Method for calculating shimmy critical initial deflection angle of undercarriage of friction type shimmy damper

Abstract

The invention belongs to the technical field of aircraft landing gear strength design, and particularly relates to a method for calculating a shimmy critical initial deflection angle of a landing gear of a friction type shimmy damper. The method comprises the following steps: step 1, acquiring an anti-swing critical damping coefficient and a shimmy frequency of the undercarriage; step 2, acquiring the friction damping torque of the undercarriage movable part rotating around the axis of the buffer strut; step 3, based on an energy equivalence principle, calculating a frictional damping torque equivalent anti-shimmy damping coefficient under different undercarriage shimmy initial deflection angles and shimmy frequency conditions; 4, according to the undercarriage anti-swing critical damping coefficient and the friction damping torque equivalent anti-swing damping coefficient, the undercarriage shimmy stability condition is determined; and step 5, determining the undercarriage shimmy critical initial deflection angle according to the shimmy stability condition of the undercarriage. According to the method, the influence analysis of the structure friction damping torque on the undercarriage shimmy characteristic can be effectively carried out, the undercarriage shimmy stability condition can be rapidly obtained, and the calculation efficiency is high.

Description

Technical Field

[0001] This application belongs to the field of aircraft landing gear strength design technology, and specifically relates to a method for calculating the critical initial deflection angle of landing gear shimmy using a friction damper. Background Technology

[0002] Landing gear shimmy is a serious malfunction during aircraft development and operation. When shimmy occurs during takeoff, it can cause not only fuselage swaying or resonance in localized areas, affecting pilot control, but also damage to the shimmy damper lever, transmission mechanism, housing and its mounting devices, landing gear, fuselage structure, wheels and tires, and even aircraft crashes. Due to considerations of cost, weight, and maintainability, small, low-cost general aviation aircraft and unmanned aerial vehicles (UAVs) rarely have complex hydraulic control systems; therefore, friction-type shimmy dampers are a common shimmy reduction design for the nose landing gear of these aircraft.

[0003] With increasing domestic expectations for the future market of low-cost general aviation aircraft and drones, the development of multiple types of low-cost general aviation aircraft and various drones has commenced. During the development process, shimmy phenomena repeatedly occurred in laboratory shimmy tests of landing gear using friction dampers. Therefore, it is necessary to conduct landing gear shimmy characteristic analysis to obtain the stability conditions for landing gear shimmy. Friction dampers rely on frictional damping generated during the movement of the damper structure to provide the necessary damping for landing gear shimmy. Frictional damping is a nonlinear parameter, characterized by its magnitude being independent of the motion velocity and its direction being opposite to the relative motion direction of the structure. The function describing this damping force is discontinuous and non-differentiable, making it difficult to describe this discontinuous motion phenomenon using the differential equations of landing gear shimmy motion. It is necessary to convert the frictional damping into a continuously differentiable anti-shimmy damping function and then substitute it into the differential equations of landing gear shimmy motion for landing gear shimmy analysis.

[0004] Therefore, there is an urgent need for a technical solution to overcome or mitigate at least one of the aforementioned defects in the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a method for calculating the critical initial deflection angle of landing gear shimmy in a friction-type shimmy damper, so as to solve at least one problem existing in the prior art.

[0006] The technical solution of this application is:

[0007] The first aspect of this application provides a method for calculating the critical initial deflection angle of landing gear shimmy in a friction-type shimmy damper, including:

[0008] Step 1: Obtain the critical damping coefficient and oscillation frequency of the landing gear;

[0009] Step 2: Obtain the frictional damping torque of the moving parts of the landing gear rotating around the axis of the buffer strut;

[0010] Step 3: Based on the principle of energy equivalence, calculate the equivalent damping coefficient of friction damping torque under different landing gear oscillation initial deflection angles and oscillation frequencies.

[0011] Step 4: Determine the landing gear sway stability condition based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent sway reduction damping coefficient.

[0012] Step 5: Determine the critical initial deflection angle of landing gear shimmy based on the landing gear shimmy stability conditions.

