INTERNATIONAL DESIGN TEAM 2008 1

International Aircraft Design Team - Spring 2008

Large Crowd Surveillance UAV

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• Aircraft Design projects since 1997• Virginia Tech and Loughborough University• International collaboration– Communication:

• Video Conferences• E-mail• Project Management Websites• MSN, Skype

– Various Competition wins and awards from NASA General Aviation Design competitions.

International Design Team

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Requirements

• Cruise Speed: 50 knots

• Top Speed: 70 knots

• Range: 15 nautical miles

• Endurance: 8 hours (minimum)

• Service Ceiling: 10,000 ft (half fuel)

• Operational Altitude: 2000 - 3000 ft

• Minimum Turn Rate: 6 degrees/sec

• Climb Rate: 200 ft/min (sea level)

• MTOGW: 300 lb

• Payload: 45 lb desired

• Noise Levels: < 50 dBA at 200 ft

• 10 knot crosswind landing capability

• Conventional landing within a

50 ft by 250 ft

RELIABILITY“1 or fewer uncontrolled crashes per 100,000 hrs of operation”

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Importance of Reliability

• Airworthiness and Safety of Flight – Is it safe to fly overhead in large crowd situations ?– Is it expendable?– Is it capable of performing to specifications?

• Acceptance– UAV restrictions due partly to unreliable systems– Key to winning confidence of FAA to regulate UAV flight

• Lower long-term costs of UAVs• Increased availability of UAVs for missions

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Definition of Reliability• Reliability according to the DoD– “The ability of a system to perform its mission without

failure, degradation, or demand on the support system.”• Mean Time Between Failure (MTBF)– Period of time a repairable system/component will

perform between failures• Mean Time To Failure (MTTF)– Same as MTBF, but for non-repairable systems

• What is aircraft failure?– Failure to return to base

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Current UAV Reliability

F-16 (Manned) Mishap Rate: 3.5 per 100,000 hours

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Improving Reliability• Methods– Redundant Systems– Backup Systems– Scheduled Maintenance– Diversification

• Implications– Cost– Weight– Increase in maintenance

responsibilities

http://www.designation-systems.net/dusrm/m-155.html

RQ-5/MQ-5 Hunter

http://www.airforce-technology.com/projects/predator/predator6.html

MQ-9 Predator

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Main Failure Modes

1

1

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Summary of Key Reliability Issues

• Engine/Propulsive Failure

• Control/Communication Failure

• Structural Failure

• Human (Ground Crew) Error

Methodology Used

-Propulsion/Autopilot – Fault Tree Analysis

-Structure – Joint Probability Distribution Function (PDF)

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Fault Tree Analysis

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Structural Reliability