A magnetic interference distribution test method and system for vertical take-off and landing fixed-wing unmanned aerial vehicle geomagnetic navigation application

Abstract

This invention discloses a magnetic interference distribution testing method and system for geomagnetic navigation applications of vertical take-off and landing (VTOL) fixed-wing unmanned aerial vehicles (UAVs), comprising the following steps: In the first test mode, the VTOL fixed-wing UAV is fixed in a non-magnetic test area, and the tail thrust system is activated to simulate a cruise state, causing the magnetic sensor to gradually move away along a direction perpendicular to the side of the aircraft, acquiring the magnetic noise attenuation curve in the lateral direction under the action of the tail thrust source; In the second test mode, a three-dimensional test suspension made of non-magnetic material is used to arrange multiple spatial test points around the UAV to acquire the three-dimensional spatial magnetic noise distribution field around the aircraft. Through coordinate unification and fusion analysis of the dual-mode test data, a three-dimensional spatial distribution map of the aircraft's magnetic noise under cruise state is generated, and a rotational speed-magnetic noise response model is established; Further, based on the magnetic noise distribution characteristics, a non-magnetic material extension rod is used to non-parallelly install the magnetic sensor on the lower front of the aircraft or the outer edge of the wing, and dynamic compensation is achieved in conjunction with a real-time magnetic interference compensation module. This invention optimizes the installation position of the magnetic sensor and suppresses magnetic interference in the VTOL fixed-wing UAV aeromagnetic system, improving the stability and reliability of the UAV magnetic measurement system.

Description

Technical Field

[0001] This invention relates to the field of airborne magnetic measurement technology, and in particular to a method and system for testing magnetic interference distribution for geomagnetic navigation applications of vertical take-off and landing fixed-wing unmanned aerial vehicles. Background Technology

[0002] Airborne magnetic surveying is a technique that uses high-precision magnetic sensors mounted on an aircraft platform to measure the Earth's magnetic field. It is widely used in mineral resource exploration, geological structure surveys, oil and gas resource exploration, environmental monitoring, and military geophysical reconnaissance. Traditional airborne magnetic surveying mainly relies on manned fixed-wing aircraft or helicopters as platforms. Although it has a large operating range and high data acquisition capabilities, it also suffers from high operating costs, complex airspace coordination, and high personnel safety risks.

[0003] In recent years, with the development of UAV technology, Vertical Take-Off and Landing Fixed-Wing UAVs (VTOL UAVs) have gradually been applied in the fields of airborne magnetic surveying and geomagnetic navigation due to their combination of vertical take-off and landing capabilities and the efficient cruise capabilities of fixed-wing aircraft. These UAVs typically rely on a multi-rotor propulsion system for lift during take-off and landing, while using a tail-thrust propulsion system for high-speed, efficient flight during cruise. Therefore, they possess the structural and dynamic characteristics of both multi-rotor and fixed-wing UAVs.

[0004] However, the complex propulsion structure of vertical takeoff and landing fixed-wing UAVs also brings about a more complex magnetic environment. On the one hand, during takeoff and landing, multiple rotor motors, electronic speed controllers, and power supply systems generate multi-source coupled magnetic interference; on the other hand, during cruise, the tail thrust source continues to operate, and the magnetic field it generates has obvious directional and spatial radiation characteristics. In addition, internal metal structural components, servos, flight control modules, and communication equipment also generate varying degrees of magnetic interference, leading to deviations in the measurement results of magnetic sensors.

[0005] Currently, there is a lack of systematic solutions for testing the magnetic interference of vertical takeoff and landing (VTOL) fixed-wing UAVs. Existing methods typically borrow from those used for multi-rotor UAVs or traditional fixed-wing aircraft, making it difficult to simultaneously consider the different dynamic conditions during the VTOL and cruise phases, and also failing to accurately describe the directional magnetic field distribution characteristics generated by the tail thrust source. Furthermore, the installation location of the magnetic sensor needs to comprehensively consider the level of magnetic interference, structural strength, and flight aerodynamic performance; traditional experience-based installation methods are insufficient to meet the requirements of high-precision geomagnetic navigation applications.

[0006] Therefore, there is an urgent need to propose a magnetic interference distribution testing method that is tailored to the characteristics of vertical take-off and landing fixed-wing UAVs. By obtaining the spatial distribution characteristics of magnetic noise around the airframe under different power states, this method can provide a reliable basis for optimizing the installation of magnetic sensors, establishing magnetic interference compensation models, and designing high-precision geomagnetic navigation systems. Summary of the Invention

[0007] The purpose of this invention is to provide a magnetic interference distribution testing method and system for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs. By combining static side-gradual distance testing with non-magnetic three-dimensional suspension multi-point testing, the spatial distribution characteristics of magnetic noise generated by the tail thrust system during cruise and the magnetic interference contribution of different areas of the airframe are obtained, solving the problems of insufficient testing methods for the magnetic environment of vertical take-off and landing fixed-wing UAVs and incomplete acquisition of spatial distribution information in the prior art.

[0008] Another objective of this invention is to provide an aeromagnetic modification system based on the above-mentioned testing method, which determines the optimal installation position of the magnetic sensor according to the spatial distribution characteristics of magnetic interference, and improves the stability and reliability of the aeromagnetic measurement system of vertical take-off and landing fixed-wing UAV by combining a non-parallel installation structure and a real-time magnetic interference compensation method.

[0009] The technical solution adopted in this invention is as follows:

[0010] A method for testing magnetic interference distribution for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs includes the following steps:

[0011] First, the first test mode is conducted, which is a static gradual distance test: the vertical take-off and landing fixed-wing UAV under test is fixed on the ground of the test site without magnetic interference, the tail thrust system is started to cruise speed, so that the tail thrust source is in a stable working state; the magnetic sensor is installed on the non-magnetic displacement slide, the initial position is close to the near field area of ​​the side of the body, and the magnetic sensor is controlled to gradually move away from the side of the body in a direction perpendicular to the side of the body. During the movement, magnetic field data is collected at each test point, the spatial coordinates of each point and the corresponding magnetic noise amplitude are recorded, and a side attenuation curve of magnetic noise as the distance from the side of the body changes is established;

[0012] Secondly, a second test mode is conducted, which is a multi-point test of a non-magnetic suspension: a non-magnetic three-dimensional test suspension is built around the drone, and multiple test points are arranged on the suspension according to a preset spatial grid. The magnetic sensor is installed sequentially at each preset test point, and magnetic field data is collected at each point to construct a three-dimensional spatial magnetic noise distribution field with the center of gravity of the drone as the origin.

