RU2038991C1 - Method of estimation and maintenance of reliability of aircraft and their power plants during operation of aviation materiel - Google Patents

Abstract

FIELD: aircraft operation. SUBSTANCE: parameters which have direct bearing on reliability of structural members are selected from those which are continuously checked in flight; these parameters are systematized and margin of serviceability of structural members is determined by probability method, thus estimating their serviceability. In case serviceability is below preset limit, measures shall be taken to restore it. Specific feature of this method is as follows: real measured parameters are not compared with standard values but expected magnitudes of these parameters are compared and level of reliability is determined through probability determination which makes it possible to take corrective measures for restoration of aircraft serviceability during their operation. EFFECT: enhanced efficiency. 5 dwg

Description

 The invention relates to the operation of aircraft, for example, type Tu-154, can find application in enterprises and civil aviation institutions and in the Air Force.

 Here, aviation technology is understood as the entire variety of aircraft devices, their individual independent units and systems that form the aircraft systems and ensure their reliable operation.

 The operation of aviation equipment is understood to mean its intended use for flights for aircraft, taking into account their features and conditions. For engines, their functioning (running hours) in flight and on the ground, taking into account the maximum operating conditions. For touchdown bodies, the number and nature of landings, etc.

 Maintenance refers to the entire range of work and organizational and technical measures aimed at ensuring a given level of reliability of aviation equipment and flight safety. Maintenance includes all types of flight preparation, preventive and scheduled maintenance, storage, transportation, minor and medium repairs in airfield conditions without removing equipment from operation and without sending it to airlines for overhaul.

 During the operation and maintenance of aircraft, changes in its condition occur, which ultimately affect the reliability and safety of flights. In this case, inevitably there are two kinds of processes.

 The first objective process of state change, depending on the structurally perfect technology, on the influence of the environment, time, operating conditions and maintenance. It is determined by objective processes occurring in the elements of technology and is characterized by its transition from a healthy state to a faulty state. This transition takes place over time and is expressed in the accumulation of quantitative changes in parts and assemblies. Such quantitative changes that accumulate over time are manifested in the wear of the working surfaces of moving parts, the appearance of fatigue cracks in the fasteners, in the change in the operational characteristics of engines, etc. Under certain conditions, quantitative changes in the elements of aircraft lead to qualitative changes in the appearance of malfunctions and failures. . These malfunctions and failures are probabilistic in nature, which means they can be predicted.

 The second subjective process of changing the state of aviation technology. It also represents a sequential change in the state of technology over time during its operation and maintenance, but conditions that depend on entities using this technique. Such a process depends on the technology for preparing equipment for flights, on the technology for its maintenance, on the qualifications, experience and condition of the flight and technical personnel, on the organization of work in the operational unit. This process of changing the state of aviation technology is also probabilistic in nature and submits to analysis using the theory of probability metetas.

 Both processes are interrelated with mutually conditioned and together have an impact on the change in the state of aviation equipment, determining its reliability. At the same time, as follows from an analysis of the operating and maintenance experience of serial aviation equipment, the main process that determines the reliability of its elements is the first objective process of state change.

 The value of the actual state of the elements of the aircraft at each moment in time allows you to make decisions with the possibility of flying or terminating operation. In this regard, monitoring the state of the aircraft (glider), its power plant, various systems, controls, landing, etc. is a determining condition in assessing reliability and allows us to judge the safety of flights.

 The operation of domestic aviation equipment is carried out according to the so-called resource system, when the supplier, by setting a regulated operating time, guarantees a predetermined level of reliability. Operation of aircraft in excess of the specified resource is not allowed.

 All types of resources are guaranteed overhaul and technical or designated resources (full service life) are established on the basis of calculations, bench tests and other tests, statistics on the operation of similar devices and analysis of the level of reliability during its operation time.

 After the development of the overhaul resource, aircraft equipment (aircraft, engines, other independent elements) are decommissioned and sent for overhaul, after which a new overhaul resource is assigned. However, the overhaul in the conditions of an aircraft repair enterprise is associated with the removal of equipment from service for a long period and at high cost.

 During major repairs, all components and critical structural parts are disassembled, inspected and fault-tested, elements are replaced with new or reconstructed ones, additional verification, assembly and testing of individual units and the aircraft as a whole.

 After major repairs for the aircraft, its power plant (engine) and other components, a new overhaul life is established, which is usually less than the previous one.

 After the development of the newly installed overhaul resource, the aircraft enters the second overhaul. The overhaul cycle is repeated until a full technical or designated resource is developed.