[0013] In at least one embodiment of this application, in step one, the critical damping coefficient for anti-swaying of the landing gear is solved according to the differential equation of landing gear sway motion.

[0014] In at least one embodiment of this application, in step one, the oscillation frequency is solved according to the differential equation of landing gear oscillation motion.

[0015] In at least one embodiment of this application, in step two, the friction damping torque of the moving part of the landing gear rotating about the axis of the buffer strut is calculated based on the friction damping of the friction damper and the installation structural parameters of the friction damper on the landing gear:

[0016] ;

[0017] Where M is the frictional damping torque of the landing gear moving part rotating around the buffer strut axis, F is the frictional damping of the friction damper, and L is the lever arm length of the frictional damping acting on the buffer strut axis.

[0018] In at least one embodiment of this application, in step two, when calculating the friction damping torque, the installation structural parameters of the friction damper on the landing gear are based on the landing gear wheels being in a neutral position.

[0019] In at least one embodiment of this application, in step three, the equivalent damping coefficient of the friction damping torque is calculated according to the equivalent damping coefficient calculation function:

[0020] ;

[0021] Among them, h mc θ is the equivalent damping coefficient for friction damping torque, f is the oscillation frequency, and θ0 is the initial oscillation angle of the landing gear.

[0022] In at least one embodiment of this application, the friction damping torque in the equivalent anti-sway damping coefficient calculation function is the friction damping torque of the landing gear after being disturbed by the ground.

[0023] In at least one embodiment of this application, the oscillation frequency in the equivalent oscillation damping coefficient calculation function is the oscillation frequency of the landing gear after being disturbed by the ground.

[0024] In at least one embodiment of this application, the landing gear sway initial deflection angle in the equivalent sway damping coefficient calculation function is the landing gear sway initial deflection angle after the landing gear is disturbed by the ground.

[0025] In at least one embodiment of this application, step four, determining the landing gear shimmy stability condition based on the landing gear anti-shimmy critical damping coefficient and the friction damping torque equivalent shimmy reduction damping coefficient, includes:

[0026] Under the condition of landing gear shimmy stability, the equivalent anti-shimmy damping coefficient of the friction damping torque is not less than the critical anti-shimmy damping coefficient of the landing gear:

[0027] ;

[0028] The stability condition for landing gear shimmy is that the initial deflection angle of the landing gear shimmy must satisfy the following condition:

[0029] ;

[0030] Among them, h cr This is the critical damping coefficient for anti-swaying of the landing gear.

[0031] In at least one embodiment of this application, steps one to four are repeated to obtain the landing gear oscillation stability conditions under different friction damping conditions of friction dampers.

[0032] In at least one embodiment of this application, steps one to four are repeated to obtain the landing gear shimmy stability conditions under different aircraft taxiing speeds.

[0033] In at least one embodiment of this application, steps one to four are repeated to obtain the landing gear shimmy stability conditions under different landing gear load conditions.

[0034] In at least one embodiment of this application, in step five, the critical initial deflection angle of the landing gear oscillation is:

[0035] ;

[0036] Where, θ cr This is the critical initial deflection angle for landing gear oscillation.

[0037] A second aspect of this application provides a device for calculating the critical initial deflection angle of a friction-type yaw damper landing gear, comprising:

[0038] The parameter solving module is used to obtain the critical damping coefficient for anti-swaying of the landing gear and the sway frequency.

[0039] The friction damping torque calculation module obtains the friction damping torque of the landing gear moving parts rotating around the buffer strut axis;

[0040] The equivalent anti-sway damping coefficient solution module is used to calculate the equivalent anti-sway damping coefficient of friction damping torque under different landing gear sway initial deflection angles and sway frequencies based on the energy equivalence principle.

[0041] The stability condition solution module is used to determine the landing gear sway stability condition based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent sway reduction damping coefficient.

[0042] The landing gear shimmy critical initial deflection angle solution module is used to determine the landing gear shimmy critical initial deflection angle based on the landing gear shimmy stability conditions.

