Post on 07-Apr-2018
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Beatriz Juliana
Managing the Reliability of Unmanned Aerial System
Luiz Carlos S. Góes
Instituto Tecnológico de Aeronáutica
Aero & Mechanical Engineering Division
Mechatronics & Aerospace Systems Dynamics
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Discuss Subjects
The importance of UAS Reliability
Why to manage the Reliability of UAS
What should be managedWhat management tools are relevant and
How they can be implemented in UAS
Conclusion: What results are expected toReliability Management in UAS
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The importance of UAS Reliability Unmanned Aerial System tecnhology is set to play a major role in the
future of the aerospace industry.
Reliability is at the core of achieving routine access once it allows toassess the risk posed by UAS operation to people and property on theground, or other aircraft in the air.
No UAS is not 100% reliable. UAS Reliability depends on the designfeatures of its platform configuration and cost that pays for it.
Admit to UAS can fail, impacting its safety or mission capability.
Failures increase the maintenance costs and their effects restrict UASavailability, especially in military application
This work outlines methods of managing UAS Reliability over its lifecycle, serving as support to research groups that develop UAS astest-beds.
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Why to manage the Reliability of UAS Developing a management system for UAS must take into account the failures
probability of different components of UAS, and how these failures affect the
overall UAS Reliability, as shown below.
Internal State
External State
UAV Component
Exemple: Sensor fault may cause false or missing actions (alarm, turning-on and
off of devices). The changed data resultant from sensor fault is an error. When theerror produces missed data in value of the UAS variable, affecting UAS mission, isconsidered that a failure takes place. If the failure is not detected and accountedfor, the UAS may crash. These flaws must be identified and managed through andanalysis of risk mitigation. This analysis tell us what happens when a fault occurrs,
describing how and how much it matters.
Information
UAV behavior deviates from specification
Fig 1. Fault vs. Error vs. Failure
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What should be managed Reliability is the ability that UAS has to carry out and to maintain its mission in
routine circumstance, as well as to survive in hostile and unexpected
environment. In other word, reliability is the probability that an item canperform 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)
Maintainability is a measure of the ease and rapidity of UAS to be retained orrestored to a specified condition after failing when maintenance action isperformanced 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
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What should be managed Availability describe how a given UAS is able to perform its mission compared
to the number of times that is tasked to do, taking into account combinedaspects of its reliability, maintainability and logistic support.
Inherent Availability (AI) is the ideal state to check out the UAS availability, representing afunction of reliability (MTBF) and maintainability (MTTR). In this type of analysis includesonly corrective maintenance actions
Achieved Availability (AA) is similar to the Inherent Availability, but includes in its analysiscorrective and preventive maintenance actions (MTTR A);
Operational Availability (AO) is the availability of real experiences that takes place with theUAS in the field. In this type of analysis includes corrective and preventive maintenanceactions, logistic time, waiting time and administrative time.
Safety is defined as the absence of mishaps. Mishaps, in turn, meansignificant damage to UAS platform that need actions of extensive repair sothat UAS can operate again.
Safety is expressed in terms of Mishap Rate (MR);
Human Errors or mistakes cause system failure or increase the risk of failurefor the safe operation of UAS. A careful analysis of human-UAS recognizesboth humans and UAS can fail, and what are their effects on UAS mission. Itis possible to construct a set of analogues to reliability parameters forobtaining good UAS design with respect to human mistake, such as:
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What should be managed Susceptibility is measured as the
probability of hit, which includes
the probability of acquisition,detection, identification, tracking,launch, guidance, anddetonation.
Susceptibility
to being hit
Vulnerability
Given a hit
Survivability
(Effectiveness)
system’s design or performanceaffecting its ability to besurvivability.
Survivability is the ability of anUAS to avoid or withstand ahostile environment withoutsuffering an abortive orcatastrophic impairment of itsability to accomplish its designed
mission;
+ =
Fig 2.: Survivability is an essential
element of UAS Mission Effectiveness
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What management tools are relevant to
UAS Managing the Reliability of UAS consists in performing various tasks at each
stage of the life cycle, as shown in table 1.
