20/45


21/45

Figure 5. Components of the manikin frangible face developed by NBDL and usedto detect head strikes.


22/45


23/45


24/45

Figure 7. Structure used with the Apache ORT airbag tests toprovide back support to the inflated airbag.

Data nrocessinq

Two primary categories of data were generated during thisproject: transducer signals and high-speed films. Less formalbut equally informative were the observations recorded on thespot during each test by the investigators and still photographswhich were taken at various stages of each test.

Quantitative film analysis can yield motion measurementswhich cannot be obtained by other recording means. However,extensive field calibration procedures must be implemented ifaccurate measurements are to be made. This was not done for thisproject, so no quantitative motion analysis was performed.However, high-speed films provided excellent visual records ofthe impacts and were reviewed to identify hardware failures andto understand the interaction between the manikin and the testedrestraint system.

Transducer data were the primary basis for assessing theseverity of head strikes with the sighting systems and, hence,the success or failure of the tested restraint system. Trans-ducer signals were digitized by the NBDL data acquisition system

19


25/45

later were analyzed by NBDL and results of the analysis forwardedto the U.S. Army Aeromedical Research Laboratory (USAAR L) for usein this report. In addition, NBD L staff extracted all transducersignals from their signal acquisition system and provided USAA RLwith the unproce ssed signals for further process ing and analysis(Muzzy, 1990).All signal processing conformed to Society of AutomotiveEngineers, SAE 5211 (1988) guideline for instrumenting andfiltering impact test accelerations. Thus, all signals weredigitized at the rate of 8000 samples per second, and all signalswere digitally filtered according to the same SAE J211 channelclass filters. Head linear acceleration signals w ere filteredusing a digital filter simulating the SAE channel class 1000which essentially is a Butterworth filter with its 3-dB corner at1650 Hz and a roll-off of 24 dB/decade. Sled pulse was filteredwith channel class 60 (lOO-Hz and 24 dB/dec.) Head angularaccelerations (pitch and roll) also were filtered with thechannel class 60 filters. Potentiometer signals, which measuredthe extension of the restraint shoulder belt, were filtered with

a channel class 180 filter (300 Hz at 24 dB/dec.)The sled acceleration pulse was integrated to produce avelocity time-history, from which the velocity change could beextracted. The onset of the sled acceleration pulse, defined asthe slope (derivative with respect to time) of pulse during itsrise, was used as an additional indicator of the severity of thecrash. This onset rate as well as other potentially significanttime derivatives (rates) were obtained from the jerk, a signalderived from acceleration by num erical differentiation.Head accelerations included the forward (X), lateral (Y), and

longitudinal (Z) componen ts. Resu ltant head acceleration signalswere computed as the point-by-point square root of the sum of thesquared components. The head injury criterion (HIC) was derivedfrom the resultant head acceleration using a standard procedure(Department of Transpo rtation, F'MVS S 08). Angu lar accelerationsof the head (pitch and roll) were integrated once to produceangular velocities and a secon d time to produce pitch and rollangular displacements of the head.Recorded signals were of sufficient duration to capture therebound impact some 300-400 ms after T-zero, the onset of thesled deceleration pulse. However, the rebound impact w as irrele-vant to the objective of the simulations, which was to assess the

severity of the first impact with the optical system . Therefore,plots of most linear and angular head accelerations were re-stricted to the first 200 ms where the impact of interest usuallyoccurred. Peak values were picked automatically by the computerprocessing program. However, the program could not cons istentlyread the correct swing between a high and an adjacent low in the

