Method and system for predicting dynamic landing loads of strut-type landing gear

Abstract

The present invention provides a method for predicting the dynamic landing load of a strut-type landing gear, comprising: a landing time determination step: determining the landing time based on the acceleration at the landing gear wheel axle point; a landing gear load determination step: calculating the landing gear load based on the compression amount and the acceleration at the landing gear wheel axle point, and the landing gear load determination step includes the following sub-steps: a first sub-step: determining the initial axial force of the landing gear based on the compression amount; a second sub-step: determining the bending force of the landing gear based on the calculated initial axial force and the acceleration at the landing gear wheel axle point; a third sub-step: determining the corrected axial force of the landing gear based on the bending force and the strut friction coefficient of the strut. Through this method, the landing gear load is obtained without strain, and the empirical formula is not used. The landing gear load in the landing scene can be quickly evaluated and analyzed directly with the help of acceleration and compression. The present invention also includes a system for predicting the dynamic landing load of a strut-type landing gear.

Description

Technical Field

[0001] The present invention relates to the field of aerospace, in particular to the field of civil aircraft, and in particular to strut-type landing gears for civil aircraft. Specifically, the present invention mainly relates to a method for predicting dynamic landing loads of a landing gear and a system for predicting dynamic landing loads of a landing gear. Background Art

[0002] The landing process of an aircraft refers to the entire process of reducing altitude and speed from an airborne state to returning to the ground. Landing load is an important component of the relevant provisions on ground loads in civil aviation regulations (for example, "Part 25 of the Civil Aviation Regulations of China: Airworthiness Standards for Transport Category Aircraft"). With the large-scale development of modern civil aircraft, the influence of fuselage elasticity on the load envelope has become greater, and the dynamic landing load considering dynamic analysis has become one of the most important design load conditions for civil aircraft. The distribution of dynamic landing loads throughout the aircraft must be given in both the detailed design stage and the certification stage of the aircraft to evaluate the load-bearing capacity of the aircraft structure. In addition, the dynamic landing load is an important input to the fatigue spectrum and affects the fatigue life of the aircraft. In particular, the landing stage is a key stage for ensuring flight safety, and adverse scenarios such as heavy landing and hard landing are prone to occur. Therefore, the calculation accuracy of the dynamic landing load is crucial to the structural strength design.

[0003] Because dynamic landing loads are particularly important to the structural strength of the fuselage, dynamic load analysis is required, and dynamic landing test flights are helpful in verifying the dynamic load analysis. Although it is known that the characteristics of the landing gear can be confirmed through the drop test, there is no aerodynamic force in the drop test, and the fuselage is simplified to a concentrated mass point. There is only interaction between the fuselage, landing gear and test bench, and the focus is on confirming the characteristics of the landing gear.

[0004] But compared with this, during the actual landing test flight, firstly, since the aerodynamic force and gravity cannot always be balanced, there are states such as lift breaking caused by the operation of spoilers and other situations. Secondly, considering the elasticity of the landing gear's own struts, the elasticity of the connection area between the landing gear and the fuselage, the mass of the landing gear, and the elastic response process of the fuselage, the vertical force, lateral force, and heading force generated by the landing gear after touching the ground are not constant. In addition, due to the influence of various factors such as wind speed and runway position during the test flight, it is easy for the left and right wheels to land asymmetrically. Therefore, how to obtain accurate landing gear time domain loads becomes the key to influencing dynamic landing load verification.

[0005] There are some methods for analyzing dynamic landing loads in the prior art. For example, it is known that US16152183 and US13267561 provide a system for analyzing landing gear loads, which uses multiple strain sensors arranged near the landing gear to process the strain in the landing scene, power the strain system through cable laying, and collect strains at several sampling rates, and then estimate the landing gear load through the deformation of the landing gear structure. However, this method uses strain to predict the landing gear load, but the structure of the civil aircraft body is complex, and the axial deformation, heading deformation and lateral deformation of the landing gear in the landing scene exist at the same time, and it is easy to cause an uneven landing. There is a risk of failure when using strain to obtain the landing gear load. This method also obviously has high requirements for the location of the strain gauge selection. It is usually necessary to disassemble the landing gear, install the landing gear on the test bench, and arrange the strain at a position that can reflect the actual strain amplitude and frequency to obtain a more realistic landing gear load. In addition, the relationship between strain and landing gear load itself requires high accuracy, which requires a large number of experiments to obtain, is time-consuming, and the accuracy is actually difficult to guarantee.

[0006] In addition, it is also known that US11225602 discloses a system for calculating and displaying the kinetic energy generated and experienced by an aircraft when performing a normal, overweight or hard landing event. The system requires the installation of a pressure sensor and an inclination sensor for each landing gear to monitor, measure and record the impact load and the vertical speed of the aircraft when the landing gear begins to contact the ground, and to perform speed regulation to correct the errors caused by the inflation pressure of each landing gear and the friction of the landing gear strut seal. The system also measures the landing load experienced by each landing gear during landing and determines whether the aircraft limit has been exceeded. The system uses the pressure value, compression amount and gross weight of the aircraft as inputs, calculates the sinking speed, and outputs the load at the moment of landing. However, this method will affect the safety of the landing gear when the landing gear load is too large.