 Since all types of resources, especially the first overhaul resource, are approximate, experimentally set and assigned operating (operating hours) times, it often turns out that overhauling the aircraft as a whole, its individual components, for example, the engine, is premature and impractical. Inspection of units, assemblies and individual parts during overhaul often shows their full conditioning and the possibility of further operation until the next overhaul. This is the main drawback of operating aviation equipment for the designated resource, leading to high costs, and this is what necessitates the search for ways to more advanced and more economical methods of operation.

 There is a known method of operating aircraft in a state where the operation process is not limited by the resource, but lasts either until a malfunction occurs, or until the time when, based on the results of ongoing objective monitoring and analysis of the state of technology, it is necessary to terminate its operation and carry out major repairs.

 This method is implemented by a number of foreign airlines (see the Guide for Airlines and Manufacturers on Planning Aircraft Maintenance Programs. Conference Materials in Zurich, 1981).

 The Guide for Airlines contains techniques for analyzing the state of aircraft systems and power plants (Section A) and techniques for analyzing the state of structural elements of a glider (Section B).

 Although the method of operation is more progressive as compared to a fixed resource (it allows minor and current repairs without taking the aircraft out of service for a long time without a smooth overhaul, which becomes an exception, which is used mainly after damage), but it requires a large amount and high reliability of information on the state of the elements of the aircraft for making an informed and correct decision on further operation or on rem ont.

 The information received during the flight, recorded by systems similar to MSRP, allows us to judge the level of individual parameters of the aircraft and engine, but not their reliability levels. We need generalized information that does not indicate a failure, but a decrease in the reliability level, when measures can still be taken to prevent a failure.

 Such generalized information can be obtained about the state of the airframe, power plant (in particular, the state of the engine), various systems, controls, landing bodies, etc., having current values of the control parameters of the nodal control based on the synthesis of measurement methods already known and used in aviation flight.

 There are also known methods for predicting changes in the reliability of aircraft (see, for example, Andreev N.N. et al. Engineering and aviation service and the operation of aircraft, edited by Fedyaev N.M., ed. VVIA named after N.E. Zhukovsky, 1970 , p. 190-194).

 They are based either on the analysis of changes in the statistical characteristics of reliability (λ-characteristics), or on the analysis of changes in the parameters of specific elements of the aircraft. To obtain λ-characteristics, a large amount of statistical data is needed for many objects of the same type, which, in turn, is associated with the long accumulation time of these data and does not allow us to evaluate the reliability of a single object. Analysis of changes in the parameters of a particular structural element gives an objective assessment of reliability at the time of control, but does not indicate the timeliness of such control. He may be late. In addition, it is difficult and economically unprofitable to check power components under operating conditions without the need.

 When operating aircraft, it is important to have information in the initial period of the occurrence of a malfunction long before a failure occurs. It is important to have a parameter that would respond to any changes and anomalies in the operation of the equipment caused by the appearance of a malfunction, although in one of the structural units. There should also be a sufficiently high reliability of such information.

 If we obtain from the calculations or experimentally during bench tests the maximum permissible values of any quantities characterizing the reliability (as the probability of failure-free operation) of a part, assembly or device as a whole, or values characterizing the maximum permissible deviations from the calculated value, then, using the theory probability, you can get a way to assess the reliability of aircraft when operating it as it is.

 The proposed method allows a probabilistic way to assess the level of reliability of even a single object of aircraft at any time during its operation. Based on the use of existing methods and means of control currently in use in operation, it allows you to quickly determine the operating margin and establish the need for preventive measures (targeted inspections, inspections, minor and ongoing repairs) in order to maintain a given level of reliability and ensure flight safety. It is this goal, i.e. operational assessment of the reliability level of parts, components and systems and determining the need for preventive measures, and pursues the proposed method.

The proposed technical solution is illustrated by the following graphic materials, in which in FIG. 1 shows a graph of the distribution density of the value of x (function f (x)); in FIG. 2 graph of the distribution density of the value of y (function f (y)); in FIG. 3 graph of the distribution density of the value of z (function f (z)); in FIG. 4 is a graph of the allowable failure rate q (t)) and the health margin K; in FIG. 5 is a graph for determining the minimum maximum permissible value of K with an acceptable probability of failure q (t) 10 ^-7 .

 If the limit (maximum permissible) value of a control parameter is denoted by y, its actual value is x, then the safety factor is z y x.

 As a control parameter for an airplane, there can be the number of maximum permissible overloads, the number of cases of occurrence of the maximum permissible vibration levels, etc.

 You can also take into account the number of landings.

 For the engine, you can use the number of exits to take-off mode and the total operating time in take-off mode. You can use the level of decrease in operational parameters, for example, reducing the power of a free turbine, etc.

