RU2599108C1 - Method of monitoring loads and accumulated fatigue damage in operating conditions of aircraft - Google Patents

Abstract

FIELD: aircraft engineering.

SUBSTANCE: invention relates to aircraft engineering and concerns a method of monitoring loads and accumulated fatigue damage design of glider aggregates in actual operation conditions. During monitoring loads and accumulated fatigue damage design of glider aggregates based on processing of realizations of flight parameters, fixed to the normal emergency recorder, and realizations of the loads obtained by calculation and experimental methods, to set between the results of such processing of average statistical relationships based on intensity and time of oscillations of the construction on the flight modes, strain sensors are used installed and used in conducting state certification tests.

EFFECT: increase in accuracy of monitoring is achieved due to tracking variable load and accumulated fatigue damage of each copy of the aircraft in each flight using average statistical links load with fixed parameters of flight to an emergency recorder, accuracy of which increases with increase of the summed flights.

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Description

This invention relates to the field of aviation, in particular to a method for monitoring loads and accumulated fatigue damage to the design of airframe assemblies of a specific instance of a transport aircraft of this type under conditions of its actual operation.

The development of methods and means of monitoring the actual load in the conditions of regular operation, obtaining and analysis of the relevant statistical materials is a prerequisite for improving the safety of aircraft operation under the conditions of structural strength (Aviation Rules AP-25, MOS 25.571). According to the current regulatory system, the design life according to the conditions of fatigue strength is set for the most loaded aircraft instance from a fleet of this type (reliability coefficient η ₃ = 2 according to ISO 25.571). In the case when a monitoring system is installed on a specific airplane instance, then for this instance the coefficient η _{3 is} taken equal to 1, i.e. if monitoring is carried out for all aircraft, the fleet’s resource on average doubles.

Similar work is being carried out at FAA, USA [.http: //aar400.tc.faa.gov/Programs/AgingAircraft/airbornedata/FAA%20HTML%20Design%20Template5a.htm]. The Federal Aviation Administration (FAA) has developed an Operational Load Monitoring System, which includes the collection of flight load data on large transport aircraft and local airlines.

The basis for monitoring the loads on the units of the aircraft, performed by the FAA, is the strain gauge of individual aircraft of this type in the conditions of regular operation. This is an expensive event.

A known method of monitoring the loads of a fleet of aircraft, aircraft or helicopters (patent US 2011112878, 2011, IPC G06F 19/00, G06Q 10/00). The flight is performed on any serial aircraft from the park. The method implements the calculation of external loads acting on the aircraft during its operation using a set of orthogonal functions and a set of coefficients (for high-frequency data) associated with these functions. These coefficients are calculated and stored on board the aircraft, and then transmitted to the ground system. The ground system includes a service database with a copy of a set of orthogonal functions. When transmitting the above set of coefficients to the ground system, the external loads acting on the aircraft during its operation are restored. According to these data, the accumulated fatigue damage to the design of the units of the glider of a serial aircraft is calculated, as well as the fatigue damage to the aircraft fleet; this data is saved. This method also allows you to calculate the external loads acting on the units of the airframe during the flight and, in addition, allows you to calculate the accumulated damage to the units of the airframe from the calculated loads and store these accumulated damage in a special database. The disadvantage of this method is the need for additional flights on an additional aircraft from the fleet, which requires additional financial costs.

A known method of monitoring loads and accumulated fatigue damage of an aircraft fleet is taken as a prototype (patent GB 2192723, 1988, IPC G07C 3/00, on the subject of OLMS-OPERATIONAL-LOAD MONITORING SYSTEM FOR AIRCRAFT).

It contains the following operations:

1. Select several aircraft from the fleet. Aircraft can be both transport and military.

2. Sensors of the same (first type) are installed in the selected sections of the design of the airframe units of each selected aircraft, designed to measure the internal loads acting in the above sections during the flight. In addition, other sensors (of the second type) are installed on board the aircraft, designed to measure the basic parameters of the flight during the flight.

