Heavy-load unmanned aerial vehicle landing impact hierarchical absorption control method

Abstract

The present disclosure provides a heavy-load unmanned aerial vehicle landing impact hierarchical absorption control method, comprising: calculating a static support force based on the pressure in the strut oil and gas cavity; inversely checking a first remaining elastic stroke based on the static support force and the elastic counterforce displacement relationship; collecting the body belly surface static pressure, performing normalization according to the paddle disc load, and calculating the residual sinking speed; calculating the over-level energy based on the static support force and the residual sinking speed; obtaining the secondary damping force initial value; calculating the rising rate threshold based on the secondary damping force initial value and the first remaining elastic stroke; calculating the support force rising rate; obtaining the impact force peak value based on the collapse stroke release action and the third collapse force; calculating the actual absorption energy of each level based on the consumption stroke of each level; outputting the return release speed; and obtaining the landing impact hierarchical absorption control conclusion based on the return release speed and the impact force peak value.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) landing buffering, and in particular to a graded absorption control method for landing impact of heavy-load UAVs. Background Technology

[0002] Heavy-duty drones (UAVs) undertake cargo transport missions, with maximum takeoff weights in the hundreds of kilograms. These aircraft are multi-rotor or compound-wing designs. They shuttle between logistics hubs, mountain logistics sites, and temporary field sites, performing multiple sorties daily. The flatness and load-bearing conditions of the takeoff and landing sites vary. Cargo is loaded inside the cabin or suspended beneath the fuselage, with the load changing with each sortie, altering the aircraft's total mass and center of gravity. At the moment of touchdown, the kinetic energy of the descent is transferred to the fuselage structure along the landing gear, with the peak load occurring at the connection joint between the fuselage and landing gear. The components on the landing gear that provide cushioning are categorized into three types based on their energy absorption mechanisms: one type generates a reaction force after being compressed and returns to its original length after unloading; another type dissipates energy by generating heat through a narrow channel where liquid is squeezed; and the third type deforms under pressure and does not recover. This method of sequentially absorbing impact energy among these three types of components is known as graded absorption. The effectiveness of graded absorption directly determines the load-bearing capacity of the fuselage joint and the integrity of the cargo; under heavy load conditions, the margin for this effect is even more critical.

[0003] The current landing buffer control operates along two chains. On the observation chain, onboard data such as strut travel displacement, strut cavity pressure, and vertical acceleration are collected. The pre-touch-off altitude and descent velocity are derived from a monotonous lift segment occurring during the rotor disk load's entry into the ground effect zone; this segment occurs once per approach. On the decision chain, the observed data are compared with the offline-set level switching threshold, which is set according to the maximum takeoff weight, and the current level is output. The execution mechanism outputs current to the magnetorheological damper winding or adjusts the throttle valve opening; the setting action is completed in one step at the preset command time before touchdown. The process from touchdown to the peak impact force is on the order of tens of milliseconds, and the magnetorheological damping force rises from zero to the upper limit of the yield force on the order of tens of milliseconds. The damping force's deactivation time is on the same order of magnitude as its establishment time. This approach operates normally in a single continuous approach: the lift segment forms during the entry process, the threshold is assigned before touchdown, and the damping force is established at the moment of touchdown. In the three situations of airfield occupation, crosswind exceeding limits, and sudden obstacle, the control command is changed to pull up and go-around. The aircraft turns into a circle at low altitude and performs a second approach. The starting altitude of the second approach is within the range of the rotor disk diameter. The aircraft is in the ground effect zone from beginning to end, and the rotor disk load is in the high-level plateau section.

[0004] Both the observation entry and execution of the graded absorption are non-reentrant, one-time actions. The observation entry is taken from the one-time process of the aircraft entering the ground effect zone from outside the zone. The execution of the arrest is completed in one go at the preset command time, and its cancellation time is on the same order of magnitude as its establishment time. When the approach is interrupted and restarted within the ground effect zone, the conditions for both actions disappear simultaneously, the threshold loses its basis for this sortie, the calibration data left over from the previous approach is no longer recorded, and the peak impact force experienced by the aircraft joint exceeds the controlled value range. Summary of the Invention

[0005] Based on this, it is necessary to propose a graded absorption control method for landing impact of heavy-load UAVs to address the aforementioned technical problems.

[0006] The present invention adopts the following technical solution.

[0007] The first aspect of this invention discloses a graded absorption control method for landing impact of a heavy-load unmanned aerial vehicle (UAV), comprising: calculating the static support force based on the pressure within the oil-gas cavity of the support column; obtaining the first-level residual elastic stroke based on the relationship between the static support force and the elastic reaction force displacement; collecting the static pressure on the ventral surface of the fuselage and calculating the residual sinking velocity by normalizing it according to the propeller disk load; calculating the super-level energy based on the static support force and the residual sinking velocity; obtaining the initial value of the second-level damping force based on the super-level energy and the first-level residual elastic stroke; and calculating the... The ascent rate threshold is used to delineate the entry boundaries of the three-stage plastic energy absorption units. The ascent rate of the support force is calculated based on the support force and sampling cycle time. If the ascent rate of the support force exceeds the ascent rate threshold, the collapse stroke release action is obtained. Based on the collapse stroke release action and the three-stage collapse force, the peak impact force is obtained. Based on the stroke consumed at each stage, the actual absorbed energy at each stage is calculated. Based on the actual absorbed energy at stage one and the return damping control value, the return release speed is output. Based on the return release speed and the peak impact force, the landing impact graded absorption control conclusion is obtained.

[0008] Furthermore, based on the relationship between static support force and elastic reaction force displacement, the first-level remaining elastic stroke is obtained by reverse calculation. Specifically, this includes: the first-level elastic energy absorption unit is an air column that generates reaction force under pressure within the landing gear strut and returns to its original length after unloading; based on the loading data of the first-level elastic energy absorption unit on a hydraulic servo testing machine, the elastic reaction force displacement relationship is obtained through a quasi-static compression calibration test; among which, the elastic reaction force displacement relationship is used to reverse calculate the static load preload stroke; based on the elastic reaction force displacement relationship and the stroke coordinate at the point of rapid reaction force increase, the upper limit of the first-level stroke is obtained; based on the elastic reaction force displacement relationship and the upper limit of the first-level stroke, the reaction force at the end of the first-level stroke is obtained; based on the static support force of the four struts, the strut with the highest static support force is selected to divide the struts for reverse calculation; based on the static support force and elastic reaction force displacement relationship of the reverse-calculated struts, the static load preload stroke is obtained by reverse calculation; based on the upper limit of the first-level stroke and the static load preload stroke, the first-level remaining elastic stroke is calculated.

[0009] Furthermore, the static pressure on the fuselage's ventral surface is collected, and the residual sink velocity is calculated by normalizing it according to the rotor disk load. Specifically, this includes: the fuselage's ventral surface being the outer surface of the fuselage facing the ground; the static pressure on the fuselage's ventral surface being the arithmetic mean of the static pressure measured at the static pressure taps on the fuselage's ventral surface; the free-flow static pressure being the air pressure measured on the fuselage's side away from the downwash airflow; the ventral surface stagnation pressure rise is calculated based on the fuselage's ventral surface static pressure and the free-flow static pressure; the rotor disk load is calculated based on the air density and rotor speed; the normalized stagnation pressure rise is calculated based on the ventral surface stagnation pressure rise and the rotor disk load; the relative ground clearance is calculated based on the ground clearance and the rotor disk diameter; and the normalized stagnation pressure rise is calculated based on the change in relative ground clearance. The measured data of monotonic stagnation were used to obtain the stagnation pressure rise calibration relationship, which holds true at every height within the ground effect zone. Based on the normalized stagnation pressure rise and the stagnation pressure rise calibration relationship, the relative ground clearance was obtained by performing a reverse lookup using Newton's iteration method. The ground clearance was calculated based on the relative ground clearance and the propeller disk diameter. The slope of the calibration relationship was calculated by differentiating the stagnation pressure rise calibration relationship based on the stagnation pressure rise calibration relationship and the propeller disk load. The time rate of change of the ventral stagnation pressure rise was calculated based on the ventral stagnation pressure rise of two adjacent sampling cycles. The residual sinking velocity was calculated based on the time rate of change of the ventral stagnation pressure rise and the slope of the calibration relationship.