 All these control parameters y, that is, their maximum permissible values, are determined in advance during the development of the aircraft or its components and are then used to assess the state of technology in operating conditions.

 It is clear that the quantities x and y are random. From probability theory it is known that random variables are usually characterized by certain distribution laws (See Smirnov N.V. and Dunin-Barkovsky I.V. Course in probability theory and mathematical statistics. M. Nauka, 1965, pp. 133-156).

и

математические ожидания величин х и у.Most often, this is the normal distribution law. If we assume that x and y obey the normal distribution law, then the distribution density of these quantities can be expressed by the functions f (x) and f (y), respectively, and presented in the form of graphs shown in FIG. 1 and FIG. 2 where

and

mathematical expectations of x and y.

 Since both the x and y values are random, then the value z will also be a random value and also obeying the normal distribution law. Then we can also represent the probability density of z in the form of a graph of the function f (x). Figure 3.

 Here z is the margin of health. It must be greater than zero.

математическое ожидание величины z.

the mathematical expectation of z.

 For z <0, a failure is possible and the declared level of reliability is not guaranteed. You can set an acceptable level of health margin.

·l

где dz

дисперсия или среднее квадратичное отклонение величины z;
dx и dy средние квадратичные отклонения величины х и у соответственно.It is known that in the case of the normal distribution law, the probability density is expressed by the dependence
f (z)

L

where dz

variance or standard deviation of z;
dx and dy are the mean square deviations of x and y, respectively.

 The probability of failure, that is, the probability that z will be less than zero (see Fig. 3) can be expressed by the integral determining the shaded area, i.e. failure area, i.e.

f(z)dz

·l

dz
Этот интервал по существу дает вероятность отказа, и если его вычислить, то легко определяется и величина надежности, т.е. вероятность безотказной работы P(t), так как
P(t) 1 q(t).q (t)

f (z) dz

L

dz
This interval essentially gives the probability of failure, and if it is calculated, then the reliability value is easily determined, i.e. probability of uptime P (t), since
P (t) 1 q (t).

 However, this integral is non-tilting and can be replaced by the Laplace function, which is close in nature to this integral.

=

l

dt
Эта функция имеет следующие особенности:
а) она четная, т.е.The Laplace function of the probability density f (z) can be represented by this expression:

=

l

dt
This feature has the following features:
a) it is even, i.e.

-

= -

б) если аргумент этой функции

стремиться к нулю, то сама функция

стремиться к

.

-

= -

b) if the argument to this function

tend to zero, then the function itself

strive to

.

Функция Лапласа табулирована, ее значения даются в таблицах, то есть, зная величину аргумента

,можно из таблиц получить значение функцию Лапласа

(см. упомянутый ранее курс теорию вероятности и математической статистики, с. 142-145 и с. 466-467).Using the Laplace function, the formula for the probability of failure can be written as
q (t)

The Laplace function is tabulated, its values are given in tables, that is, knowing the value of the argument

, you can get the value of the Laplace function from the tables

(see the previously mentioned course probability theory and mathematical statistics, pp. 142-145 and pp. 466-467).

 The last formula for the probability of failure is easily converted and reduced to a form that is convenient for use.

-1

= β(k-1) Тогда
q(t)

Φ [β(k-1)] здесь β

по существу является коэффициентом качества процессов и определяется рассеивание случайных величин;
K

характеризует запас работоспособности устройства или его элементов.The argument of the Laplace function is converted as follows:

-1

= β (k-1) Then
q (t)

Φ [β (k-1)] here β

it is essentially a quality factor of processes and the dispersion of random variables is determined;
K

characterizes the health margin of the device or its elements.

 For example. During control static tests, several identical parts, for example, attachment points of wing consoles or engine mounts, show signs of permanent deformation only at a load that is many times repeated and exceeds the calculated one. It is known that permanent deformation in operation is unacceptable. With an increase in load, signs of permanent deformation are detected with fewer loads. This makes it possible to determine the mathematical expectation Y and the variance dY of the permissible number of loads at various loads and obtain the initial data for assessing the operational margin of the structural element. A tabular or graphical processing method can be used here. In the latter case, the product nY is plotted along the ordinate axis, and the product Y along the abscissa axis, where n is the coefficient of multiplicity of the calculated load (n 1,2,3,), and Y is the number of loads at which signs of permanent deformation are detected.

 Overloads that accidentally occur during flights in a turbulent atmosphere, during rough landings, etc., may exceed the allowable overloads in operating conditions, but with a small number of them they do not always lead to the appearance of residual deformations. This is taken into account in the proposed method.