[0013] Finally, data processing and fusion analysis are performed: the fine attenuation data of the side obtained by the first test mode and the three-dimensional discrete data obtained by the second test mode are subjected to coordinate unification and fusion processing to generate a comprehensive three-dimensional spatial distribution map of the airframe magnetic noise, and the installation position of the magnetic sensor in the aeromagnetic modification is determined based on the three-dimensional spatial magnetic noise distribution map.

[0014] In the first test mode, a non-magnetic linear guide rail is arranged vertically on the side of the UAV body, and the magnetic sensor is mounted on the non-magnetic linear guide rail via a precision displacement slide. The sampling step size is no more than 5 cm in the near field region and no more than 20 cm in the far field region. The device stays at each test point for no less than 10 seconds, collecting no less than 100 data points. The collected data is corrected for diurnal variations in the geomagnetic field, and the difference between each point and the background magnetic field is calculated as the magnetic noise value of the UAV body. An exponential decay and power-law decay superposition model is used for fitting.

[0015] in, This represents the amplitude of the magnetic noise. This refers to the distance from the side of the fuselage. Near-field amplitude coefficient, For exponential decay length, The power-law decay exponent, For reference distance, The background magnetic field is used; the model parameters are determined by nonlinear least squares fitting, and the magnetic noise attenuation characteristics in the lateral direction are obtained.

[0016] In the second test mode: The non-magnetic three-dimensional test suspension is made of fiberglass square tubing or carbon fiber sheet. The suspension span is not less than 1.2 times the wingspan of the UAV, and the height is not less than 1.25 times the maximum height of the UAV. All connection nodes are fixed with non-magnetic adhesive, ensuring the overall relative magnetic permeability of the test suspension is: μ r <1.05; The preset test points are arranged at equal intervals of 20cm on the horizontal crossbeam, lateral cantilever and vertical column of the suspension, covering a spatial range of -2m to +3m in the X direction, -2m to +2m in the Y direction and 0.5m to 2.5m in the Z direction, with a total of no less than 200 test points; each test point is stayed for no less than 20 seconds, and no less than 200 data points are collected.

[0017] In the second test mode: The UAV is fixed at the center of the test site below the suspension, with its longitudinal axis parallel to the suspension span direction and its wings horizontal. The tail thrust system is activated to cruise speed. The magnetic sensors are sequentially installed at each preset test point using non-magnetic clamps, and the three-dimensional coordinates of each test point are recorded simultaneously. After performing geomagnetic field diurnal variation correction and 3σ criterion outlier removal on the collected data, a continuous three-dimensional spatial magnetic noise distribution field is constructed using radial basis function interpolation or Kriging interpolation.

[0018] in, These are the measured coordinates of the points. These are the weighting coefficients. These are radial basis functions (such as thin plate spline functions). The interpolation parameters are optimized using cross-validation, which is a trend term polynomial.

[0019] In the data processing and fusion analysis, the side gradient data acquired by the first test mode and the three-dimensional discrete data acquired by the second test mode are transformed to the same coordinate system, with the UAV's center of gravity as the origin, the longitudinal axis of the aircraft as the X-axis, the nose pointing in the negative X direction, the left wingtip pointing in the positive Y direction, and vertically upward as the positive Z direction. Fine correction is performed on the data in the near-field region of the first test mode data that is less than 1m to eliminate weak magnetic interference from the guide rail components. A weighted fusion strategy is adopted, assigning higher weights to the first test mode in the near-field region and higher weights to the second test mode in the far-field region. A smoothing function is used in the transition region to achieve a gradual change in weights.

[0020] Among them, the weighting coefficient , The condition w1+w2=1 is satisfied. In the near field region, w1>w2, and in the far field region, w2>w1. The transition region uses a smoothing function (such as the Sigmoid function) to achieve gradual weight change.

[0021] It also includes steps for magnetic interference source identification and speed response modeling. The real-time speed *n* of the tail-end thrust engine or motor is obtained using a speed sensor or motor Hall signal. A fast Fourier transform is performed on the magnetic noise time-domain data to obtain spectral characteristics. The engine's fundamental frequency *f0* = *n* / 60 and its harmonic frequencies *k* *f0* are identified. The correlation coefficient between each frequency component and the speed is calculated, and the dominant frequency with a correlation coefficient greater than 0.9 is identified. The speed of the tail-end thrust engine or motor is varied, covering 80%–120% of the typical cruising speed range. Static tests are repeated at each speed level to establish a speed-magnetic noise response model.

[0022] Among them, a, b, c or , For fitting parameters, The model parameters are determined by nonlinear fitting, using the reference rotational speed.

[0023] It also includes multi-system interference separation test steps. For vertical takeoff and landing fixed-wing UAVs with independent control capabilities, three tests are conducted: takeoff and landing phase with only the vertical takeoff and landing propulsion system operating, cruise phase with only the tail thrust system operating, and transition phase with both systems operating simultaneously. Magnetic noise is compared at the same test location for the three conditions to evaluate magnetic field superposition characteristics. If linear superposition is satisfied... If a subsystem independent compensation strategy is adopted, and if there is significant nonlinear coupling, a dual-system coupled compensation model is established, and magnetic interference is located through the dual-system coupled compensation model.

[0024] A test system for testing magnetic interference distribution based on geomagnetic navigation applications for vertical take-off and landing fixed-wing UAVs includes:

[0025] The airframe magnetic noise test module is used to execute the magnetic interference distribution test method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs, and obtain a three-dimensional spatial distribution map of airframe magnetic noise.

[0026] The magnetic sensor hoisting device, based on the optimal installation position of the magnetic sensor determined by the three-dimensional spatial distribution map, hoists the magnetic sensor to the lower or front lower part of the UAV body via a non-magnetic extension rod. The extension rod is made of carbon fiber composite material, and its length is determined according to the three-dimensional spatial distribution map. The axis of the extension rod is arranged non-parallel to the axis of the equivalent magnetic dipole of the tail thrust engine or motor, with an included angle of not less than 30°. A non-magnetic gimbal is provided at the end of the extension rod for mounting the magnetic sensor and allowing fine adjustment of the pointing angle.

[0027] The real-time magnetic interference compensation module has a built-in compensation model based on test data. It receives the speed of the tail thruster or motor, flight attitude, airspeed and the original output of the magnetic sensor, calculates the real-time compensation amount and performs real-time compensation correction on the magnetic sensor output.