[0010] Furthermore, based on the static support force and residual sinking velocity, the super-level energy is calculated, specifically including: the landing gear consists of four struts; the non-simultaneous grounding amplification factor is a dimensionless quantity characterizing the difference in the timing of the four struts' grounding; based on the static support force and gravitational acceleration of the four struts, the total mass of this sortie is calculated; based on the static support force of the four struts and the lateral coordinates of the four struts in the strut arrangement plane, the lateral offset of the center of mass is calculated; based on the lateral offset of the center of mass and the strut arrangement plane, decomposition is performed, and the static force distribution share is output; based on the load electrical parameters of the rotor drive unit and the rotor speed, the sum of the rotor disk thrust is obtained by looking up the thrust calibration table; among which, the sum of the rotor disk thrust is used to deduct the rotor lift; based on gravity and the rotor disk thrust... The following calculations are performed: The tension unloading coefficient is obtained; the vertical kinetic energy is calculated based on the total mass of this sortie and the residual sinking velocity; the free fall potential energy is calculated based on the total mass of this sortie and the height above the ground; the fall potential energy increment is calculated based on the free fall potential energy and the tension unloading coefficient; the total energy to be absorbed is calculated based on the vertical kinetic energy and the fall potential energy increment; the allocated energy to be absorbed is calculated based on the total energy to be absorbed and the static distribution share; the energy to be absorbed per leg is calculated based on the allocated energy to be absorbed and the non-simultaneous grounding amplification coefficient; the first-level elastic energy absorption capacity is calculated by using the trapezoidal method to determine the area based on the elastic reaction force displacement relationship and the first-level remaining elastic stroke; and the super-level energy is calculated based on the energy to be absorbed per leg and the first-level elastic energy absorption capacity.

[0011] Furthermore, based on the leap energy and the first-level residual elastic stroke, the initial value of the second-level damping force is obtained, specifically including: the second-level damping energy-absorbing unit is a component connected in parallel with the first-level elastic energy-absorbing unit on the same piston and relies on the liquid to squeeze through the throttling channel to generate heat and dissipate energy; the upper limit of the second-level yield force is the upper limit of the damping force generated by the second-level damping energy-absorbing unit when the coil current is saturated; the rated damping force establishment time is the rated time consumed by the second-level damping energy-absorbing unit to rise from zero damping force to the upper limit of the second-level yield force; the margin coefficient is a dimensionless quantity that ensures the convergence of current conversion; the cancellation residual ratio is the residual share of the cancellation completion; the grounding arrival time is calculated based on the ground clearance and the residual sinking velocity; the setting reachable time is calculated based on the grounding arrival time and the rated damping force establishment time; the first candidate force is calculated based on the leap energy and the first-level residual elastic stroke; the second candidate force is calculated based on the upper limit of the second-level yield force and the margin coefficient; based on the first candidate force and the second candidate force, the lower force value is selected. Output the secondary damping force setting value; based on the reciprocating traction data of the support column in the suspended state, obtain the residual damping force through the force-displacement loop identification method; based on the secondary damping force setting value and the residual damping force, inversely solve to obtain the control quantity increment; based on the control quantity increment and the first-order circuit response of the coil, calculate the increment set-up time; based on the ratio of the control quantity increment to the cancellation residual, calculate the cancellation time; if the control quantity increment is positive and the increment set-up time is lower than the settable reachable time, the initial value of the secondary damping force is taken as the secondary damping force setting value; if the control quantity increment is positive and the increment set-up time is higher than the settable reachable time, the initial value of the secondary damping force is obtained by inverse solving based on the current at the end of the settable reachable time; if the control quantity increment is negative and the cancellation time is lower than the settable reachable time, the initial value of the secondary damping force is taken as the secondary damping force setting value; if the control quantity increment is negative and the cancellation time is higher than the settable reachable time, the initial value of the secondary damping force is obtained by inverse solving based on the current at the end of the settable reachable time.

[0012] Furthermore, based on the initial value of the secondary damping force and the primary residual elastic stroke, the rate of ascent threshold is calculated, specifically including: the tertiary plastic energy absorption unit is a thin-walled cylinder connected in series with the piston, which collapses and deforms under pressure and does not return to its original length; the locking pin is a pin inserted into the thin-walled cylinder wall and locking the collapse stroke; the collapse stroke locking state is the state when the locking pin is inserted into the thin-walled cylinder wall; the electromagnetic unlocking device is the actuator that pulls out the locking pin after being energized; the bypass valve is a valve body connected in parallel to the throttling channel of the secondary damping energy absorption unit; the fuselage joint is the connection joint between the fuselage and the landing gear; the allowable load of the fuselage joint is the upper limit of the allowable load of the fuselage joint; the grounding velocity is calculated based on the residual sinking velocity and the increase in falling potential energy; the grounding process duration is calculated based on the primary residual elastic stroke and the grounding velocity; among which, the grounding process duration is used to calculate the rate of ascent threshold; based on the reaction force at the end of the primary stroke and the secondary... The yield strength upper limit is calculated to obtain the upper limit of the two-stage bearing capacity. Based on the factory crush test data of the thin-walled cylinder and the upper limit of the two-stage bearing capacity, a platform force higher than the upper limit of the two-stage bearing capacity and lower than the allowable load of the body joint is obtained, and the third-stage crushing force is output. If the energy of the overstepping stage is positive, the bypass valve is closed, and the secondary damping energy absorption unit bears the force from the initial value of the secondary damping force. Based on the reaction force of the primary elastic energy absorption unit and the bearing force of the secondary damping energy absorption unit, the piston output force is calculated. If the crushing stroke release action is established and the piston output force is higher than the third-stage crushing force, the thin-walled cylinder enters the crushing state. Based on the value of the support force of the support column in two adjacent sampling cycles, the support force of each stage is obtained by combining the three-point center difference distribution with the five-point sliding average. Based on the reaction force at the end of the primary stroke and the initial value of the secondary damping force, the two-stage actual achievable forces are calculated. Based on the two-stage actual achievable forces and the grounding process duration, the rise rate threshold is calculated.

[0013] Furthermore, based on the actual absorbed energy of the first stage and the return damping control quantity, the return release speed is output, specifically including: the secondary takeoff speed threshold is the upper limit of the speed at which the aircraft will not be pushed back off the ground during rebound; the first-stage stored energy is obtained based on the actual absorbed energy of the first stage; the assigned mass of a single outrigger is calculated based on the static allocation share and the total mass of this sortie; the residual kinetic energy is calculated based on the assigned mass of a single outrigger and the secondary takeoff speed threshold; the return dissipated energy is calculated based on the first-stage stored energy and the residual kinetic energy; the return stroke is obtained based on the actual consumed stroke of the first-stage elastic energy absorption unit; the return damping force is calculated based on the return dissipated energy and the return stroke; the return damping control quantity is obtained by performing an inverse solution based on the return damping force and the upper limit of the second-stage yield force through the exponential relationship of the yield force as the coil current tends to saturate; wherein, the return damping control quantity is used to output to the coil of the second-stage damping energy absorption unit; and the return release speed is output based on the first-stage stored energy and the return damping control quantity.

[0014] The second aspect of this invention discloses a graded absorption control system for landing impact of a heavy-load unmanned aerial vehicle (UAV), applied to the method described in the first aspect, comprising: a residual travel back-calculation module, used to calculate the static support force based on the pressure in the oil-gas cavity of the support strut, and to back-calculate the first-level residual elastic travel based on the relationship between the static support force and the elastic reaction force displacement; a pre-landing observation module, used to collect the static pressure on the ventral surface of the fuselage, and calculate the residual sinking velocity by normalizing it according to the propeller disk load; wherein the residual sinking velocity is used to calculate the super-level energy; a super-level energy calculation module, used to calculate the super-level energy based on the static support force and the residual sinking velocity; and a damping tuning and threshold assignment module, used to calculate the super-level energy based on the super-level energy and the first-level residual elastic travel. The system employs several modules: a first module to obtain the initial value of the secondary damping force and a second module to calculate the rise rate threshold based on the initial value of the secondary damping force and the primary residual elastic stroke; a second module to calculate the support force rise rate based on the support force and sampling cycle time, and to determine the collapse stroke release action when the support force rise rate exceeds the rise rate threshold; a third module to obtain the peak impact force based on the collapse stroke release action and the tertiary collapse force; and a fourth module to calculate the actual absorbed energy at each stage based on the consumed stroke at each stage. Finally, a return stroke release and conclusion synthesis module outputs the return stroke release speed based on the primary actual absorbed energy and the return stroke damping control value, and uses the return stroke release speed and the peak impact force to obtain the landing impact graded absorption control conclusion.

[0015] A third aspect of the present invention discloses a terminal, including a processor and a storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method described in the first aspect.

[0016] A fourth aspect of the present invention discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0017] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages: (1) This invention constructs the pre-grounding observation entry based on the rise of the airfoil static pressure relative to the free-flow static pressure. This rise is normalized according to the propeller disk load and varies solely with the relative ground clearance. The stagnation pressure rise calibration relationship holds true at every height within the ground effect zone. The residual sink velocity and ground clearance are obtained at each sampling cycle within this zone. The observation entry does not depend on the one-time process of the airfoil entering this zone from outside the ground effect zone. When the approach is interrupted and restarted within this zone, the stagnation pressure rise calibration relationship is re-established, the observation data is re-supplied, the rate of ascent threshold is re-assigned, and the graded absorption observation entry changes from a one-time action to a re-entry action.

