RU2631557C1 - Method of determination in flight of bending stresses on rotor shaft of helicopter with torsional rotor head - Google Patents

Abstract

FIELD: aviation.

SUBSTANCE: for determining the stresses, flight performance is measured by standard means during the entire flight time, from which the significant parameters are selected and systematized, their approximating functions are determined to obtain the final function of the stress dependence in the rotor shaft on the selected performance parameters, loads on the rotor shaft is calculated using a mathematical model, a message is generated if they are exceeded.

EFFECT: determination of the residual life and control of the admissible load level.

3 cl, 7 dwg

Description

The invention relates to the field of aviation, in particular to systems for monitoring the technical condition of aircraft, namely monitoring the level of bending stresses of the rotor shaft of a helicopter in flight, in particular for a light multi-purpose helicopter with hinged-free mounting of blades, for example, helicopters: ANSAT, VK-117, EU -145.

Transmission is the most complex element of the design of the helicopter. It is known that the largest percentage of helicopter crashes (up to 39%) according to statistics is connected precisely with the failure of helicopter transmission units.

At the stage of development of monitoring systems, the most important is the determination and establishment of diagnostic signs of the technical condition of helicopter transmission units. The main task in developing a monitoring system is to establish threshold values for diagnostic features, upon reaching which appropriate decisions should be made on further safety in operation. If any diagnostic feature has reached its threshold value, then a decision is made to limit the resource, to replace an extraordinary part, or to remove the transmission unit from operation. As a rule, the vast majority of diagnostic signs are not displayed on the cockpit during the flight. Their analysis is carried out after completion of the flight. However, some particularly critical diagnostic features may be displayed during the flight if safety conditions so require.

In recent decades, promising helicopters have begun to use the so-called hingeless rotors equipped with a hingeless sleeve, in which the functions of horizontal, vertical and axial joints are performed by an elongated elastic element - a torsion bar. The main part of the design of the torsion bar is an elastically deformable section. The presence of plywood layers and slots provides torsion streams loading mainly in a uniaxial stress-strain state with transverse shear and bending when the blades swing in a plane of rotation. This allows you to reduce the cost of operating a helicopter, but at the same time, the initial costs for the design and manufacture of such structures increase. Therefore, the accuracy of predicting loading and, accordingly, estimating the resource of the helicopter carrier system is today one of the key tasks of helicopter engineering.

The rotor shaft is loaded with forces and moments from its sleeve and the torque created at the output of the main gearbox. The length of the rotor shaft is determined by layout, aerodynamic and operational considerations.

Since a semi-rigid sleeve has a greater bending moment compared to a hinge, control of the bending stresses of the rotor shaft of a helicopter with a hinge-free sleeve in flight is an urgent task.

A known system for monitoring the loading of the rotor shaft (US patent No. 2010219987, SIKORSKY AIRCRAFT, publication date 02.09.2010, IPC G06F 15/00, G08B 21/00).

The method of virtual control of the load on the rotor system of a helicopter in accordance with one embodiment of the present invention includes the selection of at least one parameter of the aircraft for one full revolution of the rotor. The calculation of the coefficients for obtaining a set of high-frequency signals from the parameter of at least one aircraft. Multiplying each of the many high-frequency signals by a factor to obtain the totality of the analyzed signals. Estimation of the load on the rotor based on the analyzed signals.

A real-time rotor system for detecting a rotor state in accordance with one embodiment of the present invention includes a sensor system for measuring loads to obtain data. The module is capable of virtual monitoring of loads to obtain calculated data and detect faults in real time and to obtain an algorithm for subtracting calculated signals from the measured signals to obtain values that are then compared with standard values to give the final result about the state of the rotor.

