Unmanned aerial vehicle emergency recovery method and system capable of achieving unpowered autonomous homeward voyage

Abstract

The invention discloses an unmanned aerial vehicle emergency recovery method and system capable of achieving unpowered autonomous homeward voyage, and relates to the field of unmanned aerial vehicles. Comprising the steps that 1, the engine state is judged, and if it is judged that an engine fault occurs, engine fault emergency measures are automatically started; 2, judging whether the fixed wing unpowered gliding height of the unmanned aerial vehicle is met or not, and if yes, executing the step 3; otherwise, executing the step 5; 3, calculating the unpowered sliding distance of the fixed wing of the unmanned aerial vehicle, judging whether the unmanned aerial vehicle can return to the platform position or not, and if yes, generating a return route; otherwise, determining a landing candidate area and performing gliding landing; 4, the fixed wings slide down to the safe height; 5, a rotor wing control mode is switched, and the final landing position of the unmanned aerial vehicle is confirmed; and 6, after the unmanned aerial vehicle arrives at the landing position, the unmanned aerial vehicle lands autonomously at a constant speed in a rotor wing mode, and rotor wing motors of the unmanned aerial vehicle are closed after grounding. The safety and reliability of the emergency landing technology when the unmanned aerial vehicle encounters the engine failure problem are improved.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicles, and more specifically, to an emergency recovery method and system for unmanned aerial vehicles capable of autonomous return without power. Background Technology

[0002] With the continuous development and improvement of the drone industry, drone technology has gradually become a widely used technology in modern society, appearing in fields such as disaster relief and firefighting, transportation and logistics, geological surveying, and military operations. As the "heart" of a drone, the reliability of its power system has a decisive impact on its safety. Therefore, emergency landing methods for drones in a powerless state are an important issue in the field of drone technology. When a drone's engine fails and loses power, the drone is highly likely to go out of control and crash, causing serious damage to people, buildings, and the drone itself in the landing area. Currently, drone engine failure is mainly handled by manual control for landing and recovery. While this method is simple, mature, and easy to implement, it suffers from low safety and untimely operation. Therefore, having a safe and reliable emergency landing control method is crucial when a drone engine fails. Summary of the Invention

[0003] To achieve the above objectives, this invention provides an emergency recovery method and system for unmanned aerial vehicles (UAVs) capable of autonomous return without power. This method combines autonomous route planning technology with emergency landing conversion technology. It formulates a fixed-wing recovery route through energy management strategies and combines rotor mode for safe landing, thereby improving the safety and reliability of emergency landing technology when UAVs encounter engine failure.

[0004] According to a first aspect of the technical solution of the present invention, an emergency recovery method for a drone capable of autonomous return without power is provided, comprising: Step 1: The UAV control system assesses the engine status in real time. If an engine malfunction is detected, emergency engine malfunction measures are automatically activated. Step 2: After activating the emergency measures for engine failure, determine whether the unpowered descent altitude of the UAV fixed-wing aircraft is met. If it is, proceed to Step 3; otherwise, proceed to Step 5. Step 3: Based on the optimal energy conversion algorithm, calculate the UAV's taxiing ratio and the unpowered taxiing distance of the UAV's fixed-wing aircraft to determine whether it can return to the platform position. If it can, generate a return route; otherwise, determine the landing candidate area and plan a route to taxi down towards the landing candidate area. Step 4: Perform fixed-wing rappelling according to the real-time planned route, using pitch control law for pitch angle control and track control law for track control until rappelling to a safe altitude, then proceed to Step 5; Step 5: Switch the drone to rotor control mode and enter rotor energy management mode. Determine the final landing location of the drone based on the remaining battery power. Step 6: After the drone reaches the landing position, it begins to descend autonomously at a constant speed in rotor mode. Once the drone is determined to have touched down, the drone rotor motors are turned off.

[0005] Furthermore, in step 1, the UAV control system uses the fault monitoring subsystem to judge the engine status in real time. If the engine speed is lower than 1500 RPM (Revolutions Per Minute), the fault monitoring system issues an abnormal warning and determines that the engine is faulty.