[0018] (2) This invention uses the set reachable time to constrain the damping force setting action, and the set reachable time shrinks step by step with the grounding arrival time. The positive and negative directions of the control quantity increment are compared with the set reachable time. The branch with the increment establishment time longer than the set reachable time and the branch with the cancellation time longer than the set reachable time are respectively deduced from the current at the end of the time. The initial value of the secondary damping force is taken from the deduction result, and the rise rate threshold is assigned according to the actual reachable force of the two levels. The setting quantity left over from the previous approach is entered into the current assignment account. The setting quantity that is removed from the account is not left after the first approach interruption. The peak impact force is lower than the allowable load of the body joint, and the return release speed is lower than the secondary grounding speed threshold. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a system with three levels of energy-absorbing units connected in series and parallel within the support column; Figure 2 This is a schematic diagram of the system layout of the static pressure taps on the ventral side of the body and the confined flow area; Figure 3 This is a detailed image of the scene where the second approach after the go-around is entirely within the ground effect zone; Figure 4 It is a flowchart of the three-branch decision-making process for positive and negative increments under the constraint of fixed reachability time; Figure 5 This is a detailed diagram comparing the rate of increase of support force along the compression stroke with the rate of increase threshold. Figure 6 This is a schematic diagram of the framework of a graded absorption control system for landing impact of a heavy-duty unmanned aerial vehicle. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Understandably, a primary elastic energy-absorbing unit represents a gas column within the landing gear strut that generates reaction force under pressure and returns to its original length after unloading. A secondary damping energy-absorbing unit represents a component connected in parallel with the primary elastic energy-absorbing unit on the same piston, relying on liquid to generate heat and dissipate energy as it passes through a throttling channel. A bypass valve represents a valve body connected in parallel to the throttling channel of the secondary damping energy-absorbing unit. A tertiary plastic energy-absorbing unit represents a thin-walled cylinder connected in series with the piston that collapses and deforms under pressure and does not return to its original length. A locking pin represents a pin that inserts into the wall of the thin-walled cylinder and locks the collapse stroke. The collapse stroke locking state indicates the state of the locking pin when it is inserted into the wall of the thin-walled cylinder. An electromagnetic unlocker represents an actuator that pulls out the locking pin after energization. The distinction between the three types of energy-absorbing components lies in whether they return to their original length after unloading and whether they are connected in series with the piston: the primary type returns to its original length, the secondary type does not return to its original length and shares the same piston stroke as the primary type, and the tertiary type does not return to its original length and has its own collapse stroke.

[0023] like Figure 1 As shown, the body 2 is connected downwards to the support column 1 via a flange joint 24. The cylindrical wall of the support column 1 is closed by a double line, with the upper part of its inner cavity accommodating a primary elastic energy-absorbing unit 12 and the lower part accommodating a piston 11. The head of the piston 11 has a throttling orifice for a secondary damping energy-absorbing unit 13. The primary elastic energy-absorbing unit 12 and the secondary damping energy-absorbing unit 13 act in parallel on the piston 11. A bypass valve 14 is connected to two openings in the cylindrical wall of the support column 1 via a branch pipe, and its opening and closing determines whether the throttling channel is short-circuited. The lower end of the support column 1 is connected to a tertiary plastic energy-absorbing unit 15 via a common edge. A locking pin 16 is inserted laterally into the cylindrical wall of the tertiary plastic energy-absorbing unit 15. An electromagnetic unlocking device 17 is connected to the tail end of the locking pin 16 and pulls the pin out horizontally. A pressure sensor 5 is mounted on the outside of the cylindrical wall of the support column 1, and a displacement sensor 6 is connected to the cylindrical wall of the support column 1 via a pull wire. The lower end of the three-stage plastic energy absorption unit 15 is supported on the ground surface 4. The impact load is transmitted upwards step by step along the ground surface 4, the three-stage plastic energy absorption unit 15, the support column 1, the body joint 24 to the body 2.

[0024] The piston output force represents the sum of the reaction force of the primary elastic energy-absorbing unit and the bearing force of the secondary damping energy-absorbing unit. The fuselage joint represents the connection joint between the fuselage and the landing gear. The strut support force represents the force transmitted from the strut to the fuselage joint; when the thin-walled cylinder is not crushed, the strut support force is equal to the piston output force.

[0025] This invention discloses a graded absorption control method for landing impact of heavy-load unmanned aerial vehicles, comprising the following steps.

[0026] Step 1: Calculate the static support force based on the pressure inside the oil-gas cavity of the support column, and then find the first-level residual elastic stroke based on the relationship between the static support force and the elastic reaction force displacement.

[0027] Sub-step 1.1: Collect the pressure inside the oil and gas cavity of the support column to obtain the static support force.

[0028] The static support force represents the pressure borne by the strut along its axial direction when the rotor is stationary. It is obtained by measuring the pressure inside the strut's oil-gas chamber using a pressure sensor, and multiplying this pressure by the effective bearing area of ​​the piston. For example, a four-strut heavy-duty UAV is parked on a landing pad. The landing gear consists of four struts, named the left front strut, left rear strut, right front strut, and right rear strut. The static support forces of the left front strut and left rear strut are each 1470 Newtons, and the static support forces of the right front strut and right rear strut are each 1225 Newtons.

[0029] Sub-step 1.2: Calibrate the elastic reaction force-displacement relationship of the first-level elastic energy-absorbing unit.

[0030] The elastic reaction force-displacement relationship represents the relationship between the reaction force of the air column and the compression displacement. The quasi-static compression calibration test involves mounting a single-stage elastic energy-absorbing unit on a hydraulic servo testing machine and compressing it downwards at a constant rate; this test is a current method. Specifically, the test compresses at a constant rate of 0.005 meters per second. The air column decreases in volume and increases in reaction force with the compression amount. The reaction force and displacement are recorded simultaneously, and the resulting curves monotonically increase with the stroke and are stored in a lookup table.

[0031] Sub-step 1.3 involves performing a reverse lookup on the elastic reaction force-displacement relationship to obtain the first-level residual elastic stroke.

[0032] The reverse support pillar represents the pillar with the highest static support force among the four pillars, and its remaining travel is the shortest. Static load preload travel represents the travel coordinate obtained from the static support force of the reverse support pillar in the elastic reaction force displacement relationship; it signifies the elastic travel segment already compressed by the body's own weight. The upper limit of the first-stage travel represents the travel where the reaction force rises sharply in the elastic reaction force displacement relationship. The reaction force at the end of the first-stage travel represents the reaction force at the upper limit of the first-stage travel in the elastic reaction force displacement relationship. The remaining elastic travel in the first stage represents the travel obtained by subtracting the static load preload travel from the upper limit of the first-stage travel. For example, if the reverse support pillar is the left front pillar, its static support force is 1470 N, yielding a static load preload travel of 0.13 meters. The upper limit of the first-stage travel is taken as 0.20 meters, the reaction force at the end of the first-stage travel is 2930 N, and the remaining elastic travel in the first stage is 0.07 meters. Under heavy load conditions, the static load preload travel increases, while the remaining elastic travel in the first stage decreases.

[0033] Step 2: Collect the static pressure on the ventral surface of the fuselage, and calculate the residual sinking velocity by normalizing it according to the propeller disk load.

[0034] Sub-step 2.1: Collect the static pressure on the ventral surface of the body and the free-flow static pressure to obtain the ventral stagnant pressure rise.

[0035] The ventral side of the aircraft refers to the outer surface of the aircraft facing the ground, where static pressure taps are located. For example... Figure 2As shown, the lower surface of fuselage 2 is the fuselage ventral surface 21, and its vertical outer surface is the fuselage side surface 23. Four small holes, 22, are arranged on the fuselage ventral surface 21 as static pressure taps, with the four holes aligned along two ridge lines of the fuselage ventral surface 21. The rotor 3 is connected to the upper edge of fuselage 2 via a cantilever, and the rotor disk 31 is the circular surface swept by the rotor 3 during rotation, with its center coaxial with the rotor hub of rotor 3. There are four support pillars 1, with their upper ends connected to the four corners of the fuselage ventral surface 21 and their lower ends supported by the ground contact surface 4. The cavity between the fuselage ventral surface 21 and the ground contact surface 4 is a flow region where the downwash airflow is restricted. The height of this cavity changes with the extension and retraction of the support pillars 1 and the elevation and descent of fuselage 2. The static pressure measured by the static pressure taps 22 increases as this height narrows. The static pressure on the fuselage ventral surface represents the arithmetic mean of the static pressure measured by the static pressure taps on the fuselage ventral surface. Free-flow static pressure represents the air pressure measured on the side of the fuselage away from the downwash airflow. Ventral stagnation pressure rise represents the increase in ventral static pressure relative to free-flow static pressure; it signifies the excess pressure trapped between the fuselage and the ground after the rotor downwash airflow hits the ground. Sampling cycle time represents the duration between two consecutive samplings, set to 0.005 seconds. This value falls between 0.004 and 0.006 seconds, chosen because the grounding process is on the order of tens of milliseconds, and the cycle time is taken as one-tenth of this value. Blade passage frequency represents the product of rotor speed and blade number. Pressure jitter occurs at this frequency. The low-pass filter cutoff frequency is set to 0.2 times the blade passage frequency, falling between 0.18 and 0.22. This multiple is chosen because the pressure change before grounding is on the order of several hertz, and this cutoff frequency suppresses blade jitter and allows pressure changes to occur. For example, four static pressure taps are opened in the central area of ​​the ventral surface of the fuselage, the rotor speed is set to 30 revolutions per second, the number of blades is set to 2, the blade pass frequency is set to 60 Hz, the cutoff frequency is set to 12 Hz, and the ventral stagnation pressure rise is set to 1571 Pa.