Sensors read parameters such as the take-off mass of the aircraft, the height in density, the rotational speed of the rotor, the speed of the air flow, normal acceleration, the vertical speed of climb, engine torque, pitch angle, roll angle, yaw rate, pitch angle , angular roll speed, deviation in the longitudinal direction, lateral position, pedal position and set of positions for one revolution of the rotor. The vectors of the given sixteen parameters are multiplied by the given values of the matrix, which includes 10 rows and 16 columns, to obtain ten coefficients (c1, c2, c3, c4, c5, c6, c7, c8, c9, and c10) to determine ten oscillation values . Oscillation values are multiplied by a coefficient to produce amplified oscillations. If the oscillation vectors are denoted as w1, w2, w3, w4, w5, w6, w7, w8, w9, and w10, and the coefficients are c1, c2, c3, c4, c5, c6, c7, c8, c9, and c10, then the calculated signal of the shear force of the rotor shaft is written in the form:

L = c1 * w1 + c2 * w2 + c3 * w3 + c4 * w4 + c5 * w5 + c6 * w6 + c7 * w7 + c8 * w8 + c9 * w9 + c10 * w10

The amplitude and phase of the shear force are calculated through the Fourier transform.

A known system for collecting data, monitoring and diagnosing the technical condition of helicopter propeller drive assemblies (RF patent for the invention No. 2519583, publ. 02.27.2014, IPC B64D 45/00), including piezoelectric vibration sensors that are installed on the housing, at least , of one of the helicopter rotor drive aggregates and arranged so that they receive data with a completeness sufficient to diagnose the technical condition of parts, assemblies of at least one rotor helicopter drive unit of a working helicopter, and an on-board electronic unit. The electronic unit is connected to the outputs of the vibration sensors and is configured to digitally process vibration signals, control and carry out the collection, primary processing and evaluation of the signal parameters of individual sensors and / or their combinations, accumulate sensor data and store them on external and / or removable media suitable for reading by computer, and secondary processing in terrestrial conditions. The efficiency of data collection, the information content of monitoring and diagnostics of the technical condition of the drive units of the propellers of a working helicopter are increased.

The disadvantage of this control system is the inability to make an unambiguous conclusion on the level of fatigue stresses in the helicopter units from the measured vibrations in flight, including in the rotor shaft. Another disadvantage is the need to install sensors and electronic components on helicopters, the time required for secondary data processing in ground conditions.

A known method of operating a helicopter (RF patent No. 2543111, publ. 02.27.2015, IPC B64C 27/04, B64F 5/00, G01L 3/24), which consists in the fact that each flight control the actual thrust of the rotor of the helicopter, moreover preliminary, before starting the operation of the helicopter, they collect the initial data on the characteristics of the engines of the power plant in accordance with the forms and collect the initial data on the magnitude of the thrust of the rotor during the control hangs of the helicopter. Throughout the entire period of operation of the helicopter, the actual data on the magnitude of the thrust of the rotor in the helicopter hovering modes is collected and compared, using the on-board computer, the obtained statistical data on the thrust of the rotor are compared with the original values and, if the magnitude of the thrust of the rotor from the original to the specified value, form, using the on-board computer, a signal to the monitor about the need to adjust the engine parameters to values that ensure the rotor thrust deviation in the pre cases 0.5% of the original value. Regulation of engine parameters is carried out either automatically, or by maintenance personnel on the ground. EFFECT: increased efficiency of helicopter use.

The disadvantage of this method of operation is the inability to determine the level of fatigue stresses on the rotor shaft from the results obtained, because the fatigue stresses on it are determined by bending stresses. Another disadvantage is the need to install sensors and electronic components on helicopters, the time required for secondary data processing in ground conditions. Also, the disadvantage is the need to first before starting the operation of the helicopter carry out the collection of initial data on the characteristics of the engines of the power plant in accordance with the forms and the collection of initial data on the magnitude of the thrust of the rotor during the control hangs of the helicopter.