[0006] Furthermore, in step 1, after activating the engine failure emergency measures, the UAV control system shuts down the payload equipment and automatically enters the energy-saving mode.

[0007] Furthermore, the method for determining the candidate landing area is as follows: At the current location of the UAV, the ground control station uses Digital Elevation Model (DEM) data to determine the landing candidate area, rasterizes the landing candidate area, performs flatness analysis on each raster candidate area, and selects the raster with the best flatness as the landing candidate area.

[0008] Furthermore, in step 3, the optimal energy conversion algorithm refers to the aircraft descending at the airspeed and glide angle corresponding to the maximum lift-to-drag ratio (Lift-to-Drag ratio is also known as LtD, usually written as L / D, where L is lift and D is drag).

[0009] Specifically, during the descent, the drone constantly monitors whether the aircraft's airspeed is at the optimal descent airspeed, that is, the airspeed corresponding to the maximum lift-to-drag ratio. By fine-tuning the descent angle, the airspeed can be adjusted.

[0010] Furthermore, the airspeed and glide slope corresponding to the maximum lift-to-drag ratio are: in, It is the airspeed corresponding to the maximum lift-to-drag ratio, in meters per second (m / s) or knots. It refers to the mass of the aircraft, measured in kilograms (kg). It is gravitational acceleration; It's the downward angle; It is the density of air, measured in kilograms per cubic meter (kg / m³). 3 ); It is the wing reference area (also known as "wing area"); It is the zero-lift drag coefficient, which represents the drag coefficient when the lift is zero. It is mainly composed of frictional drag and pressure drag, and is dimensionless. It is related to the aircraft's shape, surface roughness, etc. It is the induced drag factor, a coefficient reflecting the increase of induced drag with the square of the lift coefficient. It is related to the wing aspect ratio, planform, etc., and is dimensionless; L is lift, and D is drag. When the value is at its minimum, Minimum, Minimum, meaning maximum lift-to-drag ratio.

[0011] Furthermore, S3 also includes: If the resolution of the landing candidate area does not meet the requirements for rotor landing, the landing candidate area is further rasterized, the flatness of each grid candidate area is calculated, and then the grid with the best flatness is selected as the landing candidate area again. The ground control station uploads the calculated coordinates of the landing candidate area to the UAV flight controller and uses them as the UAV navigation target point. At the same time, the landing route is updated in real time until the landing candidate area meets the requirements for rotor landing.

[0012] Furthermore, the unpowered gliding distance of the fixed-wing UAV is: in: For the unpowered gliding distance of a fixed-wing drone, This refers to the aircraft's relative altitude when the engine stops. To ensure a safe descent height, The rise-to-drag ratio, The lift coefficient, Drag coefficient.

[0013] Preferably, the maximum lift-to-drag ratio is used directly to estimate the maximum gliding distance, i.e.: in, This represents the maximum lift-to-drag ratio.

[0014] Furthermore, the formula for calculating the flatness is: Where n is the total number of sampling points, Let be the height of the i-th sampling point based on digital elevation data.

[0015] Furthermore, step 4 specifically includes: Step 41: The UAV performs a fixed-wing descent according to the real-time planned route, using pitch angle control law for pitch angle control and track control law for track control. Step 42: Determine if the drone has reached the safe altitude for fixed-wing gliding. If yes, proceed to step 5; otherwise, proceed to step 43. Step 43: Determine whether the UAV has reached the platform position or the landing candidate area. If so, hover and descend until it reaches the safe altitude for fixed-wing gliding; otherwise, continue flying along the flight path until it reaches the safe altitude for fixed-wing gliding.

[0016] Furthermore, in step 4, the pitch angle control rate is: in: Elevator deflection, For pitch rate feedback gain, For pitch rate, For pitch angle error feedback gain, The pitch angle, Given the pitch angle, To balance the pitch angle during a dive, This is the proportional gain for airspeed error. For optimal glide airspeed, The current airspeed, This is the integral gain for airspeed error.

