The Evolution Of The Evolution Of Energy Absorption Energy Absorption

Systems For Systems For Crashworthy Crashworthy

Helicopter SeatsHelicopter Seats

The Fourth Aircraft Fire and Cabin Safety ConferenceThe Fourth Aircraft Fire and Cabin Safety ConferenceLisbon, PortugalLisbon, Portugal

November 15-18, 2004November 15-18, 2004

Originally Presented at the Originally Presented at the AHS 59AHS 59thth Annual Forum and Technology Display Annual Forum and Technology Display

May 6 – 8, 2003May 6 – 8, 2003Phoenix, ArizonaPhoenix, Arizona

..

S. P. Desjardins

Safe, Inc

OBJECTIVE AND OBJECTIVE AND PURPOSEPURPOSE

Objective – Trace Development of Objective – Trace Development of Energy Absorbing Systems – Early Energy Absorbing Systems – Early 1960’s to Present.1960’s to Present.

Purpose – Assess the Current State-Purpose – Assess the Current State-of-the-Art, Identify Any Areas of of-the-Art, Identify Any Areas of Concern, and Recommend Future Concern, and Recommend Future Efforts. Efforts.

APPROACHAPPROACH

ReviewReview Early Work and ConceptsEarly Work and Concepts Process and Rationale That Lead to the Process and Rationale That Lead to the

Different ApproachesDifferent Approaches Approaches Used by the Different Approaches Used by the Different

SuppliersSuppliers PresentPresent

Advanced ConceptAdvanced Concept Concerns About Current RequirementsConcerns About Current Requirements ConclusionsConclusions

NEED FOR CRASHWORTHY NEED FOR CRASHWORTHY SEATSSEATS

Established in the Late 1950’s and Established in the Late 1950’s and Early 1960’s by AvCIR Early 1960’s by AvCIR

Survivable Crash Environment was Survivable Crash Environment was DeterminedDetermined

Concluded that a Properly Concluded that a Properly Restrained Occupant Could Survive Restrained Occupant Could Survive the Resultant Loading in the X and Y the Resultant Loading in the X and Y Directions, but not in the ZDirections, but not in the Z

NEED FOR CRASHWORTHY NEED FOR CRASHWORTHY SEATS, Cont’dSEATS, Cont’d

Loading in the Z Direction Exceeded Loading in the Z Direction Exceeded Human Tolerance and Needed to be Human Tolerance and Needed to be LimitedLimited

Approach – Support the Occupant in Approach – Support the Occupant in a Seat that would Stroke when the a Seat that would Stroke when the Load Reached the Tolerance Limit Load Reached the Tolerance Limit (Limit Load)(Limit Load)

DECELERATION – TIME DECELERATION – TIME RELATIONSHIPS, Z RELATIONSHIPS, Z

DIRECTIONDIRECTION

DECELERATION – TIME DECELERATION – TIME RELATIONSHIPSRELATIONSHIPS

IDEALIZED IDEALIZED RELATIONSHIPRELATIONSHIP

Where: Where: S = stroke or deformation, in.S = stroke or deformation, in. G = gravitational constant (32.2 ft/secG = gravitational constant (32.2 ft/sec22 or 386.4 or 386.4

in. /secin. /sec22)) ttmm = time to G = time to Gmm, sec., sec. GGmm = Maximum deceleration, G = Maximum deceleration, G GGLL = Limit-load deceleration, G = Limit-load deceleration, G k = constant = Gk = constant = GLL/G/Gmm

0586.0,10417.022

1S 32

kk

k

kgtG mm

SEAT STROKE SEAT STROKE CALCULATIONCALCULATION

As an example, consider a triangular pulse As an example, consider a triangular pulse representing a change in velocity of 42 ft/ per representing a change in velocity of 42 ft/ per sec. with:sec. with: GGm m = 48 G= 48 G

TTmm = 0.027 sec. = 0.027 sec.

GGLL = 14.5 G = 14.5 G k = 14.5/48 = 0.30k = 14.5/48 = 0.30

Then from the above equation :Then from the above equation :

S = 11.02 in. S = 11.02 in.

AIRFRAME STROKE AIRFRAME STROKE CALCULATIONCALCULATION

Where:Where:

S = Stroke or distance traveled, ft.S = Stroke or distance traveled, ft. VV00 = Initial velocity, ft/sec. = Initial velocity, ft/sec. VVf f = Final velocity, ft/sec.= Final velocity, ft/sec. g = 32.2 ft/sec.g = 32.2 ft/sec.22

G = Average deceleration of airframe, 14.5 GG = Average deceleration of airframe, 14.5 G

S = 1.89 ft. (or 22.67 in.)S = 1.89 ft. (or 22.67 in.)

