Qualification of Rotorcraft Seats by Modeling and Simulation Qualification of...Test Condition Peak Load Required (lbs) Seat Orientation 20 G's Forward 20*TW Aft Facing 20 G's Aft

NAWCAD_powerpoint_templateNAVAIR Public Release 2021-019; Distribution Statement A – “Approved for public release; distribution is unlimited”
Qualification of Rotorcraft Seats by Modeling and
Simulation 19 January 2021
Presented to: NARI Workshop # 3: DoD Considerations for Crashworthiness of eVTOL
Presented by: Aamir Jafri & Lindley Bark
NAVAIR Public Release 2021-019; Distribution Statement A – “Approved for public release; distribution is unlimited”
2NAVAIR Public Release 2021-XXX; Distribution Statement A – “Approved for public release; distribution is unlimited”
Objectives • Predict structural and occupant injury responses
with sufficient fidelity and accuracy to: Predict structural behavior including failures prior to
cutting metal Predict human injury criteria prior during design
iterations and for qualification • Above must be done with focus and speed to pace
and impact the design in order to be of value. • Benefits: Analytically-supported airworthiness determination
Reduced testing cost and schedule Greater insight during design process to diagnose and
correct issues early Opportunities to save weight while cost-effectively
possible
Source: MIL-S-85095A
Analyses PlanBuilding Block Approach was followed
Verification of Seat Performance
• Evaluation of structural behavior
• Evaluation of occupant motion • Evaluation of restraint efficacy • Evaluation of specified injury
criteria • Predict failures and identify at-
risk structural components • Inform design iterations • All of the above, prior to cutting
metal
Physical Testing Plan • Seat dynamic testing – 60 tests • Static testing (seat only) – 9 tests • Static testing (mounts) – 9 tests
Test Condition Peak Load Required (lbs) Seat Orientation 20 G's Forward 20*TW Aft Facing 20 G's Aft 20*TW Aft Facing 20 G's Forward 20*TW Side Facing 10 G's Up 10*TW N/A 25 G's Down 25*TW N/A 20 G's Forward, 10 G's Up, 14 G's Lateral 20*TW+10*TW+14*TW Aft Facing 20 G's Forward, 10 G's Up, 14 G's Lateral 20*TW+10*TW+14*TW Side Facing 20 G's Forward, 25 G's Down, 14 G's Lateral 20*TW+25*TW+14*TW Aft Facing 20 G's Forward, 25 G's Down, 14 G's Lateral 20*TW+25*TW+14*TW Side Facing
Seat Static Test Matrix
Seat Dynamic Test Matrix
Mount Static Test Matrix
Actual Testing Conducted • Dynamic testing – 60 tests • Static testing (seat only) – 9 tests • Static testing (mounts) – 9 tests
Seat Static Test matrix
Dynamic Test matrix
Mount Static Test matrix
Identification of load cases for Structural Risk
For the seat: 95th %tile Occupant was identified as worst case for structure
• Stresses were checked for potential failure locations Yielding (may or may not be a failure)
Rupture (failure)
30°
A/C Forward
A/C Forward
Restraint Optimization • Type A was a simplified restraint
Verified occupant excursion and integrity of the inertia reel brackets (IRB)
• Type B is an evolution of the new restraint Helped in containing the occupant – The IRB showed hot spots
• Type C was complex restraint with optimized load path Helped in containing the occupant and reduced risk of IRB failure
Restraint Webbing Optimization
• Optimized webbing used for Type B and Type C restraint to compare the strains on the IR bracket
• Rigid seat physical test conducted for load verification
Correlation - Restraints Test Model
Identify Structural Risks (example)
Clevis impacts the track fitting, 41% max strain. Failure is nearly certain
Clevis operating normally, 8% max strain
Structural behavior during crash
Identification of load cases for Occupant injury risk assessment
For Seat Performance and Occupant Risk • Explored the permutations of combined
vertical load cases. Altogether 12 different seat orientations with 4 different occupant sizes were evaluated
• Predict Energy absorber performance mitigating specific occupant injury
Combined Vertical 30Gs, 37 ft/sec, Aft facing seat
Pure Vertical 30Gs, 37 ft/sec
Combined Vertical 30Gs, 37 ft/sec, Side facing seat - Port
Combined Vertical 30Gs, 37 ft/sec, Side facing seat - Starboard
30° 10° 30° 10°
Performance of Energy Absorbers
• Lumbar spine load was within the limit
Dynamic Analysis - Setup
Correlation – Dynamic Analysis
Failure Prediction
Combined vertical load case Failure prediction of positioning pin
Test to model comparison with new pin design NAVAIR Public Release 2021-019; Distribution Statement A – “Approved for public release; distribution is unlimited”
Airframe Load Transfer - Results
Test to model comparison of reaction loads
• Input reaction loads used either from physical test or simulation (which ever has highest peak loads)
• Simulation completed prior to the physical test • Led to Airworthiness Determination
Outcome • Early identification of potential design issues • Model of the seat was kept current throughout the
program which allowed a lot of insight and flexibility during development
• Out of 60 Dynamic load cases only 21 were tested physically
• All Static load cases of seat were qualified by analysis
• Out of 12 Static load cases for floor and ceiling mounts only 2 were physically tested
• Significant amount of man hours were saved along with huge testing cost Estimated 6 months and $670K savings
Questions?
Crashworthy and Escape Systems Branch
Slide Number 1
Restraint Optimization
Performance of Energy Absorbers

Documents

Qualification of Rotorcraft Seats by Modeling and Simulation Qualification of...Test Condition Peak Load Required (lbs) Seat Orientation 20 G's Forward 20*TW Aft Facing 20 G's Aft