CN115465468A - Method and system for predicting dynamic landing load of strut type landing gear - Google Patents

Abstract

The invention provides a method for predicting dynamic landing load of a strut type landing gear, which comprises the following steps: a landing time determining step: determining a landing time based on an acceleration at an axle point of the landing gear; a landing gear load determining step: calculating a landing gear load based on the amount of compression and the acceleration at the landing gear axle point, the landing gear load determining step comprising the sub-steps of: the first substep: determining a preliminary axial force of the landing gear based on the amount of compression; the second substep: determining a bending force of the landing gear based on the calculated preliminary axial force and the acceleration at the landing gear axle point; the third substep: a corrected axial force of the landing gear is determined based on the bending force and a strut friction coefficient of the strut. By the method, the undercarriage load is obtained without strain, an empirical formula is not used, and the undercarriage load in a land scene can be quickly evaluated and analyzed by directly using the acceleration and the compression amount. The invention also includes a system for predicting landing gear dynamic landing loads for strut landing gears.

Description

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

Technical Field

The invention relates to the field of aerospace, in particular to the field of civil airplanes, and particularly relates to a strut type undercarriage for civil airplanes. In particular, the present invention relates generally to a method for predicting landing gear dynamic landing loads and a system for predicting landing gear dynamic landing loads.

Background

The landing process of an aircraft refers to the entire process of lowering altitude and speed from an airborne flight condition back to the ground. Landing loads are an important component of the relevant regulation of ground loads by civil aviation regulations (e.g., civil aviation regulation section 25 of china: airworthiness standards for transport-like aircraft). With the upsizing of modern civil aircrafts, the influence of the elasticity of an organism on a load envelope line is increased, and dynamic landing load considering dynamic analysis becomes one of the most important design load conditions of the civil aircrafts. The distribution condition of dynamic landing load in the whole aircraft needs to be given in the detailed design stage and the evidence obtaining stage of the aircraft so as to evaluate the loading capacity of the aircraft structure. In addition, dynamic landing loads are an important input to the fatigue spectrum, affecting the fatigue life of the aircraft. Particularly, the landing stage is a key stage of flight safety guarantee, and bad scenes such as heavy landing and hard landing are easy to happen. Therefore, the calculation accuracy of the dynamic landing load is crucial to the structural strength design.

Just because the dynamic landing load is particularly important to the structural strength of the fuselage, dynamic load analysis is needed, and the dynamic landing test flight is carried out, so that the dynamic load analysis verification is facilitated. Although it is known that landing gear characteristics can be confirmed through a drop test, aerodynamic force does not exist in the drop test, the airframe is simplified into a concentrated mass point, and only interaction among the airframe, the landing gear and the rack exists, and the emphasis is on confirming the landing gear characteristics.

However, in contrast, during actual landing test flight, first, aerodynamic force and gravity cannot be kept in balance at all times, and there is a state where lift force is broken due to the operation of a spoiler or the like. Secondly, considering the elasticity of the support column of the landing gear, the elasticity of the connection area of the landing gear and the machine body, the quality of the landing gear and the elastic response process of the machine body, the vertical force, the lateral force and the heading force generated by the landing gear after the landing gear is grounded are not constant. In addition, due to the influence of various factors such as wind speed and runway position in the test flight process, the situation that the left and right wheels are asymmetrically landed is easy to occur. Therefore, how to acquire accurate landing gear time-domain load becomes a key influencing dynamic landing load verification.

There are several methods in the prior art for analyzing dynamic landing loads. For example, it is known in US16152183 and US13267561 to provide a system for analysing landing gear load which uses a plurality of strain sensors arranged in the vicinity of the landing gear, processes the strain in the landing scene, powers the strain system via cabling, and performs strain collection at several sampling rates, then estimates the landing gear load by landing gear structural deformation. However, the method adopts strain to predict the landing gear load, but the civil aircraft has a complex structure, axial deformation, course deformation and lateral deformation of the landing gear exist simultaneously in a landing scene, uneven landing is easily caused, and the risk of failure exists when strain is adopted to obtain the landing gear load. It is also apparent that this method requires a high selection of the location of the strain gauge, and that it is usually necessary to disassemble the landing gear, mount the landing gear on a test bed, and place the strain at a location that reflects the true strain amplitude and frequency to obtain a more true landing gear load. In addition, the accuracy required for establishing the relationship between strain and landing gear load is high, which needs to be obtained through a large number of tests, and the time consumption is long, and the accuracy is difficult to guarantee in practice.

Further, 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 to which the landing gear is subjected when it comes into contact with the ground and the aircraft landing vertical velocity, and to make speed adjustments to correct for errors caused by the landing gear inflation pressure and the landing gear strut seal friction. The system also measures the landing loads experienced by each landing gear upon landing and determines whether aircraft limits have been exceeded. The system uses the pressure value, the compression amount and the gross weight of the airplane as input, calculates the sinking speed and outputs the load at the moment of landing. However, this approach can affect the safety of the landing gear when the landing gear is overloaded.