[0017] Furthermore, in step 4, the trajectory control rate is: in: For aileron deflection, For roll rate feedback gain, For the roll rate, For roll angle error feedback gain, For roll angle, Given the roll angle, This is the gain proportional to the side offset error. The integral gain is the side offset error. Given the lateral offset, Lateral offset, For track angle error gain, Given the track angle, Track angle.

[0018] Furthermore, step 5 specifically includes: Step 51: Switch the drone to rotor control mode, enter rotor energy management mode, and monitor the remaining battery energy in real time; Step 52: Confirm whether the drone is flying to the platform location or the predetermined landing candidate area, and confirm whether the drone meets the rotor flight distance requirements based on the remaining battery energy. If it does, the drone flies to the platform location or the predetermined landing candidate area; otherwise, the drone reselects a landing candidate area at the current location.

[0019] Furthermore, in step 6, when the throttle is less than the safe value and the relative altitude of the drone no longer changes, it is determined that the drone has landed and completed a safe landing.

[0020] According to a second aspect of the technical solution of the present invention, an emergency recovery system for unmanned aerial vehicles (UAVs) capable of autonomous return without power is provided, the system operating based on the method described in any of the preceding parties, including: The status monitoring module is used to judge the engine status in real time. If the engine is determined to be faulty, the engine fault emergency measures will be automatically activated. The glide altitude determination module is used to determine whether the unpowered glide altitude of the UAV fixed-wing aircraft is met after the engine failure emergency measures are initiated. If it is met, the glide distance is determined; otherwise, rotor control is performed. The taxiing distance determination module is used to calculate the taxiing ratio of the UAV and the unpowered taxiing distance of the UAV fixed-wing based on the optimal energy conversion algorithm, and to determine whether the UAV can return to the platform position. If it can, a return route is generated; otherwise, a landing candidate area is determined and a route is planned to taxi down towards the landing candidate area. The fixed-wing descent control module is used to control the UAV to perform fixed-wing descent according to the real-time planned route. It uses pitch angle control law for pitch angle control and track control law for track control until it descents to a safe altitude, at which point it performs rotor control. The rotor control module is used to switch the drone to rotor control mode, enter rotor energy management mode, and determine the final landing position of the drone based on the remaining battery energy. The altitude descent control module is used to begin descending at a constant speed in rotor mode after the drone reaches the landing position. Once the drone is determined to have touched down, the drone's rotor motors are turned off.

[0021] The beneficial effects of this invention are: This invention proposes an emergency recovery method for unmanned aerial vehicles (UAVs) capable of autonomous return without power. When the UAV engine is determined to be faulty, the UAV can autonomously formulate a fixed-wing gliding recovery route through an energy management strategy. After reaching a safe altitude, the UAV can be converted into rotor mode through an emergency conversion landing technology, thereby achieving a safe landing. In the emergency response process, the influence of various external uncertainties such as operating experience and operating methods during human operation is avoided. Compared with existing technologies, this invention is safer, more automated, and more robust. Attached Figure Description

[0022] Figure 1 A flowchart illustrating an emergency recovery method for a drone capable of autonomous return without power, according to the technical solution of the present invention. Figure 2 This is a flowchart illustrating the autonomous flight path recovery process for a fixed-wing aircraft according to the technical solution of the present invention. Figure 3 This is a diagram illustrating the elevation map landing candidate area selection method according to the technical solution of the present invention; Figure 4 This is a flowchart illustrating the rotor mode conversion landing process according to the technical solution of the present invention; Figure 5 This is a diagram of the level flight control structure according to the technical solution of the present invention; Figure 6 This is a diagram of the trajectory control structure according to the technical solution of the present invention. Detailed Implementation

[0023] To enable researchers in related technical fields to better understand the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0024] The present invention provides an emergency recovery method for unmanned aerial vehicles (UAVs) capable of autonomous return without power, comprising the following technical solutions: Step 1: The UAV control system uses the fault monitoring subsystem to judge the engine status in real time. If the engine speed is below 1500 RPM, the fault monitoring system will issue an abnormal warning and determine that the engine is faulty, and will automatically execute engine fault emergency measures.

