THE DEVELOPMENT OF DITCHING and WATER IMPACT DESIGN LIMITS

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THE DEVELOPMENT OF DITCHING and WATER IMPACT
DESIGN LIMITS
PRESENTED AT INTL CABIN SAFETY
CONFERENCE NOVEMBER 17, 2004 LISBON,
PORTUGAL DYNAMIC RESPONSE INC. (DRI) FEDERAL
AVIATION ADMINISTRATION (FAA-TC)
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SBIR WATER IMPACT PROGRAM

• PHASE I
• Feasibility of Hybrid and FEM Methodology
• PHASE II
• Perform Full Scale Tests, Model and Correlate
  (KRASH and MSC/DYTRAN)
• KRASH Model For Existing Scale Model Ditching
  test
• Evaluate FAR27/29 Water/impact/Ditching
  Regulations Compliance
• Develop Preliminary Water impact Design Limits
  With KRASH
• PHASE III
• Develop Military and Civil Helicopter KRASH
  Models
• Evaluate Correlation Techniques/Procedures
• Develop Design Criteria Design Envelopes (DLE)
  Procedures- Using KRASH
• --- Ditching and Water Impact
• --- Civil helicopters
• --- Military helicopters
• Recommend Ditching and Water Impact Design
  Criteria

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IMPACT ENVELOPES
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SIGNIFICANT QUESTIONS

1. Can modeling simulate /represent the significant
   aspects of full-scale impact and scale model
   ditching tests?
2. Can analytical modeling be an effective tool in
   the development of crash design criteria?

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ASPECTS OF WATER IMPACT AND DITCHING

• Kinematics Behavior
• Overall response
• Discrete location response
• Failures
• Design parameters
• Seat-occupant performance/tolerance
• Trends relationships

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FULL SCALE WATER IMPACT TESTS
1998 - 1999 Tests of UH-1H
Test S1 26 fps vertical
Test S2 28 fps vertical 39 fps longitudinal
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OVERALL RESPONSES KINEMATIC BEHAVIOR
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FLOOR ACCELERATION
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PRESSURE RESPONSE
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FLOOR PULSE
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FLOOR VERTCAL PULSES GROUND, WATER,
REGULATIONS
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SIGNIFICANT QUESTIONS

1. Can modeling simulate /represent the significant
   aspects of full-scale impact and scale model
   ditching tests?
2. Can analytical modeling be an effective tool in
   the development of crash design criteria?

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DESIGN CONSIDERATIONS-SEAT LOAD LIMIT
NO SEAT LOAD LIMIT
14.5G SEAT LOAD LIMIT
26 FPS VERTICAL WATER IMPACT
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TRENDS SEA STATE VS. CALM SEA
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S2/S1 Pressure Trend Comparison Analysis Vs.
Test
Resultant Velocity S1 Test 26 FPS S2 Test 48
FPS S2/S1 Velocity Ratio 1.85 S2/S1 KE Ratio
3.41
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TRENDS

• Correlation
• Sea State Levels
• S2/S1 Test Levels
• Pressure
• Acceleration
• Transfer Function (Accel. to Pressure)
• Filter Levels

• Design Envelopes
• Panel Failure
• Floor Acceleration
• Mass Item Response
• Occupant-Seat Response
• VS.
• Panel Strength
• Pitch Attitude
• Seat Load Limit
• Velocity Profile
• Sea State

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DITCHING COMPLIANCE
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DITCHING COMPLIANCE PROCEDURES

• Scale Model Testing
• - rigid, deficient, misleading, costly
• Similarity to Existing Designs
• - questionable basis
• Pressure Calculations
• - static flotation analysis
• Vertical Load Factor Calculations
• - stall speed, no sink velocity
• Procedures
• - under-estimate pressure acceleration

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What Exists Relative to Ditching Assessment
Capability

• Inadequate evaluation and compliance procedures
• KRASH modeling features that address significant
  issues, i.e. trends, sea state, nose-over,
  failures
• Analysis predictable within a level of acceptance
• Analysis simulation time efficient

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CURRENT DLE CONSIDERATIONSTAKE INTO ACCOUNT
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CURRENT WATER IMPACT DLE CONCEPT
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DLE-DITCHING APPLICATION
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KRASH/SOMR-HIC RESULTS
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APPLICABILITY TO FAR 25 TRANSPORT CATEGORY
AIRCRAFT

• FAR 25, FAR 27 and FAR 29 HAVE
• MANY SIMILARITIES
• Ditching Envelope
• Seat Dynamic Test Requirements
• Mass Item Retention
• Acceptance Criteria
• Compliance Procedures

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SUMMARY

• Balanced Test, Analysis, Design SBIR
• - F/S WI and Scaled Ditching Tests
• - Civil and Military Rotorcraft
  Models/Correlation
• - FAR 27/29 and Military Design
  Specifications/Compliance
• Development of Ditching Criteria and Design Limit
  Envelopes Based On
• - Occupant Seat-Restraint System Integrity
• - Structural and Mass Retention Integrity
• - In Excess of 300 Simulations Performed
• Applicability of DLE to Evaluate Design Strength,
  Operational Conditions, Acceptance Criteria, New
  Designs, FAR 25, 27, 29
• End Product Goal- Recommended Ditching and WI
  Design Criteria, DLE and Procedures

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The Fourth Triennial International Aircraft Fire
and Cabin Safety Research Conference