In addition, it is also known that CN113919597a relates to a method and apparatus for predicting landing loads of an aircraft, comprising: acquiring multiple groups of flight parameters of an aircraft in a period of time from before landing to after landing; acquiring undercarriage travel data from a displacement sensor mounted on the undercarriage; determining a landing time for the aircraft based on the landing gear travel data; determining a set of flight parameters of the aircraft at the landing time from the plurality of sets of flight parameters based on the landing time of the aircraft; and predicting a landing load of the aircraft using the landing load based on the set of flight parameters at the time of landing. However, the method needs to use a full-aircraft landing dynamic model, the accuracy requirement on the dynamic characteristics of the model is high, and the landing load prediction model is generated through training, so that the time consumption and the cost are both high.

In addition, CN112069712a is also known to provide a method for quickly analyzing landing load of a support arm landing gear based on the principle of energy conservation. According to the method, firstly, a large-side-angle supporting arm type undercarriage structure is simplified into a mass-spring system based on an energy conservation principle, in the system, the weight of an airplane is simplified and concentrated into M, a large-side-angle supporting arm type structure is simplified into a spring model, tires are simplified into the spring model, and the connection of a supporting arm and the tires is simplified into the series connection of two springs. Then, solving the energy equation of the large-side-angle support arm type structure simplified into the spring model, and solving the energy equation of the tire simplified into the spring model. And then substituting the obtained energy equation into an energy conservation equation, solving the maximum vertical load of the landing load of the undercarriage, and calculating the loads in the lateral direction and the heading direction of the undercarriage during landing. However, this method is only applicable to arm landing gear and requires the use of empirical parameters for estimation, and cannot give the time-varying landing gear load in a landing scenario.

Finally, it is also known that CN110261017a suggests an on-line monitoring system for structural load of an aircraft landing gear based on optical fiber sensing technology. However, the online monitoring system needs to use expensive fiber grating strain sensors and acceleration sensors, is mainly used for estimating the residual service life of the airplane, and has little significance for predicting dynamic landing load.

In the aspect of predicting dynamic landing loads of an aircraft, the prior art adopts a strain or optical fiber measurement mode or other modes to acquire the landing gear load, or adopts a method influencing the safety of the aircraft to analyze the landing gear load, and also adopts an empirical formula or other modes to estimate the landing gear load. On one hand, the methods and the systems have great failure risks, on the other hand, a great deal of test workload is required, and the precision is difficult to guarantee. There is therefore a constant need in the aircraft field, particularly for aircraft strut landing gear, for a rapid acquisition of landing gear dynamics and a rapid prediction of landing gear loads in landing scenarios.

Disclosure of Invention

The invention provides a method for predicting dynamic landing load of strut type landing gear, which comprises the following steps executed in sequence: a landing time determining step: the landing time may be determined based on the acceleration at the landing gear axle point; a landing gear load determining step: calculating a landing gear load based on the amount of compression of the strut of the landing gear and the acceleration at the landing gear hub point, the landing gear load may comprise an axial force and a bending force at the landing gear hub point, wherein the landing gear load determining step may comprise the sub-steps of: the first substep: a preliminary axial force of the landing gear may be determined based on the amount of compression; the second substep: determining a bending force of the landing gear based on the calculated preliminary axial force and the acceleration at the landing gear axle point; the third substep: a corrected axial force of the landing gear may be determined based on the bending force and the strut friction coefficient of the strut.

By the method, the undercarriage load is obtained without strain, an empirical formula is not used, and the undercarriage load in a land scene can be quickly evaluated and analyzed by directly utilizing the acceleration at the wheel axle point and the compression amount of the strut.

Preferably, the landing time determining step may include: determining the sudden change time when the acceleration at the wheel axle point of the landing gear is suddenly changed; determining a reference moment at which the compression of the strut of the landing gear begins to change; the moment of the mutation that is before the reference moment is determined as the moment of landing.

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

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

Optionally, the following steps may be performed in sequence after the landing gear load determining step: body acceleration response determination: determining a body acceleration response based on the landing gear load; a checking step: an actual body acceleration response is captured and the body accelerator response determined in the body acceleration response determination step is compared to the captured actual body acceleration response to verify the landing gear load.

The predicted reliability of the landing gear load obtained by the method can be determined through the checking step, namely the reliability of the load environment for test flight of the dynamic landing load is ensured, and therefore the design safety of the airplane is ensured.