[0036] Sub-step 2.2: Normalize the stagnant pressure rise on the ventral side according to the propeller disk load to obtain the stagnant pressure rise calibration relationship.

[0037] The rotor pushes air downwards into a jet, which, upon hitting the ground, transforms into a wall jet that spreads outwards along the ground, creating a confined airflow zone between the fuselage's ventral surface and the ground. Ground clearance represents the exit height of this confined airflow zone. As ground clearance decreases, the exit narrows, airflow leakage is obstructed, and ventral stagnation pressure rise increases. Disk load represents the ratio of rotor thrust to disk area, which is proportional to the product of air density, the square of rotor speed, and the square of disk diameter. Normalized stagnation pressure rise is the quotient obtained by dividing ventral stagnation pressure rise by the product of these three factors. Relative ground clearance is the quotient obtained by dividing ground clearance by disk diameter. This normalization eliminates the influence of the total mass and rotor speed of the current sortie; the remaining quantity varies solely with relative ground clearance. The stagnation pressure rise calibration relationship represents the monotonically increasing relationship between normalized stagnation pressure rise and relative ground clearance, and its form is: ; In the formula The pressure rises due to stagnant pressure on the ventral side. The air density is obtained from the aircraft's temperature and pressure sensors. The rotor speed is obtained from the motor's Hall sensor. The diameter of the propeller disk is an inherent dimension of the aircraft. Height above the ground Relative height above the ground To normalize the stagnation pressure rise. The amplitude coefficient, with a value between 0.05 and 0.07, is the ratio of stagnation pressure rise at a relative ground height of 1 to the propeller disk load, obtained by fitting from ground calibration tests. To expand the power, the value is taken between 0.9 and 1.2. The reason for this selection is that the wall jet spreads radially, and the pressure rise in the confined flow area is approximately inversely proportional to the first power of the relative height above the ground. This range covers the offset of different ventral shapes. The pressure relief attenuation coefficient is set between 0.8 and 1.1. The reason for this selection is that the downwash airflow leaks from the ventral edge of the aircraft body, and the pressure relief decreases exponentially with increasing relative ground clearance. This represents the baseline outside the ground effect zone, with values ​​ranging from 0.010 to 0.014. The rationale for this selection is that even when the organism is outside the ground effect zone, its ventral surface still experiences a small portion of the downwash dynamic pressure. For example, Take 0.06, Take 1.0, Take 1.0, Take 0.012, Take 2.0 meters, Take 1.225 kg per cubic meter. Taking 30 revolutions per second, the product of the three is 4410 Pa. Dividing 1571 Pa by 4410 Pa gives the normalized stagnation pressure rise of 0.3563.

[0038] Sub-step 2.3 involves performing a reverse lookup using the normalized stagnation pressure rise as the entry point to obtain the ground clearance.

[0039] The Newton-Raphson iteration method is a solution method that calculates the residual by substituting the initial value into the stagnation pressure rise calibration relationship and then successively correcting it. This method is an existing technique. Specifically, the residual is divided by the derivative of the formula with respect to the relative ground height to obtain the correction amount. The initial value is subtracted from the correction amount to obtain the new value. This process is repeated until the residual falls into the convergence limit. The initial value of the iteration is taken as the relative ground height of the previous sampling cycle. The initial value of the first sampling cycle is taken as the relative ground height of 1.0 at the upper boundary of the ground effect zone. The upper boundary of the ground effect zone represents the ground height where the absolute value of the calibration relationship slope drops to 100 Pa / m. This value falls between 90 Pa / m and 110 Pa / m. The reason for this choice is that the resolution of the pressure sensor is 0.5 Pa, and a height change of 0.005 meters within one sampling cycle produces a pressure rise of 0.5 Pa under this slope. For example, after substituting 0.3563 and iterating 4 times, the relative height above the ground is 0.15. Multiplying this value by the propeller disk diameter of 2.0 meters gives a height above the ground of 0.3 meters.

[0040] Sub-step 2.4 involves differentiating the stagnation pressure rise calibration relationship to obtain the slope of the calibration relationship.

[0041] The calibration slope represents the product of the derivative of the stagnation pressure rise calibration relationship with respect to relative ground clearance and the air density, the square of the rotor speed, and the rotor disk diameter. Its negative sign indicates that the ventral stagnation pressure rise increases as ground clearance decreases. The slope is: ; For example, substituting the above values ​​yields a calibration slope of -5820 Pa per meter, meaning that for every 0.01 meter decrease in ground clearance, the ventral stabilization pressure increases by approximately 58 Pa.

[0042] Sub-step 2.5: The residual sinking velocity is obtained from the time change rate of the stagnant pressure rise on the ventral side and the slope of the calibration relationship.

[0043] The rate of change of ventral stagnation pressure rise over time represents the difference in normalized stagnation pressure rise between two adjacent sampling cycles, multiplied by the product of air density, the square of rotor speed, and the square of rotor disk diameter, and then divided by the sampling cycle duration. The residual sink velocity is represented by dividing this rate of change over time by the absolute value of the calibration slope, with downward values ​​being positive. This velocity is: ; In the formula The residual sinking velocity, and These are the normalized hysteresis pressure rises of the current sampling cycle and the previous sampling cycle, respectively. For sampling beat duration, The slope is used to calibrate the relationship. The core of this formula lies in dividing the rate of change of pressure over time by the rate of change of pressure with height, with the quotient being the rate of change of height over time. For example, the difference in normalized stagnation pressure rise between two sampling cycles is 0.007918, the sampling cycle duration is taken as 0.005 seconds, and the residual sinking velocity is 1.2 meters per second.

[0044] The stagnation pressure rise calibration relationship holds true at every altitude within the ground effect zone, and the observation entry is independent of the one-time process of the aircraft entering the zone from outside. Ground clearance and residual subsidence velocity are obtained at every sampling cycle within this zone. If the approach is interrupted and restarted within this zone, the stagnation pressure rise calibration relationship is re-established, and both observations are re-dataned.

[0045] Step 3: Based on the static support force and the residual sinking velocity, the super-level energy is calculated.

[0046] Sub-step 3.1: The total mass, lateral offset of the center of gravity, and static force distribution of this flight are obtained from the static support force of the four pillars.

[0047] The total mass of this sortie is represented by the sum of the static support forces of the four struts divided by the gravitational acceleration. The lateral offset of the center of mass is represented by the sum of the products of the static support forces of the four struts and their lateral coordinates in the strut arrangement plane, divided by the sum of the static support forces of the four struts. The static load distribution is a dimensionless quantity obtained by decomposing the lateral offset of the center of mass in the strut arrangement plane; it represents the share borne by a single strut under static equilibrium. For example, the sum of the four forces is 5390 Newtons, the gravitational acceleration is 9.8 m / s², and the total mass of this sortie is 550 kg; the lateral coordinates of the two left struts are each 0.60 meters, the lateral coordinates of the two right struts are each -0.60 meters, the lateral offset of the center of mass is 0.055 meters, and the static load distribution of the left front strut is 0.2729.

[0048] Sub-step 3.2: Obtain the thrust unloading coefficient from the load electrical parameters of the rotor drive unit and the rotor speed.

[0049] During the descent of the aircraft, the rotors continue to pull upwards, and some of the work done by gravity is offset by the rotor thrust. The sum of rotor disk thrust represents the sum of the upward thrust generated by all rotors, which is obtained by looking up the load electrical parameters and rotor speed in the thrust calibration table. The thrust unloading coefficient is a dimensionless quantity obtained by dividing the difference between gravity and the sum of rotor disk thrust by gravity; this coefficient is taken as the current clock cycle value according to the sampling clock cycle. For example, the sum of rotor disk thrust is 4582 N, gravity is 5390 N, and the thrust unloading coefficient is 0.15.

[0050] Sub-step 3.3: The energy to be absorbed by a single leg is obtained from the total mass of this sortie, the residual sinking velocity, and the height above the ground.

[0051] Vertical kinetic energy is represented by multiplying the total mass of this sortie by the square of the residual sinking velocity and taking half of that. Free fall potential energy is represented by multiplying the total mass of this sortie by the height above ground and the acceleration due to gravity. The increase in fall potential energy is represented by multiplying the free fall potential energy by the tension unloading coefficient. The total energy to be absorbed is represented by adding the vertical kinetic energy to the increase in fall potential energy. The allocated energy to be absorbed is represented by multiplying the total energy to be absorbed by the static allocation share. The non-simultaneous grounding amplification factor is a dimensionless quantity characterizing the difference in the timing of the four support landings. The energy to be absorbed per leg represents the energy that lands on a single support, and is determined as follows: ; In the formula Energy needs to be absorbed by a single leg. For the number of pillars, The centroid is laterally offset. Half the wheelbase represents the lateral distance from a single support column to the centerline of the fuselage within the support column layout plane; it is an inherent dimension of the fuselage. This is the total mass of this sortie. This is the tensile unloading coefficient. It is the acceleration due to gravity. The amplification factor for non-simultaneous grounding is set between 0.15 and 0.25. This is because the grounding times of the four supports differ by several milliseconds to tens of milliseconds, and the first support to touch the ground bears a higher share than the static distribution share. This excess is statistically derived from deployment tests. The first term in parentheses represents the static distribution share. For example, multiplying the last three terms in parentheses yields 638.6 joules. Multiplying this value by 0.2729 and 1.20 gives 209 joules of energy to be absorbed by a single leg of the left front support.