[0028] The data synchronization acquisition unit integrates the magnetic sensor, RTK-GNSS positioning module, inertial measurement unit and rotation speed measurement sensor to realize the time-synchronous acquisition and storage of magnetic field data and position and attitude data.

[0029] In the real-time magnetic interference compensation module, the compensation model is established based on test data, and a speed-dominant model is adopted for cruise steady-state flight.

[0030] The compensated magnetic field value is: ,in The rotational speed-magnetic noise response model is used. This is the attitude correction function. The pitch angle, This is the roll angle. Yaw angle The data synchronization acquisition unit uses GPS second pulse or IEEE 1588 precise time protocol as a unified time reference. The sampling rate of the magnetic sensor is not less than 10Hz. The positioning accuracy of the RTK-GNSS positioning module is better than 5cm and the update frequency is not less than 10Hz. The sampling rate of the inertial measurement unit is not less than 100Hz.

[0031] It also includes a system verification module, which performs the following verification steps:

[0032] Static verification after modification: After completing the aeromagnetic modification, fix the UAV on the ground and repeat the first test mode and the second test mode at the actual installation position of the magnetic sensor to measure the residual magnetic noise. The residual magnetic noise peak value should be less than 0.05nT and the average value should be less than 0.02nT during cruise.

[0033] Dynamic verification after modification: Conduct cruise flight tests in target areas with known magnetic anomalies, simultaneously deploy ground reference magnetometers as true references, and compare the measurement results of the airborne system with those of the reference station. The dynamic measurement accuracy is required to be better than 1 nT or better than 0.5 nT.

[0034] Takeoff and landing-cruise transition verification: Test the magnetic interference characteristics of the vertical takeoff and landing fixed-wing UAV during operation, and use a dedicated multi-rotor magnetic interference compensation model for takeoff and landing phase data or mark it as compensation-limited data for takeoff and landing phase data;

[0035] Long-term stability monitoring: Static tests are repeated every 100 hours of cumulative flight or after experiencing severe landing impact to monitor the drift of the airframe's magnetic noise characteristics. When the residual magnetic noise increase exceeds 20%, the compensation model parameters are updated, including a first test mode and a second test mode. The first test mode is a gradual movement away from the side of the airframe, where the UAV is fixed to the ground and the tail thrust engine is started to simulate cruise mode. The magnetic sensor gradually moves away from the side of the airframe and collects magnetic noise at each point. The second test mode is a multi-point test with a non-magnetic suspension, using a three-dimensional suspension made of non-magnetic materials. Magnetic sensors are installed at different preset points above the suspension to collect magnetic noise at each point during the UAV's cruise mode. The data obtained from the two modes are then fused and analyzed to generate a three-dimensional spatial distribution map of the airframe's magnetic noise during cruise mode.

[0036] This invention establishes a dual-mode magnetic interference testing method to address the differences in magnetic interference characteristics caused by the different propulsion systems during the takeoff, landing, and cruise phases of a vertical takeoff and landing fixed-wing UAV. The first testing mode employs a static side-mounted gradual-away testing method. During the UAV's cruise state, the tail thrust system is activated, and the magnetic sensor is controlled to gradually move away from the side of the aircraft, acquiring the attenuation characteristics of magnetic noise with distance under the action of the tail thrust system. The second testing mode employs a non-magnetic three-dimensional suspension multi-point testing method. A spatial test area is constructed around the UAV, and three-dimensional magnetic noise distribution data around the aircraft is acquired through multi-location sampling. The data obtained from the two testing modes are subjected to coordinate unification, spatial fusion, and model analysis to establish a three-dimensional spatial distribution map of the aircraft's magnetic noise during cruise state. Combined with rotational speed response analysis, the main sources of magnetic interference are identified, providing a basis for optimizing the installation position of the magnetic sensor. During system implementation, the installation area of ​​the magnetic sensor is determined based on the magnetic noise distribution map. A non-magnetic extension rod is used for non-parallel installation, placing the magnetic sensor in the weak field region of the main magnetic interference source. Simultaneously, a real-time magnetic interference compensation model is established based on rotational speed, attitude, and other information to correct the magnetic measurement data under dynamic conditions. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the overall process of the magnetic interference distribution testing method and system described in this invention;

[0039] Figure 2 This is a schematic diagram of the device layout for the first test mode (side-gradient distance test) of the present invention;

[0040] Figure 3 This is a schematic diagram of the device layout for the second test mode (multi-point test of non-magnetic suspension) of the present invention;

[0041] Figure 4 This is a schematic diagram of the non-magnetic three-dimensional test suspension structure and the distribution of preset test points described in this invention;

[0042] Figure 5 This is a schematic diagram illustrating the principle of generating a three-dimensional spatial distribution map of the aircraft's magnetic noise during cruise mode, as described in this invention. Detailed Implementation

[0043] 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 merely some embodiments of the present invention, and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Figure 1 , 2 As shown in Figures 3 and 4, the present invention includes the following steps:

[0044] like Figures 1-5 As shown, the present invention includes the following steps. Wherein, Figure 1 This is a schematic diagram of the overall process of the magnetic interference distribution testing method and system described in this invention, showing the complete process from UAV status setting, dual-mode magnetic interference testing, data processing and fusion, magnetic interference source identification, installation optimization to system verification; Figure 2 This is a schematic diagram of the side-gradient distance test device layout in the first test mode. P1, P2, P3, and P4 represent test points at different distances set along the moving direction of the magnetic sensor. The magnetic sensor collects magnetic field data at each test point in sequence to obtain the attenuation law of magnetic noise with distance under the action of the tail thrust system. Figure 3 This is a schematic diagram of a multi-point test of a non-magnetic three-dimensional suspension in the second test mode. The discrete points on the suspension represent the spatial sampling positions of the magnetic sensor, which are used to obtain magnetic noise distribution information at different spatial locations around the drone. Figure 4 The non-magnetic 3D test suspension structure and test point layout were demonstrated to ensure that the magnetic sensor covers the preset space area around the UAV. Figure 5 The principle of generating a three-dimensional spatial distribution map of airframe magnetic noise under cruise conditions based on multi-location test data is demonstrated.

[0045] First Test Mode – Side Gradual Distance Test

[0046] Step S101: Test Site Preparation

[0047] A suitable open area, at least 100 m long and 50 m wide, away from buildings, high-voltage lines, underground pipelines, and major traffic arteries, will be selected as the test area. The background magnetic field of the test area will be measured using a proton magnetometer or an optically pumped magnetometer to confirm that the test area meets the magnetic environment requirements, with a background magnetic field gradient of less than 1 nT / m and a diurnal variation of less than 20 nT. A non-magnetic mounting base, made of wood, fiberglass, or other low-magnetic materials, will be placed at the center of the test area to secure the vertical take-off and landing fixed-wing UAV under test.

