Ground Collision Severity Study Results and Path Ahead. David Arterburn Director, RSESC (256)

Transcription

1 Ground Collision Severity Study Results and Path Ahead David Arterburn Director, RSESC (256)

2 2 Approach Development of a Taxonomy for Ground Collision Severity Identify hazardous vehicle attributes and associated physical properties Conduct Literature Search Document characteristics of various classes of UAS (materials, construction, etc.) Identify documented injury and damage mechanisms Identify injury and damage events documented among RC modelers Identify casualty and injury models/analysis, from various disciplines, used to evaluate injury probability and severity Conduct modeling/analysis/testing of suas collisions with humans Evaluate existing casualty and injury models/analysis methods for applicability to suas Evaluate mitigations to injury mechanisms

3 3 Collision Severity Taxonomy Vehicle Striking the Ground Kinetic Energy Sources of Ignition Rotating Components Mass Speed Materials Motor/Engine Payload Battery Fuels Blade Thickness Blade Stiffness RPM Payloads, batteries, and motors present unique challenges in that they are dense, and not likely to be made to come apart to dissipate impact energy. Material properties must be evaluated to determine risk of injury and damage for different types and constructions.

4 4 CONOPS, Injury Metrics CONOPS plays a large roll in defining the conditions where failures will occur Altitude and Speed effect impact KE Location defines population density and sheltering factors Operations involving Visual Line of Sight (VLOS) versus Beyond VLOS carry different operational risk Injury Metrics Manned aircraft metrics defined by fatalities and does not include ground fatalities Unmanned aircraft already eliminate fatalities of the flight crew Unmanned metrics are focused on the non-participating public Fatalities are critical to public acceptability What other injury metrics are needed for public acceptability? Equivalency Impact energies and risk to non-participating public will be similar to that of their manned counter parts Focus for study was driven to vehicles without manned equivalent masses and standards

5 5 Joint Authorities for Rulemaking of Unmanned Systems (JARUS) Working Group 6 Safety & Risk Assessment AMC RPAS.1309 Issue 2 Safety Assessment of Remotely Piloted Systems Focus on equivalency to manned aircraft certified under Part 23, Part 25, Part 27 and Part 29 based upon accident rates and number of failures Defines reliability targets and uses SAE ARP 4761 and 4754A safety assessment and Development Assurance Level (DAL) processes to show compliance Provides an approach for platforms that do not have equivalency to manned aircraft JARUS Guidelines on Specific Operations Risk Assessment (SORA) Version 1 Document Identifier JAR-DEL-WG6-D.04 Recommends a risk assessment methodology to establish a sufficient level of confidence that a specific operation can be conducted safely. It allows the evaluation of the intended concept of operation and a categorization into 6 different Specific Assurance and Integrity Levels (SAIL). It then recommends objectives to be met for each SAIL.

6 6 RCC Casualty Expectation for UAV Operating Areas Casualty Expectation formulation: CE = P F *PD*A L *P K *S (# of fatalities per flight hour) Where: Lethal Area formulation: CE = Casualty Expectation P F = Probability of Failure or Mishap per flight hour (# failures/flight hour) PD = Population Density (population/mile 2 ) A L = Lethal Area of the Impact (ft 2 ) P K = Probability of Fatality (usually assumed to be 1) S = Sheltering Factor (0 1; 0 = protective shelter, 1 = no protection) Reference: Range Commander s Safety Council, Range Safety Criteria for Unmanned Air Vehicles Rationale and Methodology Supplement; Supplement: Standard , April 2001.

7 7 Initial Framework for Injury Metrics Micro-UAS Advisory Rulemaking Committee made recommendations on impact and injury metrics Recommended energy density (KE per unit of contact area) as the metric for evaluating small UAS Energy density thresholds determined by industry consensus standard Consensus standards should not result in the probability of an AIS 3 or greater injury when hit by a UAS as defined by each performance category AIS Abbreviated Injury Scale developed by the Association for the Advancement of Automotive Medicine (AAAM)

8 8 Key Findings from the Ground Collision Severity Study Three dominant injury metrics applicable to suas Blunt force trauma injury Most significant contributor to fatalities Lacerations Blade guards required for flight over people Penetration injury Hard to apply consistently as a standard Collision Dynamics of suas is not the same as being hit by a rock Multi-rotor UAS fall slower than metal debris of the same mass due to higher drag on the drone UAS are flexible during collision and retain significant energy during impact Wood and metal debris do not deform and transfer most of their energy Payloads can be more hazardous due to reduced drag and stiffer materials Blade guards are critical to safe flight over people Lithium Polymer Batteries need a unique standard suitable for suas to ensure safety

9 Hybrid III ATD Tests 9

10 10 Comparison of Steel and Wood with Phantom 3 UAS Wood Steel Test Weight: 2.69 lbs. Impact Velocity: fps Impact Energy: ft-lbs. Motor Vehicle Standards Prob. of neck injury: 11-13% Prob. of head injury: % Range Commanders Council Standards Probability of fatality from - Head impact: 98-99% - Chest impact: 98-99% - Body/limb impact: 54-57% Test Weight: 2.69 lbs. Impact Velocity: fps Impact Energy: ft-lbs. Motor Vehicle Standards Prob. of neck injury: 63-69% Prob. of head injury: % Range Commanders Council Standards Probability of fatality from - Head impact: % - Chest impact: % - Body/limb impact: 67-70% Test Weight: 2.7 lbs. Impact Velocity: fps Impact Energy: ft-lbs. Motor Vehicle Standards Prob. of neck injury: 61-72% Prob. of head injury: % Range Commanders Council Standards Probability of fatality from - Head impact: % - Chest impact: % - Body/limb impact: 65-71%

11 Resultant Load Factor (g) = impact KE (ft lbs) 11

12 Courtesy of Tim Wright Smithsonian Air & Space Magazine 12

13 Resultant Load Factor (g) = impact KE (ft lbs) 13

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16 16 Relating Material and Structural Characteristics to Operating Limits Example Operating Envelope Knowledge of injury thresholds and UAS structural and aerodynamic behavior enables development of safe operating envelopes.