Gg

VV f

2S

220

CRASH LOAD CRASH LOAD ATTENUATOR CONCEPTSATTENUATOR CONCEPTS

Crushable ColumnCrushable Column Rolling TorusRolling Torus Inversion TubeInversion Tube Cutting or SlittingCutting or Slitting Tube and DieTube and Die Rolling/Flattening a Rolling/Flattening a

TubeTube Strap, Rod, or Wire Strap, Rod, or Wire

BenderBender Wire-Through-PlatenWire-Through-Platen

Deformable LinksDeformable Links Elongation of Tube, Elongation of Tube,

Strap, or CableStrap, or Cable Tube FlaringTube Flaring Housed Coiled CableHoused Coiled Cable Bar-Through-DieBar-Through-Die Hydraulic Hydraulic PneumaticPneumatic

FIXED LOAD ENERGY FIXED LOAD ENERGY ABSORBERS (FLEA)ABSORBERS (FLEA)

DYNAMIC OVERSHOOTDYNAMIC OVERSHOOT

FIXED LOAD DESIGN FIXED LOAD DESIGN CRITERIACRITERIA

Human tolerance is a function of Human tolerance is a function of time-under-load.time-under-load.

It was determined through analysis It was determined through analysis and test that to retain a tolerable and test that to retain a tolerable time-under-load environment, the time-under-load environment, the limit load, Llimit load, LLL, should be set at 14.5 , should be set at 14.5 G. G.

UH-60 BLACK HAWK UH-60 BLACK HAWK ARMORED CREWSEAT, ARMORED CREWSEAT, INVERSION TUBE E/AINVERSION TUBE E/A

EH101 FOLDABLE EH101 FOLDABLE TROOP SEAT, WIRE TROOP SEAT, WIRE

BENDER E/ABENDER E/A

BELL 230/430 PILOT SEAT, BELL 230/430 PILOT SEAT, CRUSHABLE COMPOSITE CRUSHABLE COMPOSITE

COLUMN E/ACOLUMN E/A

FRENCH/GERMAN TIGER FRENCH/GERMAN TIGER ARMORED CREWSEAT, ARMORED CREWSEAT,

METAL CUTTER E/AMETAL CUTTER E/A

A129 ITALIAN ARMORED A129 ITALIAN ARMORED CREWSEAT, TUBE AND DIE CREWSEAT, TUBE AND DIE

E/AE/A

BELL 230/305 MEDICAL BELL 230/305 MEDICAL ATTENDANT SEAT,STRAP ATTENDANT SEAT,STRAP

BENDER E/ABENDER E/A

V-22 OSPREY TROOP SEAT, V-22 OSPREY TROOP SEAT, TUBE AND DIE E/ATUBE AND DIE E/A

VARIABLE LOAD ENERGY VARIABLE LOAD ENERGY ABSORBERSABSORBERS

Fixed Load System is Designed for the Fixed Load System is Designed for the 5050thth Percentile Occupant Percentile Occupant

Effective Weight of the Lightly Clad 50Effective Weight of the Lightly Clad 50thth Percentile Occupant is 142.3 lb Percentile Occupant is 142.3 lb

Assuming a 60-lb Movable Seat Weight, Assuming a 60-lb Movable Seat Weight, the Limit Load,Lthe Limit Load,LLL, the Load at Which the , the Load at Which the Seat is Designed to Stroke is: Seat is Designed to Stroke is:

LLLL = G = GL L WWteffteff = (14.5) (202.3) = 2,933 lb = (14.5) (202.3) = 2,933 lb

VARIABLE LOAD ENERGY VARIABLE LOAD ENERGY ABSORBERS, Cont’dABSORBERS, Cont’d

Assuming the Same 60 lb Movable Seat Assuming the Same 60 lb Movable Seat Weight, the Total Effective Weight Range that Weight, the Total Effective Weight Range that the Load Limiting System Must Decelerate the Load Limiting System Must Decelerate are:are: 55thth- percentile: 172.6 lb- percentile: 172.6 lb

9595th th -percentile: 235.2 lb-percentile: 235.2 lb

With a Fixed Load Energy Absorber, the With a Fixed Load Energy Absorber, the Resultant Load Factors for the 95th - and 5th - Resultant Load Factors for the 95th - and 5th - Percentile Aviators are then:Percentile Aviators are then: GGLL9595thth- = 2,933/235.2 = 12.6 G- = 2,933/235.2 = 12.6 G

GGLL55thth = 2,933/172.6 = 17.0 G = 2,933/172.6 = 17.0 G

VARIABLE LOAD E/A VARIABLE LOAD E/A ADJUSTMENT RANGEADJUSTMENT RANGE

V-22 OSPREY ARMORED V-22 OSPREY ARMORED CREWSEAT, WIRE BENDER CREWSEAT, WIRE BENDER

VLEAVLEA

UH-1Y ARMORED UH-1Y ARMORED CREWSEAT, INVERSION CREWSEAT, INVERSION

TUBE VLEATUBE VLEA

FIXED PROFILE ENERGY FIXED PROFILE ENERGY ABSORBERS (FPEA)ABSORBERS (FPEA)