20


26/45

head pitch and roll acceleration and velocity signals. There-fore, this was done manually for the swing nearest the time ofhead impact.Belt extension, obtained with a potentiometer, was differen-tiated with respect to time to produce the rate (m/s) at whichthe belt was unwinding from the inertia reel. A second differen-

tiation was done to produce the acceleration (g) at which thebelt was moving. Belt acceleration triggers the locking mechan-ism in both the MA-6/8 and the MA-lo. The differentiationprocedure was used to calculate the belt linear acceleration inlieu of an actual accelerometer measurement which was difficultto accomplish.It should be noted that signals derived by numerical dif-ferentiation are extremely noisy and must be heavily smoo thedbefore a recognizable signal is produced. The process is usefulinsofar as indicating general trends but not exact measu rements.Therefore, numb ers extracted from these signals, such as the peak

onset rate of the strap an d strap peak acceleration, should beinterpreted with caution.Test conditions

In general, vertical impacts were simulated on horizontalsleds by aligning the seat back with the horizontal sled tracks.Because of gravity, the dow nward weight of the m anikin comb inedwith the acceleration forces (opposite to the direction of sledacceleration) to produce a thrust ve ctor which slightly inclinedrelative to the sled horizona l axis. Therefore, to generateimpact forces along the manikin spinal (longitudinal) axis, theseat was rotated by an offset angle determined by the averagesled acceleration. A seat back angle of 5 degrees with thehorizontal was considered adequate comp ensation for the effect ofgravity in our tests. Three directions, defined by seat backangles of 5, 20, and 35 degrees with respect to the tracks, weredesigned to generate impact forces directed 0, 15, and 30degrees, respectively, from the spinal axis.Test conditions and parameters are summarized in Tables 1, 2,and 3. Tests that d id not involve the airbag are listed in Table1 for the AH-l (Cobra) and in Table 2 for the AH-64 (Apache.)

All other tests involving the airbag are listed in Table 3.Tests with repeated or similar test conditions have been groupedtogether even though they may have been conducted in a differentorder, as reflected by their reference numbe rs.

21


27/45

Te1

Smmayoc

o

a

res

oth

ina

re

te

wihth

A

(Ca

tee

c

sgn

u

(T

Treee

nmb

L

16

11

L

10

10

L

16

10

L

25

10

L

24

10

L

24

10

L

20

13

3

L

20

13

3

L

20

11

3

L

20

11

3

L

21

12

3

Seps

v

Pc

ae

(d&

He

rea

Anaa

eao

a

eao

swinaimp

44

1

43

1

43

1

66

2

67

2

48

2

13

*

18

1

89

4

18

5

10

6

Ro

Pc

(as

(as

3

3

4

3

5

3

9

5

8

5

7

5

3

1

2

1

1

1

4

1

1

8

*Daau

ae

ocey

in

ae


28/45

Treee

nmb

LLLLLLLLLTLT

Te2

Smmayoc

o

a

res

oth

ina

re

te

wihthA6

(A

oc

rea

tu

(OR

H

rea

A

aa

eao

Seps

Pc

a

eao

swinaimp

ae

A

Vo

H

eao

iY

P

inuy

R

Pc

(G)

(m/s

(d

(G)

ceo

(as

(as

77

17

3

95

1

1

1

67

17

3

38

4

5

6

68

17

3

24

3

5

5

68

17

3

39

5

6

7

68

18

3

22

2

5

7

68

17

3

34

5

6

7

89

18

3

56

8

1

6

29

14

3

24

1

3

1

68

18

2

85

1

8

1

68

17

2

50

6

8

8

68

17

5

75

9

1

1

67

18

5

18

*

*

*

*Dau

aeocey

in

ae


29/45


30/45

Two crash severities were simulated by programm ing the sledto produce the appropriate acceleration pulses. The two pulsesselected for this project differed primarily in the magnitudes ofthe acceleration (25 g and 7 g nominal peaks) w hile essentiallymaintaining the same velocity of 11-12 m/s (36-39 ft/s). The25-g pulse simulated a severe but survivable crash. The 7-gpulse was intended to simulate the first 70-80 ms portion of acollapsing nload-limitingn gear where the acceleration dwells atthe 7-g level. In a typical crash involving the landing gear,the long-duration, low-level pulse may be followed by a 50-100 gpeak pulse which is gen erated as the landing gear bottoms out.Since this comp lex acceleration pulse was not achievable with theNBD L sled, it was deem ed more important to simulate the earlyportion of the impact with the available sled.

