Fixed-wing unmanned aerial vehicle air slip returning route guidance method based on energy planning

Abstract

The invention relates to the technical field of unmanned aerial vehicle design, in particular to an energy planning-based fixed-wing unmanned aerial vehicle airline guidance method, which comprises the following steps of: after an engine of an unmanned aerial vehicle has a parking fault, acquiring a current optimal airline return path; combining the energy consumption from the parking point to the FAF point and the glide critical energy of the FAF point to judge whether the current energy of the unmanned aerial vehicle meets the requirement of idle glide returning; if the energy is sufficient, according to the real-time flight state parameters of the unmanned aerial vehicle, dynamically determining the transverse course control mode of the unmanned aerial vehicle until the unmanned aerial vehicle enters air-slip glide guidance; controlling the longitudinal control mode at the final idle slip gliding section of the idle slip returning field until grounding; if the energy is insufficient, the target point is switched to be the forced landing point closest to the current position, and off-site forced landing is carried out; in the forced landing process, whether excess energy exists or not is judged, and circling height descending is needed. According to the method, the unmanned aerial vehicle can accurately track an air-sliding route and safely return to the field when energy is sufficient, and the unmanned aerial vehicle can be forced to land near a forced landing point when energy is insufficient.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) design technology, and in particular to a method for guiding the air glide return flight path of a fixed-wing UAV based on energy planning. Background Technology

[0002] If a drone malfunctions and loses power during flight, it is highly likely to crash outside the airport if effective control measures are not taken. Proper control methods, however, can ensure a safe landing back at the airport, minimizing damage to the drone itself and preventing further losses from a crash at an uncertain location. If a drone loses power, the energy available for its return glide consists only of kinetic and potential energy. The method of managing this kinetic and potential energy will determine the distance the drone can travel from the airport. During the return journey, it is crucial to continuously assess whether the current energy is sufficient to return to the airport. If not, the drone should fly towards the nearest emergency landing point to avoid uncontrollable hazards from a crash at an uncertain location during its return trip.

[0003] In the prior art, a Chinese invention patent document with publication number CN118131786A and publication date of June 4, 2024, was proposed. The technical solution disclosed in this patent document is as follows: a fixed-wing UAV glide return strategy and online route planning method, including the following steps: constructing an online route planning coordinate system and a coordinate transformation matrix group within the system, and obtaining the coordinates of the UAV runway endpoints A, B, and parking point S in the system; calculating the coordinates of the glide glide point Fn, the coordinates of the landing heading adjustment circle center Ofi, and the coordinates of the parking point heading adjustment circle center Osj; combining the division of the area around the runway, determining the glide return strategy based on the coordinates of each point; and generating the glide return route based on the glide return strategy.

[0004] The existing technologies represented by the above-mentioned technical solutions are mostly based on planning the optimal flight path according to the aircraft's position and the airport's position, but there is no guidance method for guiding the UAV based on the air glide path. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a fixed-wing UAV air glide return path guidance method based on energy planning, which ensures that the UAV can accurately track the air glide path and return safely when energy is sufficient, and can make an emergency landing near the emergency landing point when energy is insufficient.

[0006] This invention is achieved by adopting the following technical solution: A method for guiding the glide return flight path of a fixed-wing UAV based on energy planning includes the following steps: Step S1. After the UAV experiences an engine shutdown failure, obtain the current optimal air glide return path; Step S2. Based on the critical energy supporting the UAV's descent from the FAF point. And the energy consumed by the drone during its flight from the parking spot to the FAF point. Determine the current energy of the drone. Does the requirement for a return to the starting position be met? If yes, proceed to step S3; otherwise, skip step S4 and proceed to step S5. The FAF point is the final approach start point for the UAV's air glide return, located at the spatial position after extending along the approach direction from the runway threshold and then vertically lifting; energy consumption. The calculation method is as follows: , In the formula, The current vacuum speed of the drone, The vacuum velocity of the drone as it glides from the FAF point. , They are constant coefficients, The flight distance for the drone to glide from the parking spot to the FAF point. The slip ratio is the empty slip ratio. Step S3. Perform a glide return, and assess the drone's current energy level in real time during the glide. Can it return to the FAF point? If yes, dynamically determine its lateral control mode based on the UAV's real-time flight status parameters until it enters the air glide descent guidance mode. If no, skip step S4 and proceed to step S5. Step S4. In the final slide section of the empty slide return, control the longitudinal control mode until grounding, and do not execute step S5; Step S5. Switch the target point to the nearest forced landing point to the current location and perform an off-site forced landing; calculate the drone's current energy in real time during the forced landing process. To determine if there is excess energy that requires circling and descending.

[0007] Current drone energy The calculation method is as follows: , In the formula, The current vacuum speed of the drone, The relative altitude between the drone's current altitude and the FAF point, where g is the acceleration due to gravity; Critical energy to support drone descent from FAF point The calculation method is as follows: , In the formula, The vacuum velocity of the drone as it descents from the FAF point.

[0008] The method for calculating the flight distance D of the drone from the parking point to the FAF point is as follows: , , , , like ,but ,otherwise ; like ,but ,otherwise ; In the formula, To cut out the circular part by spiraling, For the linear tracking section, To spiral into the circular section, To cut out the radius of the circle by spiraling, This is the heading angle in radians, measured by rotating the aircraft's current track angle counterclockwise or clockwise to the point where the exit point points towards the entry point. The flight path angle of the drone at the moment of parking. The heading angle from the exit point to the entry point. The radius of the spiral tangent circle, The coordinates of the exit point of the spiraling exit circle are the airport's heading angle in radians, rotated counterclockwise or clockwise towards the landing direction. The coordinates of the point of entry of the spiraling tangent circle are: .