Furthermore, the landing gear load determining step may further comprise a fourth sub-step of: determining a nose-up moment at an intersection point where the landing gear is connected with the fuselage based on the corrected axial force, the bending force and the compression amount; and/or determining a roll torque at the intersection of the landing gear and fuselage connection based on the modified axial force, the lateral acceleration and the amount of compression at the landing gear axle point. The bending force and the axial force can determine the head-up moment and/or the roll moment, and the moments can be used as excitation input into a structure dynamic model so as to obtain the acceleration response of the body.

In some embodiments, the method may further comprise extracting bus parameters of the aircraft at the time of landing, the bus parameters selected from the group consisting of: sinking speed, forward speed, pitch angle, roll angle, pitch angle speed, roll angle speed, oil weight and rotating speed of the airplane wheel. The airframe data can be conveniently obtained by extracting the bus parameters of the aircraft, and the data can be used for judging the landing state or calculating the load of the landing gear or carrying out verification.

Furthermore, the present invention may provide a system for predicting dynamic landing loads of strut landing gears, characterized in that the system may comprise: a linear displacement sensor disposed at a strut of the landing gear to measure a compression amount of the strut; an acceleration sensor arranged at the landing gear axle point to measure acceleration at the landing gear axle point; a controller, the controller may include: a landing time determination module for determining a landing time based on an acceleration at an axle point of the landing gear; a landing gear load determination module for calculating a landing gear load after a landing time based on a compression of a strut of the landing gear and an acceleration at a landing gear hub point, the landing gear load comprising an axial force and a bending force at the landing gear hub point; wherein the landing gear load determination module may include the following sub-modules: a first sub-module for determining a preliminary axial force of the landing gear based on the amount of compression; a second sub-module for determining a bending force of the landing gear based on the preliminary axial force and the acceleration at the landing gear axle point; a third sub-module for determining a corrected axial force of the landing gear based on the bending force and a strut friction coefficient of the strut.

By arranging a linear displacement sensor and an acceleration sensor at the undercarriage and utilizing the various modules of the controller, the undercarriage dynamics can be rapidly acquired and the undercarriage load can be rapidly predicted, particularly in the landing scene of civil aircraft.

Advantageously, the acceleration sensor may be configured to measure vertical, heading and lateral acceleration at the landing gear axle point. The accelerations in the three directions can be used to calculate the support force, the bending force and the roll moment, respectively.

Preferably, the strut may comprise an outer barrel connected to the fuselage and an inner barrel translatable relative to the outer barrel, wherein one end of the linear displacement sensor may be connected to the outer barrel and the opposite end may be point connected to the landing gear axle. With the linear displacement sensor thus arranged, the amount of strut compression can be accurately obtained for use in determining landing gear load.

In some embodiments, the landing gear load determination module may further comprise: an airframe acceleration response determination module to determine an airframe acceleration response based on the landing gear load; and the checking module acquires the actual acceleration response of the body, receives the accelerator response of the body from the acceleration response module of the body and compares the accelerator response with the acquired actual acceleration response of the body so as to check the load of the undercarriage. The body acceleration response determining module and the checking module can determine the prediction reliability of the landing gear load obtained by the controller, namely the load environment reliability of the test flight of the dynamic landing load, so that the design safety of the airplane is ensured.

In particular, an acceleration sensor may be disposed on at least one of the fuselage, the wing, and the horizontal tail, and the actual acceleration response of the airframe obtained by the verification module is the actual acceleration response of the at least one. The acceleration arranged in this way can take different physical conditions such as elasticity and the like of each part of the body into consideration, so that the accuracy of acceleration response verification is improved.

Furthermore, the landing time determination module may be configured to determine an abrupt change time at which the acceleration at the axle point of the landing gear abruptly changes and a reference time at which the amount of compression of the strut of the landing gear starts to change, and to determine the abrupt change 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 the accuracy of determining the landing time can be improved, and the risk of misjudgment of the landing time can be reduced.

Drawings

FIG. 1 schematically illustrates a block diagram of a strut landing gear of one embodiment of a system for predicting dynamic landing loads of a strut landing gear in accordance with the present invention, showing a linear displacement sensor;

FIG. 2 schematically illustrates a top view of an aircraft having a system for predicting column landing gear dynamic landing loads according to the present invention, showing acceleration sensors (shown with gray circles) disposed on various portions of the airframe;

figure 3 shows schematically a diagram of the landing stress state of the strut landing gear according to the embodiment of figure 1;

FIG. 4 illustrates the steps of one embodiment of a method for predicting landing gear dynamic landing loads for a strut, according to the present invention.

List of reference numerals

100. Machine body

110. Acceleration sensor

120. Linear displacement sensor

132. Landing gear wheel axle point

134. Inner cylinder

136. Outer cylinder

138. Anti-torsion arm

F axial force

N bending force

D support force

Ground friction.

Detailed Description

The present invention will be further described with reference to the following specific examples and drawings, but the scope of the present invention should not be limited thereto.