Two different settings of the MA-6/8 were tested: l-2 g and2-3 g settings. This was done to test whether the lower g set-ting wou ld activate the inertia reel lock sooner resulting in anoticeable reduction of head strikes. The MA-10 had a dualsensing system which locked the reel at a l-2 g setting or whenthe impact produced a seat acceleration level of 4-5 g in the X-or Z-axis.Several preinflated airbag tests were conducted to explorethe kinematics of interaction between the manikin and the airbag.No presentable data w ere produced from these "dry runs" so noresults are reported here. The airbags in the remaining tests(five Cobra TSU and six Apache ORT) were allowed to inflate uponimpact, triggered by a signal from an automotive-type crashsensor. This device, which was designed for use in automobiles,detects the onset (initial rise portion) of a crash pulse andelectronically triggers the locking mechanism of the car seat

belts or the sguib used to inflate the airbag. In the sledairbag tests, the crash sensor was attached to the sled so as togenerate the triggering signal when the sled acceleration pulsereached 4-5 g. All 10 airbag tests (Table- 3) simulated 35-degreeimpact direction and most used the M-10 dual mode inertia reels.The test conditions described above were not designed tofully simulate all potential crash scenarios n or were they in-tended for statistical analyses. However, they do form a repre-sentative sample and serve to illustrate some advantages andshortcomings of current and future restraint systems.


31/45

Test resultsDetailed results of the data analysis are presented inAppendixes A, B, and C, found in Volume II, in the form ofprocessed transducer signals. Volume II may be obtained uponrequest from the Scientific Information Center (SIC) at USAA RL.Several tests were run in addition to the 32 included in thisreport. Most of these were developmental runs and did notgenerate reportable data. Only the fully instrumented tests arereported. Selected response parameters were extracted from thesesignals and summ arized in Tables 1, 2, and 3. The first twotables summ arize the results from tests which did not involve theuse of an airbag. The third table sum marizes data from all testswith airbags. The tables list peak resultant linear acceleration(g) of the head and the computed HIC. The validity of the HIC asan assessmen t method will be discussed in the next section. Thehead angular motion is reported in the tables as the 18sw ingt1between the low and high nearest the time of head strike. Swingsof angu lar acce lerations (rad/s') and velocities (rad/s) aretabulated for both roll and pitch. Head pitch is defined as a

rotation of the head about its lateral (Y) axis. Head roll isdefined as a rotation of the head about its forward (X) axis. Noyaw is reported since this rotation, defined as the twist of thehead about its longitudinal (2) axis, is minimal due to thedesign of the neck in the Hybrid III man ikin.The amo unt of extens ion (cm) of the restraint belt out of theinertia reel are listed but only when it was judged to be valid.Some of the signal processing results produced by the automatedsoftware did not make sense, particularly when compared to filmdata, and were discarded as erroneous. In many tests, it waspossible to estimate the belt extension from film analysis byrelying on the checkered pattern attached to the belt. In fact,this was the only method available for measuring the belt exten-sion when the signal from the string potentiometer was clearly inerror (because of a breakdown in the instrumentation). Theseestimates have been incorporated in the tables of results.Also reported in tabular format are qualitative evaluationsof the high-speed films of the tests and examinations of post-test photographs . All test films were reviewed to detect andreport unusual events which could help explain certain signals orthe final outcome of so me tests. Film reviews focused on twoareas of concern: The extens ion of the restraint belt out of theinertia reel, and the head strikes with the TSU or ORT . The type

of inertia reel, its lock setting and action, the amount of beltextension, as well as observations of head strikes are listed inTables 4, 5, a nd 6.