3. Flights are performed on the selected planes, during which data are collected from the above two types of sensors (internal loads acting in the above sections during the flight and the main flight parameters) during the flight, these data are transmitted to the on-board computer. In the on-board computer, according to the readings of the sensors of the first type, the external loads acting on each of the selected aircraft during the flight of each selected aircraft are calculated; this data is processed and reduced.

4. After completing the flight of each of the above aircraft, data on external loads and basic flight parameters are transmitted to the ground system. In the ground-based system, data on external loads are statistically processed and, together with data on the main flight parameters, are transferred for storage to a special data bank, which has the ability to store data on 500 flights on one medium.

5. According to the data stored in a special data bank, diagnostics and prediction of fatigue damage of the selected aircraft are performed, and also according to these data, diagnostics and forecasting of fatigue damage of the aircraft fleet are performed.

The disadvantage of the method of monitoring the prototype: operations are performed on individually selected aircraft from the fleet, which leads to insufficient accuracy in determining the residual damage to the fleet. The disadvantage of this method can also be attributed to the need for additional flights on an additional aircraft from the fleet, which requires additional financial costs. The monitoring of loads in this method is based on the strain gauge of individual aircraft instances under the conditions of regular operation. This is an expensive event.

The technical result of the invention is the ability to improve monitoring accuracy by tracking the variable load and accumulated fatigue damage of each aircraft instance in each flight using averaged statistical relationships of load with fixed flight parameters to the emergency recorder, the accuracy of which increases with increasing total flights.

The technical result is achieved by the fact that in the method for monitoring loads and accumulated fatigue damage under operating conditions of the aircraft, based on the fact that aggregates, cross-sections of the airframe design and types of loads are selected, strain gauges are installed in the selected sections, the flight of the airplane is carried out, said strain gauges are measured during load flights, operating in the above units and sections, register flight parameters on board the aircraft with a standard emergency recorder in the ground system Atistically process data from strain gauges, based on the results of statistical processing and data on the main flight parameters, they perform an analytical determination of the fatigue damage of the units and structures of the aircraft of the selected type, strain gauges install and measure their loads during state certification tests or similar tests, the analytical determination of fatigue damage is carried out by dividing the entire flight into modes, obtaining statistical statistics for each mode depending on the flight parameters recorded by a regular emergency recorder, on the basis of strain analysis during state certification tests, critical elements are selected: aggregates, sections and power elements of the airframe design and the types of loads acting on them - determining the design life according to the conditions of fatigue strength, analytically determine the contribution different flight modes in their damage, for each of which and each critical element based on multiple processing but repeated flight modes establish statistical dependences of damage and extreme loads on functioning loads, intensity (standard deviation - standard deviation of overloads) and oscillation time (equivalent to conditional damage damage on overloads) of integral force factors - overloads recorded by the emergency recorder from their regular sensors; when any instance of this type of aircraft is returned to the base airfield, the emergency recorder information is copied and processed on a computer, while the flight modes of interest are identified by the recorded parameters, for each mode, for each load of interest, the operating loads are analytically determined using the recorded parameters, for each flight mode determine the standard deviations of the overloads and the equivalent overload fatigue damage values, determine the equivalent the values of the considered loads with respect to fatigue damage for each flight mode using the dependences obtained during state certification tests determine the extremes of the loads of the ground-air-ground cycle by analyzing the extreme loads for all flight modes and determine the damage from its impact, determine the total damage damage each load for the flight as a sum of the regimes and the cycles of "ground-air-ground", damage, document and store in a data bank.

In FIG. Figure 1 shows an example of the restoration of fatigue damage from the action of a bending moment in one of the wing sections of a passenger aircraft (SKOny is the standard deviation of the vertical overload).

In FIG. Figure 2 shows the effect of the polling frequency on damage from vertical overload in the take-off mode.