[0048] Step S102: Simulation of UAV stationary and cruise states

[0049] The VTOL fixed-wing UAV is secured to the test base using a non-magnetic clamp, ensuring the UAV is horizontal and its longitudinal axis aligns with the main direction of the test area. The UAV's tail thrust system is activated, bringing the tail thrust engine or motor to typical cruise operating speed and maintaining stable operation. For UAVs using a hydraulic tail thrust system, ground-based fixing devices are used to restrict airframe movement, ensuring the exhaust direction is away from the test area. For UAVs using an electric tail thrust system, the cruise throttle is set via an electronic speed controller. When the UAV has an independently controlled VTOL propulsion system, the VTOL propulsion system is shut down to reduce its impact on the cruise magnetic interference test results.

[0050] Step S103: Magnetic sensor placement and initial positioning

[0051] A non-magnetic linear guide rail is installed on the side of the UAV fuselage. This rail is arranged perpendicular to the longitudinal axis of the fuselage and corresponds to the area where the tail thrust source is located. The non-magnetic linear guide rail is made of carbon fiber, fiberglass, or other low-magnetic materials and has a length of at least 5 m. A high-precision magnetic sensor is mounted on a precision displacement slide, which controls the movement of the magnetic sensor along the guide rail. The initial test position is set 0.3 m from the outer surface of the UAV fuselage side as the starting position for near-field testing. The sensitive direction of the magnetic sensor is perpendicular to the side of the fuselage, i.e., along the test movement direction.

[0052] Step S104: Gradual movement away from data acquisition on the side

[0053] The precision displacement slide is controlled to gradually move the magnetic sensor away from the UAV along the side of the drone. During this movement, the speed should not exceed 5 cm / s to reduce additional interference generated during sensor movement. The sampling step size is set according to the spatial attenuation characteristics of the magnetic field: 5 cm for distances between 0.3 m and 1.0 m; 10 cm for distances between 1.0 m and 3.0 m; and 20 cm for distances between 3.0 m and 5.0 m. The device remains at each test point for at least 15 seconds, collecting at least 150 magnetic field data points, and calculating the mean and standard deviation of the magnetic field at the corresponding location. The spatial coordinates of the magnetic sensor are recorded synchronously. A spatial coordinate system is established with the tail thrust source reference position, where the longitudinal axis of the drone is the X-axis, the horizontal lateral direction is the Y-axis, and the vertical upward direction is the Z-axis.

[0054] Step S105: Magnetic noise data processing and attenuation model establishment

[0055] The collected magnetic field data were corrected for diurnal variations in geomagnetism, and the influence of environmental magnetic field changes was eliminated using synchronous data from nearby benchmark magnetic stations or other correction methods. The difference between the magnetic field value at each test point and the background magnetic field was calculated as the magnetic noise of the machine at that location.

[0056]

[0057] in: This indicates the distance from the side of the aircraft is... The amplitude of magnetic noise at that location; Indicates the magnetic field value at the test point; This represents the background magnetic field. Based on the results of the side-gradual-distance test, a model for the attenuation of magnetic noise as a function of distance is established:

[0058]

[0059] in: This represents the near-field magnetic noise amplitude coefficient. For reference distance; The power-law decay exponent; The exponential decay length is denoted by . Model parameters are determined by nonlinear least squares fitting to obtain the lateral magnetic noise decay characteristics under the action of the tail thrust system.

[0060] Second test mode – Multi-point test with non-magnetic suspension

[0061] Step S201: Fabrication of Non-Magnetic 3D Test Suspension

[0062] To obtain the magnetic noise distribution characteristics in the spatial range surrounding a vertical takeoff and landing fixed-wing UAV, a non-magnetic three-dimensional test suspension was constructed around the UAV. The non-magnetic three-dimensional test suspension was made of fiberglass square tubing, carbon fiber sheets, or other low-magnetic materials, and all connection points were fixed with non-magnetic adhesives to reduce the influence of the test device's own magnetism on the measurement results. The overall relative permeability of the non-magnetic three-dimensional test suspension satisfies: The suspension span is no less than 1.2 times the drone's wingspan, and the height is no less than 1.25 times the drone's maximum height, to ensure that the test area covers the main magnetic interference areas around the drone. The non-magnetic three-dimensional test suspension includes: a vertical column for supporting the overall test structure; a horizontal beam for arranging spatial sampling points; and a lateral cantilever for extending the lateral test range of the drone. This structure enables the magnetic sensor to perform multi-location magnetic field sampling within a preset spatial area around the drone.

[0063] Step S202: Setting up preset test points

[0064] Multiple preset test points are set on the horizontal beam, lateral cantilever, and vertical column of the non-magnetic three-dimensional test suspension. For example... Figure 3 and Figure 4 As shown, the discrete markers on the suspension represent the spatial sampling positions of the magnetic sensors. The magnetic sensors are sequentially installed at each test point to acquire magnetic noise data at different spatial locations around the drone. The test points are arranged at 20cm intervals, covering the following spatial ranges: X-direction: −2m to +3m, Y-direction: −2m to +2m, Z-direction: 0.5m to 2.5m. The origin of the coordinate system is the drone's center of gravity, with the longitudinal axis of the drone as the X-axis, the lateral axis as the Y-axis, and the vertical upward axis as the Z-axis. The total number of test points is no less than 200.

[0065] Step S203: Simulation of UAV stationary and cruise states

[0066] The VTOL fixed-wing UAV is fixed at the center of the test area below a non-magnetic three-dimensional test suspension, with the UAV's longitudinal axis parallel to the suspension span direction and the wings horizontal. The tail thrust system is activated, bringing the tail thrust engine or motor to cruise operating speed and maintaining stable operation. When the UAV has an independently controlled VTOL propulsion system, the VTOL propulsion system is shut down during cruise magnetic interference testing to obtain the magnetic noise distribution characteristics under tail thrust system dominance.

[0067] Step S204: Point-by-point magnetic field data acquisition

[0068] The magnetic sensor is sequentially installed at each preset test point using a non-magnetic clamp. It remains at each test point for at least 20 seconds, collecting at least 200 magnetic field data points, and calculating the mean and standard deviation of the magnetic field at that location. The three-dimensional spatial coordinates of each test point are recorded simultaneously. ,in , , Let represent the position coordinates of the i-th test point in the spatial coordinate system.