[0025] Step 2: After the UAV initiates engine failure emergency measures, it shuts down payload and other equipment, automatically enters energy-saving mode to reduce unnecessary energy consumption, and analyzes the current flight status, monitoring the flight status and attitude in real time. If the UAV's fixed-wing unpowered descent altitude (i.e., minimum safe transition altitude) is met, proceed to Step 3; otherwise, proceed to Step 5, where the UAV will forcefully rotate its rotors at the current position and land autonomously.

[0026] Step 3: If the UAV meets the unpowered descent altitude of the fixed-wing aircraft, calculate the unpowered descent distance of the UAV's fixed wings. Based on the optimal energy conversion algorithm, calculate the descent ratio of the UAV and the range that the UAV can extend outward from its current position. The optimal energy conversion algorithm is as follows: = = Where L is lift and D is drag. For the glide angle, when When the value is at its minimum, Minimum, Minimum, meaning maximum lift-to-drag ratio.

[0027] have ,in It is the zero-lift drag coefficient. This is the induced drag factor. Substituting it into the lift formula, we can calculate the optimal lift coefficient and drag coefficient. The optimal airspeed (corresponding to the maximum lift-to-drag ratio) and the optimal glide angle are: in, It is the airspeed corresponding to the maximum lift-to-drag ratio, in meters per second (m / s) or knots. It refers to the mass of the aircraft, measured in kilograms (kg). It is gravitational acceleration; It's the downward angle; It is the density of air, measured in kilograms per cubic meter (kg / m³). 3 ); It is the wing reference area (also known as "wing area"); It is the zero-lift drag coefficient, which represents the drag coefficient when the lift is zero. It is mainly composed of frictional drag and pressure drag, and is dimensionless. It is related to the aircraft's shape, surface roughness, etc. It is the induced drag factor, a coefficient reflecting the increase of induced drag with the square of the lift coefficient. It is related to the wing aspect ratio, planform, etc., and is dimensionless; L is lift, and D is drag. When the value is at its minimum, Minimum, Minimum, meaning maximum lift-to-drag ratio.

[0028] In control, the UAV uses the optimal airspeed as the airspeed command and the optimal glide angle as the trim glide angle. Based on this, the airspeed is controlled by PI to ensure that the aircraft glides stably and reliably to the landing area.

[0029] If the UAV's taxiing distance is sufficient to return to the platform position, a return route from the UAV's current position to the platform position is automatically generated. If not, the ground control station uses DEM (Digital Elevation Model) data to determine landing candidate areas. The ground control station then rasterizes the landing candidate areas and performs flatness analysis on each raster candidate area. The raster with the best flatness is selected as the landing candidate area, and a route is planned to taxi towards the candidate area. If the resolution of the candidate area does not meet the requirements for rotor landing, the above landing candidate areas are rasterized a second time, and the flatness of each raster candidate area is calculated. Then, the raster with the best flatness is selected again as the landing candidate area. The ground control station uploads the calculated coordinates of the landing candidate area to the UAV flight controller and uses them as the UAV's navigation target point. At the same time, the landing route is updated in real time until the landing candidate area meets the requirements for rotor landing.

[0030] The above-mentioned fixed-wing gliding distance is: in: For the unpowered gliding distance of a fixed-wing drone, This refers to the aircraft's relative altitude when the engine stops. To ensure a safe descent height, The rise-to-drag ratio, The lift coefficient, Drag coefficient.

[0031] The flatness mentioned above is: Where n is the total number of sampling points, Let be the height of the i-th sampling point based on digital elevation data.

[0032] Step 4: The UAV performs a fixed-wing descent according to the real-time planned route, using pitch angle control to control the airspeed and keep the UAV near the optimal descent speed, ensuring that the UAV's attitude remains controllable and lift is dynamically balanced even when power is lost. At the same time, a trajectory control law is used to control the trajectory, ensuring that the UAV descents along the planned route. If the UAV's altitude decreases to a safe altitude during descent due to environmental or other external factors, proceed to Step 5. If the UAV descents to the designated descent position, it continues to circle and descend until its relative altitude reaches a safe level, then proceed to Step 5.

