ground collision severity study results and path...

Ground Collision Severity Study Results and Path Ahead

David Arterburn Director, RSESC

(256) 824-6846

[email protected]

http://www.uah.edu/rsesc

mailto:[email protected]

mailto:[email protected]

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

2

Collision Severity Taxonomy

3

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

4

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.”

5

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:

6

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)

7

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

8

Hybrid III ATD Tests

9

Comparison of Steel and Wood with Phantom 3

10

UAS Wood Steel

Test Weight: 2.69 lbs.

Impact Velocity: 49-50 fps

Impact Energy: 100-103 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%



• Prob. of head injury: 99-100%


Standards







• Prob. of head injury: 99-100%


Standards





11

𝑅𝑒𝑠𝑢𝑙𝑡𝑎𝑛𝑡 𝐿𝑜𝑎𝑑 𝐹𝑎𝑐𝑡𝑜𝑟 (𝑔)= 1.094 ∗ 𝑖𝑚𝑝𝑎𝑐𝑡 𝐾𝐸 (𝑓𝑡 − 𝑙𝑏𝑠)

12

Courtesy of Tim Wright Smithsonian Air & Space Magazine

13

𝑅𝑒𝑠𝑢𝑙𝑡𝑎𝑛𝑡 𝐿𝑜𝑎𝑑 𝐹𝑎𝑐𝑡𝑜𝑟 (𝑔)= 1.094 ∗ 𝑖𝑚𝑝𝑎𝑐𝑡 𝐾𝐸 (𝑓𝑡 − 𝑙𝑏𝑠)

Relating Material and Structural Characteristics to Operating Limits

16

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

17

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

18

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)

19

20

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

21

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

26

ground collision severity study results and path...

Documents