[0007] In addition, CN113919597A is also known to involve a method and device for predicting the landing load of an aircraft, which includes: obtaining multiple sets of flight parameters of the aircraft in a period of time from before to after landing; obtaining landing gear travel data from a displacement sensor installed on the landing gear; determining the landing time of the aircraft based on the landing gear travel data; determining a set of flight parameters of the aircraft at the landing time from multiple sets of flight parameters based on the landing time of the aircraft; and predicting the landing load of the aircraft based on a set of flight parameters at the landing time using the landing load. However, this method requires the use of a landing dynamics model of the entire aircraft, and the accuracy of the dynamic characteristics of the model is relatively high. The landing load prediction model is generated after training, so it is more time-consuming and costly.

[0008] In addition, it is also known that CN112069712A proposes a method for rapid analysis of landing load of a support arm landing gear based on the principle of energy conservation. This method first simplifies the structure of a large side angle support arm landing gear into a mass-spring system based on the principle of energy conservation. In this system, the weight of the aircraft is simplified and concentrated as M, the large side angle support arm structure is simplified into a spring model, the tire is simplified into a spring model, and the support arm and the tire are connected to simplify two springs in series. Then, the energy equation of the large side angle support arm structure simplified into a spring model is solved, and the energy equation of the tire simplified into a spring model is solved. After that, the obtained energy equation is substituted into the energy conservation equation to solve the maximum vertical load of the landing gear landing load, and the loads in the lateral and heading directions on the landing gear are calculated. However, this method is only applicable to support arm landing gear, and it is necessary to use empirical parameters for estimation, and it is impossible to give the change of the landing gear load over time in the landing scenario.

[0009] Finally, CN110261017A also proposes an online monitoring system for aircraft landing gear structural loads based on optical fiber sensing technology. However, this online monitoring system requires the use of relatively expensive fiber grating strain sensors and acceleration sensors, and is mainly used to estimate the remaining life of the aircraft, and is of little significance for predicting dynamic landing loads.

[0010] So far, in terms of aircraft dynamic landing load prediction, the existing technologies either use strain or fiber optic measurement to obtain landing gear loads, or use methods that affect aircraft safety to analyze landing gear loads, and also use empirical formulas for estimation, etc. These methods and systems have a great risk of failure on the one hand, and on the other hand, they also require a lot of experimental work, and the accuracy is difficult to guarantee. Therefore, in the field of aircraft, especially in the field of aircraft strut landing gear, there is always a need to quickly obtain the dynamic characteristics of the landing gear in the landing scene and quickly predict the landing gear load. Summary of the invention

[0011] The present invention provides a method for predicting the dynamic landing load of a strut-type landing gear, which may include the following steps performed in sequence: a landing time determination step: the landing time may be determined based on the acceleration at the landing gear wheel axle point; a landing gear load determination step: the landing gear load may be calculated based on the compression amount of the landing gear strut and the acceleration at the landing gear wheel axle point, and the landing gear load may include the axial force and the bending force at the landing gear wheel axle point, wherein the landing gear load determination step may include the following sub-steps: a first sub-step: the initial axial force of the landing gear may be determined based on the compression amount; a second sub-step: the bending force of the landing gear may be determined based on the calculated initial axial force and the acceleration at the landing gear wheel axle point; a third sub-step: the corrected axial force of the landing gear may be determined based on the bending force and the strut friction coefficient of the strut.

[0012] By using the method of the present invention, the landing gear load is obtained without strain and without using empirical formulas, and the landing gear load in the landing scene can be quickly evaluated and analyzed by directly using the acceleration at the wheel axle point and the compression of the strut.

[0013] Preferably, the step of determining the landing time may include: determining the mutation time when the acceleration at the landing gear axle point suddenly changes; determining the reference time when the compression amount of the landing gear strut begins to change; and determining the mutation time before the reference time as the landing time.

[0014] By using the compression amount of the strut as an auxiliary reference for the landing time, the efficiency and accuracy of determining the landing time can be improved, and the risk of misjudging the landing time can be reduced.

[0015] Advantageously, the second sub-step may include: determining the ground support force on the landing gear based on the preliminary axial force and the vertical acceleration at the landing gear axle point; determining the ground friction force based on the support force and the ground friction coefficient; determining the bending force based on the ground friction force and the heading acceleration at the landing gear axle point. The bending force is calculated by the preliminary axial force and other available parameters, and the bending force can then be used to correct the preliminary axial force.

[0016] Optionally, after the landing gear load determining step, the following steps may be sequentially executed: an airframe acceleration response determining step: determining the airframe acceleration response based on the landing gear load; a verification step: acquiring the actual airframe acceleration response, and comparing the airframe accelerator response determined in the airframe acceleration response determining step with the acquired actual airframe acceleration response to verify the landing gear load.

[0017] The reliability of the prediction of the landing gear load obtained by the aforementioned method can be determined through the verification step, that is, the reliability of the load environment of the dynamic landing load test flight can be ensured, thereby ensuring the safety of the aircraft design.