26


32/45


33/45

Tbe5

Rran

semaoanmanknineao

withthORnthA

htes

Inare

Amo

T

ob

nmb

L

eeo

Obvo

t

T

sn(C

(cm)

IX

MA1

l-245

54

F

a

a

oe

IX

MA68

23

57

F

a

acnimp

LX

MA68

l-2

70

F

a

acnimp

IX

MA1

l245

57

Cnarg

fa

imp

IX

MA68

23

10

Lwea

acnimp

L

MA68

l2

57

F

fa

sk

L

MA1

peo

49

F

fa

imp

L

MA1

l245

28

H

mp

wihOR

L

MA1

l245

45

L

foe

amoh

L

MA68

23

45

Moha

oe

ca

Ix

MA68

l2

32

Fe

a

a

imp

L

MA1

l245

*

U

n

a

oe

*Emaefommays

*Dau

aeoceyin

ae

tB

oreewohgs

msa

pe

poa


34/45


35/45

Head strikes with the TSU or ORT also were easily detectedfrom the head acceleration signals and by posttest examination ofthe frangible face. Figures 8 and 9 are typical of the defonn a-tions which were observed. Evidence of head strikes in some ORTtests also w as obtained from the shearing of the nylon screws andthe collapse of the ORT into its base, as shown in Figure 10.R~masaion of tests and results

The preliminary nature of this study limited the numb er andtype of tests that were conducted. It also restricted theexploration of the airbag concept to the use of off-the-shelfM;g;re with minimal allowance for hardware redesign or mod ifi- ,Despite these limitations, the study succeeded indearonstrating a problem exists and a supplemental airbag may be aViable solution.

Figure 8. Deformations to the manikin frangible face producedin test LX6202. These deformations are typical ofthose observed in most head strikes with the ORT andTSU.

30


36/45

Figure 9. Deformation to the manikin frangible face produced intest LX6212.

Figure 10. Evidence of severe head strikes with the ORT wasobtained from stroking of the tube and shearing ofthe nylon mounting screws.

31


37/45

Epidemiological data as well as the impact tests performedunder this project indicate the TSU and the ORT pose a substan-tial hazard to copilot/gunners in the event of a crash. The mostcommonserious injury is facial injury, frequently assoc iatedwith severe brain trauma and death. In this study, HIC wascalculated from head linear accelerations to provide an objectivepredictor o f potential irreversible brain injury. Caution shouldbe exercised in interpreting HIC values since strict cond itionsmust be met before any valid conclusions about head injuryoutcome can be derived. For example, the HIC is invalid if therewere no head strikes with the ORT or TSU. Even in case of a headcontact, the HIC is invalid if the duration of contact excee ds 15Ins. Usua lly, the duration of contact is much longer tha n theinterval over which the HIC was determined. Finally, the HICshould not be used as a pass-fail criterion; instead, it shouldbe used to assign probab ility of irreversible brain injuryoccurring. Thus , assuming all conditions for using the HIC havebeen satisfied, HIC values of 500, 1000, and 1500 may be con-verted respectively to 5, 15, an d 50 percent approximate proba-bilities of brain injury (Mertz, 1984).

Furthermore, it m ust be stressed that HIC is a predictor ofclosed head injury resulting from impacts to the calvarium. Mostfatal TSU injuries were open brain injuries arising from impactsto the face. The significance of this finding is that facialbones are considerably weaker than the more dense calvarial bonesand yield under relatively low force. In a facial impact withthe TSU/ORT, brain injury results from direct trauma from col-lapsing facial bones and not from the brain's inertial responseto an applied force. Therefore, HIC probably is not an accuratepredictor of serious injury under these conditions and can onlybe used as a relative measure comparing the severity of differenttests.