The invention relates firstly to the field of aircraft design, in particular civil aircraft design. Secondly, the load prediction method and system of the invention are primarily directed to aircraft with strut landing gear, but other aircraft with similar landing gear structures are not excluded.

With respect to the description of orientations presented herein, the terms "upper/top", "lower/bottom", "forward/forward", "aft/aft", etc. are all with reference to the normal attitude of the aircraft, e.g., the landing gear is located at the bottom forward position of the aircraft fuselage.

In the present invention, the term "based on" means associated with, but not understood to be based only on, the factors described later, but the factors by which the contents described later are included may include, but not be limited to, the contents described later

Finally, it is noted that the numerical values given in the embodiments are only examples and do not limit the scope of the invention.

As mentioned above, the dynamic landing load of the landing gear 130 when the aircraft lands is a component of the ground load of the aircraft, and determines whether the aircraft can land safely, which is an important basis for designing the landing gear of the aircraft and an important factor to be considered in checking the strength of the aircraft. The invention relates to a method for predicting dynamic landing load of strut landing gear. The term "prediction" refers to the prejudgment or prediction of the load of the strut landing gear during landing so as to evaluate the loading capacity of the aircraft structure, thereby providing guarantee for the aircraft verification.

The load prediction method is completed through determination or calculation of corresponding data or numerical values in the aircraft landing process, and is particularly suitable for load prediction of the landing gear 130 after a civil aircraft performs landing test flight. The data or parameters that are expected to be obtained before a landing event, and in particular a test flight launch, include the gross aircraft weight, 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 wheel hub point. More preferably, the aircraft drop test is completed before landing, particularly before test flight development, to thereby learn the relationship between the vertical force of the landing gear 130 and the strut compression, and to learn the proportional relationship between the vertical force and the heading force

In order to increase the accuracy of the load prediction method of the present invention, it is desirable that the aircraft (test flight) be landed at a high sinking speed, and that the landing moment be as short as possible without using a lifting device so as to maintain the equilibrium state between aerodynamic force and gravity as long as possible. Furthermore, considering that the typical time of the landing process is 0.3s to 0.6s, it is desirable that the sampling rate of the parameters should be as high as possible. In addition, it is desirable that the pitch angle at landing is not too large.

The method for predicting the load of the invention can firstly comprise a step of confirming the landing scene time period. In the landing scenario period confirmation step, the entry or imminent entry of a particular landing scenario period may be confirmed by checking bus parameters, the amount of compression of the strut of the landing gear 130, and the like. For example, a landing scenario period may be considered to have been entered when the flight altitude approaches airport altitude, the pitch angle approaches 0 degrees, abrupt changes in the amount of compression of the landing gear strut occur, and the like. Preferably, the determination of whether the landing time is reached may be started only after the landing scene time period is confirmed, so as to eliminate the misdetermination of the landing time due to abnormal factors, thereby improving the efficiency and accuracy of determining the landing time, but this step is not essential.

The method of predicting load of the present invention generally includes a landing time determination step. In the landing time determination step, the landing time may be determined based on the acceleration at the landing gear wheel axis point 132, because at the moment of touchdown of the aircraft landing, the tire may begin to deform and the acceleration at the wheel axis point of the strut landing gear may change abruptly.

It will be appreciated that determining the landing time based on the acceleration at the wheel axle point does not mean that other factors need not be considered in determining the landing time, but rather that determining the landing time is primarily based on the acceleration at the wheel axle point. For example, the amount of compression of the strut may also be referenced to assist in determining the moment to land.

In particular, in a preferred embodiment, the landing moment determining step may comprise several sub-steps: it is first possible to determine the moment of the sudden change in acceleration at the landing gear wheel axle point 132. In this context, "sudden change in acceleration" means that the vertical and heading accelerations of the landing gear wheel pivot point simultaneously produce a 30% change (or delta) in relative (earlier time) acceleration to the initial value of acceleration. Second, a reference time at which the amount of compression of the strut of the landing gear 130 begins to change may be determined. Finally, the mutation time preceding the reference time can be finally determined as the landing time. The moment at which the linear displacement begins to be displaced (i.e., the reference moment) is later than the abrupt change in acceleration at the landing gear wheel axle point 132, since the cushioning strut (e.g., the inner barrel 134 of the strut) begins to compress due to the cushioning effect of the landing gear strut. The mutation moment before the reference moment can be determined as the landing moment and should not be the landing moment if the mutation moment is later than the reference moment.

If the landing moment of the aircraft is confirmed, in an advantageous embodiment the bus parameters of the aircraft can be extracted or pulled. For example, at least one of the following parameters may be obtained: the aircraft body oil weight, the pitch angle, the roll angle, the pitch angle speed, the roll angle speed, the aircraft sinking speed, the forward speed, the rotating speed of the undercarriage wheels, the undercarriage wheel load signal and the like are all current parameters acquired at the landing moment.