[0069] Step S205: Construction of three-dimensional spatial magnetic noise distribution field

[0070] First, the data collected at each test point were corrected for diurnal variations in the geomagnetic field, and outlier data were removed using the 3σ criterion. The magnetic noise of the aircraft at each spatial location was then calculated.

[0071]

[0072] Where: represents the magnetic field value at the test point; represents the background magnetic field. Subsequently, the discrete test point data is mapped to a three-dimensional spatial grid, and a continuous magnetic noise distribution field is constructed using radial basis function interpolation or Kriging interpolation.

[0073]

[0074] in: Let i be the coordinates of the i-th measured point; These are the corresponding weighting coefficients; These are radial basis functions; The trend term is represented by a function. Interpolation parameters are optimized through cross-validation to obtain a continuous three-dimensional magnetic noise distribution model around a vertical takeoff and landing fixed-wing UAV during cruise mode.

[0075] Data fusion and aeromagnetic modification

[0076] Step S301: Unify the coordinates of dual-mode data

[0077] The side-gradient distance test data obtained from the first test mode and the three-dimensional spatial discrete test data obtained from the second test mode are converted to the same spatial coordinate system. Specifically, a spatial rectangular coordinate system is established with the center of gravity of the vertical take-off and landing fixed-wing UAV as the origin: the longitudinal axis of the aircraft is defined as the X-axis; the direction of the nose is defined as the negative direction of the X-axis; the direction of the left wingtip is defined as the positive direction of the Y-axis; and the vertical upward direction is defined as the positive direction of the Z-axis.

[0078] A unified coordinate system is used to achieve spatial correspondence of magnetic noise data under different testing modes. Since the first testing mode uses a gradual lateral movement away from the device to acquire continuously attenuated near-field data, while the second testing mode uses discrete spatial sampling to acquire three-dimensional distributed data, spatial matching processing is required for the two types of data. For test data in the first testing mode located in areas closer to the device (less than 1m), corrections are made for potential weak magnetic interference from the test rails and mounting structure to reduce the impact of the testing device on the near-field magnetic noise measurement results.

[0079] Step S302: Near-field-far-field data fusion

[0080] The first test mode can obtain high spatial resolution magnetic noise attenuation data near the tail thrust source, suitable for describing the magnetic field variation in the near field region; the second test mode can cover a larger spatial range around the UAV, suitable for describing the spatial distribution of magnetic noise in the mid-to-far field region. Therefore, a weighted fusion method is used to fuse the two types of test data:

[0081]

[0082] in: Indicates distance and location The magnetic noise value after fusion; This represents the magnetic noise value obtained in the first test mode; This indicates the magnetic noise value obtained in the second test mode; and These represent the fusion weights corresponding to the two test modes. The two weights satisfy: In the near-field region: That is, increase the weight of the data in the first test mode; in the far field region: This involves increasing the weight of the data from the second test mode. Through this weighted fusion method, near-field high-resolution attenuation information is combined with far-field spatial coverage information, improving the completeness of the magnetic noise spatial distribution model.

[0083] Step S303: Generation of three-dimensional spatial magnetic noise distribution map

[0084] Based on the fused magnetic noise data, a three-dimensional magnetic noise distribution map around the fuselage of a vertical takeoff and landing fixed-wing UAV in cruise mode is generated. Figure 5 As shown in the figure, this figure illustrates the basic process of generating a magnetic noise distribution map around the aircraft by spatial interpolation fusion based on magnetic noise data from multiple spatial sampling points. By analyzing the changes in magnetic noise amplitude at different spatial locations, the spatial diffusion law of magnetic interference from the tail thrust system around the aircraft can be obtained, providing a basis for the subsequent selection of magnetic sensor installation areas. The three-dimensional spatial magnetic noise distribution map includes: (1) a magnetic noise isosurface map, used to display the spatial boundaries corresponding to different magnetic interference levels; (2) a spatial profile map, used to analyze the magnetic noise attenuation gradient in different directions; and (3) equivalent parameters of magnetic interference sources, used to describe the spatial distribution characteristics of the main magnetic interference sources. In one embodiment, different levels of spatial regions can be set according to the magnetic noise amplitude, such as: high magnetic interference region; restricted installation region; and low magnetic interference region. Based on the three-dimensional magnetic noise distribution map, and combined with the structural dimensions, aerodynamic layout, and installation space constraints of the vertical take-off and landing fixed-wing UAV, the magnetic sensor installation area is determined.

[0085] Magnetic Interference Source Identification and Rotational Speed ​​Response Model

[0086] Step S401: Spectrum-Speed ​​Correlation Analysis

[0087] After generating the three-dimensional spatial distribution map of the airframe's magnetic noise, further identification and dynamic response analysis of the main magnetic interference sources were conducted. During the acquisition process in either the first or second test mode, the real-time rotational speed of the tail thrust system was obtained through speed sensors, motor Hall signals, or feedback data from the flight control system. A Fast Fourier Transform (FFT) was performed on the time-domain data of the magnetic noise acquired at different test locations to obtain the magnetic noise spectral characteristics. The periodic magnetic interference generated by the tail thrust system is usually related to the rotational speed of the propulsion system, and its fundamental frequency can be expressed as:

[0088]

[0089] in: This is the fundamental frequency of the tail thrust system; The rotational speed of the power system is expressed in r / min. Further analysis of the harmonic components of the power system is needed. .in: The integer represents the harmonic order. The correlation between the amplitude of each frequency component and the speed variation of the power system is calculated to identify frequency components highly correlated with the speed and to determine the main sources of magnetic interference.

[0090] Step S402: Establishment of Rotational Speed-Magnetic Noise Response Model

[0091] To describe the variation of magnetic interference in the tail thrust system with rotational speed during cruise, multiple sets of tests were conducted within the typical cruise speed range by varying the operating speed of the tail thrust system. Specifically, the tail thrust system speed was adjusted to cover 80%–120% of the typical operating range, and magnetic noise data was repeatedly collected under different speed conditions. The magnetic noise amplitude at different speeds was extracted, and the response relationship between rotational speed and magnetic noise was established. In one implementation, a quadratic polynomial model was used for fitting:

[0092]

[0093] in: Indicates the rotational speed as The amplitude of magnetic noise at that time; , , These are the parameters for model fitting.

[0094] In another implementation, a power function model is used to describe the rotational speed response relationship:

[0095]

[0096] in: Reference speed The amplitude of magnetic noise under; The speed response index is denoted by . Model parameters are obtained through nonlinear fitting, and test data under different speed conditions are used to verify the model's ability to describe the changing trend of magnetic disturbances in the power system.