[0018] In addition, the landing gear load determination step may further include a fourth sub-step: determining a nose-up moment at the intersection where the landing gear is connected to the fuselage based on the corrected axial force, the bending force and the compression amount; and / or determining a rolling moment at the intersection where the landing gear is connected to the fuselage based on the corrected axial force, the lateral acceleration at the landing gear wheel axis point and the compression amount. The nose-up moment and / or the rolling moment may be determined by the bending force and the axial force, and these moments may be used as excitation input into the structural dynamics model to obtain the acceleration response of the fuselage.

[0019] In some embodiments, the method may further include extracting the bus parameters of the aircraft at the time of landing, the bus parameters being selected from the following group: sinking speed, forward speed, pitch angle, roll angle, pitch angular velocity, roll angular velocity, fuel weight, and wheel speed. By extracting the bus parameters of the aircraft, it is convenient to obtain the body data, which can be used to determine the landing state or to calculate the landing gear load or to perform calibration.

[0020] In addition, the present invention can provide a system for predicting the dynamic landing load of a strut-type landing gear, characterized in that the system can include: a linear displacement sensor, which is arranged at the strut of the landing gear to measure the compression of the strut; an acceleration sensor, which is arranged at the axle point of the landing gear to measure the acceleration at the axle point of the landing gear; a controller, which can include: a landing time determination module, which is used to determine the landing time based on the acceleration at the axle point of the landing gear; a landing gear load determination module, which is used to calculate the landing gear load based on the compression of the strut of the landing gear and the acceleration at the axle point of the landing gear after the landing time, and the landing gear load includes the axial force and bending force at the axle point of the landing gear; wherein the landing gear load determination module can include the following submodules: a first submodule, which is used to determine the preliminary axial force of the landing gear based on the compression; a second submodule, which is used to determine the bending force of the landing gear based on the preliminary axial force and the acceleration at the axle point of the landing gear; and a third submodule, which is used to determine the corrected axial force of the landing gear based on the bending force and the strut friction coefficient of the strut.

[0021] By arranging linear displacement sensors and acceleration sensors at the landing gear and utilizing various modules of the controller, the dynamic characteristics of the landing gear, especially in the landing scenario of a civil aircraft, can be quickly acquired and the landing gear load can be quickly predicted.

[0022] Advantageously, the acceleration sensor can be configured to measure vertical acceleration, heading acceleration and lateral acceleration at the axle point of the landing gear, and the accelerations in the three directions can be used to calculate the supporting force, bending force and rolling moment respectively.

[0023] Preferably, the strut may include an outer cylinder connected to the fuselage and an inner cylinder capable of translating relative to the outer cylinder, wherein one end of the linear displacement sensor may be connected to the outer cylinder, and the other end opposite thereto may be connected to the landing gear wheel axle point. With the linear displacement sensor arranged in this way, the compression amount of the strut may be accurately obtained to determine the landing gear load.

[0024] In some embodiments, the landing gear load determination module may further include: an airframe acceleration response determination module, used to determine the airframe acceleration response based on the landing gear load; and a verification module, the verification module acquires the actual airframe acceleration response, receives the airframe accelerator response from the airframe acceleration response module, and compares it with the acquired actual airframe acceleration response to verify the landing gear load. The predicted reliability of the landing gear load obtained by the aforementioned modules of the controller can be determined by the airframe acceleration response determination module and the verification module, that is, the reliability of the load environment of the dynamic landing load test flight can be ensured, thereby ensuring the safety of the aircraft design.

[0025] In particular, an acceleration sensor may be arranged on at least one of the fuselage, the wing, and the horizontal tail, and the actual acceleration response of the fuselage obtained by the verification module is the actual acceleration response of the at least one. The acceleration arranged in this way can take into account the different elasticity and other physical conditions of various parts of the fuselage, thereby increasing the accuracy of the acceleration response verification.

[0026] In addition, the landing time determination module can be configured to determine the mutation time when the acceleration at the landing gear axle point suddenly changes and the reference time when the compression amount of the landing gear strut begins to change, and determine the mutation time before the reference time as the landing time. By using the compression amount of the strut as an auxiliary reference for the landing time, the efficiency and accuracy of determining the landing time can be improved, and the risk of misjudging the landing time can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A structural diagram of a strut-type landing gear according to an embodiment of the system for predicting dynamic landing loads of a strut-type landing gear according to the present invention is schematically shown, wherein a linear displacement sensor is shown;

[0028] Figure 2 A schematic top view of an aircraft having a system for predicting dynamic landing loads of a strut-type landing gear according to the present invention is shown, wherein acceleration sensors (shown by gray circles) arranged at various parts of the aircraft body are shown;

[0029] Figure 3 Schematically shows the Figure 1 A force state diagram of the strut-type landing gear during landing of an embodiment;

[0030] Figure 4 The steps of one embodiment of a method for predicting dynamic landing loads of a strut-type landing gear according to the present invention are shown.

[0031] Reference numerals list

[0032] 100 Body

[0033] 110 Acceleration sensor

[0034] 120 Linear Displacement Sensor

[0035] 132 Landing gear axle point

[0036] 134 Inner tube

[0037] 136 outer cylinder

[0038] 138 Anti-twist arm

[0039] F Axial force

[0040] N Bending force

[0041] D Support

[0042] V Ground friction. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with specific embodiments and drawings, but the protection scope of the present invention shall not be limited thereto.