Results of the TSU tests (Table 1 and Appendix A, Volume II)show for the six nearly vertical (5-degree) simulated crashes ,head strikes were associated with lower head accelerations andHIC values than those produced by the five more pitched (35-degree) tests. That is, the severity of head strikes was lowerfor vertical impacts than for those with large horizontal com-ponen ts, as the test results indicate. This may be attributed tothe difference in head trajectories relative to the impact vectorproduced in the two groups.The difference between the severities would be explained asfollows: At the onset of a nearly vertical impact, the head andbody of the pilot travels along a vertical path that does notpass through the sighting unit. As the pitch angle of impactincreases, a greater horizontal componen t is added to the impactvector, so the initial path of travel of the pilot's body and

32


38/45

head passes near or through the sighting system. The headtrajectory is complicated further by the unavo idable slack of theshoulder belt which is produced automatically by the slumping ofthe upper torso. As a result, the pilot's head would likelystrike the sighting system , even when the impact primarily isvertical. This explanation is supported by field data whichshows TSU impact is strongly dependent on longitudinal velocityat impact and only weakly dependent on vertical velocity.In general, these tests were inconclusive regarding therelative effectiveness of the different inertia reels and locksettings. Using amount of belt extension and head pitch angularaccelerations as indicators of inertia reel performan ce, theresults were quite inconsistent. In the six nearly verticalCobra TSU impacts, belt extensions varied from 1.5 to 10.8 cm(0.6 to 4.3 in). Although all reels locked, three runs had beltextensions that exceeded 6 cm (2.4 in), one run for each inertiareel condition. Ideally, belt extens ion should be limited to theextent poss ible and, preferably, to less than 5 cm (2 in) inorder to prevent flail injury. The reason for such a wide range

of extensions for essentially identical test cond itions is notknown.The same degree of variability of belt extension was obtainedin the severe TSU runs even when prelocked reels were used. TestLX6203 used a MA-10 dual sen sing reel and the belt extension ob-tained from a string potentiometer signal was 17.5 cm (7 in).The validity of this value cou ld not be confirmed from test filmor onsite observations. The sam e uncertainty of belt extensionapplies to test LX6204, so it cannot be directly ascertainedwhether or not the two inertia reels locked upon impact. How-ever, peak linear head accelerations (138.3 and 128.8 g), headpitch acce leration swings (17,000 and 11,500 rad/s'), and pitchvelocity swings (79.5 and 61.0 rad/s), as well as the damage tothe frangible face, are strong indicators that the two inertiareels did not properly lock allowing the head to strike with suchseverity that it wou ld have caused serious head injuries in areal crash. .Three TSU tests, LX6274, LX 6275 and LX6276, were conductedlater in the project under test conditions similar to the twosevere TSU tests discussed above. This time, extensions of thebelt were mon itored with a string potentiometer, a fairly accu-rate transducer. These were run with a prelocked inertia reel inorder to demonstrate the occurrence of head strikes, even if the

restraint system were given the best chance of functioningproperly. Two of the tests resulted in belt extensions of 3.5and 2.0 cm (1.4 and 0.8 in), indicating the belt remained fairlytight and did not extend. Immediate posttest examination of theinertia reel confirmed this assertion. The third test producedan extension of 11 cm (4.3 in), indicating some slippage of the

33


39/45

reel or a stretch of the belt must have occurred. Posttestobservations indicated the reel, in fact, did lock.Regardless of the action of the inertia reels or restraintbelt, head strikes did occur in tests, as indicated by observeddamage to the frangible faces and head acceleration signals.Peak head accelerations in the 85 g to 195 g range and HIC valuesnear 600 produced by all the 35-degree pitch tests were suffi-cient to cause facial fractures and lacerations and, possibly,irreversible brain damage in actual m ishaps.The Apache ORT tests (Table 2 and Appendix B, Volume II) wereall run at the 7 g sled pulse to simulate the early portion ofcollapse of the landing gear during a crash. All these testsproduced head strikes to the ORT regardless of inertia reelconfiguration. No inertia reel configuration produced consis-tently better results, as in the TSU test series. Belt exten-sions remained below 7 cm (2.8 in), except for test LX6212 wherethe restraint belt extended by 12 cm (4.7 in). Even then, theHIC and peak acceleration of this test were the lowest among thisgroup, despite obvious damage to the frangible face (Figure 8).

