Assessment of the limits of signs of health and usage monitoring system for helicopter transmission

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Procedia Computer Science 00 (2019) 000–000

Procedia Computer Science 149 (2019) 252–257

ICTE in Transportation and Logistics 2018 (ICTE 2018) ICTE in Transportation and Logistics 2018 (ICTE 2018)

Assessment of the limits of signs of health and usage monitoring system forofhelicopter transmission Assessment of the limits signs of health and usage monitoring system for helicopter transmission Dmitry Nedelkoa Aleksandrs Urbahsb,*, Vladislavs Turkoc, Margarita Urbahab, ,

d b Kristīne Carjova Nagaraj Dmitry Nedelko , Aleksandrs Urbahsb,*, ,Pavithra Vladislavs Turkoc, Margarita Urbahab, d b Kristīne , Pavithra Kazan National Research Technical UniversityCarjova named after A.N.Tupolev, 55,Nagaraj Bol`shaya Krasnaya, Kazan, Russia a

a

a

b Institute of Aeronautics, Riga Technical University, Kalku str. 1, LV-1658 Riga, Latvia c AviatestUniversity LNK Ltd, Rēzeknes str. A.N.Tupolev, 1, LV-1073 Rīga, Latvia Krasnaya, Kazan, Russia Kazan National Research Technical named after 55, Bol`shaya d b Latvian Maritime Flotes University, Street, 12 kKalku – 1, LV Riga,Riga, LatviaLatvia Institute of Aeronautics,Academy, Riga Technical str.–1,1016 LV-1658 c Aviatest LNK Ltd, Rēzeknes str. 1, LV-1073 Rīga, Latvia d Latvian Maritime Academy, Flotes Street, 12 k – 1, LV – 1016 Riga, Latvia

Abstract Abstract The authors have developed a method that uses a probabilistic approach to determining the limits of signs of a helicopter transmission monitoring system during operation and servicing. This paper analyses the conditions of the reasonable The authors have developed a method thatdiagnostic uses a probabilistic the limits of stresses signs ofacting a helicopter determination of limiting values for critical signs by theapproach example to of determining displaying actual bending during transmission monitoring operation and servicing. This paper analyses the conditions of the reasonable the flight on the main rotorsystem shaft of during a single-rotor helicopter. determination of limiting values for critical diagnostic signs by the example of displaying actual bending stresses acting during the flight on the main rotor shaft of a single-rotor helicopter. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published by Elsevier B.V. This is open access article the license (http://creativecommons.org/licenses/by-nc-nd/4.0/) (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is an an open accessPublished article under under the CC CC BY-NC-ND BY-NC-ND license © 2019 The Authors. by Elsevier B.V.committee Peer review under responsibility of the scientific of the and Logistics Logistics 2018 2018 (ICTE2018). (ICTE2018). Peer review under responsibility of the scientific committee of the ICTE ICTE in in Transportation Transportation and This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the and scientific committeesystems; of the ICTE in Transportation and Logistics 2018 (ICTE2018). Keywords: Helicopter transmission; Health usage monitoring Unit failure Keywords: Helicopter transmission; Health and usage monitoring systems; Unit failure

1. Introduction 1. Introduction In the eighties of the last century, several flight incidents occurred with European and American helicopters both

due to the failure of the flight crews, control services and dispatchers and due to the failure of aviation equipment in In over the eighties of the last century, several flight incidents with European and American helicopters both flight water surface. In this regard, the question arose ofoccurred taking urgent effective measures to improve the safety due to the failure of the flight crews, control of services and dispatchers andelectronic due to thecompanies, failure of aviation in of helicopter flights. Thanks to the efforts European operators and the firstequipment specialized flight over water surface. In this regard, the question arose of taking urgent effective measures to improve the safety of helicopter flights. Thanks to the efforts of European operators and electronic companies, the first specialized * Corresponding author. Tel.: +371 67089990; fax: +371 67089968. E-mail address: [email protected] * Corresponding author. Tel.: +371 67089990; fax: +371 67089968. E-mail address: [email protected] 1877-0509 © 2019 The Authors. Published by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review©under of the scientific committee 1877-0509 2019 responsibility The Authors. Published by Elsevier B.V. of the ICTE in Transportation and Logistics 2018 (ICTE2018). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018).