[0044] First, the present invention mainly relates to the field of aircraft design, especially the field of civil aircraft design. Secondly, the load prediction method and prediction system of the present invention are mainly aimed at aircraft with strut landing gear, but do not exclude other aircraft with similar landing gear structure.

[0045] Regarding the descriptions of directions appearing in the text, the terms "upper / top", "lower / bottom", "front / front", "rear / rear", etc. are all based on the normal posture of the aircraft. For example, the landing gear is located at the bottom front of the aircraft fuselage.

[0046] In the present invention, the term "based on" means related to the factors described later, but should not be understood as being based only on, but the factors based on may include the content described later, but are not limited to the content described later.

[0047] Finally, it should be noted that the numerical values ​​given in the examples are only for illustration and are not intended to limit the scope of the present invention.

[0048] As mentioned above, the dynamic landing load of the landing gear 130 when the aircraft lands is a component of the aircraft ground load, which determines whether the aircraft can land safely. It is an important basis for the design of the aircraft landing gear and an important factor to be considered in the aircraft strength verification. The present invention relates to a method for predicting the dynamic landing load of a strut-type landing gear. Here, the term "prediction" refers to prejudging or estimating the load of the strut-type landing gear when landing to evaluate the load-bearing capacity of the aircraft structure, thereby providing a guarantee for the aircraft verification.

[0049] The load prediction method of the present invention is completed by determining or calculating corresponding data or values ​​during the aircraft landing process, and is particularly suitable for load prediction of the landing gear 130 after a civil aircraft conducts a landing test flight. Before landing occurs, especially before the test flight is carried out, the data or parameters expected to be obtained include the gross weight of the aircraft, the inflation pressure of the landing gear struts, the inflation pressure of the aircraft tires, and the equivalent mass of the landing gear concentrated at the axle point. More preferably, the aircraft drop shock test has been completed before landing occurs, especially before the test flight is carried out, so as to master the relationship between the vertical force of the landing gear 130 and the compression of the struts, and to master the proportional relationship between the vertical force and the heading force.

[0050] In order to increase the accuracy of the load prediction method of the present invention, when the aircraft (test flight) lands, it is expected to land at a larger sinking speed, and try not to use the lifting device at the moment of landing to keep the balance of aerodynamic force and gravity as much as possible. In addition, considering that the typical time of the landing process is 0.3s to 0.6s, it is expected that the sampling rate of each parameter should be as high as possible. In addition, it is also expected that the pitch angle at landing should not be too large.

[0051] The load prediction method of the present invention may first include a landing scenario time period confirmation step. In the landing scenario time period confirmation step, the entering or about to entering a specific landing scenario time period may be confirmed by checking bus parameters, the compression amount of the landing gear 130 struts, and the like. For example, when the flight altitude approaches the airport altitude, the pitch angle approaches 0 degrees, the landing gear buffer struts produce a sudden change in compression amount, etc., it can be considered that the landing scenario time period has been entered. Preferably, it is possible to determine whether the landing moment has been reached only after confirming that it is in the landing scenario time period, thereby eliminating the misjudgment of the landing moment due to abnormal factors, thereby improving the efficiency and accuracy of the landing moment determination, but this step is not necessary.

[0052] The load prediction method of the present invention generally includes a landing time determination step. In the landing time determination step, the landing time can be determined based on the acceleration at the landing gear axle point 132. This is because at the moment of the aircraft landing, the tires will begin to deform, and the acceleration at the axle point of the strut landing gear will suddenly change.

[0053] It is understood that determining the landing time based on the acceleration at the axle point does not mean that other factors do not need to be considered when determining the landing time, but means that the landing time is mainly based on the acceleration at the axle point. For example, the compression amount of the strut can also be referred to to assist in determining the landing time.

[0054] Specifically, in a preferred embodiment, the step of determining the landing time may include several sub-steps: first, the mutation time at which the acceleration at the landing gear axle point 132 suddenly changes may be determined. In this article, "acceleration suddenly changes" means that the vertical and directional accelerations of the landing gear axle point simultaneously produce a 30% change (or mutation amount) relative to the initial value of the acceleration (earlier time). Secondly, the reference time at which the compression amount of the strut of the landing gear 130 begins to change may be determined. Finally, the mutation time before the reference time may be finally determined as the landing time. Due to the buffering effect of the landing gear strut, the buffer strut (for example, the inner tube 134 of the strut) begins to compress, so the moment when the linear displacement begins to have displacement (that is, the reference time) will be later than the mutation time at which the acceleration at the landing gear axle point 132 suddenly changes. Therefore, the mutation time before the reference time can be determined as the landing time. If the mutation time is later than the reference time, the mutation time should not be the landing time.

[0055] If the landing time of the aircraft is confirmed, in an advantageous embodiment, the bus parameters of the aircraft can be extracted or drawn. For example, at least one of the following parameters can be obtained: body fuel weight, pitch angle, roll angle, pitch angular velocity, roll angular velocity, aircraft sinking speed, forward speed, landing gear wheel rotation speed, landing gear wheel load signal, etc. These parameters are all current parameters obtained at the landing time.