[0052] Sub-step 3.4: Calculate the area based on the elastic reaction force-displacement relationship to obtain the first-level elastic energy absorption capacity, and obtain the super-level energy.

[0053] The trapezoidal method represents a numerical integration method that divides the stroke into multiple equal segments, multiplies the average of the reaction forces at both ends of each segment by the segment length, and then sums the results. This method is a current technique. The first-stage elastic energy absorption capacity represents the energy the air column can absorb within the remaining elastic stroke of the first stage. The super-stage energy represents the energy to be absorbed by a single leg minus the first-stage elastic energy absorption capacity; it signifies the portion of energy that cannot be absorbed in the first stage and is transferred downstream. For example, dividing 0.07 meters into seven 0.01-meter segments increases the reaction force from 1470 N to 2930 N, resulting in a first-stage elastic energy absorption capacity of 144 J and a super-stage energy of 65 J.

[0054] Step 4: Based on the super-level energy and the first-level residual elastic stroke, obtain the initial value of the second-level damping force, and based on the initial value of the second-level damping force and the first-level residual elastic stroke, calculate the rate of ascent threshold.

[0055] Sub-step 4.1: Obtain the grounding arrival time from the ground height and the residual sinking velocity, and obtain the set reachable duration.

[0056] The grounding arrival time represents the time from the current sampling cycle until the support touches the ground, calculated by dividing the ground clearance by the residual sinking velocity. The upper limit of the secondary yield force represents the upper limit of the damping force generated by the secondary damping energy absorption unit when the coil current is saturated, and is given by the damper manufacturer. The rated damping force build-up time represents the rated time required for the secondary damping energy absorption unit to rise from zero damping force to the upper limit of the secondary yield force. This time includes the closing time of the bypass valve and falls between 0.008 seconds and 0.012 seconds. The rationale is that the sum of the magnetization response time of the magnetorheological fluid, the coil current rise time, and the bypass valve closing time falls within this range. The adjustable reachable time represents the time obtained by subtracting the rated damping force build-up time from the grounding arrival time. For example, if the grounding arrival time is 0.25 seconds, the rated damping force build-up time is 0.010 seconds, and the adjustable reachable time is 0.240 seconds.

[0057] Sub-step 4.2: Obtain the secondary damping force setting value from the first candidate force and the second candidate force.

[0058] The first candidate force represents the force required to distribute the excess energy across the first-stage residual elastic stroke. The margin factor is a dimensionless quantity ensuring convergence of the current conversion, with a value between 0.85 and 0.95. This value is chosen because the logarithmic divergence of the converted current occurs when the setting value approaches the upper limit of the second-stage yield force. The second candidate force represents the force obtained by multiplying the upper limit of the second-stage yield force by the margin factor. The second-stage damping force setting value represents the lower of the first and second candidate forces, and its selection method is as follows: ; In the formula This is the set value for the secondary damping force. It is a first-order elastic energy absorption capacity. For higher levels of energy, This represents the first level of residual elastic travel. This represents the upper limit of the second-order yield strength. This is the margin factor. For example, dividing the first-stage energy of 65 joules by 0.07 meters yields a first candidate force of 929 N; multiplying the margin factor of 0.9 by the upper limit of the second-stage yield force of 4000 N yields a second candidate force of 3600 N; the lower of the two force values ​​is 929 N, and the second-stage damping force setting value is 929 N.

[0059] Sub-step 4.3: Obtain the residual damping force from the reciprocating traction data.

[0060] The residual damping force represents the damping force left in the secondary damping energy-absorbing unit from the previous approach and not yet dissipated. The force-displacement loop identification method is an identification method that uses a fixed frequency and fixed amplitude to traction the strut in reciprocating compression and reads the closed loop at half the force difference at zero displacement. This method is an existing technique, and its principle is based on the Bingham plasticity model, which decomposes the damping force into a viscous term that varies with velocity and a yield term that does not vary with velocity. Specifically, the strut is tractioned in reciprocating compression at a frequency of 0.5 Hz and an amplitude of 0.005 m, and the strut's support force and displacement are simultaneously recorded and plotted as a closed loop. For example, the force difference at zero displacement of the loop for the left front strut is 1800 N, and the residual damping force is 900 N.

[0061] Sub-step 4.4: The initial value of the secondary damping force is obtained by using the set value of the secondary damping force and the increment of the control quantity of the residual damping force inverse solution according to the four-branch judgment.

[0062] The control increment represents the additional coil current required to raise the residual damping force to the second-order damping force setpoint. It is obtained by performing an inverse solution to the exponential relationship between yield force and coil current saturation, and then subtracting the two currents. The magnetization saturation coefficient represents the coefficient characterizing the rate of saturation in this exponential relationship, with a value between 1.6 amperes and 2.2 amperes. This value is chosen because the yield stress of the magnetorheological fluid initially increases approximately linearly with the magnetic field strength before saturating. The increment settling time represents the time required to inject additional current into the coil and allow the fluid to catch up. It is obtained by adding the yield response time of the magnetorheological fluid to the first-order circuit response of the coil inductance and resistance. The yield response time of the magnetorheological fluid is between 0.0020 seconds and 0.0030 seconds, chosen because the time required for magnetic particles to form chains within the fluid is on the order of milliseconds. The cancellation residual ratio represents the proportion of residuals after cancellation, and its value falls between 0.04 and 0.06. The reason for this selection is that after the residuals drop to this proportion of the initial difference, the damping force deviation is less than one percent of the upper limit of the secondary yield force. The cancellation duration represents the time taken for the coil current to decay to the secondary damping force setting value until the residuals fall into the cancellation residual ratio.

[0063] For a control quantity increment that is positive and whose increment establishment time is less than the settable reachable time, the increment is output to the coil within the settable reachable time. The initial value of the secondary damping force is taken as the set value of the secondary damping force. For example, the coil inductance is 0.50 henries, the coil resistance is 5.0 ohms, the drive voltage is 48 volts, the residual control quantity is 0.134 amps, the control quantity increment is 0.005 amps, and the increment establishment time is 0.0026 seconds, which is less than the settable reachable time of 0.240 seconds. The left front support completes the setting before grounding, and the initial value of the secondary damping force is 929 N.

[0064] The control increment is positive and the increment establishment time is higher than the set reachable time. The set reachable time minus the magnetorheological fluid yield response time is used to obtain the actual climb time. This time is substituted into the current response formula of the first-order circuit to perform the inverse solution to obtain the terminal current. This current is substituted into the exponential relationship to obtain the actual damping force established. The initial value of the second-order damping force is taken as this damping force. For example, in the same sortie, if a gust of wind occurs during a descent, the residual descent velocity increases to 2.0 m / s and the ground clearance is 1.0 m, the energy to be absorbed by a single outrigger is 625 joules, the energy exceeding the threshold is 481 joules, the secondary damping force settling value is 3600 N, the control increment is 1.078 A, and the increment settling time is 0.0146 seconds. On the last sampling cycle, the ground clearance drops to 0.05 meters, the grounding arrival time is 0.019 seconds, the settling reach time is 0.009 seconds, the actual climb time is 0.0065 seconds, the inverse kinematics yields a current of 0.730 A, and the initial value of the secondary damping force is 3000 N.

[0065] For the branch where the control increment is negative and the cancellation duration is less than the settable reachable duration, the cancellation action reduces the driving voltage to the value required to maintain the secondary damping force setpoint. The initial value of the secondary damping force is taken from the secondary damping force setpoint. For the branch where the control increment is negative and the cancellation duration is greater than the settable reachable duration, the actual decay duration is obtained by subtracting the magnetorheological fluid yield response duration from the settable reachable duration. This duration is substituted into the current response equation and inversely solved to obtain the terminal current. This current is then substituted into the exponential relationship to obtain the actual decayed damping force. The initial value of the secondary damping force is taken from this damping force. For example, the residual damping force after the go-around pull-up was measured to be 1680 N, the residual sinking velocity at a ground clearance of 0.1 m on the second approach was 1.5 m / s, the energy to be absorbed by a single leg was 229 J, the energy exceeding the threshold was 85 J, the secondary damping force setting value was 1214 N, the control increment was -0.096 A, the cancellation residual ratio was 0.05, the cancellation duration was 0.30 seconds, the grounding arrival time was 0.067 seconds, the set reachable duration was 0.057 seconds, the actual decay duration was 0.0545 seconds, the inverse solution yielded a current of 0.246 A, and the initial value of the secondary damping force was 1495 N.

