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The Evolution Of Energy Absorption Systems For Crashworthy Helicopter Seats The Fourth Aircraft Fire and Cabin Safety Conference Lisbon, Portugal November.

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Presentation on theme: "The Evolution Of Energy Absorption Systems For Crashworthy Helicopter Seats The Fourth Aircraft Fire and Cabin Safety Conference Lisbon, Portugal November."— Presentation transcript:

1 The Evolution Of Energy Absorption Systems For Crashworthy Helicopter Seats The Fourth Aircraft Fire and Cabin Safety Conference Lisbon, Portugal November 15-18, 2004 Originally Presented at the AHS 59 th Annual Forum and Technology Display May 6 – 8, 2003 Phoenix, Arizona. S. P. Desjardins Safe, Inc

2 OBJECTIVE AND PURPOSE Objective – Trace Development of Energy Absorbing Systems – Early 1960’s to Present. Objective – Trace Development of Energy Absorbing Systems – Early 1960’s to Present. Purpose – Assess the Current State-of-the-Art, Identify Any Areas of Concern, and Recommend Future Efforts. Purpose – Assess the Current State-of-the-Art, Identify Any Areas of Concern, and Recommend Future Efforts.

3 APPROACH Review Review Early Work and Concepts Early Work and Concepts Process and Rationale That Lead to the Different Approaches Process and Rationale That Lead to the Different Approaches Approaches Used by the Different Suppliers Approaches Used by the Different Suppliers Present Present Advanced Concept Advanced Concept Concerns About Current Requirements Concerns About Current Requirements Conclusions Conclusions

4 NEED FOR CRASHWORTHY SEATS Established in the Late 1950’s and Early 1960’s by AvCIR Established in the Late 1950’s and Early 1960’s by AvCIR Survivable Crash Environment was Determined Survivable Crash Environment was Determined Concluded that a Properly Restrained Occupant Could Survive the Resultant Loading in the X and Y Directions, but not in the Z Concluded that a Properly Restrained Occupant Could Survive the Resultant Loading in the X and Y Directions, but not in the Z

5 NEED FOR CRASHWORTHY SEATS, Cont’d Loading in the Z Direction Exceeded Human Tolerance and Needed to be Limited Loading in the Z Direction Exceeded Human Tolerance and Needed to be Limited Approach – Support the Occupant in a Seat that would Stroke when the Load Reached the Tolerance Limit (Limit Load) Approach – Support the Occupant in a Seat that would Stroke when the Load Reached the Tolerance Limit (Limit Load)

6 DECELERATION – TIME RELATIONSHIPS, Z DIRECTION

7 DECELERATION – TIME RELATIONSHIPS

8 IDEALIZED RELATIONSHIP Where: Where: S = stroke or deformation, in. S = stroke or deformation, in. G = gravitational constant (32.2 ft/sec 2 or in. /sec 2 ) G = gravitational constant (32.2 ft/sec 2 or in. /sec 2 ) t m = time to G m, sec. t m = time to G m, sec. G m = Maximum deceleration, G G m = Maximum deceleration, G G L = Limit-load deceleration, G G L = Limit-load deceleration, G k = constant = G L /G m k = constant = G L /G m

9 SEAT STROKE CALCULATION As an example, consider a triangular pulse representing a change in velocity of 42 ft/ per sec. with: As an example, consider a triangular pulse representing a change in velocity of 42 ft/ per sec. with: G m = 48 G G m = 48 G T m = sec. T m = sec. G L = 14.5 G G L = 14.5 G k = 14.5/48 = 0.30 k = 14.5/48 = 0.30 Then from the above equation : S = in. S = in.

10 AIRFRAME STROKE CALCULATION AIRFRAME STROKE CALCULATION Where: Where: S = Stroke or distance traveled, ft. S = Stroke or distance traveled, ft. V 0 = Initial velocity, ft/sec. V 0 = Initial velocity, ft/sec. V f = Final velocity, ft/sec. V f = Final velocity, ft/sec. g = 32.2 ft/sec. 2 g = 32.2 ft/sec. 2 G = Average deceleration of airframe, 14.5 G G = Average deceleration of airframe, 14.5 G S = 1.89 ft. (or in.)

11 CRASH LOAD ATTENUATOR CONCEPTS Crushable Column Crushable Column Rolling Torus Rolling Torus Inversion Tube Inversion Tube Cutting or Slitting Cutting or Slitting Tube and Die Tube and Die Rolling/Flattening a Tube Rolling/Flattening a Tube Strap, Rod, or Wire Bender Strap, Rod, or Wire Bender Wire-Through-Platen Wire-Through-Platen Deformable Links Elongation of Tube, Strap, or Cable Tube Flaring Housed Coiled Cable Bar-Through-Die Hydraulic Pneumatic

12 FIXED LOAD ENERGY ABSORBERS (FLEA)

13 DYNAMIC OVERSHOOT

14 FIXED LOAD DESIGN CRITERIA Human tolerance is a function of time-under- load. Human tolerance is a function of time-under- load. It was determined through analysis and test that to retain a tolerable time-under-load environment, the limit load, L L, should be set at 14.5 G. It was determined through analysis and test that to retain a tolerable time-under-load environment, the limit load, L L, should be set at 14.5 G.