[0043] The invention has at least the following beneficial technical effects:

[0044] The method for calculating the critical initial deflection angle of landing gear shimmy using a friction damper in this application can quickly realize the setting and adjustment of friction damping generated when the moving structure of the landing gear moves around the axis of the buffer strut. It can effectively carry out the influence analysis of the structural friction damping torque on the shimmy characteristics of the landing gear, and can quickly obtain the stability conditions of the landing gear shimmy, with high calculation efficiency. Attached Figure Description

[0045] Figure 1 This is the landing gear yaw reduction critical damping curve under different runway speed conditions according to one embodiment of this application;

[0046] Figure 2 This is a landing gear oscillation frequency curve under different taxiing speed conditions according to one embodiment of this application;

[0047] Figure 3 This is a schematic diagram of a landing gear employing a friction damper according to one embodiment of this application;

[0048] Figure 4 This is a schematic diagram of the installation structure of a friction damper on the landing gear according to one embodiment of this application;

[0049] Figure 5 This is a landing gear shimmy critical initial deflection angle curve according to one embodiment of this application. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0051] The following is in conjunction with the appendix Figures 1 to 5 This application will be described in further detail.

[0052] This application provides a method for calculating the critical initial deflection angle of landing gear shimmy in a friction-type shimmy damper, including the following steps:

[0053] Step 1: Obtain the critical damping coefficient and oscillation frequency of the landing gear;

[0054] Step 2: Obtain the frictional damping torque of the moving parts of the landing gear rotating around the axis of the buffer strut;

[0055] Step 3: Based on the principle of energy equivalence, calculate the equivalent damping coefficient of friction damping torque under different landing gear oscillation initial deflection angles and oscillation frequencies.

[0056] Step 4: Determine the landing gear sway stability condition based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent sway reduction damping coefficient.

[0057] Step 5: Determine the critical initial deflection angle of landing gear shimmy based on the landing gear shimmy stability conditions.

[0058] The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper in this application, in step one, can use existing mature differential equations of landing gear shimmy motion to solve for the critical damping coefficient and shimmy frequency of the landing gear. The differential equations of landing gear shimmy motion should include tire dynamic parameters, landing gear torsional stiffness, landing gear lateral stiffness, etc. In one embodiment of this application, such as... Figure 1 As shown, the critical damping curves for anti-sway of the landing gear under different runway speeds are presented, obtained by solving the differential equation of landing gear sway motion. Figure 2 As shown, the shimmy frequency curves of the landing gear under different running speeds are given, which are obtained by solving the differential equation of the landing gear shimmy motion.

[0059] In the method for calculating the critical initial deflection angle of landing gear shimmy using a friction damper in this application, step two involves calculating the friction damping torque of the landing gear moving parts rotating around the axis of the buffer strut based on the friction damper's friction damping and the installation structural parameters of the friction damper on the landing gear.

[0060] ;

[0061] Where M is the frictional damping torque of the landing gear moving part rotating around the buffer strut axis, F is the frictional damping of the friction damper, and L is the lever arm length of the frictional damping acting on the buffer strut axis.

[0062] Landing gear equipped with friction dampers, such as Figure 3 As shown, the installation structure of the friction damper on the landing gear is as follows: Figure 4 As shown. When calculating the friction damping torque, it is recommended to take the structural parameters when the landing gear wheels are in the neutral position, with the magnitude of the friction damping being a fixed value and the direction opposite to the direction of motion.

[0063] In the method for calculating the critical initial deflection angle of landing gear oscillation in the friction damper of this application, step three involves calculating the equivalent damping coefficient corresponding to the friction damping torque under different landing gear oscillation initial deflection angles and oscillation frequencies using the principle of energy equivalence.

[0064] The equivalent sway damping coefficient calculation function is as follows:

[0065] ;

[0066] Among them, h mc Let f be the equivalent damping coefficient for friction damping torque, f be the shimmy frequency, and θ0 be the initial shimmy angle of the landing gear. The initial shimmy angle of the landing gear is the initial shimmy angle of the landing gear wheel.