As the closest analogue selected US patent No. 20111112806, publ. 2011.05.12, IPC G06F 17/10. The invention relates to a method for providing critical condition information for a component of a rotorcraft, including at least one engine driving a rotor including a cowl, a shaft and a plurality of blades. The sensor for measuring bending and cyclic loads acting on the rotor of an aircraft includes a computing unit for calculating (a) the current temperature of the bearing of the rotor assembly using the first calculation model, (b) predicting the temperature of the bearing using the first calculation model, and (c) applying a load to the selected component of the rotor assembly using the second calculation model, the first and second calculation models are designed to calculate, respectively venno, the predicted value and current bearing temperature, load acting on the component selected on the basis of flight control parameters; and a display unit for displaying on a single scale a movable indicator that is driven by the highest value of the projected bearing temperature and the load acting on the selected component. The display shows another moving indicator, driven by the current temperature of the bearing.

The disadvantage of the prototype is the need to install freelance sensors, which poses certain difficulties, since the design of serial helicopters is not adapted for the installation of freelance sensors, in addition, in the maintenance and field repair procedures, freelance sensors are not fully integrated with other aircraft equipment, require additional guidance and manuals on technical operation and additionally trained specialists.

The objective of the proposed technical solution is to create a method for controlling bending stresses on the rotor shaft during the entire flight (from take-off to landing) to detect fatigue damage to the shaft and to prevent emergency situations.

The technical result is the determination of the residual resource and the control of the permissible level of loads.

The technical result is achieved in that the method for determining in flight bending stresses on the rotor shaft of a helicopter with a rotor torsion hub includes measuring during the entire flight time using standard means of monitoring the helicopter’s flight performance, calculation using the mathematical model of the rotor shaft loads and signaling if they are exceeded, significant parameters are selected and systematized from among the measured flight performance characteristics that have a direct effect on y the load level of the rotor shaft, the approximating functions of the significant parameters are determined in order to determine the final function of the dependence of the stresses in the rotor shaft σ (t) on the selected flight performance parameters, the absolute values of the rates of change of the rotation angles of the swash plate in the longitudinal and transverse direction:

The proposed method allows to evaluate the level of load of the rotor shaft at any time during its flight operation. Based on the use of standard means of controlling the helicopter flight parameters, it allows you to determine the level of bending stresses during the entire duration of the flight, use it to register flight restrictions and inform the crew about exceeding the permissible load level, as well as determining the residual life.

In the claimed invention, an analysis is made of the conditions for the reasonable establishment of limit values for especially critical diagnostic features by the example of the indication of the actual in-flight bending stresses of the rotor shaft of a rotor of a single-rotor helicopter, in particular for ANSAT helicopters.

The essence of the invention lies in the fact that from among the parameters monitored in flight, those parameters are selected and systematized that have a direct effect on the level of loading of the HB shaft. The approximating functions of significant parameters are determined in order to determine the final function of the dependence of the stresses in the LV shaft on the selected LTH parameters. The absolute values of the rates of change of the angles of rotation of the plate of the swash plate in the longitudinal and transverse directions are added to the final function.

Spend a flight experiment. The choice of the critical parameter is determined from the current values of the flight technical characteristics (LTX) of the helicopter. To do this, a strain gauge is mounted on the helicopter’s shaft and in real flight the values of voltages σ _ist (t), as well as the values of the trajectory parameters measured by standard means of controlling the helicopter’s flight parameters, for example: longitudinal and transverse tilt angle of the swash plate, common rotor pitch , helicopter speed, helicopter pitch angle, helicopter roll angle, rate of change of the tilt angle of the swash plate in the longitudinal and transverse directions, etc.

A preliminary analysis selects the LTX parameters that most affect the voltage on the HB shaft, for which graphs of the voltage on the shaft are plotted depending on the values of the parameters recorded by standard means of control, and correlation coefficients are found and evaluated to filter the LTX parameters.

The trajectory parameters of the LTX with a correlation coefficient of more than 0.2 are selected as significant.

Approximating curves are constructed (the dependences of the rotor shaft stresses on the selected LTX parameters) and a system of equations is compiled with the aim of determining the approximation of the function for bending stress over time σ _calculation (t):

and the corresponding weights A1, A2, A3, ..., An are found.