17 17 RCC Casualty Expectation Applied to Graduation Ceremony CE = P F *PD*A L *P K *S Scenario CE (fatalities/flight hour) P F (#/flight hour)* PD (#/mile 2 ) A L (ft 2 ) P K (%) S (0-1) Conversion Factor (mile 2 /ft 2 ) Phantom 3 over Graduation Ceremony 5.62E E-08 Rigid Phantom 3 over Graduation Ceremony 1.12E E-08 Rigid Phantom 3 with Inexperienced Pilot 1.12E E-08 Large Flexible UAS over Graduation 1.35E E-08 Large Rigid UAS over Graduation 2.25E E-08 Large Rigid UAS with Inexperienced Pilot 2.25E E-08 *Probability of failure is based on DJI analysis and accounts for material reliability and pilot experience as sources of in-flight failure Reference: Stockwell, W., Schulman, B., Defining a Lowest-Risk UAS Category, DJI Research LLC., 9 December 2016

18 18 Proposed Standard for Risk Assessment using Injury Severity No Operator s Manual Resources available for CFD? Required Payload CONOPS Required H-V Capabilities Operational Procedures Penetration and Laceration Design Modifications Provided by Applicant Provided by Applicant in Draft Form Completed by Applicant or Representative Completed Jointly with Applicant Yes Vehicle Selection Analyze/Test Modifications Aircraft CAD Models CAD Evaluation for CFD Analysis CFD Flow Field Simulation Develop Initial H-V Boundaries Is risk of penetration or laceration acceptable? Yes (For draft ORA only) Revise H-V Boundaries, Adjust Procedures No Operational Risk Assessment Identification and Evaluation of Residual Risk No Flight Test Ballistic Characterization Resultant Impact Load/Injury Analysis Prevent 30% Chance of AIS 3 or greater injury? Yes Sharp points, edges, and small contact areas will be evaluated against the impact energy density threshold of 12J/cm 2. Exceeding this threshold may be permissible based on a low likelihood of contact during impact.

19 19 What s Next? Continue research to refine metrics developed in Task A4 Assess injury potential of a broader range of vehicles Refine modeling effort to address more scenarios Develop a simplified test method for characterizing injury potential of suas Validate proposed standard and models using potential injury test data Period of Performance 1 Aug Jan 2019 (18 months) Performers University of Alabama in Huntsville Principal Investigator (Flight Test, Vehicle Dynamic Modeling, Metrics Analysis and Assessment, Overall Project Management) Wichita State University (Hybrid III 50 th Percentile Male ATD Testing and Human Body Modeling) Mississippi State University (Biofidelic Neck and Head Finite Element Model) Ohio State University (PMHS Testing) Virginia Tech University (Consulting on Human Injury)

20 20 Simplified Impact Testing Correlation data Aircraft Failure Dynamics Flight Test Correlation data Impact velocity, angle, and orientation FEA HBM and BF Modeling Worst case impacts for validation Cadaver Aircraft Failure Dynamics Modeling Test cases and calibration data Calibration data ATD Impact Testing Test cases

21 21 Three Methods of Compliance The following approaches will be investigated as part of the work Analysis Small vehicles Impact Energies less than 54 ft-lbs Simplified suas platforms less than 10 lbs and larger vehicles with parachutes Low cost testing to assess impact characteristics Flight test to demonstrate failure modes and impact KE Safety margins applied to apply conservatism Complete ATD Testing PMHS Testing Full human injury potential evaluated

22 Injury Metric Simplified Method Vehicle Energy Transfer Unsafe operating region with increased injury potential beyond metric Safe operating region with reduced injury potential relative to the metric Maximum Impact KE based on CONOPS, failure modes and vehicle characteristics Impact KE (Ft-lbs.)

23 Resultant Acceleration (g) Injury Metric Safe operating region with reduced injury potential relative to the metric Simplified Method Vehicle Energy Transfer Unsafe operating region with increased injury potential beyond metric Maximum Impact KE based on CONOPS, failure modes and vehicle characteristics Impact KE (Ft-lbs.)

24 Probability of an AIS3 or greater Concussion Injury Metric Safe operating region with reduced injury potential relative to the metric Simplified Method Vehicle Energy Transfer Unsafe operating region with increased injury potential beyond metric Maximum Impact KE based on CONOPS, failure modes and vehicle characteristics Impact KE (Ft-lbs.)

25 Probability of an AIS3 or greater Neck Injury Injury Metric Safe operating region with reduced injury potential relative to the metric Simplified Method Vehicle Energy Transfer Unsafe operating region with increased injury potential beyond metric Maximum Impact KE based on CONOPS, failure modes and vehicle characteristics Impact KE (Ft-lbs.)

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