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

16 EH101 FOLDABLE TROOP SEAT, WIRE BENDER E/A

17 BELL 230/430 PILOT SEAT, CRUSHABLE COMPOSITE COLUMN E/A

18 FRENCH/GERMAN TIGER ARMORED CREWSEAT, METAL CUTTER E/A

19 A129 ITALIAN ARMORED CREWSEAT, TUBE AND DIE E/A

20 BELL 230/305 MEDICAL ATTENDANT SEAT,STRAP BENDER E/A

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

22 VARIABLE LOAD ENERGY ABSORBERS Fixed Load System is Designed for the 50 th Percentile Occupant Fixed Load System is Designed for the 50 th Percentile Occupant Effective Weight of the Lightly Clad 50 th Percentile Occupant is lb Effective Weight of the Lightly Clad 50 th Percentile Occupant is lb Assuming a 60-lb Movable Seat Weight, the Limit Load,L L, the Load at Which the Seat is Designed to Stroke is: Assuming a 60-lb Movable Seat Weight, the Limit Load,L L, the Load at Which the Seat is Designed to Stroke is: L L = G L W teff = (14.5) (202.3) = 2,933 lb L L = G L W teff = (14.5) (202.3) = 2,933 lb

23 VARIABLE LOAD ENERGY ABSORBERS, Cont’d Assuming the Same 60 lb Movable Seat Weight, the Total Effective Weight Range that the Load Limiting System Must Decelerate are: Assuming the Same 60 lb Movable Seat Weight, the Total Effective Weight Range that the Load Limiting System Must Decelerate are: 5 th - percentile: lb 5 th - percentile: lb 95 th -percentile: lb 95 th -percentile: lb With a Fixed Load Energy Absorber, the Resultant Load Factors for the 95th - and 5th - Percentile Aviators are then: With a Fixed Load Energy Absorber, the Resultant Load Factors for the 95th - and 5th - Percentile Aviators are then: G L 95 th - = 2,933/235.2 = 12.6 G G L 95 th - = 2,933/235.2 = 12.6 G G L 5 th = 2,933/172.6 = 17.0 G G L 5 th = 2,933/172.6 = 17.0 G

24 VARIABLE LOAD E/A ADJUSTMENT RANGE

25 V-22 OSPREY ARMORED CREWSEAT, WIRE BENDER VLEA

26 UH-1Y ARMORED CREWSEAT, INVERSION TUBE VLEA

27 FIXED PROFILE ENERGY ABSORBERS (FPEA)

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

29 LOAD-STROKE PROFILE VS CONSTANT LOAD, MILITARY REQUIREMENTS

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

31 ADVANCED SYSTEMS OBJECTIVES To Combine the Advantages of the Fixed Profile (FPEA) with those of the Variable Load (VLEA) to Produce the Variable Profile Energy Absorber (VPEA) To Combine the Advantages of the Fixed Profile (FPEA) with those of the Variable Load (VLEA) to Produce the Variable Profile Energy Absorber (VPEA) To Automatically Adjust the Load Level of the Profile to Eliminate the Possibility of Human Error in Selecting the Load To Automatically Adjust the Load Level of the Profile to Eliminate the Possibility of Human Error in Selecting the Load

32 OBJECTIVES, Cont’d To Provide all occupants With Comparable Protection Regardless of Weight, 5 th Percentile Female to 95 th Percentile Male To Provide all occupants With Comparable Protection Regardless of Weight, 5 th Percentile Female to 95 th Percentile Male

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

34 CONCLUSIONS, 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 Helicopter Crashes. Equipped Seats Have Performed Well in Helicopter Crashes.

35 CONCLUSIONS, Cont’d A problem Likely Exists With Certification Requirements for Civil Seats. A problem Likely Exists With Certification Requirements for Civil Seats. Efforts to Improve Efficiency Have Lead to Use of Fixed Profile Energy Absorbers. Efforts to Improve Efficiency Have Lead to Use of Fixed Profile Energy Absorbers. Performance is Sensitive to Occupant Weight and Response Characteristics. Performance is Sensitive to Occupant Weight and Response Characteristics. Civil Certification Requires Testing With Only One Size of Dummy, the 50 th Percentile. Civil Certification Requires Testing With Only One Size of Dummy, the 50 th Percentile. This Process Can Result in a Seat Tuned to the Characteristics of a Specific 50 th Percentile Dummy with disregard for its Performance with all Occupants of Different Sizes or Response Characteristics. This Process Can Result in a Seat Tuned to the Characteristics of a Specific 50 th Percentile Dummy with disregard for its Performance with all Occupants of Different Sizes or Response Characteristics.

36 COMPARISON OF FIXED PROFILE SHAPES

37 CONCLUSIONS, Cont’d Since Systems are Now Being Developed That Take Advantage of the Unique Response Characteristics of the Test Dummy, Since Systems are Now Being Developed That Take Advantage of the Unique Response Characteristics of the Test Dummy, All Development and Certification Testing Should Include a Range of Dummy Sizes Representative of the Entire Spectrum Of Occupant Weights Expected to Use the Seat. All Development and Certification Testing Should Include a Range of Dummy Sizes Representative of the Entire Spectrum Of Occupant Weights Expected to Use the Seat. Dummies Should be Developed and Used that More Accurately Simulate the Human Response to Rapid Loading in the Z Direction. Dummies Should be Developed and Used that More Accurately Simulate the Human Response to Rapid Loading in the Z Direction.


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