[0066] by Figure 3As an example, the horizontal line filled with a diagonal line below represents the ground surface, and the dashed line above it represents the upper boundary of the ground effect zone. The solid line diagonally downwards from the upper left represents the previous approach, and the hollow dot at its end indicates the location of the pull-up. The curve upwards from this dot turns back below the upper boundary of the ground effect zone, and the dotted line extends diagonally downwards from the turning point to the ground surface; this segment represents the second approach, which lies entirely between the upper boundary of the ground effect zone and the ground surface. The hollow dot on the second approach line is marked by a leader line indicating the location of residual damping force. The two double-arrow span lines below the ground surface indicate the set reachability time and the withdrawal time, respectively. The right ends of the two span lines are aligned with the intersection of the second approach and the ground surface, and the span of the withdrawal time is longer than the span of the set reachability time. The process can be referenced... Figure 4 As shown.

[0067] The residual damping force left over from the previous approach is remeasured using the force-displacement lap identification method and then incorporated into this calculation. No amount of data is left out of the accounting records after an approach interruption.

[0068] Sub-step 4.5: The rise rate threshold is obtained from the actual reachable forces at the two levels and the duration of the grounding process.

[0069] The grounding velocity is the square root of the sum of the square of the residual sinking velocity and twice the increase in falling potential energy, divided by the sum of the total mass of this sortie. The grounding duration is the time obtained by dividing twice the remaining elastic travel of the first stage by the grounding velocity. The actual reachable force of both stages is the force obtained by adding the reaction force at the end of the first stage travel and the initial value of the damping force of the second stage. The rate of ascent threshold is the quantity obtained by dividing the actual reachable force of both stages by the grounding duration, and its form is: ; In the formula Ascendance rate threshold, For grounding speed, This is the reaction force at the end of the first stage of the stroke. This is the initial value of the secondary damping force. The numerator of the threshold is the force actually generated by the two stages of this landing. For example, the reaction force at the end of the primary stroke of the left front strut, 2930 N, is added to the initial value of the secondary damping force, 929 N, to obtain 3859 N. The ground contact velocity is 1.524 m / s, the primary residual elastic stroke is 0.07 m, and the rate of ascent threshold is 4.2 x 10^4 N / s. Substituting the initial value of the secondary damping force of the gust strut, 3000 N, and the ground contact velocity, 2.634 m / s, the rate of ascent threshold is 1.12 x 10^5 N / s. Substituting the initial value of the secondary damping force of the retracted strut, 1495 N, and the ground contact velocity, 1.595 m / s, the rate of ascent threshold is 5.0 x 10^4 N / s.

[0070] Step 5: Based on the support force and sampling cycle time, calculate the support force rise rate, and obtain the collapse stroke release action, actual absorbed energy at each stage, and peak impact force according to the rise rate threshold.

[0071] Sub-step 5.1: Collect the support force of the support column to obtain the support force at each level and the rate of increase of the support force.

[0072] The support force at each level represents the support force value of the first-level elastic energy-absorbing unit, the second-level damping energy-absorbing unit, and the third-level plastic energy-absorbing unit in the load-bearing section. The support force rise rate represents the amount of rise in the support force between two adjacent sampling beats divided by the sampling beat duration. This amount is obtained by combining the three-point central difference distribution with a five-point moving average. This method is a current technique. Its principle is that the central difference is used to obtain the force of two consecutive sampling beats, subtract them, and then divide by twice the sampling beat duration. The symmetrical method cancels out the first-order drift. The five-point moving average adds the results of five consecutive sampling beats and divides by five to reduce random fluctuations. The single outrigger assigned mass represents the product of the static assigned mass and the total mass of this sortie. This product does not include the amplification factor for non-simultaneous grounding. The sum of the assigned masses of the four outriggers is equal to the total mass of this sortie. For example, the single leg of the left front support has a mass of 150 kg, the air column stiffness at the moment of grounding is 11200 N / m, and the compression speed is 1.524 m / s. Multiplying the two together gives 1.7 x 10^4 N / s, which is consistent with the rate of increase of the support force at the same sampling cycle.

[0073] In sub-step 5.2, if the energy level is positive, close the bypass valve and the secondary damping energy absorption unit bears the load from the initial value of the secondary damping force.

[0074] When the bypass valve is open, the throttling channel is short-circuited, and the secondary damping energy absorption unit does not bear any force; when the bypass valve is closed, the yield force of this unit is connected to the force-bearing path. The positive or negative value of the super-level energy is the boundary between the primary and secondary levels. For example, the super-level energy of 65 J in the left front strut is a positive value. The bypass valve closes at the moment of grounding, and the secondary damping energy absorption unit bears a force of 929 N. The reaction force of the primary elastic energy absorption unit is added to this bearing force to obtain the piston output force.

[0075] In sub-step 5.3, if the rate of increase of the support force is higher than the rate of increase threshold, the electromagnetic unlocker pulls out the locking pin, resulting in the collapse stroke release action.

[0076] The collapse stroke release action indicates that the electromagnetic unlocker pulls out the locking pin and releases the collapse stroke locking state. The two-stage load limit refers to the force obtained by adding the reaction force at the end of the first-stage stroke and the upper limit of the second-stage yield force. The third-stage collapse force represents the platform force maintained after the thin-walled cylinder wrinkles and collapses, taken from the cylinder's factory collapse test. Its value is higher than the two-stage load limit but lower than the allowable load of the body joint. When the value is lower than the two-stage load limit, the thin-walled cylinder collapses before the second stage is fully utilized, and the stage sequence is short-circuited. The allowable load of the body joint represents the upper limit of the allowable load of the body joint, given by the static strength test of the joint. The collapse state indicates the state in which the thin-walled cylinder enters when the collapse stroke release action is completed and the piston output force is higher than the third-stage collapse force. Afterward, the support force of the strut is limited to the level of the third-stage collapse force. After the first-stage compression stroke reaches the upper limit of the first-stage stroke, the air column enters the rigid section. This section of the stroke is less than twice the resolution of the displacement sensor, and its absorbed energy is included in the actual absorbed energy of the first stage. For example, the upper limit of the two-stage load is 6930 N, the allowable load of the body joint is 8000 N, and the three-stage collapse force is 7400 N; the peak of the support force rise rate of the left front strut occurs at 0.045 m of the compression stroke, reaching 1.9 x 10^4 N / s, which is lower than the rise rate threshold of 4.2 x 10^4 N / s, and the thin-walled cylinder maintains the collapse stroke lock state; the support force rise rate of the gust support increases to 1.4 x 10^5 N / s after the air column enters the rigid section, which is higher than the rise rate threshold of 1.12 x 10^5 N / s, the electromagnetic unlocker pulls out the locking pin, and the thin-walled cylinder enters the crushing state when the piston output force is higher than 7400 N.

[0077] Sub-step 5.4 calculates the area within each level of the consumption path to obtain the actual absorbed energy and peak impact force of each level.

[0078] Each stage of the energy-absorbing stroke represents the compression stroke traversed by the three types of energy-absorbing components during the grounding process. The actual absorbed energy at each stage represents the energy obtained by calculating the area along the energy-absorbing stroke using the trapezoidal method. The peak impact force represents the highest value reached by the support force of the strut during the entire grounding process. When the thin-walled cylinder maintains the collapse stroke lock-in state, the highest value of the piston output force is taken; when the thin-walled cylinder enters the crushing state, the third-stage collapse force is taken. For example, the first-stage actual energy-absorbing stroke of the left front strut is 0.07 meters, the reaction force increases from 1470 N to 2930 N, and the first-stage actual absorbed energy is 144 J. The second stage shares the same piston stroke as the first stage, with an actual energy-absorbing stroke of 0.07 meters and a damping force of 929 N, resulting in an actual absorbed energy of 65 J. The sum of these two values ​​is 209 J, consistent with the 209 J of energy to be absorbed by a single leg. The piston velocity returns to zero at the end of the stroke, and both the third-stage actual absorbed energy and the third-stage actual energy-absorbing stroke are zero, resulting in a peak impact force of 3859 N. The actual energy absorbed by the first stage of the gust was 144 joules, the actual energy absorbed by the second stage was 252 joules, and the actual energy absorbed by the third stage was 229 joules, with a corresponding collapse distance of 0.031 meters. The sum of the three is 625 joules, and the peak impact force is 7400 Newtons.

[0079] The rate of ascent threshold is assigned a value based on the actual achievable forces of the two stages during this landing, and the threshold moves synchronously with the initial value of the secondary damping force. For example... Figure 5 As shown, the horizontal axis represents the compression stroke, the vertical axis represents the rate of rise of the support force, and the dashed line running across the entire graph represents the rate of rise threshold. The solid line represents the rate of rise of the support force during normal landing, which rises and falls along the compression stroke, with the peak value below the rate of rise threshold and never intersecting with this threshold. The dotted line represents the rate of rise of the support force during gust landing, which rises continuously along the compression stroke, sharply bends upward at the point where the air column enters the rigid section, and crosses the rate of rise threshold. The intersection is marked by a hollow circle with a leader line indicating the collapse stroke release action. The two double-arrow span lines below the horizontal axis mark the remaining elastic stroke and the rigid section of the first stage, respectively, and the two span lines connect at the upper limit of the first stage stroke. The calibration load left over from the previous approach raises and lowers the actual output of the second stage. The peak impact force falls at the highest value of the piston output force during normal landing, and is limited by the third stage collapse force during gust landing. In both cases, the load on the fuselage joint is lower than the allowable load of the fuselage joint.