1877-0509 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of the scientific committee of the ICTE in Transportation and Logistics 2018 (ICTE2018). 10.1016/j.procs.2019.01.131

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information diagnostic systems called Health and Usage Monitoring Systems (HUMS) (a system of monitoring working capacity and application) was created. Systems for monitoring the technical state of helicopters have been developed most intensively over the past 2025 years. At present, almost all the systems and assemblies of helicopters responsible for flight safety are monitored with their help. In forums and periodical scientific publications, questions of structural schemes and methodological foundations of system construction are widely discussed [1- 6]. HUMS algorithms and diagnostic techniques are applied not only to helicopter technology but also to unmanned aerial vehicles [7]. At the same time, such monitoring systems were initially oriented primarily towards the monitoring of the current state of helicopter transmission units (main and tail gear, transmission shaft supports, etc.). This is the main function they perform today, since the transmission is the most complex element in helicopter design. It is known that the largest percentage of helicopter crashes (up to 39%), according to statistics, is associated with the failure of helicopter transmission units. It is known that, at the stage of monitoring system development, the most important thing is to determine and establish the diagnostic signs of the technical condition of helicopter transmission units [1-3]. At the present time, several types of diagnostic signs are known. Among them are, for example, the parameters of high frequency vibrations, parameters of kinematometry, temperature parameters, oil pressure in the main gearbox oil system, etc. The main objective in the development of a monitoring system is to establish the threshold values of diagnostic signs at which appropriate decisions on further flight safety shall be taken in the course of operation. In case any diagnostic sign has reached its threshold value, a decision on the limitation of service life, extraordinary replacement of any component or removal of transmission unit from the operation shall be further made. As a rule, the overwhelming majority of diagnostic signs are not indicated on the cockpit display during the flight. The analysis of these signs is to be made after the completion of the flight. However, some critical diagnostic signs can be displayed on the display during the flight if it is required by safety conditions. It is known that, for example, monitoring the bending stresses of helicopter main rotor shaft with a hingeless hub in flight is a very important task. For this purpose, Eurocopter specialists have developed for the EC-145 helicopter a special system of measurements and indication of these stresses in the most loaded section of the main rotor shaft. 2. Probabilistic approach to determining the limits of signs of a helicopter transmission monitoring system during operation and servicing This paper analyses the conditions of the reasonable determination of limiting values for critical diagnostic signs by the example of displaying actual bending stresses acting during the flight on the main rotor shaft of a single-rotor helicopter. The analysis of sources [1-6] shows that the main purpose of the research associated with the development of advanced HUMS systems is their structural optimization and expansion of the range of parameters to be diagnosed. At the same time, the issues of the reliability of determining the limit values of the diagnosed signs mentioned in sources [1-3] are not discussed. Let us assume there is a process of bending stress change during the time of flight t in the most loaded crosssection of the main rotor shaft  (t) with some current actual value f. The current value f is a random variable. This variable has a random character due to several obvious circumstances. Firstly, there is objectively a spread of actual geometrical characteristics in the most loaded cross-section of the main rotor shaft due to the errors of serial production. Secondly, there is a spread in the mechanical properties of the material of the main rotor shaft due to the deviations of the percentage of alloying components of different casts and due to the tolerances of the heat treatment modes of parts. Thirdly, there are always a variety of meteorological conditions of flight and various peculiarities of piloting by one or another pilot. Let us assume there is a certain flight configuration (including takeoff or landing) which causes the highest level of actual stresses f in the most loaded cross-section of the main rotor shaft. Let us assume as well that there is a way of measuring these actual bending stresses, including the most loaded flight configuration. Of course, this requires setting a certain limiting value pv the exceeding of which entails rapid exhaustion of the fatigue life of the main rotor shaft and its possible destruction during the subsequent flight. Since this parameter or diagnostic feature is particularly important or critical, the indication of its current value on the cockpit display is necessary. Let us designate the current measured value f, which is permitted by the display (indicator), as 1pv.