In FIG. Figure 3 shows the implementations of the cutting force in the tensometric root section of the GO and the forces in the MPS (stabilizer rearrangement mechanism) in different flights and in different modes

All instances of operating aircraft are equipped with regular emergency flight information recorders, on the carriers of which time basic flight parameters are recorded: aircraft weight, fuel weight, centering, overloads and angular speeds of the aircraft, altitude, pressure head, Mach number, steering surfaces deviation angles and mechanization , engine mode, etc. The maximum frequency of polling and recording parameters, as a rule, does not exceed 8 Hertz and is different for different parameters. As a rule, when the aircraft returns to the base airfield, information from the emergency recorder is copied to an intermediate medium and processed by the ground express analysis service. Using the developed software with a minimum frequency of registration of determining parameters, the functional loads (average loads) acting on the aircraft units are restored. The available recording frequencies are sufficient for their accurate recovery. In addition, using special algorithms and recorded parameters, the entire flight is divided into modes that monitor, as a rule, changes in the functioning loads on aircraft units.

In addition to changing operating loads, fatigue damage is determined by variable loads caused by atmospheric turbulence, airfield irregularities, stray flows from deviations of wing mechanization, spoilers, reverse thrust of engines on the run, etc. Spectral, correlation and regression analysis of the results of strain gauges during flight tests show that the basis for monitoring the repeatability of variable loads (fatigue damage) by determining flight modes can be laid s only a statistical connection with the loading of integral power factors (congestion). In general, for the flight modes under consideration, the correlation between increments of loads and overloads is not rigid, it can be significant only in certain frequency ranges. For various components of the design, the fatigue-determining frequency range of load changes is 0-10 Hz, therefore, the recording frequency of 8 Hz overloads in emergency drives is clearly not sufficient.

In the algorithms for restoring damage from forces and moments in different sections of the aircraft structure, statistical dependences of the load on the intensity (rms overload) and time (equivalent to damage overload value) of the oscillations according to flight modes are used. The repeatability of increments of variable loads (damageability) is determined with a certain error (due to the averaging of statistical relationships) in each specific flight (mode), which decreases with an increase in the number of averaged (summed) flights. Cycle formation is based on extreme loads. Damage is determined by calculation (appropriate software) using full cycles, linear summation, power-law form of endurance curve (below are examples of dependencies for metal structures with exponent 4).

In FIG. Figure 1 shows an example of the restoration of fatigue damage from the action of a bending moment in one of the wing sections of a passenger aircraft (SKOny is the standard deviation of the vertical overload). The coefficient k1 is calculated for each flight mode as:

,

,

- эквивалентный изгибающий момент за режим полета;Where

- equivalent bending moment per flight mode;

- средний изгибающий момент за режим полета;

- average bending moment per flight mode;

- эквивалентная вертикальная перегрузка за режим полета.

- equivalent vertical overload for flight mode.

Under equivalent loads, we mean the maximum of the zero load cycle, giving fatigue damage equal to the damage from the initial load for the flight mode.

Correction factors associated with a low polling frequency were determined for all flight modes for correction in the system for monitoring damage from overloads from standard sensors. An example of such dependencies is shown in FIG. 2. Here k is the ratio of damage from vertical overload at a given polling to damage at a sampling frequency of 128 Hz. The dependence of the standard deviation on the frequency of the survey of overloads is practically absent.

All of the materials listed above were obtained by processing the results of strain gauges at the State Logistics Institute (state certification tests), which are mandatory for certification of the aircraft under the conditions of strength.