Coefficients A1, A2, A3 are found by polynomial approximation by the least squares method (for a particular helicopter with specific LTX).

The final formula takes the form:

where Dprod is the angle of inclination of the plate of the swash plate in the longitudinal direction,

Dпоп - the angle of the plate of the swash plate in the transverse direction,

Dosh is the main rotor pitch,

X _n - other significant flight performance parameters,

- абсолютное значение скорости изменения угла поворота тарелки автомата перекоса в продольном направлении,

- the absolute value of the rate of change of the angle of rotation of the plate of the swash plate in the longitudinal direction,

- абсолютное значение скорости изменения угла поворота тарелки автомата перекоса в поперечном направлении.

- the absolute value of the rate of change of the angle of rotation of the plate of the swash plate in the transverse direction.

The calculation of the bending stress of the rotor shaft of the helicopter is carried out in real time during the entire flight time in the computing unit of the on-board computer based on the program laid down. If the safe voltage level is exceeded, the pilot is signaled and the calculation of the consumed resource in hours begins according to the formula:

where Pr - damage caused by stress levels in excess of safe;

Fri. - damage per hour typical flight, taken when calculating the resource for normal operating conditions.

Damage caused by a voltage level exceeding the safe Pr is determined by the following procedure:

- for each loading level exceeding safe, using the fatigue curve (the curve is taken according to the results of rotor shaft fatigue tests), the corresponding number of cycles to failure (Ni) is determined;

- damage caused by stress levels exceeding safe Pr is defined as the ratio of the number of cycles at this level to the number of cycles before failure (Ni).

Thus, after each flight, the consumed rotor shaft resource is calculated. If there were no excesses of the maximum level of loading, then the consumed resource of the rotor shaft is equal to the actual flight time, if excesses of the safe loading level were recorded, then the time determined by the method described above is added to the actual flight time.

Since there is always a measurement procedure necessary to obtain reliable information for each diagnostic feature, accordingly, the account of the inevitable measurement errors for each diagnostic feature is also required. Then, the decision to exceed or not exceed its limit values should also be made taking into account the upper (or lower) tolerance of the region of limit states.

- допустимое по индикатору значение текущего измеренного значения σф.A certain limiting value of σ _PR must be established, the excess of which entails the rapid exhaustion of the fatigue life of the rotor shaft and its possible destruction in the subsequent flight time. Since this parameter, or a diagnostic sign, is especially responsible, an indication of its current value in the cockpit is necessary. Denote by

- the indicator value of the current measured value σf.

The actual current value of σf can be represented as a sum:

where mσ is the mathematical expectation of bending stresses in the most loaded section of the rotor shaft in the considered flight mode, Δσ is the deviation of the actual value of σf from its mathematical expectation.

Description of the invention

Practical determination of parameters affecting the level of shaft loading.

1. A helicopter flight experiment was conducted with the ANSAT single-rotor circuit, during which the values of bending loads were measured at a specific time interval using a strain gauge mounted on the rotor shaft. The experimental dependence σ _ist (t) is shown in FIG. 1 (curve 1). This dependence is obtained on a typical flight mode, including the following modes:

a) Hanging (including hanging turns)

b) Acceleration

c) Low speeds near the ground

d) Climb

e) Horizontal flight at different speeds

e) Turns

g) motor planning

h) Braking

During the flight, using the standard means of helicopter control, the following trajectory parameters were measured in time.

1. Speed, unit of measurement km / h.

It was measured by the USVITS-350 speed indicator with digital output device. The error of digital signal output of the current instrument speed in normal climatic conditions at nominal input signals does not exceed ± 6 km / h.

2. Height, unit of measure m.

Measured by instruments:

- “VMTS-10 height indicator” - mechanical altimeter with digital output. The error of the digital signal relative height of the flight, the variation of the readings when installed on the meter atmospheric pressure 760 mm RT.article (1013 hPa) in normal climatic conditions depending on the height is: from ± 10 m (at a height of Ohm) to ± 30 m (at a height of 6000 m);

- “Radio altimeter A-053-05.02” - an on-board radar station with continuous emission of frequency-modulated radio waves. The error of altitude measurement when flying over any smooth surface (such as runways) with a horizontal speed of up to 120 m / s and a vertical speed of not more than 8 m / s with roll and pitch angles of up to ± 20 ° in the altitude range from 0 to 1500 m in 95% height measurements, m: by digital output 0.45 or ± 0.02N (which is more).