/dz)
Эта зависимость, как уже указывалось, легко приводится к виду, удобному для вычислений с использованием таблиц функции Лапласа, то есть:
q(t) 0,5 Φ[β (k-1)]
где β=

/dz; K=

/

; dz

Наконец, уровень надежности определяется как
P(t) 1 q(t).All overloads recorded in each flight are taken into account. The following is a table or graphical processing method. In the latter case, the product of vertical overload n _y by the number of loads X (i.e., n _y X) and the number of loads X by the abscissa axis are plotted along the ordinate axis. This allows us to obtain the mathematical expectation X and the variance dx of a possible residual deformations and evaluate the probability of failure
q (t) 0.5 Φ (

/ dz)
This dependence, as already indicated, is easily reduced to a form convenient for calculations using tables of the Laplace function, that is:
q (t) 0.5 Φ [β (k-1)]
where β =

/ dz; K =

/

; dz

Finally, the level of reliability is defined as
P (t) 1 q (t).

 If this reliability value is less than the established value, then this is a signal to check for the possible occurrence of residual deformations of the parts mentioned and their possible replacement.

 In a similar way, you can evaluate the performance of other elements of the aircraft. In this case, the capabilities and effectiveness of the method will increase with an increase in the number of controlled parameters, and its efficiency depends on the degree of computer use.

) до некоторых значений, которые должны быть больше единицы, используя таблицы функции Лапласа и принимая допустимые значения вероятностей отказов, строят такой график (см.фиг.4): q(t) Φ (k, β).For β const, it is possible, given various values (K) of 1 (when q (t)

) to some values, which should be greater than unity, using the tables of the Laplace function and taking the acceptable values of the failure probabilities, construct such a graph (see Fig. 4): q (t) Φ (k, β).

 In this case, it is convenient to construct the function q (t) on a logarithmic scale.

 Having such a schedule, you can use it to assess the reliability of the device: P (t) 1 q (t).

.Let, for example, let the admissible probability of failure q _add (t) 10 ^-7 be specified, then, knowing the operating conditions of the device, its element or, finally, one of the most critical part, determine its quality factor β ′

.

 It is known from the theory of probability and the practice of assessing reliability that the quality factor β must be at least 6, then the requirement of a sufficiently high level of reliability is satisfied.

Further, according to the well-known schedule (see Fig. 5), the value K ' _{required is found} .

 This is the minimum maximum permissible value of K, characterizing the margin of health.

Any change in K is a consequence of a change in the current value of the controlled parameter x, and if it leads to the value K << K 'is _necessary , then the probability of failure q _dop (t) becomes higher than the maximum permissible.

 Failure has not yet occurred, but the greater the likelihood of its occurrence, the more urgent measures must be taken to eliminate the causes of a decrease in reliability.

 So, the proposed method for assessing reliability, based on the above calculations, preserves all existing standardized control operations confirmed by operating experience associated with the operation and maintenance of aircraft, but makes it possible to abandon the extremely disadvantageous, time-consuming, expensive and, most importantly, not always necessary planned overhaul.

 The proposed method makes it possible in a timely manner, in advance of failure, to detect a decrease in the reliability of individual elements or the aircraft as a whole and take measures to ensure flight safety. In some cases, for reasons of a subjective nature or when there is a natural decrease in reliability for objective reasons, aircraft should be sent for major repairs, but this is not a scheduled repair after the resource has been exhausted, but the inevitable repair if necessary.

 Thus, this is not a comparison of a real measured value with a reference value, but a comparison of the probabilities of occurrence of such values.

 The proposed method can find application in the operation of aircraft for a resource, but it acquires special value in the operation of the state.

Claims (1)

METHOD FOR ASSESSING AND MAINTAINING THE RELIABILITY OF AIRCRAFT AND THEIR POWER INSTALLATIONS WHEN OPERATING THE AERONAUTICAL TECHNIQUES AS CONDITION, including statistical accounting and system analysis of changes in the controlled parameters, characterized in that among the controlled parameters, those parameters that directly affect the reliability of the parameters that have a direct impact on reliability structural elements, in a probabilistic way, using the Laplace function tables, determine the health reserves Z of these elements as the difference of the admissible Y and current X values of the controlled parameter, the probability of failure q (t) is estimated, while the probability of failure q (t) is determined by the dependence:
q (t) = 0.5-Φ [β (K-1)],
where Φ [...] is the Laplace function;

mathematical expectation and standard deviation of the permissible value of the controlled parameter;

mathematical expectation and standard deviation of the actual value of the controlled parameter;
dz standard deviation of the safety margin Z,
assess the reliability level D (t) 1 q (t) and, if it falls below the established level, take measures to restore reliability.

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