The highes t head linear acceleration for this series was 94 g intest LX6208 and the highest HIC value was 160 in the same test,an indication of the relative "mildnessW1 of head strikes.Nevertheless, all acce lerations exceeded facial bone tolerancesto fracture. Also, it should be rememb ered that these tests onlysimulated crashes where the landing gear did not fully stroke.In crashes that exceed the landing gear sink speed, the 7 g pulsewill be followed by a considerably higher m agnitude pulse,potentially leading to a secondary ORT strike more severe thanthe initial strike.The tests and results discussed so far pertain to the first

phase of investigation that d id not involve airbags. Clearly,head strikes do occur in realistic impact scenarios, in spite ofthe use of a properly functioning restraint system.Biscussion of airbaa tests

After review of the experiments and the preliminary analysisof Phase 1 data, it was decided the second phase of testing wouldfocus on simulations of "severen crashes . After all, if theairbag were to be introduced into the AH-l and AH-64 to supple-ment the current restraint system s, it would be primarily toprevent injury in the severest of head strikes. All tests withairbags were designed to simulate the 35-degree impact as de-scribed in Table 3. Several tests were run with a preinflatedairbag to refine the experimental procedures, but they did notproduce any reportable results. Although LX6269 was a full-scale

34


40/45

airbag test, no manikin transducer signals could be processed.Results from 10 (4 Cobra TSU and 6 Apache ORT) airbag tests arepresented in Table 3 and in Appendix C, Volume II.In all airbag tests, the maninkin's head rebounded afterbeing stopped by the airbag and struck the armored seat. Thisrebound action is undes irable and would have been reduced withrefinement of the airbag deployment or the design of an airbagspec ifically for the AH-l or AH-64 cockpit interior. The second-ary (rebound) impact produced lower acceleration levels thanearlier interaction with the airbag or the underlying supportstructures. Generally, head contact with the airbag lasted morethan 15 ms, so the H IC as an injury assessm ent tool was notvalid. However, the HIC is reported here and was used only forthe purpose of com paring one test to another and not to predictinjury.The four Cobra TSU airbag tests (LX6270 through LX6273)produc ed cons istent results. A slight undersetting of amplifiergains caused the head acceleration signals to be clipped, as maybe seen in Appendix C, Volume II. As noted in Table 3, true peak

head accelerations may be slightly higher than those given forthe four TSU tests. The MA-6 in test LX6270 and MA-10 in LX6271appear to have locked and restricted the belt extensions to under5.9 cm (2.3 in). Data from tests LX6272 and LX273 were inclusivedue to unreliable string potentiometer signals. Howev er, angularpitch accelerations recorded in test LX6273 suggest the reel m ayhave failed to lock.The remaining six airbag tests (Table 3) were Apache ORTtests. Two of these tests were run at the lower crash pulseseverity (7 g, 9 m/s) to simulate the early portion of landinggear collapse during a crash. These were test conditions similar

to the seven nonairbag tests (LX6208 thru Lx6213, and LX6277)reported in the top half of Table 2. This enabled us to makedirect comparisons between the head strike parameters to deter-mine the effects of supplementing the restraint system with anairbag. The last four tests reported in Table 3 have no directcomparison in Table 2. The inertia reels (MA-lo) all lockedduring the ORT tests; however, belt extension appeared to beexcessive for all 25 g runs. This is particularly true forLX6280 where the belt extension was 15.8 cm (6.2 in) and headpitch acceleration was 11,440 rad/s'.In order to'evaluate the effect of the airbag on the headstrike, the four Cobra airbag tests were compared to the group offive nonairbag tests discussed earlier and presented in thebottom half of Table 1. The two groups simulated the same 35-degree impact angle, and the severity of the crash pulses

