design of uav systems reliability, maintainability, supportability & safety © 2002 lm...

Design of UAV Systems

Reliability, Maintainability, Supportability & Safety © 2002 LM Corporation 12-1

Lesson objective - to discuss

Reliability, Maintainability, Supportability, and Safety

Expectations - You will understand the issues (benefits and penalties) associated with UAV supportability and safety.



Why Consider Supportability?

• Operations & Support and Safety are Key Cost Drivers for the Overall UAV System- Operations & Support (O&S) Represent the Largest Percentage

of the Life Cycle Cost (LCC)- Reliability & Maintainability Attributes of the Air Vehicle Drive

Support Manpower- Affordability Issues Due to High Attrition Rates Constrain UAV

Market Penetration (Military and Civilian)

• O&S and Safety Issues Need to be Seriously Addressed During Pre-Concept Design - It is Not Something That Can be Delayed- You Get What You Pay For



Definitions

Reliability The probability that an item can perform its intended function for a

specified interval under stated conditions. Mean Time Between Failures (MTBF) (ususally in terms of flight hours) Failure Rate (failures per unit time) Probability (expressed as a decimal or percentage)

Tasks and Responsibilities During Pre-Conceptual Design* Allocations Predictions Functional Failure Modes & Effects Analysis Design Reviews Trade Studies

* For purposes of this course, a discussion of the reliability issues and your proposed approach will suffice



Definitions

Maintainability The measure of the ability of an item to be retained or restored to a

specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures and resources, at each prescribed level of maintenance and repair. Mean Time to Repair – average of repair times Maintenance Manhours Per Flight Hour Crew Size – Average number of individuals required to accomplish the

maintenance action

Tasks and Responsibilities During Pre-Conceptual Design* Allocations Predictions Time Line Analyses (Combat Turns, etc.) Design Reviews Trade Studies

* For purposes of this course, a discussion of maintainability issues and your proposed approach will suffice



Definitions

Supportability The degree to which system design characteristics and planned

logistics resources, including manpower, meet system requirements. Direct Maintenance Manpower per Aircraft Logistics Footprint (# transport aircraft sorties to deploy squadron’s

support equipment, manpower and spares) Mission Capable Rate Not Mission Capable Supply (NMCS) Rate

Tasks and Responsibilities During Pre-Conceptual Design* Define Support (Maintenance & Supply) Concept Estimate Manpower; Sortie Generation Rates Define Deployment Concept & Predict Logistics Footprint Trade Studies

* Requirements for this course underlined



Support Locations

Main Base

Forward Base

Emergency Base



Support Concept

http://www.fas.org/man/dod-101/sys/ac/row/cl-327.htm

Contractor

Organic

http://www.fas.org/irp/program/collect/predator.htm



What Kinds of R&M Analyses AreExpected in Pre-Conceptual Design?

Parametric EstimatesParametric Estimates

Concept &Concept & Technology DevelopmentTechnology Development

System Development & System Development & DemonstrationDemonstration Operations & Operations &

SupportSupport

Production & Production & DeploymentDeployment

IOCOT&E

Supplier PredictionsSupplier Predictions

Component TestsComponent Tests

IntegrationIntegrationTestsTests

Flight TestFlight Test

R&M Predictions Fidelity Increase with Design FidelityR&M Predictions Fidelity Increase with Design Fidelity

• M Demos• Surges• Environmental Extremes• Military Maintainers

Field DataField Data

AssessmentsAssessmentsPredictionsPredictions

• Weight• Parts Count• Surface Area• Duty Cycle• Sortie Length • Part Stress

• Environ Mod & Sim• Thermal Surveys• FMEA/FMECA• PHM Mod & Sim• Virtual Human M&S

• Durability Tests• Growth Tests• Qual Tests

• End Users & Maintainers• Production Configuration

Acquisition & Life Cycle Phases

R&M Data Sources & Techniques



What Is It About UAVsThat Affects Supportability?

