ground collision severity study results and path...
TRANSCRIPT
Ground Collision Severity Study Results and Path Ahead
David Arterburn Director, RSESC
(256) 824-6846
http://www.uah.edu/rsesc
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
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Collision Severity Taxonomy
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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.
Vehicle Striking
the Ground
Rotating
Components
Mass
Sources of
Ignition
Kinetic
Energy
Speed Materials
Battery Fuels
Blade
Stiffness
RPM Blade
Thickness Payload
Motor/Engine
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
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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.”
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http://jarus-rpas.org/publications
RCC Casualty Expectation for UAV Operating Areas
• Casualty Expectation formulation:
CE = PF*PD*AL*PK*S (# of fatalities per flight hour) Where:
CE = Casualty Expectation PF = Probability of Failure or Mishap per flight hour (# failures/flight hour) PD = Population Density (population/mile2) AL = Lethal Area of the Impact (ft2) PK = Probability of Fatality (usually assumed to be 1) S = Sheltering Factor (0 – 1; 0 = protective shelter, 1 = no protection)
• Lethal Area formulation:
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Reference: Range Commander’s Safety Council, Range Safety Criteria for Unmanned Air Vehicles Rationale and
Methodology Supplement; Supplement: Standard 3231-99, April 2001.
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)
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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
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Hybrid III ATD Tests
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Comparison of Steel and Wood with Phantom 3
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UAS Wood Steel
Test Weight: 2.69 lbs.
Impact Velocity: 49-50 fps
Impact Energy: 100-103 ft-lbs.
Test Weight: 2.69 lbs.
Impact Velocity: 52-54 fps
Impact Energy: 116-120 ft-lbs.
Test Weight: 2.7 lbs.
Impact Velocity: 52-53 fps
Impact Energy: 114-121 ft-lbs.
Motor Vehicle Standards
• Prob. of neck injury: 11-13%
• Prob. of head injury: 0.01-0.03%
Range Commanders Council
Standards
• Probability of fatality from…
- Head impact: 98-99%
- Chest impact: 98-99%
- Body/limb impact: 54-57%
Motor Vehicle Standards
• Prob. of neck injury: 63-69%
• Prob. of head injury: 99-100%
Range Commanders Council
Standards
• Probability of fatality from…
- Head impact: 99-100%
- Chest impact: 99-100%
- Body/limb impact: 67-70%
Motor Vehicle Standards
• Prob. of neck injury: 61-72%
• Prob. of head injury: 99-100%
Range Commanders Council
Standards
• Probability of fatality from…
- Head impact: 99-100%
- Chest impact: 99-100%
- Body/limb impact: 65-71%
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𝑅𝑒𝑠𝑢𝑙𝑡𝑎𝑛𝑡 𝐿𝑜𝑎𝑑 𝐹𝑎𝑐𝑡𝑜𝑟 (𝑔)= 1.094 ∗ 𝑖𝑚𝑝𝑎𝑐𝑡 𝐾𝐸 (𝑓𝑡 − 𝑙𝑏𝑠)
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Courtesy of Tim Wright Smithsonian Air & Space Magazine
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𝑅𝑒𝑠𝑢𝑙𝑡𝑎𝑛𝑡 𝐿𝑜𝑎𝑑 𝐹𝑎𝑐𝑡𝑜𝑟 (𝑔)= 1.094 ∗ 𝑖𝑚𝑝𝑎𝑐𝑡 𝐾𝐸 (𝑓𝑡 − 𝑙𝑏𝑠)
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Relating Material and Structural Characteristics to Operating Limits
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Knowledge of injury thresholds and UAS structural and aerodynamic behavior
enables development of safe operating envelopes.
Example Operating
Envelope
RCC Casualty Expectation Applied to Graduation Ceremony
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CE = PF*PD*AL*PK*S
Scenario CE (fatalities/flight hour) PF (#/flight hour)* PD (#/mile2) AL (ft2) PK (%) S (0-1) Conversion Factor (mile2/ft2)
Phantom 3 over Graduation Ceremony 5.62E-05 0.01 6282816.9 0.25 0.1 1 3.58E-08
Rigid Phantom 3 over Graduation Ceremony 1.12E-04 0.01 6282816.9 0.25 0.2 1 3.58E-08
Rigid Phantom 3 with Inexperienced Pilot 1.12E-03 0.1 6282816.9 0.25 0.2 1 3.58E-08
Large Flexible UAS over Graduation 1.35E-03 0.01 6282816.9 2 0.3 1 3.58E-08
Large Rigid UAS over Graduation 2.25E-03 0.01 6282816.9 2 0.5 1 3.58E-08
Large Rigid UAS with Inexperienced Pilot 2.25E-02 0.1 6282816.9 2 0.5 1 3.58E-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
Proposed Standard for Risk Assessment using Injury Severity
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Provided by Applicant
Provided by Applicant in Draft Form
Completed by Applicant or Representative
Completed Jointly with Applicant
Operator’s ManualOperational Procedures
Required H-V Capabilities
Resources available for CFD?
Is risk of penetration
or laceration acceptable?
Prevent 30% Chance of AIS 3 or greater
injury?
Vehicle Selection
Develop Initial H-V Boundaries
Identification and Evaluation of Residual Risk
Aircraft CAD Models
CAD Evaluation for CFD Analysis
Operational Risk Assessment
Penetration and Laceration Design
Modifications
Resultant Impact Load/Injury Analysis
CONOPS
Required Payload
Ballistic Characterization
Analyze/Test Modifications
Revise H-V Boundaries, Adjust Procedures
Flight Test
CFD Flow Field Simulation
Sharp points, edges, and small contact areas will be evaluated against the impact energy density threshold of 12J/cm2. Exceeding this threshold may be permissible based on a low likelihood of contact during impact.
(For draft ORA only)
Yes
No
No
No
Yes
Yes
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 2017-31 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 50th 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)
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Aircraft Failure
Dynamics Flight Test
Aircraft Failure
Dynamics Modeling
Simplified Impact
Testing
ATD Impact Testing
FEA HBM and BF
Modeling Cadaver
Impact
velocity,
angle, and
orientation
Correlation
data
Correlation
data
Test cases
and
calibration
data
Test cases
Calibration
data
Worst case
impacts for
validation
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
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Simplified Method
Impact KE (Ft-lbs.)
Injury Metric
Vehicle Energy
Transfer
Maximum
Impact KE
based on
CONOPS,
failure modes
and vehicle
characteristics
Unsafe operating
region with
increased injury
potential beyond
metric
Safe operating
region with
reduced injury
potential relative
to the metric
Simplified Method
Resultant
Acceleration
(g)
Impact KE (Ft-lbs.)
Injury Metric
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
Simplified Method
Probability of
an AIS3 or
greater
Concussion
Impact KE (Ft-lbs.)
Injury Metric
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
Simplified Method
Probability of
an AIS3 or
greater Neck
Injury
Impact KE (Ft-lbs.)
Injury Metric
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
Questions
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