[0097] Step S403: Multi-system interference separation test

[0098] For vertical takeoff and landing (VTOL) fixed-wing UAVs with both a vertical takeoff and landing propulsion system and a tail thrust system, magnetic interference tests were conducted under different propulsion conditions to analyze the magnetic field contribution and coupling relationship between the different propulsion systems. Specifically, the following three test conditions were included:

[0099] (1) Vertical take-off and landing power system working status: The vertical take-off and landing power system is turned on and the tail thrust system is turned off to simulate the magnetic interference characteristics of the UAV during take-off and landing;

[0100] (2) Tail thrust system operating status: The vertical take-off and landing power system is turned off, and the tail thrust system is turned on to simulate the magnetic interference characteristics of the UAV cruise phase;

[0101] (3) Dual power system working state: The vertical take-off and landing power system and the tail thrust system are activated at the same time to simulate the transition phase during the take-off and landing and cruise transition.

[0102] Magnetic noise data were collected at the same test point for three different operating conditions, and the superposition relationship between the magnetic fields generated by different power systems was analyzed. When the following conditions are met:

[0103]

[0104] When it is assumed that the magnetic disturbances of different dynamic systems satisfy an approximately linear superposition relationship, the independent compensation method of the subsystems can be adopted; when there are obvious nonlinear differences, a comprehensive compensation model including the coupling effect of the dynamic systems is established.

[0105] Implementation of Aeromagnetic Modification System

[0106] Step S501: Design of magnetic sensor hoisting device

[0107] Based on the aforementioned generated three-dimensional spatial distribution map of the airframe's magnetic noise, and considering the structural layout, aerodynamic characteristics, and load installation conditions of the vertical takeoff and landing fixed-wing UAV, the installation area for the magnetic sensor is determined. Preferably, the magnetic sensor is installed in a weak magnetic region far from the main sources of magnetic interference, such as the area below the front of the airframe or the outer edge of the wing, to reduce the influence of the tail thrust system on the magnetic measurement results. Based on the determined installation location, a non-magnetic extension rod hoisting structure is designed. The extension rod is made of carbon fiber composite material or other low-magnetic materials, and its length is determined according to the three-dimensional spatial magnetic noise distribution map, ensuring the magnetic sensor is located in a predetermined low-magnetic-interference region. A vibration isolation structure is installed at the connection point between the extension rod and the UAV airframe to reduce the transmission of airframe vibration to the magnetic sensor; a non-magnetic gimbal is installed at the end of the extension rod to mount the magnetic sensor and adjust its spatial attitude.

[0108] Because the magnetic field generated by the tail thrust system of a vertical takeoff and landing fixed-wing UAV has a distinct directionality during the cruise phase, its equivalent magnetic field can be approximated as a magnetic dipole field distributed along the longitudinal axis of the aircraft. Therefore, the axis of the extension rod is set to be non-parallel to the axis of the equivalent magnetic dipole of the tail thrust source, causing the magnetic sensor to deviate from the main magnetic field radiation direction. The angle between the axis of the extension rod and the axis of the equivalent magnetic dipole of the tail thrust source is not less than 30°. This non-parallel arrangement places the magnetic sensor in a region where the magnetic field radiation of the tail thrust source is weaker, reducing the influence of magnetic interference from the propulsion system on the measurement results.

[0109] Step S502: Integration of Real-time Magnetic Interference Compensation Module

[0110] A real-time magnetic interference compensation module is integrated into the airborne flight control system or independent data processing unit. This module corrects the magnetic sensor output data in real time during flight based on the magnetic noise model established during the testing phase. The input parameters for the compensation module include:

[0111] (1) Rotation speed of the tail thrust system ;

[0112] (2) Flight attitude parameters of the UAV, including pitch angle Roll angle Yaw angle ;

[0113] (3) Flight speed or airspeed parameters ;

[0114] (4) Raw output data of magnetic sensor .

[0115] Establish a magnetic interference compensation model:

[0116]

[0117] in: This represents the real-time magnetic interference compensation amount. For stable cruise flight, a speed-dominated model can be used:

[0118]

[0119] in: This represents the magnetic noise response model established based on the rotational speed; This represents the correction function that takes into account the effects of attitude changes. The compensated magnetic field output is:

[0120]

[0121] Real-time compensation reduces the impact of tail thrust system and flight attitude changes on magnetic measurement data.

[0122] Step S503: Configure the data synchronization acquisition unit

[0123] To ensure time consistency between magnetic field data and UAV status information, a multi-source synchronous acquisition unit is constructed. The synchronous acquisition unit includes:

[0124] (1) Magnetic sensor, used to collect changes in the space magnetic field;

[0125] (2) RTK-GNSS positioning module, used to acquire the spatial location information of the UAV;

[0126] (3) Inertial measurement unit, used to acquire UAV attitude information;

[0127] (4) Rotation speed measurement module, used to obtain the real-time rotation speed of the tail thrust system.

[0128] All sensors are synchronized using a unified time reference, including GPS pulse-per-second (PPS) or the IEEE 1588 precise time protocol. Specifically: the magnetic sensor sampling rate is no less than 10Hz; the RTK-GNSS positioning accuracy is better than 5cm; and the inertial measurement unit sampling rate is no less than 100Hz. Through synchronous acquisition of multi-source data, a time correspondence between magnetic field data and the UAV's motion and dynamic states is achieved, providing a foundation for subsequent compensation and data processing.

[0129] System Validation and Accuracy Evaluation

[0130] After completing the aeromagnetic modification of the vertical take-off and landing fixed-wing UAV, in order to verify the effectiveness of the magnetic sensor installation structure, magnetic interference compensation model and data synchronization acquisition system, static verification, dynamic verification, power state switching verification and long-term stability monitoring were carried out on the modified system.

[0131] Step S601: Static verification after modification

[0132] After completing the installation of the magnetic sensor and the integration of the compensation system, the VTOL fixed-wing UAV was fixed in a non-magnetic test area. At the actual installation location of the magnetic sensor, the first and second test modes were re-executed to acquire lateral gradual movement away test data and multi-point spatial magnetic noise data, respectively. By comparing the changes in magnetic noise amplitude at corresponding locations before and after the modification, the optimization effect of the magnetic sensor installation location and the effectiveness of the physical isolation measures were evaluated. Simultaneously, the parameters of the magnetic interference compensation model were updated based on the test results to ensure the compensation model could adapt to the magnetic field environment under actual installation conditions.