[0056] Based on the obtained fuselage oil weight and the known fuselage structure weight, the total weight of the aircraft can be obtained, and the total weight can be used for calculation when obtaining the body acceleration response (further described below). After obtaining the force at the aircraft wheel axle point, the force conversion can be performed based on the pitch angle and roll angle to convert to the body coordinate system. The pitch angular velocity combined with the pitch angle, roll angle, yaw angle, etc. can be used to determine the landing state, such as the degree of symmetry of the aircraft during landing. The sinking speed is generally used to determine the impulse size during landing, that is, the greater the sinking speed means the greater the landing impact. The slip ratio (or slip rate) of the tire of the aircraft during landing can also be calculated by obtaining the forward speed of the aircraft during landing and combining it with other parameters, such as the rotation speed of the wheel. The ground friction coefficient can be calculated with the help of the slip ratio, which can then be used to determine the bending force (further described below). The rotation speed of the wheel can be used to determine the moment when the wheel spins, rebounds, and pure rolls occur. In addition, as mentioned earlier, the wheel rotation speed combined with the forward speed can determine the slip ratio, and the ground friction coefficient can be calculated by the slip ratio. Then, combined with parameters such as heading acceleration, the bending force can be solved together.

[0057] After determining the landing time, the prediction method of the present invention includes a landing gear load determination step in which the landing gear load can be calculated based on the compression of the struts of the landing gear 130 and the acceleration at the landing gear axle point 132 .

[0058] Although other data or parameters, such as the rotational speed of the wheels and various known airframe parameters, are not excluded from being used in the calculation process of the landing gear load, it should be understood that one of the important differences between the prediction method of the present invention and the prior art is that there is no need to use a traditional strain system to determine the structural deformation of the landing gear 130 and perform a force analysis, nor is there any need to use empirical formulas. Instead, the acceleration signal at the wheel axle point and the compression signal of the strut are directly collected, so that the landing gear load in the landing scenario can be quickly evaluated and analyzed.

[0059] It can be understood that the compression of the strut and the acceleration at the wheel axle point used in the landing gear load determination step are expected to be obtained within a very short predetermined time period after the landing moment, such as 0.3 seconds to 0.6 seconds.

[0060] Advantageously, the compression of the strut and the acceleration at the wheel axle point (eg, heading acceleration, vertical acceleration, lateral acceleration) can be processed within the predetermined time period, wherein the physical quantities containing initial values ​​need to be subtracted from the initial values.

[0061] In order to measure or acquire the acceleration at the axle point, the prediction system according to the present invention may include an acceleration sensor 110. The acceleration sensor 110 may be arranged at the axle point, such as on a platform, and whether the acceleration sensor 110 is precisely oriented does not affect its accurate reflection of the acceleration.

[0062] Preferably, the acceleration sensor 110 may be configured to measure the vertical acceleration, the heading acceleration and the lateral acceleration at the landing gear axle point 132, thereby facilitating rapid acquisition of various landing gear loads.

[0063] In the prediction system of the present invention, the strut of the landing gear 130 may include an outer cylinder 136 connected to the fuselage and an inner cylinder 134 capable of translating relative to the outer cylinder 136, such as Figure 1 As shown in . An anti-torsion arm 138 may also be arranged between the inner tube 134 and the outer tube 136. In order to measure or obtain the compression amount of the strut, a linear displacement sensor 120 may be arranged, one end of which is connected to the outer tube 136 of the strut, and the other end of which is connected to the landing gear wheel axle point 132. In this way, the compression stroke of the landing gear during landing can be conveniently measured.

[0064] The landing gear load determined by the prediction method of the present invention may refer to force, such as axial force and bending force at the landing gear axle point 132. In addition, the landing gear load may also refer to moment, such as nose-up moment and rolling moment.

[0065] like Figure 3As shown in , the landing gear load determination step of the prediction method according to the present invention is mainly determined or calculated based on the following principles. When the strut-type landing gear 130 touches the ground during landing, taking the strut-type landing gear 130 as an example, the landing gear 130 is mainly subjected to the combined action of four forces: the support force D of the ground on the landing gear 130, the ground friction force V, the bending force N (acting at the wheel axle point) generated by the bending deformation of the strut-type landing gear 130, and the compression force F generated by the compression deformation of the strut-type landing gear 130. The support force D, the ground friction force V, the bending force N and the compression force F act together to generate an acceleration response at the wheel axle point.

[0066] Specifically, the landing gear load determination step of the prediction method of the present invention may include multiple sub-steps. In the first sub-step, the preliminary axial force F' of the landing gear strut can be determined based on the compression of the strut. Depending on the specific structure of the strut, the axial force of the strut can be composed of oil force, air force and friction force, among which the friction force accounts for a relatively small proportion. After completing the aircraft drop test, the relationship between the oil force, air force and compression can be obtained. For example, in some embodiments, oil force = coefficient × rate of change of compression 2 , and air force = (initial inflation volume / (initial inflation volume-piston area*compression amount))^variable index×initial inflation force. Therefore, by obtaining the compression amount of the strut and the rate of change of the compression amount, the oil force and air force of the strut can be determined. The initial axial force F' of the strut can be determined by the sum of the oil force and the air force. As mentioned above, since the friction force of the strut accounts for a small proportion, the initial axial force F' can be used for subsequent load calculations without significantly affecting the calculation accuracy.