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The actual current value f can be represented as a sum:

 f  m   ,

(1)

where mf is a mathematical expectation of bending stresses in the most loaded cross-section of the main rotor shaft during the flight configuration under study,  is a deviation of the actual value f from its mathematical expectation. Since the measurement of the actual value of bending stresses is performed, their measured value is determined by the following sum:

 i   f   m     ,

(2)

where  is an error of parameter measurement (deviation of the measured value from its real value). It should be noted that the magnitude  also has a random nature because all modern digital recording systems, in their turn, contribute additional errors. The most significant among these errors are shifts in time occurring due to the inaccurate synchronization of heterogeneous information streams as well as due to failure to take into account the sequence of sensors within a single data frame [8]. Thereby, the magnitude i is random as well. It is evident that the limit values of the parameters pv and pv in the general case cannot be equal due to the presence of the measurement error . To determine the allowable indicator values pv, we will use a probabilistic model similar to that proposed in studies [9, 10]. The above-mentioned probabilistic model is an all-purpose model and can be used in the description of the control processes of various technical and economic systems. As mentioned above, the range of permissible parameter f status with the upper limitation needs to be known: tol = (-∞; pv). At the same time, the upper limitation of the range of permissible measured value tol = (-∞; pv) shall be determined on the basis of the considerations below. Let us consider the following hypotheses. An event А1: the actual value f is within the permissible range f  tol. In case the value f is out of the permissible value range f  tol, an event А2 takes place. To determine the measured value i, a certain measuring model is always used. Then an event В1 will take place if i tol, when the value i determined using the measuring model is within the permissible value range. In case the measured value i is out of the permissible value range i tol, an event В2 takes place. Let us describe different situations in which the above-mentioned events occur. А1  В1 – the actual value and the value determined using the measuring model are within the permissible status range, and we have a reliable representation of the permissible current level of the parameter. А2  В2 – the actual value and the value determined using the measuring model are out of the permissible status range and this is confirmed by the monitoring system. А1  В2 – the actual values are within the permissible status range, but the display system shows that the permissible value pv has been exceeded. А2  В1 – the actual values are out of the permissible status range, but the display system does not indicate that the permissible value pv has been exceeded. The first two situations result in correct conclusions about the status of the system. However, the last two situations create a significant risk of making wrong decisions about the possibility of further operation of the helicopter. Let us determine the probability of the events А1  В2 and А2  В1 using the probabilistic model stated in books [9, 10]. The probability of false display system actuation is as follows: Рfa(А1  В2) = Рfa (f  tol ; i tol) = Рfa(f < pv; i > pv). Taking into account (1) and (2) for Рfa, we will obtain: Рfa(m + f < pv; m +  +  > pv) = Рfa(f < pv – m;  > pv – m – ) =

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Dmitry Nedelko et al. / Procedia Computer Science 149 (2019) 252–257 Author name / Procedia Computer Science 00 (2019) 000–000  pv  m

 





i pvm 

W ( ;  )d d 

255

(3)

The probability of omitting a dangerous situation with disastrous effects: Рpv(А2  В1) = Рpv (f  tol ; i  tol) = Рpv(f > pv; i < pv). Taking into account (1) and (2) for Рpv, we will obtain: Рpv(m +  f > pv; m +  +  <pv) = Рpv( f >pv - m;  <pv - m - ) =





 ipvm 

 1pv  m 



W ( ;  )d d 

(4)

In expressions (3) and (4), the function W ( ;  ) is a joint density of the distribution of the random variables  and . An assumption that the random variables  and  are independent is evident. Thus, we will obtain the following equality:

W ( ;  )  W ( ) W ( )

(5)

The graphical interpretation of the distribution of the random variables  and  as well as their limiting values for the situations under consideration are given in Fig. 1 where:  = pv - m and 1 = pv - m.