[0133] Step S602: Dynamic verification after modification

[0134] Cruise flight tests were conducted in areas with known magnetic anomaly characteristics, with a ground-based reference magnetometer deployed simultaneously. During the flight, airborne magnetic sensors collected geomagnetic field data, simultaneously recording: the UAV's spatial position; flight attitude; tail thrust system rotation speed; and the compensated magnetic field output. By comparing the results with those from the ground-based reference magnetometer, the measurement stability and magnetic interference compensation effect of the modified aeromagnetic system were evaluated. In one implementation, the dynamic measurement accuracy can be set to better than 1 nT or a higher accuracy level, depending on the actual application requirements.

[0135] Step S603: Takeoff and landing-cruise transition verification

[0136] To address the changes in magnetic interference generated by a vertical takeoff and landing (VTOL) fixed-wing UAV during the transition between different power states, tests were conducted during the takeoff / landing-cruise transition phase. The results were recorded separately.

[0137] (1) The working phase of the vertical take-off and landing power system;

[0138] (2) The tail thrust system working phase;

[0139] (3) Dual power system switching stage.

[0140] Analyze the variation patterns of magnetic noise under different power states. When the magnetic interference level during takeoff and landing is significantly higher than that during cruise, the data for this stage can be marked with a state label during data processing, and a compensation model established under the corresponding power state can be used for correction.

[0141] Step S604: Long-term stability monitoring

[0142] Establish a regular magnetic environment retesting mechanism to assess the long-term operational stability of the system. After accumulating a certain flight time or experiencing severe landing impact, conduct static magnetic interference tests again to monitor changes in the airframe's magnetic noise characteristics. If the residual magnetic noise change exceeds a preset threshold, check the following: the integrity of the extension rod structure; the installation status of the magnetic sensors; the magnetization status of the airframe's metal components; and the validity of the compensation model parameters. Based on the retest results, re-execute the magnetic interference data update and compensation model parameter optimization to ensure the long-term stable operation of the aeromagnetic system.

[0143] The above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

[0144] In the description of this invention, it should be noted that directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0145] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0146] Note that the above description is merely a preferred embodiment and application of the technical principles of the present invention. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the specific embodiments described herein, and may include many other effective embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for testing magnetic interference distribution for geomagnetic navigation applications of vertical takeoff and landing fixed-wing unmanned aerial vehicles (UAVs), characterized in that: Includes the following steps: First, the first test mode is conducted, which is a static gradual distance test: the vertical take-off and landing fixed-wing UAV under test is fixed on the ground of the test site without magnetic interference, the tail thrust system is started to cruise speed, so that the tail thrust source is in a stable working state; the magnetic sensor is installed on the non-magnetic displacement slide, the initial position is close to the near field area of ​​the side of the body, and the magnetic sensor is controlled to gradually move away from the side of the body in a direction perpendicular to the side of the body. During the movement, magnetic field data is collected at each test point, the spatial coordinates of each point and the corresponding magnetic noise amplitude are recorded, and a side attenuation curve of magnetic noise as the distance from the side of the body changes is established; Secondly, a second test mode is conducted, which is a multi-point test of a non-magnetic suspension: a non-magnetic three-dimensional test suspension is built around the drone, and multiple test points are arranged on the suspension according to a preset spatial grid. The magnetic sensor is installed sequentially at each preset test point, and magnetic field data is collected at each point to construct a three-dimensional spatial magnetic noise distribution field with the center of gravity of the drone as the origin. Finally, data processing and fusion analysis are performed: the fine attenuation data of the side obtained by the first test mode and the three-dimensional discrete data obtained by the second test mode are subjected to coordinate unification and fusion processing to generate a comprehensive three-dimensional spatial distribution map of the airframe magnetic noise, and the installation position of the magnetic sensor in the aeromagnetic modification is determined based on the three-dimensional spatial magnetic noise distribution map.

2. The magnetic interference distribution testing method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs according to claim 1, characterized in that... In the first test mode, a non-magnetic linear guide rail is arranged vertically on the side of the UAV body, and the magnetic sensor is mounted on the non-magnetic linear guide rail via a precision displacement slide. The sampling step size is no more than 5cm in the near field region and no more than 20cm in the far field region. The device stays at each test point for no less than 10s, collecting no less than 100 data points. The collected data is corrected for diurnal variations in the geomagnetic field, and the difference between each point and the background magnetic field is calculated as the magnetic noise value of the UAV body. An exponential decay and power-law decay superposition model is used for fitting. in, This represents the amplitude of the magnetic noise. This refers to the distance from the side of the fuselage. Near-field amplitude coefficient, For exponential decay length, The power-law decay exponent, For reference distance, The background magnetic field is used; the model parameters are determined by nonlinear least squares fitting, and the magnetic noise attenuation characteristics in the lateral direction are obtained.

3. The magnetic interference distribution testing method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs according to claim 1, characterized in that... In the second test mode: The non-magnetic three-dimensional test suspension is made of fiberglass square tubing or carbon fiber sheet. The suspension span is not less than 1.2 times the wingspan of the UAV, and the height is not less than 1.25 times the maximum height of the UAV. All connection nodes are fixed with non-magnetic adhesive, ensuring the overall relative magnetic permeability of the test suspension is: μ r <1.05; The preset test points are arranged at equal intervals of 20cm on the horizontal crossbeam, lateral cantilever and vertical column of the suspension, covering a spatial range of -2m to +3m in the X direction, -2m to +2m in the Y direction and 0.5m to 2.5m in the Z direction, with a total of no less than 200 test points; each test point is stayed for no less than 20 seconds, and no less than 200 data points are collected.

4. The magnetic interference distribution testing method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs according to claim 1, characterized in that... In the second test mode: the UAV is fixed at the center of the test site below the suspension, with the longitudinal axis of the aircraft parallel to the span direction of the suspension, the wings kept horizontal, and the tail thrust system activated to cruise speed; the magnetic sensors are sequentially installed at each preset test point using non-magnetic clamps, and the three-dimensional coordinates of each test point are recorded simultaneously; after performing geomagnetic field diurnal variation correction and 3σ criterion outlier removal on the collected data, a continuous three-dimensional spatial magnetic noise distribution field is constructed using radial basis function interpolation or Kriging interpolation. in, These are the measured coordinates of the points. These are the weighting coefficients. These are radial basis functions (such as thin plate spline functions). The interpolation parameters are optimized using cross-validation, which is a trend term polynomial.