[0067] The landing gear load determination step may also include a second sub-step. In the second sub-step, the bending force N of the landing gear may be determined based on the preliminary axial force F' and the acceleration at the landing gear axle point 132 calculated in the first sub-step. The calculation principle of the second sub-step is roughly as follows: the ground support force can be obtained by the preliminary axial force F' and the acceleration at the axle point, and then the friction force can be obtained by the ground support force and the friction coefficient, and the bending force N is obtained by the friction force. That is, in the present invention, the determination of the bending force N is mainly based on the obtained preliminary axial force F' and the acceleration (for example, vertical acceleration and heading acceleration) at the landing gear axle point 132.

[0068] In some embodiments, the ground support force D on the landing gear 130 can be determined by the preliminary axial force F'. For example, this can be done by combining the preliminary axial force F' with the vertical acceleration at the wheel axle point through force analysis (see Figure 3) to obtain the supporting force D. After obtaining the supporting force D, the ground friction force V can be determined based on the supporting force D and the ground friction coefficient. Here, the ground friction coefficient can be determined by obtaining the forward speed of the aircraft and the rotation speed of the wheels and calculating the slip ratio therefrom, but it can also be obtained by other methods. Generally, the ground friction force V is equal to the product of the supporting force D and the ground friction coefficient. Finally, the bending force N can be determined by the ground friction force V and the heading acceleration at the landing gear wheel axle point 132. More specifically, the bending force N=the concentrated mass M at the wheel axle point×the heading acceleration+the ground friction force.

[0069] The landing gear load determination step may further include a third sub-step. In the third sub-step, a modified axial force F of the landing gear may be determined based on the bending force N and the strut friction coefficient of the strut. The modified axial force F is corrected by the strut friction force relative to the preliminary axial force F', and is therefore more accurate, and is one of the important parameters of the landing gear load to be obtained by the prediction method of the present invention.

[0070] In some embodiments, when designing the strut landing gear 130, the friction coefficient of the strut (for example, the friction coefficient between the inner barrel 134 and the outer barrel 136) can be obtained. Based on the bending force N determined in the second sub-step and combined with the friction coefficient of the strut, a strut friction force with a smaller value can be obtained.

[0071] As mentioned above, the axial force of the strut is actually composed of three forces, namely, oil force, air force and friction force. The first two can be obtained from the compression amount of the strut and its change rate, while the friction force can be obtained in this step, thereby finally obtaining the corrected axial force F of the strut.

[0072] After determining the landing gear loads including the bending force and the axial force, the landing gear load determination step may further include a fourth sub-step. In the fourth sub-step, the nose-up moment at the intersection where the landing gear 130 is connected to the fuselage may be determined based on the modified axial force F, the bending force N, and the compression amount of the strut. Depending on the specific arrangement of the aircraft, in some embodiments, the nose-up moment may be calculated, for example, by the following formula:

[0073] Nose-up moment = bending force × (distance from intersection to wheel axle point - compression) × cos (pitch angle + heading installation angle of landing gear) + axial force × (distance from intersection to wheel axle point - compression) × sin (pitch angle + heading installation angle of landing gear).

[0074] Alternatively or additionally, in the fourth sub-step, alternatively or additionally, the rolling moment at the intersection where the landing gear is connected to the fuselage can be determined based on the modified axial force F, the lateral acceleration at the landing gear axle point 132, and the compression of the strut. In some embodiments, the rolling moment can be calculated, for example, by the following formula:

[0075] Rolling moment = lateral acceleration × mass of the wheel × (distance from the intersection point to the wheel axle point - compression) * cos (roll angle + lateral installation angle of landing gear) + axial force × (distance from the intersection point to the wheel axle point - compression) * sin (roll angle + lateral installation angle of landing gear).

[0076] In addition, the load prediction method according to the present invention may further perform a landing gear load verification step after the landing gear load determination step to determine the accuracy of the landing gear load determined by the above method. Specifically, the landing gear load verification step may include an airframe acceleration response determination step, in which the airframe acceleration response, especially the whole aircraft acceleration response, may be determined based on the landing gear load.

[0077] In some advantageous embodiments, after the landing gear load is obtained, the landing gear load can be applied as an external excitation to the structural dynamics model, for example, a transient dynamics solution module in finite element software (ANSYS, MSC, Nastran, etc.) can be used to obtain the acceleration response of each part of the body 100. However, this is not restrictive, and those skilled in the art can know the method of obtaining the acceleration response of the body through the landing gear load.

[0078] The landing gear load verification step may further include a verification step, in which an actual acceleration response of the airframe may be obtained, and the airframe accelerator response determined in the airframe acceleration response determination step may be compared with the obtained actual acceleration response of the airframe to verify the accuracy or credibility of the landing gear load.

