apres_cobem09 [modo de compatibilidade

8/6/2019 Apres_COBEM09 [Modo de Compatibilidade

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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



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



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.



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



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



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:



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



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



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.



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



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



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



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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