It is advisable to study the accuracy of restoration of variable load and accumulated fatigue damage of monitoring using strain gauge records of the entire flight (from the moment the engines are started until they are turned off, and not by mode). Table 1 shows an example of the accuracy analysis of an amphibian aircraft monitoring system (Mekv - fatigue damage equivalent in fatigue damage per flight, SBI - continuous flight strain gauge, Resource - calculation by monitoring algorithms; 6 - firefighting flight, 1 - transport flight, 7 - training flight). It can be seen that with an increase in the number of averaged flights, the accuracy of finding the total damage is increased (k is a coefficient equal to the ratio of damage accumulated during previous flights obtained in the monitoring system to damage calculated according to strain gauge data). The total damage for 10 flights over the wing cross section differs from the true one by 12% (in reserve), and over the cross section of the boat by 3% (not into the reserve), while this follows from the table, the heaviest flight differs from the lightest in 67 time. 12% in terms of damage corresponds to an error in the restoration of loads <3%, which is determined by the accuracy of the restoration of loads during flight and full-scale strength tests. It should also be borne in mind that the aircraft’s resource according to the conditions of fatigue strength is determined by tens of thousands of flights, the maintenance schedule (inspections, improvements, replacement of parts with a limited resource), as a rule, is carried out with a frequency of at least hundreds - thousands of flights.

Horizontal plumage (GO) is one of the most complex units from the standpoint of load recovery, since it is influenced by the bevels of the flow behind the wing (deviations of slats, flaps, spoilers, oscillations). In FIG. Figure 3 shows the realizing cutting forces in the root tensometric section of the right half of the stabilizer (Q1 tensor) in the defining modes of several flights and the corresponding values restored from the flight parameters (Q1 calculation) using theoretical relations with corrections of some aerodynamic derivatives based on the results of flight tests. The frequency of polling tensometry and flight parameters is 64 Hz. Here is an example of the restoration of the force (S) in the thrust of the stabilizer rearrangement mechanism, which is affected not only by the cutting forces, but also by the bending and torques in the side sections of the right and left halves of the GO.

A very good correspondence is demonstrated not only in terms of functioning loads (which can still be improved, taking into account the asymmetrical flow around the left and right halves of the GO), but also in dynamic superposition of loads. Those. an increase in the frequency of interrogation of the leading parameters recorded on an emergency or operational storage will significantly abandon statistical monitoring approaches (where the damage in each particular flight is estimated with some error due to the use of averaged statistical dependencies, which decreases with an increase in the number of averaged flights) and improve the accuracy of the restoration of the repeatability of variable loads in each flight.

The method is as follows.

1. The units, structural sections and types of loads (cutting forces, bending and torques, forces in the elements) are determined, which must be controlled in operation (by calculation and experimental method).

2. Allocate flight modes that determine the load of interest. According to the results of tensometry at the stage of the GSI, dependencies of the type shown in FIG. 1. In these modes, according to the results of tensometry at the stage of the GSI, dependences of the type of FIG. one.

3. During ground processing of information of regular emergency recorders of serial aircraft in the express analysis system from each side of aircraft of this type:

- distinguish flight modes of interest with special algorithms for registered parameters;

- нагрузки функционирования (средние нагрузки - получают аналитически с корректировкой по результатам тензометрии при ГСИ) специальными алгоритмами по регистрируемым параметрам;- at each mode for each load of interest determine

- functioning loads (average loads - are obtained analytically with adjustment according to the results of strain gauge for GSI) with special algorithms for the recorded parameters;

и СКОny, фиг. 1);- at each flight mode, the standard deviation and the equivalent overload fatigue damage values are determined (for example, for vertical overload:

and SKOny, FIG. one);

);- using dependencies similar to FIG. 1, determine the equivalent fatigue damage values of the considered loads in each flight mode (

);

- determine the extremes of the loads of the cycle "ground-air-ground" (ZVZ) by analysis of extreme loads for all flight modes and determine the damage from its impact;

- determine the total damage for each load per flight (the sum of the modes and ZVZ);

- damage is documented and stored in a data bank.

The software for processing data recorded on a regular emergency recorder during flight for each serial aircraft was developed in the operating environment of the express analysis system and works automatically without operator intervention.