[0033] The airspeed control rate mentioned above is: in: Elevator deflection, For pitch rate feedback gain, For pitch rate, For pitch angle error feedback gain, The pitch angle, Given the pitch angle, To balance the pitch angle during a dive, This is the proportional gain for airspeed error. For optimal glide airspeed, The current airspeed, This is the integral gain for airspeed error.

[0034] The above track control control rate is: in: For aileron deflection, For roll rate feedback gain, For the roll rate, For roll angle error feedback gain, For roll angle, Given the roll angle, This is the gain proportional to the side offset error. The integral gain is the side offset error. Given the lateral offset, Lateral offset, For track angle error gain, Given the track angle, Track angle.

[0035] Step 5: If the drone meets the transition altitude requirement, force the drone to switch to rotor control mode. After switching to rotor mode, the drone enters rotor energy management mode, monitors the remaining battery energy in real time, and determines the final landing position based on the remaining energy. If the drone prioritizes landing at the platform location and meets the remaining energy flight distance requirement, the drone flies to the platform location and lands autonomously; otherwise, it checks whether the distance between the drone and the optimal landing candidate area meets the remaining energy flight distance requirement. If it does, the drone flies to the optimal landing candidate area and lands autonomously; otherwise, the drone selects the optimal landing candidate area at the current location and lands autonomously using the same method. Step 6: Once the drone is at the designated location, it begins to descend autonomously at a constant speed in rotor mode. When the trim throttle is less than the safe value and the drone's relative altitude no longer changes, the drone is considered to have landed, and the drone's rotor motors are turned off.

[0036] Example like Figure 1The diagram shows a flowchart of an emergency recovery method for a drone capable of autonomous return without power. During the drone's flight, the fault monitoring system continuously monitors the engine's status, including data such as oil pressure, engine speed, cylinder temperature, and current. If the platform issues a fault warning, the flight control software automatically identifies the fault type. If the fault indirectly affects flight safety, such as cylinder temperature or oil pressure exceeding normal ranges, the flight control software issues a warning and executes corresponding avoidance plans. If the fault directly affects flight safety, such as when the engine manager or engine speed deviates from normal conditions, the fault monitoring system issues an abnormality warning and identifies it as an engine fault. Simultaneously, the drone initiates the engine fault emergency handling procedure. If the drone's current relative altitude meets the landing altitude requirements for fixed-wing mode, it autonomously plans its flight path in fixed-wing mode. If the relative altitude does not meet the landing altitude requirements, it switches to rotor mode and lands in rotor mode.

[0037] like Figure 2 The diagram shows the flowchart for autonomous flight path recovery in fixed-wing mode. When the UAV experiences engine failure, it enters the emergency response procedure, confirming the UAV's current status, including speed, altitude, and position. The longitudinal control mode is switched to dive control, using the optimal airspeed as the target airspeed. Gravity is used to slightly lower the UAV's nose, increasing airflow and maintaining stability and optimal descent speed, thus extending the descent time. Figure 5 The diagram shows the dive control structure. The flight control computer processes pitch angle and altitude signals measured by sensors such as the barometer, inertial navigation system, and magnetic heading sensor on the UAV, and generates signals that meet control requirements through a dive control law. This signals then control the elevator servo, allowing the UAV to continuously track the given airspeed during fixed-wing descent. The UAV's relative altitude is used for homing judgment. If the relative altitude meets the fixed-wing descent altitude, the distance the UAV can descent without power is calculated. If the descent distance is sufficient to reach the platform, a flight path is generated. Otherwise, the UAV flies to the optimal landing candidate area, and the flight path is updated in real time during the descent. If the UAV's relative altitude does not meet the safe fixed-wing descent altitude during the descent, an emergency switch to rotor mode is forced. If the UAV has already descented to the landing position but its relative altitude has not reached the safe fixed-wing descent altitude, it performs a fixed-wing circling descent until it reaches the safe fixed-wing descent altitude, at which point the UAV switches to rotor mode. To ensure the UAV flies along the planned path, the lateral control mode is switched to trajectory control, as shown below. Figure 6The diagram shows the fixed-wing trajectory control structure. The flight control computer processes the roll angle, side offset, and other data measured by the sensors on the UAV, and combines them with the current trajectory angle of the UAV calculated in real time. It then uses the trajectory control law to generate a signal that meets the control requirements, thereby controlling the aileron servo motor, so that the UAV can continuously track the given trajectory during the fixed-wing descent.