Size

CONOPS

Basing

Micro, Mini, or Larger? Proximity to Ground

Interface with Loading Equipment Access to Daily Servicing Points Engine Removal

Transportation / Deployment Considerations Hangar Space Refueling Times / Turnaround Times

Storage vs. Flying Deployment Timelines Optempo Crew Sizes Weapons

Self-Sufficiency Contractor Logistics Support Considerations Infrastructure



What Is It About UAVsThat Affects Supportability?

Endurance

GroundSegment

Airframe Life Inspection Criteria Consumables Redunancy / Mission Reliability Autonomous Refueling vs. Sizing for Range

Deployment of Ground Stations LOS vs. BLOS Comms Mission Planning for Satellite Coverage Coordination with ATC Coordination with Ground Crews

Design for Testability How Much Redundancy Can You Afford? How Much Safety Analysis Can You Afford? Approach to Support

Cost /Fleet Size



Air Vehicle Eliminates Man-Rated Systems

O&S Cost Reduction of 8% in Personnel Alone!

• No Egress Shop• Eliminate Survival Skill• Smaller, Less Costly ECS• No LOX Consumables• Less Support Equipment

Man-Rated Systems Are Eliminated Crew Station Instruments Cockpit Structure / Boarding Ladders Canopy Ejection Seat / Escape Provisions Throttle/Control Stick/Rudder Pedal Control Panels

Crew Station Environmental Controls Heating/Cooling Pressurization Defog

Oxygen System LOX or OBOGS Regulator

Emergency/Survival Equipment



Crew Station Benefits

Equipment Moved Into Ground Control Station Flight Instruments / Information Displays Data Recording

Reduced Environmental Qualification Testing No High “g” Testing Required Reduced Vibration Requirement (Maybe) No High Altitude Testing

Increased Reliability Some Equipment 2-5 Times More Reliable Less Manpower Required for Maintenance Cheaper to Implement Redundancy



Weapons Loading / Engine Removal

Proximity to Ground For Most UCAVs Complicates Weapons Loading Innovative Loading Schemes Can Mitigate Restricted Access

Consider Hoists; Alternate Lifting Devices X-45 Demo Uses Weapons Dolly and Ejectors Mounted on Weapon Robotic Loading May Help

Considered By Navy for Ships Engine Removal Also Challenging

Drop Down or Lift Out? Existing SE Sufficient?



Deployment and Transportation

Storable UAVs Can Be Airlifted in Individual Storage Containers USAF UCAV Concept is to Deploy via C-17 (See Demo Below)

Autonomous Aerial Refueling and/or Rearming May Allow Self-Ferry



This Study Assumed A Similar Level of Maintainability

Pilot Physical Limitations Limit Effective Sortie Length Endurance UAV Sortie Durations May Approach 48-60 Hours! Ground Operators Can Work in Shifts UAVs Have Potential to Remain Aloft Indefinitely

Requires Autonomous Refueling Technology 4 to 5 UCAVs Can Displace 24 Manned Fighters in 24-Hour CAP

Longer Sorties Mean Less Wear and Tear Cycle-Related Fatigue and Duty Cycles Reduced

80% of Fighter Failures are Constant on a Per-Sortie Basis Maintenance Manhours Per Flight Hour Reduction

Knee in Curve at Approximately 24 Hour Sortie Length

Endurance Benefits



0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0 24 48 72 96 120 144

Average Sortie Length, Hrs

MF

TB

M1

MFTBM1

MMH/FH

This Study Assumed A Similar Level of Maintainability

MFTBM1 - Mean Flight Time Between Maintenance (Inherent)MMH/FH - Maintenance Manhours Per Flight Hour

Long Endurance MeansFewer Sorties Per Flight Hour

• Assumes 80% of Failures are Constant on a Per Sortie Basis

• Manpower Eventually Reduces to a Constant to Retain a Minimum Number of Personnel of Each Specialty for All Shifts



Pilot Physical Limitations Limit Effective Sortie Length Endurance UAV Sortie Durations May Approach 48-60 Hours! Ground Operators Can Work in Shifts UAVs Have Potential to Remain Aloft Indefinitely