Based on the obtained airframe oil weight and the known airframe structure weight, a gross weight of the aircraft can be obtained and used for calculations in obtaining an airframe acceleration response (described further below). After the forces at the axle points of the aircraft are acquired, force conversion may be performed based on pitch and roll angles for conversion into the body coordinate system. The pitch angle rate in combination with the pitch angle, the roll angle, the 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 judge the impulse magnitude during landing, i.e. a larger sinking speed means a larger landing impact. The slip ratio (or slip ratio) of the tires when the aircraft lands can also be calculated by acquiring the forward speed of the aircraft when the aircraft lands in combination with other parameters, such as the rotating speed of the wheels. The coefficient of ground friction can be calculated from the slip ratio and can then be used to determine the bending force (as will be further described below). The rotational speed of the wheel can be used to determine when wheel spin, bounce, and pure roll occur. In addition, as mentioned above, the rotation speed of the wheels in combination with the forward speed can determine the slip ratio, the ground friction coefficient can be calculated through the slip ratio, and then the bending force can be jointly calculated in combination with the heading acceleration and other parameters.

After determining the landing moment, the prediction method of the invention comprises a landing gear load determination step. In this landing gear load determination step, the landing gear load may be calculated based on the amount of compression of the strut of the landing gear 130 and the acceleration at the landing gear wheel axis point 132.

Although it is not excluded that other data or parameters are also required in the calculation of the landing gear load, such as the rotation speed of the wheels and various known body parameters, it should be understood that one of the important differences between the prediction method of the present invention and the prior art is that it is not necessary to use a conventional strain system to determine the structural deformation of the landing gear 130 and to perform a force analysis, nor to use empirical formulas, but rather to directly collect the acceleration signal at the wheel hub and the compression signal of the strut, thereby enabling a fast evaluation and analysis of the landing gear load in a landing scenario.

It will be appreciated that the amount of strut compression and acceleration at the axle point used in the landing gear load determining step is desirably obtained as soon as possible within a very short predetermined period of time after the landing time. The predetermined period of time may be, for example, 0.3 seconds to 0.6 seconds.

Advantageously, the compression of the strut and the acceleration at the wheel axle point (e.g. heading acceleration, vertical acceleration, lateral acceleration) can be processed during the predetermined period of time, wherein the physical quantity containing the initial value is subtracted from the initial value.

In order to measure or detect the acceleration at the wheel axle point, the prediction system according to the invention may comprise an acceleration sensor 110, which acceleration sensor 110 may be arranged at the wheel axle point, for example on a platform, whether it is precisely oriented or not does not affect its exact reflection of the acceleration.

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

In the prediction system of the present invention, the strut of the landing gear 130 may include an outer barrel 136 connected to the fuselage and an inner barrel 134 translatable relative to the outer barrel 136, as shown in FIG. 1. A torsion arm 138 may also be disposed between the inner and outer barrels 134, 136. In order to measure or detect the compression of the strut, a linear displacement sensor 120 can be arranged, which is connected at one end to the outer cylinder 136 of the strut and at the opposite end to the landing gear wheel axle point 132. Therefore, the compression stroke of the landing gear during landing can be conveniently measured.

The landing gear load determined according to the prediction method of the present invention may refer to a force, including, for example, an axial force, a bending force, etc., at the landing gear wheel pivot point 132. Further, landing gear load may also refer to moments, including, for example, head-up moment, roll moment, and the like.

As shown in fig. 3, the landing gear load determination step of the prediction method according to the invention is mainly determined or calculated based on the following principle. When the strut landing gear 130 contacts the ground when landing, taking the strut landing gear 130 as an example, the landing gear 130 is mainly subjected to the combined action of four forces: the ground-to-landing gear 130 support force D, the ground friction force V, the bending force N (acting at the axle point) resulting from the bending deformation to which the strut landing gear 130 is subjected, and the compression force F resulting from the compression deformation to which the strut landing gear 130 is subjected. The support force D, the ground friction force V, the bending force N and the compression force F act together to generate acceleration response at the wheel axle point.

In particular, the landing gear load determination step of the inventive prediction method may comprise a plurality of sub-steps. In this first sub-step, a preliminary axial force F' of the strut of the landing gear may be determined on the basis of the compression of the strut. Depending on the specific construction of the strut, the axial force of the strut may consist of oil hydraulic force, air force and friction, with the friction being relatively small. After the airplane drop test is finished, the relation between the hydraulic force, the air force and the compression amount of the oil can be obtained. For example, in some embodiments, the oil force = coefficient x rate of change of compression ² And air force = (initial charge volume/(initial charge volume-piston area × -compression)) ^ polytropic exponent × initial charge force. Thus, by taking the compression amount of the strut and thus the rate of change of the compression amount, the oil hydraulic force and the air force of the strut can be determined. The preliminary axial force F' of the strut can be determined by the sum of the hydrodynamic and aerodynamic forces. As mentioned above, this preliminary axial force F' can be used for subsequent load calculations without the accuracy of the calculation being significantly affected, since the friction of the strut is comparatively small.