[0038] like Figure 3 The diagram illustrates the method for selecting landing candidate areas based on DEM data. The ground control station loads pre-stored DEM (Digital Elevation Model) data. Using the unpowered descent distance calculated by the UAV, the range of landing candidate areas is determined. A multi-resolution method is used to rasterize the elevation map, forming a first-level raster map. Elevation information is then taken from each raster at fixed intervals, and the flatness of each raster is calculated. The center of the raster map with the best flatness after rasterization (candidate area 12) is selected as the UAV's descent endpoint. A distance from the UAV's current position to the raster is established. The descent route shown in Figure (candidate area 12) is followed by the UAV descent along this route. Simultaneously, it is determined whether the resolution of the grid map (candidate area 12) meets the requirements for rotor landing. If not, the grid map (candidate area 12) is further rasterized to form a secondary grid map. The flatness of each secondary grid map is then recalculated, and the center of the grid map with the best flatness is selected as the descent endpoint. The coordinates of this point are then uploaded to the UAV flight control system, and the descent route is updated. The above steps are repeated until the resolution of the landing candidate area meets the requirements for rotor landing.

[0039] like Figure 4 The diagram shows the rotor mode transition landing process. After the UAV reaches the safe altitude for fixed-wing gliding, to ensure attitude stability when switching to rotor mode, the lateral control mode is first switched to horizontal control, and then the flight mode is switched to rotor mode. The UAV monitors its remaining energy in real time. If the UAV prioritizes flying to the platform location, the distance between the UAV's current position and the target landing location is calculated. If the rotor flight distance meets the remaining energy requirements, the UAV flies to the target location and lands autonomously. Otherwise, it checks whether the distance between the UAV and the optimal landing candidate area meets the remaining energy flight distance requirements. If it does, the UAV flies to the optimal landing candidate area and lands autonomously. If the above conditions are not met, the UAV selects the candidate area with the best flatness for autonomous landing using the same method. After the UAV reaches the landing location, the flight control program provides the desired altitude in real time based on the current relative altitude, thereby controlling the UAV's rotor thrust. During the landing process, the rotor torque is calculated in real time to maintain attitude stability. The electrical signals distributed to each motor are adjusted in real time based on the thrust and torque required by the rotor, and finally converted into throttle commands to reduce rotor altitude, ultimately resulting in a safe landing.

[0040] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for emergency recovery of a drone capable of autonomous return without power, characterized in that, include: Step 1: The UAV control system assesses the engine status in real time. If an engine malfunction is detected, emergency engine malfunction measures are automatically activated. Step 2: After activating the emergency measures for engine failure, determine whether the unpowered glide altitude of the UAV fixed-wing aircraft is met. If it is, proceed to Step 3. Otherwise, proceed to step 5; Step 3: Based on the optimal energy conversion algorithm, calculate the drone's taxiing ratio and the unpowered taxiing distance of the drone's fixed wings to determine whether it can return to the platform position. If it can, generate a return flight path. Otherwise, identify a landing candidate area and plan a route to glide towards the landing candidate area; Step 4: Perform fixed-wing rappelling according to the real-time planned route, using pitch control law for pitch angle control and track control law for track control until rappelling to a safe altitude, then proceed to Step 5; Step 5: Switch the drone to rotor control mode and enter rotor energy management mode. Determine the final landing location of the drone based on the remaining battery power. Step 6: After the drone reaches the landing position, it begins to descend autonomously at a constant speed in rotor mode. Once the drone is determined to have touched down, the drone rotor motors are turned off.

2. The emergency recovery method for a drone capable of autonomous return without power as described in claim 1, characterized in that, In step 1, the UAV control system uses the fault monitoring subsystem to judge the engine status in real time. If the engine speed is below 1500 RPM, the fault monitoring system issues an abnormal warning and determines that the engine is faulty.