5. The magnetic interference distribution testing method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs according to claim 1, characterized in that... In the data processing and fusion analysis, the side gradient data acquired by the first test mode and the three-dimensional discrete data acquired by the second test mode are transformed to the same coordinate system, with the UAV's center of gravity as the origin, the longitudinal axis of the aircraft as the X-axis, the nose pointing in the negative X direction, the left wingtip pointing in the positive Y direction, and vertically upward as the positive Z direction. Fine correction is performed on the data in the near-field region of the first test mode data that is less than 1m to eliminate weak magnetic interference from the guide rail components. A weighted fusion strategy is adopted, assigning higher weights to the first test mode in the near-field region and higher weights to the second test mode in the far-field region. A smoothing function is used in the transition region to achieve a gradual change in weights. Among them, the weighting coefficient , The condition w1+w2=1 is satisfied. In the near field region, w1>w2, and in the far field region, w2>w1. The transition region uses a smoothing function (such as the Sigmoid function) to achieve gradual weight change.

6. The magnetic interference distribution testing method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs according to claim 1, characterized in that... It also includes the steps of magnetic interference source identification and speed response modeling. The real-time speed n of the tail thrust engine or motor is obtained by using a speed sensor or motor Hall signal. The magnetic noise time domain data is subjected to fast Fourier transform to obtain the spectrum characteristics. The engine fundamental frequency f0=n / 60 and its harmonic frequencies k·f0 are identified. The correlation coefficient between each frequency component and the speed is calculated, and the dominant frequency with a correlation coefficient greater than 0.9 is identified. By varying the speed of the tail-end thruster or electric motor to cover 80%–120% of the typical cruising speed range, and repeating static tests at each speed level, a speed-magnetic noise response model was established. Among them, a, b, c or , For fitting parameters, The model parameters are determined by nonlinear fitting, using the reference rotational speed.

7. The magnetic interference distribution testing method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs according to claim 1, characterized in that: It also includes multi-system interference separation test steps. For vertical takeoff and landing fixed-wing UAVs with independent control capabilities, three tests are conducted: takeoff and landing phase with only the vertical takeoff and landing propulsion system operating, cruise phase with only the tail thrust system operating, and transition phase with both systems operating simultaneously. Magnetic noise is compared at the same test location for the three conditions to evaluate magnetic field superposition characteristics. If linear superposition is satisfied... If a subsystem independent compensation strategy is adopted, and if there is significant nonlinear coupling, a dual-system coupled compensation model is established, and magnetic interference is located through the dual-system coupled compensation model.

8. A test system for testing magnetic interference distribution based on the method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs as described in any one of claims 1-7, characterized in that, include: The airframe magnetic noise test module is used to execute the magnetic interference distribution test method for geomagnetic navigation applications of vertical take-off and landing fixed-wing UAVs as described in any one of claims 1-7, and to obtain a three-dimensional spatial distribution map of airframe magnetic noise. The magnetic sensor hoisting device, based on the optimal installation position of the magnetic sensor determined by the three-dimensional spatial distribution map, hoists the magnetic sensor to the lower or front lower part of the UAV body via a non-magnetic extension rod. The extension rod is made of carbon fiber composite material, and its length is determined according to the three-dimensional spatial distribution map. The axis of the extension rod is arranged non-parallel to the axis of the equivalent magnetic dipole of the tail thrust engine or motor, with an included angle of not less than 30°. A non-magnetic gimbal is provided at the end of the extension rod for mounting the magnetic sensor and allowing fine adjustment of the pointing angle. The real-time magnetic interference compensation module has a built-in compensation model based on test data. It receives the speed of the tail thruster or motor, flight attitude, airspeed and the original output of the magnetic sensor, calculates the real-time compensation amount and performs real-time compensation correction on the magnetic sensor output. The data synchronization acquisition unit integrates the magnetic sensor, RTK-GNSS positioning module, inertial measurement unit and rotation speed measurement sensor to realize the time-synchronous acquisition and storage of magnetic field data and position and attitude data.

9. The magnetic interference distribution testing system for geomagnetic navigation applications of vertical takeoff and landing fixed-wing UAVs according to claim 8, characterized in that, In the real-time magnetic interference compensation module, the compensation model is established based on test data, and a speed-dominant model is adopted for cruise steady-state flight. The compensated magnetic field value is: ,in The rotational speed-magnetic noise response model is used. This is the attitude correction function. The pitch angle, This is the roll angle. Yaw angle The data synchronization acquisition unit uses GPS second pulse or IEEE 1588 precise time protocol as a unified time reference. The sampling rate of the magnetic sensor is not less than 10Hz. The positioning accuracy of the RTK-GNSS positioning module is better than 5cm and the update frequency is not less than 10Hz. The sampling rate of the inertial measurement unit is not less than 100Hz.

10. The magnetic interference distribution testing system for geomagnetic navigation applications of vertical takeoff and landing fixed-wing UAVs according to claim 8, characterized in that, It also includes a system verification module, which performs the following verification steps: Static verification after modification: After completing the aeromagnetic modification, fix the UAV on the ground and repeat the first test mode and the second test mode at the actual installation position of the magnetic sensor to measure the residual magnetic noise. The residual magnetic noise peak value should be less than 0.05nT and the average value should be less than 0.02nT during cruise. Dynamic verification after modification: Conduct cruise flight tests in target areas with known magnetic anomalies, simultaneously deploy ground reference magnetometers as true references, and compare the measurement results of the airborne system with those of the reference station. The dynamic measurement accuracy is required to be better than 1 nT or better than 0.5 nT. Takeoff and landing-cruise transition verification: Test the magnetic interference characteristics of the vertical takeoff and landing fixed-wing UAV during operation, and use a dedicated multi-rotor magnetic interference compensation model for takeoff and landing phase data or mark it as compensation-limited data for takeoff and landing phase data; Long-term stability monitoring: Static tests are repeated every 100 hours of cumulative flight or after experiencing severe landing impact to monitor the drift of the airframe's magnetic noise characteristics. When the residual magnetic noise increase exceeds 20%, the compensation model parameters are updated, including a first test mode and a second test mode. The first test mode is a gradual movement away from the side of the airframe, where the UAV is fixed to the ground and the tail thrust engine is started to simulate cruise mode. The magnetic sensor gradually moves away from the side of the airframe and collects magnetic noise at each point. The second test mode is a multi-point test with a non-magnetic suspension, using a three-dimensional suspension made of non-magnetic materials. Magnetic sensors are installed at different preset points above the suspension to collect magnetic noise at each point during the UAV's cruise mode. The data obtained from the two modes are then fused and analyzed to generate a three-dimensional spatial distribution map of the airframe's magnetic noise during cruise mode.

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