The landing gear load determining step may further comprise a second sub-step. In this second sub-step, the bending force N of the landing gear may be determined based on the preliminary axial force F' calculated in the first sub-step and the acceleration at the landing gear wheel axle point 132. The second substep is calculated in principle, whereby the ground support force is obtained from the preliminary axial force F' and the acceleration at the wheel axle point, and then the friction force is obtained from the ground support force and the friction coefficient, and the bending force N is obtained again from the friction force. That is, in the present invention, the determination of the bending force N is primarily done based on the learned preliminary axial force F' and the acceleration (e.g., vertical acceleration and heading acceleration) at the landing gear wheel axle point 132.

In some embodiments, the ground-facing landing gear 130 support force D may be determined first from the preliminary axial force F'. This may be done, for example, by combining the preliminary axial force F' with the vertical acceleration at the wheel axle point, and obtaining the support force D by force analysis (see fig. 3). After the support force D is obtained, the ground friction force V may be determined based on the support force D, the ground friction coefficient. The ground friction coefficient may be determined by detecting the forward speed of the aircraft and the rotational speed of the wheels and calculating the slip ratio therefrom, but other methods may be used. Generally, the ground friction force V is equal to the product of the support force D and the ground friction coefficient. Finally, the bending force N may be determined from the ground friction force V and the heading acceleration at the landing gear wheel axle point 132. More specifically, bending force N = lumped mass M × heading acceleration + ground friction at the wheel axle point.

The landing gear load determining step may further comprise a third sub-step. In this third sub-step, the corrected axial force F of the landing gear may be determined on the basis of the bending force N and the strut friction coefficient of the strut. This corrected axial force F is corrected by the strut friction with respect to the preliminary axial force F' and is therefore more precise, one of the important parameters of the landing gear load to be obtained by the prediction method of the invention.

In some embodiments, the coefficient of friction of the strut (e.g., the coefficient of friction between the inner barrel 134 and the outer barrel 136) may be obtained when the strut landing gear 130 is designed. A lower value of the strut friction can be obtained, in combination with the coefficient of friction of the strut, based on the bending force N determined in the second substep.

As mentioned above, the axial force of the strut is actually composed of three forces, i.e., hydraulic force, air force, and friction. The first two are obtained from the compression of the strut and its rate of change, while the friction is obtained in this step, from which the corrective axial force F of the strut can be finally obtained.

After determining the landing gear load including the bending force and the axial force, the landing gear load determining step may further include a fourth substep. In this fourth sub-step, the head-up moment at the intersection of the landing gear 130 with the fuselage may be determined based on the corrected axial direction F, the bending force N and the compression of the strut. Depending on the particular arrangement of the aircraft, in some embodiments, the nose-up moment may be calculated, for example, by the following formula:

head-up moment = bending force × (intersection to axle point distance-compression amount) × (pitch angle + landing gear heading mount angle) + axial force × (intersection to axle point distance-compression amount) × (pitch angle + landing gear heading mount angle).

Alternatively or additionally, in the fourth sub-step, the roll moment at the point of intersection of the landing gear with the fuselage connection may be determined based on the modified axial force F, the lateral acceleration at the landing gear wheel axle point 132 and the amount of compression of the strut. In some embodiments, roll torque may be calculated, for example, by the following equation:

roll torque = lateral acceleration x mass of the wheel x (intersection to axle point distance-compression) × cos (roll angle + landing gear lateral setting angle) + axial force x (intersection to axle point distance-compression) × sin (roll angle + landing gear lateral setting angle).

Furthermore, the load prediction method according to the invention may also 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 method described above. In particular, the landing gear load verification step may include a body acceleration response determination step in which a body acceleration response, in particular a full body acceleration response, may be determined based on the landing gear load.

In some advantageous embodiments, after the landing gear load is obtained, the landing gear load may 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.) may be used to obtain the acceleration response of various parts of the body 100. This is not limiting and those skilled in the art will know the method of obtaining the body acceleration response through landing gear loading.

The landing gear load verification step may also include a verification step. In this verification step, the actual body acceleration response may be captured and the body accelerator response determined in the body acceleration response determination step compared to the captured actual body acceleration response to verify the accuracy or trustworthiness of the landing gear load.