[0080] Step 6: Based on the actual absorbed energy and return damping control quantity, output the return release velocity, and based on the return release velocity and the peak impact force, obtain the landing impact graded absorption control conclusion.

[0081] Sub-step 6.1: Obtain primary stored energy and obtain residual kinetic energy by distributing mass to a single leg and setting a secondary takeoff speed threshold.

[0082] The primary stored energy represents the energy accumulated by the air column during compression and released upon release; its value is equivalent to the actual energy absorbed in the first stage. The upper bound of the rectangle is obtained by multiplying the actual first-stage travel by the reaction force at the end of compression. This upper bound serves as a check for the integral result; an integral value below the upper bound indicates a valid lookup, while a value above it indicates the elastic reaction force-displacement relationship is invalid and requires recalibration. The secondary takeoff speed threshold represents the upper speed limit at which the aircraft will not be pushed back off the ground during rebound; its value falls between 0.45 m / s and 0.55 m / s. This value is chosen because the kinetic energy generated by the mass of a single outrigger and this speed is lower than the buffer margin at the end of the return stroke. Residual kinetic energy is the amount obtained by multiplying the mass of a single outrigger by the square of the secondary takeoff speed threshold and taking half of that value. For example, the primary energy storage is 144 joules, the upper bound of the rectangle is 205 joules, 144 joules is lower than 205 joules, so the table lookup is valid; the secondary takeoff speed threshold is 0.45 meters per second, and the residual kinetic energy is 15.2 joules.

[0083] Sub-step 6.2: The return dissipated energy is obtained from the primary stored energy and residual kinetic energy, and the return damping force and return damping control quantity are obtained.

[0084] The return stroke represents the stroke length equal to the actual stroke consumed in the first stage, during which the bypass valve remains closed. Return dissipated energy represents the amount obtained by subtracting residual kinetic energy from the first-stage stored energy. Return damping force represents the force obtained by dividing the return dissipated energy by the return stroke. Return damping control quantity represents the coil current obtained by inversely solving the relationship between the return damping force and the upper limit of the second-stage yield force, using the exponential relationship where the yield force tends towards saturation with the coil current. For example, with a return dissipated energy of 128.8 joules, a return stroke of 0.07 meters, and a return damping force of 1840 N, and an actual output of 1850 N, substituting the upper limit of the second-stage yield force (4000 N) and the magnetization saturation coefficient (1.9 amps) into the inverse solution, the return damping control quantity is 0.327 amps.

[0085] Sub-step 6.3: Perform the release according to the return damping control value to obtain the return release speed and obtain the landing impact graded absorption control conclusion.

[0086] The return release velocity represents the speed at which the fuselage moves upward after the air column regurgitates its stored energy. The landing impact grading and absorption control conclusion represents the judgment result output after comparing the peak impact force with the allowable load of the fuselage joint. If the peak value is lower than the allowable load, the output is controlled; if the peak value is higher than the allowable load, the output exceeds the limit, and the fuselage joint is classified as requiring flaw detection. For example, the return release velocity of the left front strut is 0.44 m / s, which is lower than the secondary takeoff velocity threshold of 0.45 m / s, and the fuselage remains grounded; the peak impact force of 3859 N is lower than the allowable load of 8000 N for the fuselage joint, and the landing impact grading and absorption control conclusion is controlled; the actual third-stage travel is 0, which is lower than the total collapse travel of the thin-walled cylinder of 0.12 m, and the grading order is correctly determined.

[0087] This invention also discloses a graded absorption control system for landing impact of heavy-load unmanned aerial vehicles, such as... Figure 6 As shown, the system includes a remaining stroke reverse lookup module, a pre-grounding observation module, a super-energy calculation module, a damping tuning and threshold assignment module, a tiered deployment module, and a return stroke venting and conclusion synthesis module. The remaining stroke reverse lookup module calculates the static support force based on the pressure within the propeller's oil and gas cavity, and then reverse-looks up the first-level remaining elastic stroke based on the relationship between the static support force and the elastic reaction force displacement. The pre-grounding observation module collects the static pressure on the fuselage's ventral surface and performs normalized calculations based on the propeller disk load to obtain the residual sinking velocity. The super-energy calculation module calculates the super-energy based on the static support force and the residual sinking velocity. The damping tuning and threshold assignment module obtains the initial value of the second-level damping force based on the super-energy and the first-level remaining elastic stroke, and then calculates the rate of ascent threshold based on the initial value of the second-level damping force and the first-level remaining elastic stroke. The tiered deployment module calculates the support force rise rate based on the support force and sampling cycle duration. When the support force rise rate exceeds a threshold, it triggers the collapse stroke release action. Based on the collapse stroke release action and the three-stage collapse force, it obtains the peak impact force and calculates the actual absorbed energy for each stage based on the consumed stroke at each stage. The return stroke release and conclusion synthesis module outputs the return stroke release velocity based on the actual absorbed energy of the first stage and the return stroke damping control quantity. Based on the return stroke release velocity and the peak impact force, it obtains the landing impact tiered absorption control conclusion.

[0088] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for graded absorption control of landing impact from heavy-load unmanned aerial vehicles (UAVs), characterized in that, include: Based on the pressure inside the oil-gas cavity of the support, the static support force is calculated; based on the relationship between the static support force and the elastic reaction force displacement, the first-order residual elastic stroke is obtained by reverse lookup. The static pressure on the ventral surface of the fuselage was collected, and the residual sinking velocity was calculated by normalizing the pressure according to the propeller disk load. The super-level energy is calculated based on the static support force and the residual sinking velocity; Based on the leap energy and the first-level residual elastic stroke, the initial value of the second-level damping force is obtained; Based on the initial value of the second-level damping force and the first-level residual elastic stroke, the rise rate threshold is calculated; among which, the rise rate threshold is used to delineate the input boundary of the third-level plastic energy absorption unit; Based on the support force and sampling cycle duration, the support force rise rate is calculated; if the support force rise rate is higher than the rise rate threshold, the collapse stroke release action is obtained; based on the collapse stroke release action and the three-level collapse force, the peak impact force is obtained. Based on the consumption stroke at each stage, the actual absorbed energy at each stage is calculated; based on the actual absorbed energy at the first stage and the return damping control value, the return release velocity is output; based on the return release velocity and the peak impact force, the landing impact graded absorption control conclusion is obtained.

2. The method for graded absorption control of landing impact of heavy-load UAVs according to claim 1, characterized in that, Based on the relationship between static support force and elastic reaction force displacement, the first-order residual elastic stroke is obtained by reverse lookup, specifically including: The primary elastic energy-absorbing unit is an air column that generates reaction force when compressed within the landing gear strut and returns to its original length after unloading. Based on the loading data of the primary elastic energy-absorbing unit on a hydraulic servo testing machine, the elastic reaction force displacement relationship is obtained through a quasi-static compression calibration test. The elastic reaction force displacement relationship is used to check the static load preload stroke. Based on the elastic reaction force displacement relationship and the stroke coordinates at the point of sharp increase in reaction force, the upper limit of the first-level stroke is obtained; based on the elastic reaction force displacement relationship and the upper limit of the first-level stroke, the reaction force at the end of the first-level stroke is obtained; based on the static support force of the four pillars, the pillar with the highest static support force is selected to divide the pillars into reverse-lookup pillars; based on the static support force and elastic reaction force displacement relationship of the reverse-lookup pillars, the static load preload stroke is obtained by reverse lookup; based on the upper limit of the first-level stroke and the static load preload stroke, the remaining elastic stroke of the first-level stroke is calculated.

3. The method for graded absorption control of landing impact of heavy-load UAVs according to claim 1, characterized in that, The static pressure on the ventral surface of the fuselage is collected, and the residual sinking velocity is calculated by normalizing it according to the propeller disk load. Specifically, this includes: The ventral surface of the fuselage is the outer surface of the fuselage facing the ground; the ventral surface static pressure is the arithmetic mean of the static pressure measured at the static pressure taps on the ventral surface of the fuselage; the free-flow static pressure is the air pressure measured on the side of the fuselage away from the downwash airflow; based on the ventral surface static pressure and the free-flow static pressure, the ventral surface stagnation pressure rise is calculated. Based on air density and rotor speed, the disk load is calculated; based on ventral stagnant pressure rise and disk load, the normalized stagnant pressure rise is calculated. Based on the ground clearance and propeller diameter, the relative ground clearance is calculated; based on the measured data of normalized stagnation pressure rise monotonically increasing with relative ground clearance, the stagnation pressure rise calibration relationship is obtained; wherein, the stagnation pressure rise calibration relationship holds at every height within the ground effect zone; Based on the normalized stagnation pressure rise and the stagnation pressure rise calibration relationship, the relative ground clearance is obtained by performing a reverse lookup using Newton's iteration method; the ground clearance is then calculated based on the relative ground clearance and the propeller disk diameter. Based on the stagnation pressure rise calibration relationship and the propeller disk load, the derivative of the stagnation pressure rise calibration relationship is performed to calculate the slope of the calibration relationship; based on the ventral stagnation pressure rise of two adjacent sampling cycles, the time change rate of the ventral stagnation pressure rise is calculated; based on the time change rate of the ventral stagnation pressure rise and the slope of the calibration relationship, the residual sinking velocity is calculated.