3. The angle of heel and the pitch angle of the helicopter, degrees.

Measured by the device "Horizon AGB-96D" - gives out the signals of the roll and pitch of the helicopter. The error of the horizon according to roll and pitch on a vibrating base is not more than ± 2.5 °.

4. Position of governing bodies, unit of measure degrees.

Measured by the device "Potentiometric two-channel position sensors DP-M". Measurement error ± 30 '.

5. The position of the output links (rods) of the steering drives (tilt angles of the swash plate in the longitudinal and transverse directions) RP-14, mm.

Measured by the instrument "Potentiometric sensors MU-615A Series 1". Error in measuring angles under normal conditions: ± 2% of the nominal measuring range.

6. Angular speeds, rad / s.

Measured by the instrument "Block of primary information sensors BDPI-09" - provides information on the projections of the angular velocity and linear acceleration vectors.

In figures 2-7 shows the dependence of the voltage on the rotor shaft from the measured parameters. The list of the given parameters is not limited to the given parameters and depends on the particular helicopter.

During the experiment, the following parameters were measured in time:

σ (t) is the value of the bending stress over time, measured by a strain gauge on the shaft,

Dprod (t) - the angle of inclination of the plate of the swash plate in the longitudinal direction,

Dпоп (t) - the angle of inclination of the plate of the swash plate in the transverse direction,

Dosh (t) is the common pitch of the rotor,

V (t) is the speed of the helicopter,

f _t (t) is the pitch angle of the helicopter,

f _to (t) is the angle of heel of the helicopter.

The correlation coefficients for each parameter are determined.

All parameters (correlation coefficient> 0.2) were selected significant and approximating curves were constructed for them and equations were compiled for each moment in time and for each parameter:

According to the selected significant parameters, the final formula takes the form:

The coefficients A1, A2, A3, A4, A5, A6 are found by solving the matrix equation:

A1 = 0.105864

A2 = 1,02273

A3 = 0.06855

A4 = 1.86659

A5 = 0.17941

A6 = 0.472461

The calculated values of the bending stress are shown in figure 1 (curve σ _calculation (t)).

The proposed method allows to evaluate the level of loading of the HB shaft at any time during its flight operation. Based on the use of standard means of controlling the helicopter flight parameters, it allows you to determine the level of bending stresses during the entire duration of the flight, use it to register flight restrictions and inform the crew about exceeding the permissible load level, as well as determining the residual life.

Claims (4)

1. The method of determining in flight bending stresses on the rotor shaft of a helicopter with a rotor torsion hub, including measuring the flight characteristics of the helicopter during the entire flight time, calculating the loads on the rotor shaft using a mathematical model and signaling in case of their excess, characterized in that among the measured flight performance characteristics, significant parameters are selected and systematized that have a direct effect on the level of loaded the main rotor shaft, determine the approximating functions of the significant parameters in order to determine the final function of the dependence of the stresses in the main rotor shaft σ (t) on the selected flight performance parameters, the absolute values of the rates of change of the angles of rotation of the swash plate in the longitudinal and transverse are added to the final function direction:

2. A method for determining in flight bending stresses on a rotor shaft of a helicopter with a rotor torsion hub according to claim 1, characterized in that, to determine the significance of the flight performance parameters, the dependences of the stresses on the rotor shaft on the selected parameters are constructed and the coefficients are calculated and evaluated correlations. 3. The method for determining in flight bending stresses on the rotor shaft of a helicopter with a rotor torsion hub of a rotor according to claim 2, characterized in that the significance of the parameters is determined by the value of the correlation coefficient> 0.2.

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