35


41/45

essentially were the same. In all runs except LX627 3, theinertia reels app eared to lock properly. Aside from minorvariations in the test cond itions, the primary difference betweenthe two groups was the presence of the airbag. Therefore, anyimprovement in the response parameters may be reasonably at-tributed to use of the airbag. A similar comparison was madebetween the two Apache airbag tests and the seven nonairbagtests.The small number of tests did not allow formal statisticalanalysis of the reduction of severity. How ever, the trend is soclear tha t some informal characterization of the improvement ispossible. To this end, the average values of three parameterswere compared: Peak head accelerations (g), the HIC, and theswings of head pitch accelerations (rad/s') and velocities(rad/s) at the instant of head strike. In using these param -eters, no injury prediction was made. Rather, these parameterswere used as indicators to assess the mitigating effects of theairbag on the severity of simulated head strike. The. averagevalue is defined simply as the sum of observed values divided bythe number of observations. No other statistics were derived

because of the small number of observations.The result of comparisons are presented in Table 7. Theaverage values were computed from results already presented inTables 1, 2, and 3. The reader may compute additional responsemeasures from the table. Regardless o f the response parameterused to compare tests with airbags to those without airbags, theairbag parameter wa s considerably lower. It is evident airbagsare effective in reducing the severity of guns ight head strikes.Conclusions

This study demonstrated that, during a mishap involving theCobra or the Apache attack helicopters, the copilot/gunner is atrisk for striking his head against the TSU in the Cobra or theORT in the Apache. This occu rs in spite of the proper use andfunctioning of the standard restraint system . Epidemiologicaland experimental data suggest the probab ility of striking thesighting system mainly is dependen t on the crash dynam ics and,particularly, on the longitudinal velocity at terrain impact.Aircraft roll or yaw at impac t may be influential in directingthe head trajectory away from the sighting system, and mayaccount for the relatively small percentage of ground impactsresulting in head strikes.

36


42/45

_--- -__ ._..._. .._--- ---Table 7.

Com parison of means of head response parametersof inertia reel tests with and without airbags.Test group and

improvementdue to airbagCobra TSU tests(')without airbag

Head Head Acceleration Velocitypeak injury pitch swing pitch swing(G ) criterion (rad/s') (rad/s)

141 871 12850 70.5

Cobra TSU tests(2)with airbag 47.8 170 3328 22.5

Improvement 66% 80% 74% 68%Apache ORT testst3) 59.9 93 9920 40.5without airbagApache ORT testc4) 13.8 31 1300 6.3with airbag

Improvement 77 % 67% 87% 84%

(') Group of five tests: LX6203, LX6204, LX6274, LX275, and LX6276.(2) Group of four tests: LX6270, LX6271, LX6272, an d LX6273.(3) Group of seven tests: LX6208 through LX6213, and LX6277.14) Group of two tests: LX6278 and lX6279.

Although it was hypothesized the use of an inertia reel thatlocked at a lower strap acceleration rate or one that sensed animpact would reduce the severity of head impact, these testsfailed to show an advantage in using one of these types ofmodified reels. Even when runs with technical difficulties inmeasuring strap extension were excluded, no clear pattern ofextension versus crash dynamics or reel type could be discerned.The variability in am ounts of extension for similar cond itions iseither due to stretch of webbing, reel pack down, or variation inthe rapidity of reel locking. In any case, these tests suggestthe MA-10 dual sen sing reel may not provide the solution toexcessive upper torso strap extension identified from crashinvestigations and other sled tests. Clearly, an inertial reelthat gives more consistent results should be developed and

37


43/45

qualified to anticipate dynamic conditions. Supplementing theimproved system with a passive system such as the airbag may berequired for optimum protection, particularly in special situa-tions such as the copilot/gunner positions in attack helicopters.The observations made in this preliminary study clearly showa reduction in head strike severity when an airbag is utilized tosupplement current restraint systems. No attempt was made tooptimize the airbag design, inflation param eters, or deflationrates. Further studies need to be accom plished to properlydesign an airbag system for use in Army helicopter cockpits. Webelieve this concept offers a significant potential for reducingcontact injuries in all survivable helicopter crashes and furtherdevelopment of the concept should be given priority.