In order to obtain the actual acceleration response of the body, an acceleration sensor 110, especially a low frequency acceleration sensor, may be arranged on at least one of the fuselage, the wing, and the horizontal tail for measuring the actual acceleration response of various parts of the body 100. The acceleration sensor 110 is installed in a position considering a region where the body has a large elasticity and a small elasticity. In the preferred embodiment, taking the fuselage as an example, the acceleration sensors 110 are disposed on the middle fuselage, the front fuselage, the rear fuselage, the nose, and the tail, for example, see the encircled area in fig. 2, but this is not limiting. More preferably, the response acceleration in the trial flight of the processing body is processed within a predetermined period of time from the landing time. The predetermined period of time may also be, for example, 0.3 seconds to 0.6 seconds, but this is not limiting.

An exemplary flow chart of a load prediction method according to the present invention is shown in fig. 4. In this preferred embodiment, the method of the invention first performs a landing scenario time period validation in a first step and determines the landing time in a second step, e.g. based on the acceleration at the landing gear wheel axle point 132, optionally using the amount of strut compression as an auxiliary judgment condition. In a third step, aircraft general parameters such as sinking speed, forward speed, pitch angle, roll angle, pitch angle speed, roll angle speed, oil weight, and rotating speed of the wheels are extracted. The amount of compression of the strut at the time of landing (or for a very short predetermined period of time thereafter) and the acceleration at the landing gear wheel point 132 are processed in a fourth step. In the fifth step, the landing gear loads, primarily bending and axial forces, are determined based on the amount of compression of the strut and the acceleration at the landing gear wheel pivot point 132. Then in a sixth step, the body acceleration response is determined with the landing gear load as the excitation. In a seventh step the body acceleration response is processed (test flight) and learned, for example, by means of acceleration sensors 110 actually arranged on various parts of the body 100. And finally, comparing the calculated body acceleration response with the actually measured body acceleration response to verify the accuracy of the undercarriage load. One or more of the above steps may be omitted and thus the above process flow is merely exemplary.

In order to ensure that the load prediction method according to the invention can be implemented, the invention may also provide a system for predicting dynamic landing loads on strut landing gears.

A system for predicting landing gear dynamic landing loads of the strut type may include a linear displacement sensor 120 disposed at a strut of a landing gear 130 to measure an amount of compression of the strut and an acceleration sensor 110 disposed at a landing gear wheel point 132 to measure an acceleration at the landing gear wheel point 132.

Furthermore, the prediction system of the present invention may also comprise a controller comprising modules for performing various functions, in particular the various method steps described in detail above. For example, the controller may include a landing time determination module for determining the landing time based on the acceleration at the landing gear wheel hub point 132. Also for example, the controller may include a landing gear load determination module to calculate landing gear loads after a landing time based on the amount of compression of the landing gear leg and the acceleration at the landing gear wheel point 132, where the landing gear loads may include axial and bending forces at the landing gear wheel point 132, but may also include other forces and moments, such as a nose-up moment and a roll moment.

To determine the axial and bending forces, the landing gear load determination module may be further subdivided into a plurality of sub-modules. The electronic components necessary for performing functions, including but not limited to comparators, signal transmitting terminals, signal receiving terminals, and the like, may be included in the modules and sub-modules of the controller.

For example, the landing gear load determination module may include a first sub-module for determining a preliminary axial force F' of the landing gear 130 based on an amount of strut compression. The landing gear load determination module may also include a second sub-module 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 pivot point 132. The landing gear load determination module may further include a third sub-module for determining a corrected axial force F of the landing gear 130 based on the bending force N and the strut friction coefficient of the strut.

It will be appreciated that each of the foregoing steps or sub-steps may have a corresponding controller module or sub-module to facilitate the execution of the method in accordance with the present invention. For example, the landing gear load determination module may further include a body acceleration response determination module to determine a body acceleration response based on the landing gear load; and a verification module that can acquire the body actual acceleration response, receive the body accelerator response from the body acceleration response module, and compare it to the acquired body actual acceleration response to verify the landing gear load.

To this end, the present invention provides a method and a system for predicting a dynamic landing load of an aircraft strut-type landing gear, in which a linear displacement sensor 120 and an acceleration sensor 110 are disposed at a landing gear 130, so that a response characteristic of the landing gear 130 can be obtained after a landing test flight. The landing gear excitation for landing can be obtained by combining airplane parameters, landing data, landing gear characteristic parameters and the like, and the landing gear excitation is used for researching the response characteristics of all parts, main systems and equipment under the landing excitation.

Although various embodiments of the present invention are described in the drawings with reference to strut-type landing gear for civilian 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 functionality.

The foregoing description has set forth numerous features and advantages, including various alternative embodiments, as well as details of the structure and function of the devices and methods. The intent herein is to be exemplary and not exhaustive or limiting.