[0079] In order to obtain the actual acceleration response of the fuselage, an acceleration sensor 110, especially a low-frequency acceleration sensor, can be arranged on at least one of the fuselage, wing, and horizontal tail to measure the actual acceleration response of each part of the fuselage 100. The location of the acceleration sensor 110 should take into account the areas with greater and lesser elasticity of the fuselage. In a preferred embodiment, taking the fuselage as an example, the acceleration sensors 110 are arranged on the middle fuselage, the front fuselage, the rear fuselage, the nose, and the tail, for example, see Figure 2 The circled part is processed, but this is not restrictive. More preferably, the response acceleration of the aircraft body during the test flight is processed within a predetermined time period after the landing moment. The predetermined time period can also be, for example, 0.3 seconds to 0.6 seconds, but this is not restrictive.

[0080] exist Figure 4An exemplary flow chart of the load prediction method according to the present invention is shown in FIG. In the preferred embodiment, the method of the present invention first performs the landing scene time period confirmation in the first step, and determines the landing moment in the second step, for example, based on the acceleration at the landing gear wheel axle point 132, and optionally uses the compression of the strut as an auxiliary judgment condition. In the third step, the aircraft general parameters are extracted, such as the sinking speed, forward speed, pitch angle, roll angle, pitch angular velocity, roll angular velocity, fuel weight, and the rotation speed of the wheel. In the fourth step, the compression of the strut and the acceleration at the landing gear wheel axle point 132 at the landing moment (or within a very short predetermined time period thereafter) are processed. In the fifth step, the landing gear load is determined based on the compression of the strut and the acceleration at the landing gear wheel axle point 132, mainly the bending force and the axial force. Then in the sixth step, the acceleration response of the fuselage is determined using the landing gear load as an excitation. In the seventh step, the acceleration response of the fuselage is processed (fly-tested), for example, by the acceleration sensor 110 actually arranged at various parts of the fuselage 100. Finally, the calculated body acceleration response is compared with the actually measured body acceleration response to verify the accuracy of the landing gear load. One or more of the above steps may be omitted, and thus the above method flow is merely exemplary.

[0081] In order to ensure that the load prediction method according to the present invention can be implemented, the present invention may also provide a system for predicting the dynamic landing load of a strut-type landing gear.

[0082] The system for predicting the dynamic landing load of a strut-type landing gear may include a linear displacement sensor 120 and an acceleration sensor 110, wherein the linear displacement sensor 120 is arranged at the strut of the landing gear 130 to measure the compression of the strut, and the acceleration sensor 110 may be arranged at the landing gear axle point 132 to measure the acceleration at the landing gear axle point 132.

[0083] In addition, the prediction system of the present invention may further include a controller, which includes modules for performing various functions, especially the various method steps described in detail above. For example, the controller may include a landing time determination module, which is used to determine the landing time based on the acceleration at the landing gear axle point 132. For another example, the controller may include a landing gear load determination module, which is used to calculate the landing gear load based on the compression amount of the landing gear strut and the acceleration at the landing gear axle point 132 after the landing time, wherein the landing gear load may include the axial force and the bending force at the landing gear axle point 132, but may also include other forces and moments, such as the nose-up moment and the rolling moment.

[0084] In order to determine the axial force and the bending force, the landing gear load determination module can be further divided into a plurality of submodules. Each module and submodule of the controller may include necessary electronic components for performing functions, including but not limited to comparators, signal transmitters and signal receivers, and the like.

[0085] For example, the landing gear load determination module may include a first submodule for determining the preliminary axial force F' of the landing gear 130 based on the compression amount of the strut. The landing gear load determination module may also include a second submodule for determining the bending force N of the landing gear 130 based on the preliminary axial force F' and the acceleration at the landing gear wheel axle point 132. In addition, the landing gear load determination module may also include a third submodule for determining the corrected axial force F of the landing gear 130 based on the bending force N and the strut friction coefficient of the strut.

[0086] It can be understood that the aforementioned steps or sub-steps according to the present invention may have corresponding controller modules or sub-modules to facilitate the execution of the method. For example, the landing gear load determination module may also include an airframe acceleration response determination module for determining the airframe acceleration response based on the landing gear load; and a verification module, which may obtain the actual airframe acceleration response, receive the airframe accelerator response from the airframe acceleration response module, and compare it with the obtained actual airframe acceleration response to verify the landing gear load.

[0087] Thus, the present invention provides a method and system for predicting the dynamic landing load of a strut-type landing gear of an aircraft. By arranging a wire displacement sensor 120 and an acceleration sensor 110 at the landing gear 130, the response characteristics of the landing gear 130 can be obtained after a landing test flight. Combining aircraft parameters, landing data, and landing gear characteristic parameters, etc., the landing landing gear excitation can be obtained, which is used to study the response characteristics of various components, main systems and equipment under landing excitation.

[0088] Although various embodiments of the present invention are described in the drawings with reference to strut-type landing gear for civil aircraft, it should be understood that embodiments within the scope of the present invention may be applied to other landing gear or other aircraft applications having similar structure and / or function.

[0089] The foregoing description has presented numerous features and advantages, including various alternative embodiments, and details of the structure and function of apparatus and methods. This disclosure is intended to be illustrative, not exhaustive or limiting.