Recommendations1. RecommendU.S. Army Aviation Systems Comm and nitiateresearch and development efforts to develop the airbag conceptfor use in Army helicopter cockp its to supp lement currently

available restraint systems.2. Triservice research efforts shou ld be directed towardinvestigating the dynamics of inertia reel lock activation.Several reports have documen ted excessive extension of uppertorso straps and cited this as a mechanism of injury in crashes.

38


44/45

ReferencesAdam s, B. H., and Hicks, J. E. 1979. Ensineerina analysis ofcrash iniurv in Army OH-58A ircraft. Fort Rucker, AL: U.S.Army Safety Center. USAS C4 79-l.Alem, N. M., Nusholtz, G. S., and Melvin, J. W. 1984. Head and

neck response to axial impacts. Proceedinas of 28th Stanpcar crash conference. Warrendale, PA: SAE Proceedings P-152, pp. 275-288.Bezreh , A. A. 1963 . Helicopter versus fixed-wing crash injuries.Aerosnace medicine. 34:11-14.Department of Transportation. National H iahwav Traffic SafetvAdm inistration Notice 9. 36 F.R. 4600, Occuoant crash orotec-tion--Head iniurv criterion. S6.2 of FMVS S 208.Haley, J. L., Jr. 1971. Analysis of U.S. Army Helicopter acci-dents to define impact injury problems. Linear accelerationof the impact tvne. Neuilly-sur-Seine, France: AGA RDCon-ference Proceedings No . 88-71, pp. 9-l to 9-12.Hicks, J. E., Adam s, B. A., and Shanahan, D. F. 1982. Analysisof U.S. Army mishap patterns. Imoact iniurv caused bv linearacceleration: Mechanism s, orevention an d cost. Neuilly-sur-Seine, France: AGARDConference Proceedings No. 322, pp.34-l to 34-12.Mattox, K. L. 1968. Iniurv exnerience in Army helicoDteraccidents. Fort Rucker, AL: U.S. Army Board for AviationAccident Research. HF 68-l.Mertz, H. J. 1984. Iniurv assessm ent values used to evaluateHybrid III resoonse measurem ents. USG 2264, part III,attachment I, enclosure 2. February.Muzzy, W. H., III. 1990 . Eva luation of air b ags in attackhelicopters - summ ary report. New Orleans, LA: Naval Biody-namics Laboratory, Enclosure 12, USAARLMIPR No. 89-04,28 September.Sand, L. D. 1978. Com parative injury patterns in U.S. Armyhelicopters. Ooerational helicoDter aviation medicine.

Neuilly-sur-Seine, France: AGARDConference Proceedings No.255, pp. 54-l to 54-7.Shanahan , D. F., and Shanahan , M. 0. 1989a. Injury in U.S. Armyhelicopter crashes October 1979 - September 1985. Journal oftrauma. 29:415-423.

39


45/45

Shanahan, D. F., and Shanahan, M. 0. 1989b. Kinematics of U.S.Army helicopter crashes 1980-1985. Aviation sDace andenvironmental medicine. 60:112-121.Society of Automo tive Engineers. 1988. Instrumen tation forimpact tests. SAE J211 JUL86. Recommendedpractice. SAEhandbook. Warrendale, PA: Society of Automo tive Engineers.

Documents

Usaarl Report No 91-6 Vol 1