Fig. 1. Distribution densities of the random variables  and 

All random variables associated with the operation of technical systems as a rule conform to the normal Gaussian law of distribution. Assuming that this is true for the random variables  and , expressions (3) and (4) with account of (5) will be as follows:

1 Pfa  2

 pv  m



1  e s1

(   m  )2 2 s12





pvm 

1  e s2

( )2 2 s22

d d 

(6)

Dmitry Nedelko et al. / Procedia Computer Science 149 (2019) 252–257 Author name / Procedia Computer Science 00 (2019) 000–000

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1 Ppv  2





pvm

e



(   m  )2 2 s12

 pvm 



1  e s2

5

( )2 2 s22

d d 

(7)

where S1 and S2 represent the mean square deviation of the values  and . For the convenience of the numerical integration of equations (6) and (7), let us change the variables by analogy with a similar probabilistic task solution described in the book [11]. Here we will introduce new variables  pv  m   m  y1  y2  and, and designate the parameter C  . Then, expressions (6) and (7) will be as S1 S2 S1 follows:

where, a 

Pfa 

1 2

Pfv 

1 2

c

 

c

e

y2  1 2

e



b  ay

1

y2  1 2

b  ay1



e

y2  2 2

e

dy2 dy1

y2  2 2

dy2 dy1

(8)

(9)

 ipv  m S1 , b . S2 S2

The result of solving the system of equations (8) and (9), obtained by using the well-known numerical methods, is given in Fig. 2 in the form of nomograph for the parameters a, b and c. As we can see from Fig. 2, at the given probabilities Рfa and Рpv, as well as at the parameters of the distributions of the random variables m, S1 and S2, and at the given value pv, the value of the limit parameter pv can be determined.

Fig. 2. Nomograph for determining the parameters a, b and с: the probability of omitting a dangerous situation with disastrous effects (1- Ppv=1.5 ·10-1; 2- Ppv=10-1; 3- Ppv=10-2; 4- Ppv=10-3; 5- Ppv=10-4); the probability of the false actuation of the display system (6- Pfa=10-4; 7- Pfa=10-3; 8- Pfa=10-2; 9- Pfa=10-1;10- Pfa=2 ·10-1).

3. Conclusion Thus, it is possible to solve the problem of the proper determination of the maximum allowable parameter or diagnostic sign for indication in the cockpit when the predetermined limit of its actual value is known in advance.

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It should be noted that the above-mentioned method can be used not only for determining the limiting values for critical parameters requiring indication in the cockpit. The measurement procedure is always used to obtain reliable information for each diagnostic sign, so, accordingly, a record of unavoidable errors of measurement for each diagnostic sign is also required. Thus, a decision about exceeding or not exceeding its limiting values should be made also taking into account the upper (or lower) tolerance of the limit condition range tol, the limits of which can be determined by the method stated above. Acknowledgements This work has been supported by the European Regional Development Fund within the Activity 1.1.1.2 “Postdoctoral Research Aid” of the Specific Aid Objective 1.1.1 “To increase the research and innovative capacity of scientific institutions of Latvia and the ability to attract external financing, investing in human resources and infrastructure” of the Operational Programme “Growth and Employment” (No. 1.1.1.2/VIAA/1/16/104 “Development of Structural Health Monitoring System for In-flight Monitoring (FLY-SAFE)”) References [1] Hasty, J.C., K.W. Speaks, and J. S. Kennedy. (2009) “Comparison of HUMS benefits -A readiness approach”, in Proceedings of the American Helicopter Society 65th Annual Forum, May 27-29, Grapevine, Texas, 1789-1797. [2] Keller, J. et al. (2012) “AH-64D main transmission accessory drive spur gear Manufacturing, Volume 23, (2): 205-211.

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Dmitry Nedelko is a Senior Researcher in the field of strength and aircraft design. He graduated from Kazan National Research Technical University named after A. N. Tupolev (KAI) in 2013 and received Dr.sc.ing degree. He is an associate Professor of faculty of "Helicopters" in Kazan National Research Technical University named after A. N. Tupolev. His fields of research: improvement of the airworthiness rotorcraft, nonlinear mechanics of rod systems, applied hydrodynamics helicopters, fatigue strength. He is the author of two monographs, over 70 scientific papers and four patents. Under his leadership, prepared one candidate of technical Sciences. Participated in the execution of the work by grants of the Ministry of Education and Science of Russian Federation. Contact him at [email protected].