STAGES TOOLS APPLICATION IN UAS
FRACAS Analysis of UAS field data
Aid in choosing the best design of the UAV platform
FMEA Aid to validate the design parameters of the UAS
DESIGN Failure Modes and Effects Analysis from UAS similar or previous versions
FTA Qualification and Validation of the UAS design
RELIABILITY Calculate RAMS parameters based on the UAS life data
FAULT PREDICTION Estimate the reliability or failures probability in UAS systems via RDB
MANUFACTURE ESS Remove latent failures of UAS
FMEA Identify faults in the UAS manufacture
FRACAS Data collection, analysis and corrective actions
OPERATION Highlight critical points that need improvements
FTA Assess the impact of changes introduced by UAS hardware and software
Investigate the causes of field failures, or accidents with UAS
MAINTENANCE FTA When we want to focus on a specific system failure
Assist in management activities for major COTS components of UAS maintenance
FMEA Aid the fault diagnosis processFRACAS Record of failure analysis and corrective and/or preventive actions in UAS
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How they can be implemented in UAS’ life cycle phase How to estimate the Reliability of UAS or its failure probability?
Fault Prediction is a process that can be used to quantitativelyestimate the reliability of an UAS design prior to its actualoperation. Once the UAS platform was designed, we canestimate its reliability and compared it with acceptable
,
number of components via Reliability Block Diagram (RDB),where reliability is calculated through series and / or parallelsystems, using the reliability or failure rate as parameter, as
shown in fig. 3 .
Fig. 3: For a series system of UAS operating successfully, all componentsmust be operate successfully.
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How they can be implemented in UAS’ life cycle phase How to not introduce UAS flaws or to minimize their occurrence?
Fault Prevention aims at preventing or minimizing the failure occurrence in the systemduring the UAS development and operation, and avoiding its fault reoccurrence in field,
driving to an improvement of UAS reliability and safety.FMEA FRACAS
General “proactive” “reactive”
Purpose affect the UAS design before launch correct problems after launch
Errors may occur – the potential errors
must be enumerated
have occurred – observed
errors are simply counted
Error rate is assumed is measured
Issues withtechnique
Is it complete? Modelscan be wrong.
All errors counted?Culture inhibitsreporting errors.
Can be combined with FTA FTA
Evaluate qualityof the technique
difficult – completeness,reasonableness of mitigations is qualitative
simple -measure error rate
FMEA and FTA are compatible tools of UAS risk analysis, being that the choice of proper tool depends on risk nature to be evaluated.However, FMEA considers only single failure in its analysis while FTA considers multiples failures, requiring a greater skill level than FMEA.
When an UAS is designed, the modes it might fail can be captured in a FTA and FMEA. After the UAS is launched to field operation, themodes in which the UAS has failed can be captured through FRACAS and this knowledge can be used to update the FTA of the UAS in study.
Table 2:Use of FTA, FMEA and FRACAS to detect faults in UAS
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How they can be implemented in UAS’
life cycle phase
How to find out hidden flaws in UAS prototypes or new design?
Environmental Stress Screening (ESS) aims at exposing, identifying
and eliminating weak components, workmanship defects, flaws ordefects, and other conformance anomalies which cannot be detectedand removed by visual inspection or electrical testing but which willcause UAS failures in the field.
O purpose of ESS is to compress a system’s early mortality period andreduce its failure rate to acceptable level as quickly as possible, as
shown in figure 4
t
InfantMortality
UsefulLife
Wear-out
Reliabilitymeasure
Durability measure
λ
ESS
Fig 4: Bathtube Curve for UAS electronic items
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How they can be implemented in UAS’ life cycle phase
How to develop UAS that maintains a safeoperation even when some faults take placein real flight conditions?
Fault Tolerance: Monitoring faults infeedback control system componentsis known as Fault Detection and
Fault
noise Disturbation
UAS
EstimationState or Output
Isolation (FDI).
FDI unit is a basic element of the faulttolerant control schemes. Faulttolerance aims at controlling the UAS
flight and mission in an uninterruptedoperation thus increasing the UASsurvivability and safety even after afault takes places.
Fig 5: Fault Tolerance
Residuals
Detection
Isolation
Accommodation
Keep onMission
CorrectedEstimate
N
Y
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Conclusion: What results are expectedto Reliability Management in UAS
No UAS is 100% reliable or safe.
Components failures must be expected on an UAS; The impossible really does happen!
The Reliability must be considered from the beginning of the UAS design.
It’s possible to introduce concepts about reliability managementapp e o e process o ec s on n e es gn, opera on, anmaintenance phases for UAS team starting from an overview of thesystem up to an analysis more specific of the system.
Obviously, the presented directives will have resulted differentdepending on the type of analyzed UAS, especially for parameters
of Reliability, Availability and Safety It is expected great most of UAS developers will be able benefit
with the directives presented considering the impact of reliability inthe design, development, operation and maintenance of UAS.
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An i n ?