Requires Autonomous Refueling Technology

Longer Sorties Mean Less Wear and Tear Cycle-Related Fatigue and Duty Cycles Reduced

80% of Fighter Failures are Constant on a Per-Sortie Basis Maintenance Manhours Per Flight Hour Reduction

Knee in Curve at Approximately 24 Hour Sortie Length

Endurance Benefits



Preprogrammed Routes Using dGPS Accurate, Hands-Off Requires Site Survey, Detailed Mission Planning Likely Requires Deconflicted Ops with Other Aircraft

Remote Control By Ground Crew Good Ground Situational Awareness Adds Complexity to Air Vehicle Design

Remote Control By Ground Operator Good Ground Situational Awareness Minimal Impact on Manpower Hardware Intensive

Needs On-Board Camera

Ground Handling Options



Redundancy Exists for 3 Reasons: Safety Survivability Mission Reliability

Consider Life Cycle Cost Sensitivities Maintenance Savings vs. Increased Loss of Aircraft Consider Mission Reliability Requirements

For Flight Critical Systems (failure = crash): Generally required to fail operational/fail safe (at a minimum) Triplex Redundancy is Most Cost-Effective on $/Flight Hour Basis Extremely High Reliability (>10,000 hrs MTBF) or Extremely Low Cost

(<$1000/Channel) Are Required for Dual Redundancy to Be Cost Effective

For Mission Critical Systems (mission fails or degraded) Generally required to fail operational (albeit degraded) Typically back-up most mission critical systems (radios, GPS, etc)

Redundancy Considerations



Trade Studies Will Determine Level of Redundancy

Module Cost/Channel: $18,400Average Repair Cost: $6000 Average Sortie Duration: 4 .5 HoursUAV Unit Cost: $10 MillionCritical Failure Rate: 1/3 of MTBF

Redundancy Cost Trades

Redundancy vs. Cost

1.00

10.00

100.00

1000.00

10000.00

100000.00

1000000.00

1 2 3 4

Level of Redundancy

Co

st p

er F

ligh

t H

ou

r

MTBF = 2000

MTBF = 3000

MTBF = 5000

MTBF = 8000

MTBF = 10000



Manned Aircraft Pilots Maintain Proficiency By Flying Require Minimum of 30 Flight Hours/Month Most Flight Hours In Lifetime are for Training

UAV/UCAV Operator Interface Is Unique Actual vs. Simulated Flight Similar Keep UCAV In Storage Until War

Reduced Spares/Consumables Reduced O&S Costs Note – this ConOps is changing

as we speak

Training Concept



Next Subject

Review of RM&S Functions

UAV & UCAV RM&S Considerations Supportability Attributes Subsystem Considerations Manpower O&S Cost

UAV Safety Lessons Learned



UAV and Drone Experience

Mishaps Per 100,000 Flight Hours

Fighter* 4.5

Manned QF-106 Drones* 130Unmanned QF-106 Drones* 70

Pioneer UAV** 167Hunter UAV** 140Predator UAV** 27

*Class A Cumulative Mishap Rate, 1997**Loss Rate (non-combat)

Primary Cause of Drone Mishaps is Old Age and Structural Integrity Primary Causes of UAV Mishaps:

Non-Aviation Qualified Parts (Pioneer & Hunter) Inadequate Emergency Procedures Training / Lack of Concurrency Lack of Redundancy in Flight Critical Systems Inadequate Testing & Configuration Control



Attrition Cost vs. Flight Hours

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

50 100 150 200 250 300 350 400 450 500

Flight Hours, 1000s

Typical Manned FighterGeneral AviationLow Cost UAVHigh Cost UAV

Attrition Cost Comparison

Losses Per100K Flt. Hrs.

5.0

7.0

167

27

Cost PerVehicle

$25-50M

$200K

$1.0M

$3.0M

Typical Fighter

General Aviation

Low Cost UAV

High Cost UAV

Global Hawk Goal is 10 per 100K Flight Hours

Lower Unit Cost Does Not Necessarily Mean Lower Life Cycle Cost!