It will be obvious to those skilled in the art that various modifications may be made, especially in matters of structure, materials, elements, components, shape, size and arrangement of parts including combinations of these aspects within the principles described herein, to the full extent indicated by the broad, general meaning of the terms in which the appended claims are expressed. To the extent that such various modifications do not depart from the spirit and scope of the appended claims, they are intended to be included therein as well.

Claims (12)

1. A method for predicting dynamic landing loads of strut landing gears, comprising the steps of, in order:

a landing time determining step: determining a landing time based on an acceleration at an axle point of the landing gear;

a landing gear load determining step: calculating a landing gear load based on the amount of compression of the strut of the landing gear and the acceleration at the landing gear hub point, the landing gear load comprising an axial force and a bending force at the landing gear hub point,

wherein the landing gear load determining step comprises the sub-steps of:

the first substep: determining a preliminary axial force (F') of the landing gear based on the amount of compression;

the second substep: determining a bending force (N) of the landing gear based on the calculated preliminary axial force (F') and the acceleration at the landing gear axle point;

the third substep: a corrected axial force (F) of the landing gear is determined based on the bending force and the strut friction coefficient of the strut.

2. The method of claim 1, wherein the landing time determination step comprises: -determining a sudden change moment at which the acceleration at the landing gear wheel axle point changes suddenly;

-determining a reference moment at which the compression of the strut of the landing gear starts to change;

-determining the mutation moment in advance of the reference moment as the landing moment.

3. The method of claim 1, wherein the second substep comprises:

-determining a ground-to-landing-gear support force (D) based on the preliminary axial force (F') and the vertical acceleration at the landing-gear wheel axle point;

-determining a ground friction force (V) based on the support force and a ground friction coefficient;

-determining the bending force (N) based on the ground friction force (V) and the heading acceleration at the landing gear wheel axle point.

4. The method of claim 1, wherein the following steps are performed in sequence after the landing gear load determining step:

body acceleration response determination: determining a body acceleration response based on the landing gear load;

and (3) a verification step: acquiring an actual body acceleration response and comparing the body accelerator response determined in the body acceleration response determination step with the acquired actual body acceleration response to verify the landing gear load.

5. The method according to claim 1, wherein the landing gear load determining step further comprises a fourth sub-step of:

determining a nose-up moment at an intersection of the landing gear and the fuselage connection based on the modified axial force (F), the bending force (N) and the amount of compression; and/or

Determining a roll torque at the intersection of the landing gear and the fuselage connection based on the modified axial force (F), the lateral acceleration at the landing gear wheel axle point and the amount of compression.

6. The method of claim 1, further comprising extracting bus parameters of the aircraft at the landing time, the bus parameters selected from the group consisting of:

sinking speed, forward speed, pitch angle, roll angle, pitch angle speed, roll angle speed, oil weight and rotating speed of the airplane wheel.

7. A system for predicting column landing gear dynamic landing loads, the system comprising:

a linear displacement sensor disposed at a strut of a landing gear to measure an amount of compression of the strut;

an acceleration sensor arranged at a landing gear axle point to measure acceleration at the landing gear axle point;

a controller, the controller comprising:

a landing time determination module for determining a landing time based on an acceleration at an axle point of a landing gear;

a landing gear load determination module for calculating a landing gear load after the landing time based on an amount of compression of a strut of the landing gear and an acceleration at a landing gear hub point, the landing gear load comprising an axial force and a bending force at the landing gear hub point;

wherein the landing gear load determination module comprises the following sub-modules:

a first submodule for determining a preliminary axial force (F') of the landing gear on the basis of said compression;

a second sub-module 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 sub-module for determining a corrected axial force (F) of the landing gear based on the bending force and the strut friction coefficient of the strut.

8. The system of claim 7, wherein the acceleration sensor is configured to measure vertical acceleration, heading acceleration, and lateral acceleration at an axle point of the landing gear.

9. The system of claim 7, wherein the strut comprises an outer barrel connected to the fuselage and an inner barrel translatable relative to the outer barrel, wherein one end of the linear displacement sensor is connected to the outer barrel and an opposite end is connected to the landing gear hub point.

10. The system of claim 7, wherein the landing gear load determination module further comprises:

an airframe acceleration response determination module to determine an airframe acceleration response based on the landing gear load;

a verification module that obtains an actual body acceleration response, receives the body accelerator response from the body acceleration response module, and compares it to the obtained actual body acceleration response to verify the landing gear load.

11. The system of claim 10, wherein an acceleration sensor is disposed on at least one of the fuselage, the wing, and the horizontal tail, and the actual acceleration response of the body obtained by the verification module is the actual acceleration response of the at least one.

12. The system according to claim 7, wherein the landing time determination module is configured to determine an abrupt time at which an abrupt change in acceleration occurs at the landing gear wheel axle point and a reference time at which a change in compression of a strut of the landing gear begins, and to determine the abrupt time before the reference time as the landing time.

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