[0067] In this embodiment, in the equivalent anti-sway damping coefficient calculation function, the friction damping torque is the friction damping torque of the landing gear after being disturbed by the ground, the sway frequency is the sway frequency of the landing gear after being disturbed by the ground, and the initial sway angle of the landing gear is the initial sway angle of the landing gear after being disturbed by the ground. When using a safety factor to determine the anti-sway damping of the steering anti-sway system, the equivalent anti-sway damping coefficient of the friction damping torque does not need to be multiplied by the corresponding safety factor.

[0068] In the method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper in this application, step four involves determining the landing gear shimmy stability conditions based on the critical anti-shimmy damping coefficient of the landing gear and the equivalent shimmy damping coefficient of the friction damping torque, including:

[0069] To prevent landing gear shimmy, under the condition of landing gear shimmy stability, the equivalent shimmy reduction damping coefficient of the friction damping torque shall not be less than the critical anti-shimmy damping coefficient of the landing gear:

[0070] ;

[0071] The stability condition for landing gear shimmy is that the initial deflection angle of the landing gear shimmy must satisfy the following condition:

[0072] ;

[0073] Among them, h cr This is the critical damping coefficient for anti-swaying of the landing gear.

[0074] By repeating steps one through four, the solution parameters are obtained under different friction damping of friction dampers, different aircraft takeoff speeds, and different landing gear load conditions, thereby obtaining the landing gear shimmy stability conditions under different conditions.

[0075] The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper in this application determines whether shimmy will occur in a given landing gear system, depending on the initial deflection angle of the wheels after being excited by ground disturbance. Finally, in step five, the critical initial deflection angle of landing gear shimmy is determined based on the landing gear shimmy stability condition as follows:

[0076] ;

[0077] Where, θ cr This is the critical initial deflection angle for landing gear oscillation.

[0078] Therefore, it can be seen that by increasing the friction damping of the friction-type shimmy damper, the critical initial deflection angle of the landing gear shimmy can be increased, thereby improving shimmy stability. In one embodiment of this application, such as Figure 5 As shown, the critical initial deflection angle curves of landing gear shimmy under different runway speed conditions are presented.

[0079] This application presents a method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper. This method solves for the landing gear anti-shimmy damping coefficient and shimmy frequency using the landing gear shimmy motion equations. It then calculates the equivalent shimmy damping coefficient provided by the friction-type shimmy damper under different initial deflection angles and shimmy frequencies using the energy equivalence principle. Finally, it determines the landing gear shimmy stability conditions under different friction damping conditions of the friction-type shimmy damper. This method enables the analysis of landing gear shimmy characteristics using friction-type shimmy dampers.

[0080] Based on the above-mentioned method for calculating the critical initial deflection angle of landing gear shimmy using a friction damper, this application also provides a device for calculating the critical initial deflection angle of landing gear shimmy using a friction damper, comprising:

[0081] The parameter solving module is used to obtain the critical damping coefficient for anti-swaying of the landing gear and the sway frequency.

[0082] The friction damping torque calculation module obtains the friction damping torque of the landing gear moving parts rotating around the buffer strut axis;

[0083] The equivalent anti-sway damping coefficient solution module is used to calculate the equivalent anti-sway damping coefficient of friction damping torque under different landing gear sway initial deflection angles and sway frequencies based on the energy equivalence principle.

[0084] The stability condition solution module is used to determine the landing gear shimmy stability condition based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent shimmy reduction damping coefficient.

[0085] The landing gear shimmy critical initial deflection angle solution module is used to determine the landing gear shimmy critical initial deflection angle based on the landing gear shimmy stability conditions.

[0086] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for calculating the critical initial deflection angle of landing gear shimmy in a friction-type shimmy damper, characterized in that, include: Step 1: Obtain the critical damping coefficient and oscillation frequency of the landing gear; Step 2: Obtain the frictional damping torque of the moving parts of the landing gear rotating around the axis of the buffer strut; Step 3: Based on the principle of energy equivalence, calculate the equivalent damping coefficient of friction damping torque under different landing gear oscillation initial deflection angles and oscillation frequencies. Step 4: Determine the landing gear sway stability condition based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent sway reduction damping coefficient. Step 5: Determine the critical initial deflection angle of landing gear shimmy based on the landing gear shimmy stability conditions.

2. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 1, characterized in that, In step one, the critical damping coefficient for anti-swaying of the landing gear is solved based on the differential equation of landing gear sway motion.

3. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 2, characterized in that, In step one, the oscillation frequency is solved based on the differential equation of the landing gear oscillation motion.

4. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 3, characterized in that, In step two, based on the friction damping of the friction damper and the installation structural parameters of the friction damper on the landing gear, the friction damping torque of the moving part of the landing gear rotating around the axis of the buffer strut is calculated: ； Where M is the frictional damping torque of the landing gear moving part rotating around the buffer strut axis, F is the frictional damping of the friction damper, and L is the lever arm length of the frictional damping acting on the buffer strut axis.

5. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 4, characterized in that, In step two, when calculating the friction damping torque, the installation structural parameters of the friction damper on the landing gear are based on the landing gear wheels being in a neutral position.

6. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 5, characterized in that, In step three, the equivalent damping coefficient of the friction damping torque is calculated using the equivalent damping coefficient calculation function. ； Among them, h mc θ is the equivalent damping coefficient for friction damping torque, f is the oscillation frequency, and θ0 is the initial oscillation angle of the landing gear.

7. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 6, characterized in that, The friction damping torque in the equivalent sway reduction damping coefficient calculation function is the friction damping torque of the landing gear after being disturbed by the ground.

8. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 7, characterized in that, The oscillation frequency in the equivalent oscillation damping coefficient calculation function is the oscillation frequency of the landing gear after being disturbed by the ground.

9. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 8, characterized in that, The initial deflection angle of the landing gear sway in the equivalent sway damping coefficient calculation function is the initial deflection angle of the landing gear sway after it is disturbed by the ground.

10. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 9, characterized in that, In step four, the landing gear sway stability condition is determined based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent sway reduction damping coefficient, including: Under the condition of landing gear shimmy stability, the equivalent anti-shimmy damping coefficient of the friction damping torque is not less than the critical anti-shimmy damping coefficient of the landing gear: ； The stability condition for landing gear shimmy is that the initial deflection angle of the landing gear shimmy must satisfy the following condition: ； Among them, h cr This is the critical damping coefficient for anti-swaying of the landing gear.

11. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 10, characterized in that, Repeat steps one through four to obtain the landing gear shimmy stability conditions under different friction damping conditions of friction dampers.

12. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 11, characterized in that, Repeat steps one through four to obtain the landing gear shimmy stability conditions under different aircraft taxiing speeds.

13. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 12, characterized in that, Repeat steps one through four to obtain the landing gear shimmy stability conditions under different landing gear load conditions.

14. The method for calculating the critical initial deflection angle of landing gear shimmy using a friction-type shimmy damper according to claim 13, characterized in that, In step five, the critical initial deflection angle of the landing gear oscillation is: ； Where, θ cr This is the critical initial deflection angle for landing gear oscillation.

15. A device for calculating the critical initial deflection angle of landing gear shimmy in a friction-type shimmy damper, characterized in that, include: The parameter solving module is used to obtain the critical damping coefficient for anti-swaying of the landing gear and the sway frequency. The friction damping torque calculation module obtains the friction damping torque of the landing gear moving parts rotating around the buffer strut axis; The equivalent anti-sway damping coefficient solution module is used to calculate the equivalent anti-sway damping coefficient of friction damping torque under different landing gear sway initial deflection angles and sway frequencies based on the energy equivalence principle. The stability condition solution module is used to determine the landing gear sway stability condition based on the landing gear anti-sway critical damping coefficient and the friction damping torque equivalent sway reduction damping coefficient. The landing gear shimmy critical initial deflection angle solution module is used to determine the landing gear shimmy critical initial deflection angle based on the landing gear shimmy stability conditions.

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