- The accuracy of monitoring in each specific flight depends on the averaged statistical dependencies used. The accuracy of restoring the repeatability of loads (fatigue damage) increases with the number of accumulated flights and, as the test results show, already on the basis of ~ 10 flights it becomes comparable (determined) with the accuracy of strain gauging. Improving the accuracy of monitoring in each specific flight is associated with the need to increase the frequency of the survey used parameters of the staff recorder.

Advantages and features of the system

The technical result of the invention is the ability to improve monitoring accuracy by tracking the variable load and accumulated fatigue damage of each aircraft instance in each flight using averaged statistical relationships of load with fixed flight parameters to the emergency recorder, the accuracy of which increases with increasing total flights.

- the monitoring system used in this work allows you to track the variable load of each aircraft instance from the fleet in each flight. This is a significant qualitative improvement in monitoring with accuracy characteristics commensurate with strain gauge. The fact that the system allows organizing individual tracking of the resource consumption by each aircraft instance makes it possible to increase the fleet’s resource by 1.5–2 times on average and will bring significant economic effect.

- this system does not require additional investments, i.e. there are no operational costs, since nothing is additionally installed on the plane, and the system is integrated into the express-analysis system of flight information (using special recording processing software);

- allows you to organize optimal maintenance planning (inspections, replacement of parts with a limited resource, refinement), which is also cost-effective;

- increase the safety of operation, since the load characteristics will be determined using a significantly larger number of parameters affecting it than is done so far, which is also cost-effective;

- control of loads during rough landing (reduction of financial losses during shutdown of operation with minimization of control and restoration work);

- development of recommendations on the style of piloting (trajectory of set and decrease, landing, use of mechanization, take-off, etc.) in order to reduce loads and damage;

- monitoring of the state of high-altitude aerodromes and taxiways by the reaction of the aircraft;

- accumulation of a data bank on extreme loads in order to clarify the regulatory requirements for static strength;

- allows you to get materials on the statistical characteristics of variable load and damage in order to properly build programs of full-scale fatigue tests and obtain reliable characteristics of fatigue strength, which increases the safety of operation.

Claims (1)

A method for monitoring loads and accumulated fatigue damage under aircraft operating conditions, based on the choice of units, sections of the aircraft glider structure and types of loads, load cells are installed in the selected sections, the aircraft is flying, the load cells are measured during the flight, the loads acting in the above units and sections, register the flight parameters on board the aircraft with a regular emergency recorder, statistics from the strain gauge are statistically processed in the ground system s, based on the results of statistical processing and data on the main flight parameters, an analytical determination of the fatigue damage of the units and structures of the aircraft of the selected type is performed, characterized in that the load cells are installed and measured by them during state certification tests or similar tests, the analytical determination of fatigue damage is carried out by dividing the entire flight into modes, obtaining for each mode statistical dependencies of the loads about t flight parameters recorded by a regular emergency recorder, based on the analysis of strain gauges during state certification tests, critical elements are selected: aggregates, sections and power elements of the airframe design and the types of loads acting on them - determining the design life under fatigue strength conditions, analytically determine the contribution of various modes flight to their damage, for each of which and each critical element based on the processing of repeatedly repeated modes the flight establish statistical dependences of damage and extreme loads on functioning loads, intensity (standard deviation - standard deviation of overloads) and oscillation time (equivalent value of conditional damage on overloads) of integral force factors - overloads recorded by the emergency recorder from their regular sensors when any aircraft is returned this type of information to the base airfield emergency recorder information and process it on a computer, while The flight modes of interest are identified by the recorded parameters, for each mode of interest, the operating loads are analytically determined using the registered parameters, the mean-square deviations of the overloads and the equivalent overload values for fatigue damage are determined for each flight mode, the values of the considered loads for each fatigue damage are determined flight mode using dependencies obtained in state During the tests, determine the extremes of the loads of the “ground-air-ground” cycle by analyzing the extreme loads for all flight modes and determine the damage from its impact, determine the total damage for each load per flight as the sum of the regimes and the cycles “ground-air-ground” , damage is documented and stored in a databank.

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