4. The method for graded absorption control of landing impact of heavy-load UAVs according to claim 1, characterized in that, Based on the static support force and residual sinking velocity, the super-level energy is calculated, specifically including: The landing gear consists of four struts; the non-simultaneous grounding amplification factor is a dimensionless quantity that describes the difference in the timing of the four struts' grounding; the total mass of this sortie is calculated based on the static support force and gravitational acceleration of the four struts. Based on the static support force of the four pillars and the lateral coordinates of the four pillars in the pillar arrangement plane, the lateral offset of the center of mass is calculated; based on the lateral offset of the center of mass and the pillar arrangement plane, decomposition is performed to output the static force allocation share; based on the load electrical parameters of the rotor drive unit and the rotor speed, the sum of the rotor disk thrust is obtained by looking up the thrust calibration table; the sum of the rotor disk thrust is used to deduct the rotor lift. The tension unloading coefficient is calculated based on the sum of gravity and propeller thrust; the vertical kinetic energy is calculated based on the total mass of this sortie and the residual sinking velocity; and the free fall potential energy is calculated based on the total mass of this sortie and the height above the ground. Based on the free fall potential energy and the tension unloading coefficient, the increase in fall potential energy is calculated; based on the vertical kinetic energy and the increase in fall potential energy, the total amount of energy to be absorbed is calculated; based on the total amount of energy to be absorbed and the static distribution share, the distributed energy to be absorbed is calculated. Based on the energy to be absorbed by the assigned energy and the amplification factor for non-simultaneous grounding, the energy to be absorbed by a single leg is calculated. Based on the elastic reaction force-displacement relationship and the first-stage residual elastic stroke, the area is calculated using the trapezoidal method to obtain the first-stage elastic energy absorption capacity; based on the energy to be absorbed by a single leg and the first-stage elastic energy absorption capacity, the super-stage energy is calculated.

5. The method for graded absorption control of landing impact of heavy-load UAVs according to claim 1, characterized in that, Based on the leap-level energy and the first-level residual elastic stroke, the initial value of the second-level damping force is obtained, specifically including: The secondary damping energy absorption unit is a component connected in parallel with the primary elastic energy absorption unit on the same piston and relies on the liquid to squeeze through the throttling channel to generate heat and dissipate energy; the upper limit of the secondary yield force is the upper limit of the damping force generated by the secondary damping energy absorption unit when the coil current is saturated; the rated damping force build-up time is the rated time taken for the secondary damping energy absorption unit to rise from zero damping force to the upper limit of the secondary yield force; the margin coefficient is a dimensionless quantity that ensures the convergence of current conversion; the cancellation residual ratio is the proportion of residuals after cancellation is completed; Based on the ground clearance and residual subsidence velocity, the ground contact arrival time is calculated; based on the ground contact arrival time and the rated damping force establishment time, the settling time is calculated; based on the overshoot energy and the first-level residual elastic stroke, the first candidate force is calculated; based on the second-level yield force upper limit and margin coefficient, the second candidate force is calculated; based on the first and second candidate forces, the lower force value is selected, and the second-level damping force set value is output; based on the reciprocating traction data of the support in the suspended state, the residual damping force is obtained through the force-displacement loop identification method. Based on the secondary damping force setting value and the residual damping force, the control quantity increment is obtained by inverse solving. Based on the control quantity increment and the first-order circuit response of the coil, the increment settling time is calculated. Based on the control quantity increment and the revocation residual ratio, the revocation time is calculated. If the control quantity increment is positive and the increment settling time is lower than the settable reachable time, the initial value of the secondary damping force is taken as the secondary damping force setting value. If the control quantity increment is positive and the increment settling time is higher than the settable reachable time, the initial value of the secondary damping force is obtained by inverse solving based on the current at the end of the settable reachable time. If the control quantity increment is negative and the revocation time is lower than the settable reachable time, the initial value of the secondary damping force is taken as the secondary damping force setting value. If the control quantity increment is negative and the revocation time is higher than the settable reachable time, the initial value of the secondary damping force is obtained by inverse solving based on the current at the end of the settable reachable time.

6. The method for graded absorption control of landing impact of heavy-load UAVs according to claim 1, characterized in that, Based on the initial value of the second-order damping force and the first-order residual elastic stroke, the rise rate threshold is calculated, specifically including: The three-stage plastic energy absorption unit is a thin-walled cylinder connected in series with the piston, which collapses and deforms under pressure and does not return to its original length; the locking pin is a pin that is inserted into the wall of the thin-walled cylinder and locks the collapse stroke; the collapse stroke locking state is the state when the locking pin is inserted into the wall of the thin-walled cylinder; the electromagnetic unlocker is the actuator that pulls out the locking pin after being energized; the bypass valve is a valve body connected in parallel to the throttling channel of the two-stage damping energy absorption unit; the fuselage joint is the connection joint between the fuselage and the landing gear; the allowable load of the fuselage joint is the upper limit of the allowable load of the fuselage joint; the grounding velocity is calculated based on the residual sinking velocity and the increase in falling potential energy; Based on the primary residual elastic stroke and grounding velocity, the grounding process duration is calculated; the grounding process duration is used to calculate the rise rate threshold; based on the primary stroke end reaction force and the secondary yield force upper limit, the two-stage bearing capacity upper limits are calculated; based on the factory crush test data of the thin-walled cylinder and the two-stage bearing capacity upper limits, a platform force higher than the two-stage bearing capacity upper limits but lower than the allowable load of the body joint is obtained, and the tertiary crushing force is output; if the over-stage energy is positive, the bypass valve is closed, and the secondary damping energy absorption unit bears the force from the initial value of the secondary damping force; Based on the reaction force of the first-stage elastic energy absorption unit and the bearing force of the second-stage damping energy absorption unit, the piston output force is calculated. If the collapse stroke release action is successful and the piston output force is higher than the third-stage collapse force, the thin-walled cylinder enters the crushing state. Based on the values ​​of the support force of the support column in two adjacent sampling cycles, the support force of each stage is obtained by combining the three-point center difference distribution with the five-point moving average. Based on the reaction force at the end of the first-stage stroke and the initial value of the second-stage damping force, the actual reachable forces of the two stages are calculated. Based on the actual reachable forces of the two stages and the grounding process duration, the rise rate threshold is calculated.

7. The method for graded absorption control of landing impact of heavy-load UAVs according to claim 1, characterized in that, Based on the actual absorbed energy and return damping control, the output return release speed is calculated, specifically including: The secondary takeoff speed threshold is the upper limit of the speed at which the aircraft will not be pushed off the ground again during rebound; the primary stored energy is obtained based on the actual absorbed energy of the primary stage; the assigned mass of a single leg is calculated based on the static allocation share and the total mass of this sortie; the residual kinetic energy is calculated based on the assigned mass of a single leg and the secondary takeoff speed threshold; the return trip dissipated energy is calculated based on the primary stored energy and the residual kinetic energy. Based on the actual energy consumption stroke of the primary elastic energy absorption unit, the return stroke is obtained; based on the return dissipated energy and the return stroke, the return damping force is calculated; based on the return damping force and the upper limit of the secondary yield force, the return damping control quantity is obtained by performing an inverse solution through the exponential relationship between the yield force and the coil current tending to saturation; the return damping control quantity is used to output to the coil of the secondary damping energy absorption unit; based on the primary stored energy and the return damping control quantity, the return release speed is output.

8. A graded absorption control system for landing impact of heavy-load unmanned aerial vehicles, applied to the method described in any one of claims 1-7, characterized in that, include: The remaining stroke lookup module is used to calculate the static support force based on the pressure in the oil and gas cavity of the support, and to look up the first-level remaining elastic stroke based on the relationship between the static support force and the elastic reaction force displacement. The pre-grounding observation module is used to collect the static pressure on the fuselage surface and calculate the residual sinking velocity by normalizing it according to the propeller disk load; the residual sinking velocity is used to calculate the supercharged energy. The super-level energy calculation module is used to calculate the super-level energy based on the static support force and the residual sinking velocity; The damping tuning and threshold assignment module is used to obtain the initial value of the secondary damping force based on the overshoot energy and the primary residual elastic stroke, and to calculate the rate of ascent threshold based on the initial value of the secondary damping force and the primary residual elastic stroke. The graded input module is used to calculate the support force rise rate based on the support force and sampling cycle duration, and to obtain the collapse stroke release action when the support force rise rate is higher than the rise rate threshold. It is also used to obtain the peak impact force based on the collapse stroke release action and the three-level collapse force, and to calculate the actual absorbed energy of each level based on the consumption stroke of each level. The return release and conclusion synthesis module is used to output the return release speed based on the actual absorbed energy of the first stage and the return damping control quantity, and to obtain the landing impact graded absorption control conclusion based on the return release speed and the peak impact force.

9. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-7.

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