[0090] It will be apparent to those skilled in the art that various modifications may be made within the full scope indicated by the broad general meaning of the terms expressed in the appended claims, especially in terms of structure, material, element, component, shape, size and arrangement of components, including the combination of these aspects within the scope of the principles described herein. To the extent that these various modifications do not depart from the spirit and scope of the appended claims, it is intended that they are also included herein.

Claims

1. A method for predicting dynamic landing loads of a strut-type landing gear, characterized in that: The process includes the following steps, which are performed in sequence: The step of determining the landing time is as follows: determining the landing time based on the acceleration at the landing gear wheel axle point; The landing gear load determination step is as follows: the landing gear load is calculated based on the compression amount of the landing gear strut and the acceleration at the landing gear axle point, wherein the landing gear load includes the axial force and the bending force at the landing gear axle point. The landing gear load determination step includes the following sub-steps: First sub-step: determining a preliminary axial force (F') of the landing gear based on the compression amount; Second sub-step: determining the bending force (N) of the landing gear based on the calculated preliminary axial force (F') and the acceleration at the landing gear axle point; Third sub-step: determining a modified axial force (F) of the landing gear based on the bending force and the strut friction coefficient of the strut.

2. The method according to claim 1, characterized in that The step of determining the landing time comprises: - determining the sudden change time when the acceleration at the landing gear axle point suddenly changes; - determining the reference moment at which the compression of the landing gear strut begins to change; -determining the sudden change time before the reference time as the landing time.

3. The method according to claim 1, characterized in that The second sub-step comprises: - determining the ground support force (D) on the landing gear based on the preliminary axial force (F') and the vertical acceleration at the landing gear axle point; - determining the ground friction force (V) based on the supporting force and the ground friction coefficient; - Determining the bending force (N) based on the ground friction force (V) and the heading acceleration at the landing gear axle point.

4. The method according to claim 1, characterized in that After the landing gear load determination step, the following steps are performed in sequence: The step of determining the airframe acceleration response: determining the airframe acceleration response based on the landing gear load; Verification step: acquiring an actual acceleration response of an airframe, and comparing the airframe accelerator response determined in the airframe acceleration response determination step with the acquired actual acceleration response of the airframe to verify the landing gear load.

5. The method according to claim 1, characterized in that The landing gear load determination step further comprises a fourth sub-step: determining a nose-up moment at an intersection of the landing gear and the fuselage based on the modified axial force (F), the bending force (N) and the compression; and / or A rolling moment at the intersection point where the landing gear is connected to the fuselage is determined based on the modified axial force (F), the lateral acceleration at the landing gear wheel axis point and the compression.

6. The method according to claim 1, characterized in that The method further comprises extracting bus parameters of the aircraft at the landing moment, wherein the bus parameters are selected from the following group: Sinking speed, forward speed, pitch angle, roll angle, pitch rate, roll rate, fuel weight, wheel speed.

7. A system for predicting dynamic landing loads of a strut-type landing gear, characterized in that: The system comprises: A linear displacement sensor is arranged at a strut of the landing gear to measure the compression of the strut; An acceleration sensor is arranged at the landing gear axle point to measure the acceleration at the landing gear axle point; A controller, the controller comprising: A landing timing determination module, used to determine the landing timing based on the acceleration at the landing gear axle point; a landing gear load determination module, configured to calculate a landing gear load based on a compression amount of a landing gear strut and an acceleration at a landing gear axle point after the landing moment, wherein the landing gear load includes an axial force and a bending force at the landing gear axle point; Wherein, the landing gear load determination module includes the following submodules: A first submodule is configured to determine a preliminary axial force (F') of the landing gear based on the compression amount; A second submodule, for determining a bending force (N) of the landing gear based on the preliminary axial force (F') and the acceleration at the landing gear axle point; A third submodule is configured to determine a modified axial force (F) of the landing gear based on the bending force and a strut friction coefficient of the strut.

8. The system according to claim 7, characterized in that The acceleration sensor is configured to measure vertical acceleration, heading acceleration and lateral acceleration at the landing gear wheel axle point.

9. The system according to claim 7, characterized in that The support comprises an outer cylinder connected to a fuselage and an inner cylinder capable of translating relative to the outer cylinder, wherein one end of the linear displacement sensor is connected to the outer cylinder, and the other opposite end is connected to the landing gear wheel axle point.

10. The system according to claim 7, characterized in that The landing gear load determination module also includes: an airframe acceleration response determination module, configured to determine an airframe acceleration response based on the landing gear load; A verification module is provided, wherein the verification module obtains an actual acceleration response of an airframe, receives the airframe accelerator response from the airframe acceleration response module, and compares the airframe accelerator response with the obtained actual acceleration response of the airframe to verify the landing gear load.

11. The system according to claim 10, characterized in that An acceleration sensor is arranged on at least one of the fuselage, the wing, and the horizontal tail, and the actual acceleration response of the fuselage obtained by the verification module is the actual acceleration response of the at least one.

12. The system according to claim 7, characterized in that The landing timing determination module is configured to determine a sudden change timing at which the acceleration at the landing gear wheel axle point suddenly changes and a reference timing at which the compression amount of the landing gear strut begins to change, and determine the sudden change timing before the reference timing as the landing timing.

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