… and there’s a reason!



Carefully Weigh Risk When Considering Redundancy Establish Acceptable Mission Reliability Goals Trade Cost of Redundancy vs. Reduced Attrition Affordability is Usually Achieved at Higher Risk Recognize UAV/UCAV Mishap Rates Will Probably

Exceed Manned Tactical Aircraft Mishap Rates As a Minimum, Consider Redundancy for:

Data Links Flight Controls Propulsion System Controls

Utilize Mil-Spec or Commercial Aviation-Grade Parts Already Qualified for Operating Environment (Temperature, Altitude,

Vibration, EMI, etc.) Better Reliability May Obviate Need for Expensive Qualification Testing Expensive for a Reason

m of n

?

?

?

UAV Lessons Learned



Use Qualified Test Pilot During Testing Understands Aerodynamics & Engineering First Responsibility is to Save Aircraft Trained to React to Unexpected Events

Place Increased Emphasis on Operator-Vehicle Interface Provide Adequate Fault Annunciation to Operator

Must Be Immediately Recognized Should Indicate Appropriate Operator Response

Consider Operator Workload In Emergency Conditions Consider Operator Skill Level (Pilot, Novice, etc.) Segregate Houskeeping & Maintenance Functions from Flight Ops

Functions Train Emergency Procedures! (Especially for Flight Test)

Adequately Test Hardware Prior to First Flight End-to-End Comms Loop (Including AV Antenna Multipath) Hardware-In-the-Loop Testing is Critical

UAV Lessons Learned



Software Configuration Control Hazard Analysis Should Include Software Hazards A Software Change is a Configuration Change! Utilize Software-In-The-Loop Testing Automate Repetitive Functions to Alleviate Operator Fatigue and

Improve Safety Plan Adequate Schedule for Software Test

UAV Lessons Learned



How to Achieve Reliability

Simplification – Fewer parts means less things to fail Standardization – Quality and tolerances all match Stress/Strength Derating – Particularly for avionics Function Isolation – Improved mission reliability Packaging Design – Hermeticity, vibration isolation, etc. Redundancy – Judicious use! Producibility and Tolerance Evaluation – Quality issue Local Environment Evaluation – Avoid “hot” spots Sensitivities – Trade studies Drift and Degradation – Design for it or test for it Development – Test, test, test Reliability Design Checklists – Lessons learned



Empirical Analysis of Reliability Trends

0.1

1.0

10.0

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year of Initial Production Delivery

MF

HB

F (

Inh

ere

nt

)

5.0

EW = 30Klb3.0

7-9

HistoricalTrend

TREND: Reliability Doubles Every 15 YearsTREND: Reliability Doubles Every 15 Years• Newer TechnologiesNewer Technologies• Improved Manufacturing Processes (Quality)Improved Manufacturing Processes (Quality)• Increased Emphasis on Design for RM&SIncreased Emphasis on Design for RM&S

EW = 20Klb



UAV maintenance personnel

Parametric Data Shows Manpower Requirements are a Function of Aircraft Speed, Weight (EW + Wpay) and Type

• UAV Comparison- Global Hawk fits

overall manpower parametric

- Predator falls well outside other aircraft norms

• Use this parametric to estimate maintenance manpower required for your design projects

Maintenance personnel parametric

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 250 500 750 1000 1250 1500

Maximum speed (kts)

FightersTransportsBombersEWRecceUAV

Predator

Global Hawk



Homework

Assess RMSS for your project (1) What redundancy levels do you think are

appropriate the following subsystems - Flight control computer- Air vehicle up link- Payload down link

(2) From the internet, Janes or other sources pick a UAV that you think is closest to your project UAV- What are the maximum speed and empty and

payload weights?(3) Estimate the number of personnel required to

maintain itSubmit your homework via Email to Egbert by COB

next Thursday. Document all calculations

design of uav systems reliability, maintainability, supportability & safety © 2002 lm...

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