3. The emergency recovery method for a drone capable of autonomous return without power according to claim 2, characterized in that, In step 1, after activating the engine failure emergency measures, the UAV control system shuts down the payload equipment and automatically enters the energy-saving mode.

4. The emergency recovery method for a drone capable of autonomous return without power as described in claim 1, characterized in that, The method for determining the landing candidate area is as follows: At the current location of the UAV, the ground control station determines the landing candidate area by combining digital elevation model data, rasterizes the landing candidate area, and then performs flatness analysis on each raster candidate area, selecting the raster with the best flatness as the landing candidate area.

5. The emergency recovery method for a drone capable of autonomous return without power according to claim 1, characterized in that, In step 3, the optimal energy conversion algorithm refers to the UAV descending at the airspeed and descent angle corresponding to the maximum lift-to-drag ratio.

6. The emergency recovery method for a drone capable of autonomous return without power according to claim 4, characterized in that, S3 further includes: If the resolution of the landing candidate area does not meet the requirements for rotor landing, the landing candidate area is further rasterized, the flatness of each grid candidate area is calculated, and then the grid with the best flatness is selected as the landing candidate area and used as the UAV navigation target point. The landing route is updated in real time until the landing candidate area meets the requirements for rotor landing.

7. The emergency recovery method for a drone capable of autonomous return without power according to claim 1, characterized in that, Step 4 specifically includes: Step 41: The UAV performs a fixed-wing descent according to the real-time planned route, using a pitch control law to control the UAV's pitch angle, and a track control law to control the track. Step 42: Determine if the drone has reached the safe altitude for fixed-wing gliding. If yes, proceed to step 5; otherwise, proceed to step 43. Step 43: Determine whether the UAV has reached the platform position or the landing candidate area. If so, hover and descend until it reaches the safe altitude for fixed-wing gliding; otherwise, continue flying along the flight path until it reaches the safe altitude for fixed-wing gliding.

8. The emergency recovery method for a drone capable of autonomous return without power as described in claim 1, characterized in that, Step 5 specifically includes: Step 51: Switch the drone to rotor control mode, enter rotor energy management mode, and monitor the remaining battery energy in real time; Step 52: Confirm whether the drone is flying to the platform location or the predetermined landing candidate area, and confirm whether the drone meets the rotor flight distance requirements based on the remaining battery energy. If it does, the drone flies to the platform location or the predetermined landing candidate area; otherwise, the drone reselects a landing candidate area at the current location.

9. The emergency recovery method for a drone capable of autonomous return without power according to claim 1, characterized in that, In step 6, when the throttle is less than the safe value and the relative altitude of the drone no longer changes, it is determined that the drone has landed and completed a safe landing.

10. An emergency recovery system for unmanned aerial vehicles (UAVs) capable of autonomous return without power, characterized in that: The system operates based on the method according to any one of claims 1 to 9, including: The status monitoring module is used to judge the engine status in real time. If the engine is determined to be faulty, the engine fault emergency measures will be automatically activated. The glide altitude determination module is used to determine whether the unpowered glide altitude of the UAV fixed-wing aircraft is met after the engine failure emergency measures are initiated. If it is met, the glide distance is determined; otherwise, rotor control is performed. The taxiing distance determination module is used to calculate the taxiing ratio of the UAV and the unpowered taxiing distance of the UAV fixed-wing based on the optimal energy conversion algorithm, and to determine whether the UAV can return to the platform position. If it can, a return route is generated; otherwise, a landing candidate area is determined and a route is planned to taxi down towards the landing candidate area. The fixed-wing descent control module is used to control the UAV to perform fixed-wing descent according to the real-time planned route. It uses pitch angle control law for pitch angle control and track control law for track control until it descents to a safe altitude, at which point it performs rotor control. The rotor control module is used to switch the drone to rotor control mode, enter rotor energy management mode, and determine the final landing position of the drone based on the remaining battery energy. The altitude descent control module is used to begin descending at a constant speed in rotor mode after the drone reaches the landing position. Once the drone is determined to have touched down, the drone's rotor motors are turned off.

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