BELL 230/260 PILOT SEAT, BELL 230/260 PILOT SEAT, STRAP BENDER, FPEASTRAP BENDER, FPEA

LOAD-STROKE PROFILE VS LOAD-STROKE PROFILE VS CONSTANT LOAD, CONSTANT LOAD,

MILITARY REQUIREMENTSMILITARY REQUIREMENTS

UH-1Y TROOP SEAT, WIRE UH-1Y TROOP SEAT, WIRE BENDER, FPEABENDER, FPEA

ADVANCED SYSTEMSADVANCED SYSTEMS

OBJECTIVESOBJECTIVES To Combine the Advantages of the Fixed To Combine the Advantages of the Fixed

Profile (FPEA) with those of the Variable Profile (FPEA) with those of the Variable Load (VLEA) to Produce the Variable Load (VLEA) to Produce the Variable Profile Energy Absorber (VPEA)Profile Energy Absorber (VPEA)

To Automatically Adjust the Load Level To Automatically Adjust the Load Level of the Profile to Eliminate the Possibility of the Profile to Eliminate the Possibility of Human Error in Selecting the Loadof Human Error in Selecting the Load

OBJECTIVES, Cont’dOBJECTIVES, Cont’d

To Provide all occupants With To Provide all occupants With Comparable Protection Regardless Comparable Protection Regardless of Weight, 5of Weight, 5thth Percentile Female to Percentile Female to 9595thth Percentile Male Percentile Male

CONCLUSIONSCONCLUSIONS

The Following Concepts Suggested in the The Following Concepts Suggested in the Late1960’s and Early 1970’s for Use in Late1960’s and Early 1970’s for Use in Energy Absorbing Crashworthy Seats Have Energy Absorbing Crashworthy Seats Have Been Developed, Incorporated into Seats Been Developed, Incorporated into Seats and Are Now in Common Use Around the and Are Now in Common Use Around the World:World: Inversion TubeInversion Tube Wire BenderWire Bender Strap BenderStrap Bender Metal CutterMetal Cutter Tube and DieTube and Die

CONCLUSIONS, Cont’dCONCLUSIONS, Cont’d

The Evolutionary Process Has Produced:The Evolutionary Process Has Produced: Fixed Load Energy Absorbers (FLEA)Fixed Load Energy Absorbers (FLEA) Variable Load Energy Absorbers (VLEA)Variable Load Energy Absorbers (VLEA) Fixed Profile Energy Absorbers (FPEA)Fixed Profile Energy Absorbers (FPEA) Variable Profile Energy Absorbers (VPEA)Variable Profile Energy Absorbers (VPEA) An Advanced Energy Absorber Concept (AEA)An Advanced Energy Absorber Concept (AEA)

Equipped Seats Have Performed Well in Equipped Seats Have Performed Well in Helicopter Crashes.Helicopter Crashes.

CONCLUSIONS, Cont’dCONCLUSIONS, Cont’d A problem Likely Exists With Certification A problem Likely Exists With Certification

Requirements for Civil Seats.Requirements for Civil Seats. Efforts to Improve Efficiency Have Lead to Use Efforts to Improve Efficiency Have Lead to Use

of Fixed Profile Energy Absorbers.of Fixed Profile Energy Absorbers. Performance is Sensitive to Occupant Weight Performance is Sensitive to Occupant Weight

and Response Characteristics.and Response Characteristics. Civil Certification Requires Testing With Only Civil Certification Requires Testing With Only

One Size of Dummy, the 50One Size of Dummy, the 50thth Percentile. Percentile. This Process Can Result in a Seat Tuned to the This Process Can Result in a Seat Tuned to the

Characteristics of a Specific 50Characteristics of a Specific 50thth Percentile Percentile Dummy with disregard for its Performance with Dummy with disregard for its Performance with all Occupants of Different Sizes or Response all Occupants of Different Sizes or Response Characteristics.Characteristics.

COMPARISON OF FIXED COMPARISON OF FIXED PROFILE SHAPESPROFILE SHAPES

CONCLUSIONS, Cont’dCONCLUSIONS, Cont’d Since Systems are Now Being Developed Since Systems are Now Being Developed

That Take Advantage of the Unique That Take Advantage of the Unique Response Characteristics of the Test Response Characteristics of the Test Dummy, Dummy, All Development and Certification Testing All Development and Certification Testing

Should Include a Range of Dummy Sizes Should Include a Range of Dummy Sizes Representative of the Entire Spectrum Of Representative of the Entire Spectrum Of Occupant Weights Expected to Use the Seat.Occupant Weights Expected to Use the Seat.

Dummies Should be Developed and Used Dummies Should be Developed and Used that More Accurately Simulate the Human that More Accurately Simulate the Human Response to Rapid Loading in the Z Response to Rapid Loading in the Z Direction.Direction.