[0009] The real-time flight status parameters of the UAV in step S3 include the current flight path angle of the UAV and the distance to be flown between the UAV and the entry point of the circling entry circle.

[0010] Based on the real-time flight status parameters of the UAV, its lateral control mode is dynamically determined, specifically: Based on the direction of the spiraling circle, the lateral navigation mode is activated using the circular tracking control mode; when the UAV's current track angle... The heading angle between the point of entry and the point of exit. If the deviation meets the preset conditions, the horizontal heading exits the circular tracking control mode and switches to the straight-line tracking control mode; when the distance between the UAV and the point of entry of the circling entry circle meets the corresponding preset conditions, the horizontal heading calls the circular tracking control mode; if the following conditions are met simultaneously, the UAV exits the circular tracking control mode and enters the air glide descent guidance mode: ; in, This is the heading cross angle lead that the UAV must meet when gliding from the FAF point. The airport heading angle for the landing direction. To determine the altitude lead time at which the drone can descend from the FAF point.

[0011] When determining the current energy of the drone It can return to the FAF point. During the air gliding process, the longitudinal speed is controlled by the pitch angle, and the speed target is the emergency air gliding speed.

[0012] The longitudinal control mode specifically refers to the following: during the final glide phase of the glide return, the longitudinal control mode adopts the altitude trajectory control mode to track the glide glide line; when the UAV altitude is less than the flattening altitude Hf, the longitudinal control mode switches to the vertical speed maintenance control mode.

[0013] The glide path specifically refers to: taking the instantaneous position point of the UAV exiting its hovering and descent phase and beginning its glide phase as a reference, projecting the orthographic projection of this point onto the vertical plane determined by the two airport reference points. The resulting projection point is denoted as point A. A local rectangular coordinate system is established using the orthographic projection of point A onto the airport's horizontal plane as the origin O. The intersection of the vertical plane containing the two airport reference points and the airport's horizontal plane is used as the X-axis, with the positive direction of the X-axis being the airport direction of the UAV's landing, and the positive direction of the Y-axis being the positive direction of the sky (H). Point A is taken as the starting point of the glide, and a preset glide angle is used... Construct a downward-sloping glide path starting from point A, and denote the intersection of the glide path and the OX axis as point P.

[0014] During the final glide phase of the return glide, the lateral navigation mode is switched to straight-line tracking control.

[0015] During the emergency landing process, the lateral direction adopts the straight-line tracking control mode, which enables the UAV to track and call the virtual flight path generated by connecting the UAV's position at the moment of emergency landing with the landing point. The longitudinal direction adopts the pitch angle control speed mode, and the speed target is the emergency glide speed.

[0016] Current energy of the drone during the forced landing process The calculation method is as follows: , In the formula, The current vacuum speed of the drone, The current altitude of the drone and The relative height between the points, where g is the acceleration due to gravity; The point is above the forced landing point. The point at that location, and , To force a landing, the radius of the high circle is reduced during the circumduction. This is the slip ratio.

[0017] If the distance to the emergency landing point is less than or equal to At that time, the energy is satisfied: The lateral navigation uses a circular arc tracking control mode, enabling the UAV to track the radius around the forced landing point. The circle, awaiting the current energy of the drone Less than or equal to critical energy When the drone exits its circling and descent phase, it adopts a straight-line tracking control mode in the lateral direction, tracking the virtual flight path generated by connecting the drone's position when it exits the circling and descent phase with the forced landing point, and then using an air glide descent method until the drone lands; among these... The constant coefficient, This represents the current ground speed of the drone.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes a fixed-wing unmanned aerial vehicle (UAV) air-glide return route guidance method based on energy planning. When the UAV experiences engine failure, under powerless conditions, the system can autonomously determine whether it has the capability to return to base based on the current flight status and dynamically select to execute an air-glide return or an off-site emergency landing strategy.

[0019] When energy is sufficient, the UAV flies along a pre-set optimal glide path (such as a three-segment path of circular arc-straight line-circular arc). The guidance system achieves high-precision tracking of the path through coordinated lateral and longitudinal control. Before approaching the final approach positioning point (FAF), it ensures that the optimal glide distance requirement is met. If there is excess energy (especially high potential energy), the UAV will deplete its energy by extending the flight or increasing the number of circles during the circling phase. A reasonable exit window will be designed based on heading and altitude criteria to ensure that the energy is moderate when entering the glide phase, avoiding premature touchdown or runway overrun.

[0020] When the energy is insufficient to support a return, the system automatically switches the target to the nearest safe landing point, guides the drone to the area, and assesses the remaining energy in real time during the landing process. If necessary, it performs circling and altitude reduction to ensure that the landing energy is within the safe envelope.

[0021] This method effectively enhances the autonomous decision-making and safe recovery capabilities of UAVs in the event of power failure. It can ensure accurate return to the field under normal conditions and achieve controlled forced landing under extreme energy conditions, significantly reducing the risk of equipment damage, personnel casualties, and property loss caused by uncontrolled crashes.

[0022] This invention focuses on guidance implementation methods after the optimal air glide path is known, and focuses on solving the problems of mode switching, control law invocation and terminal alignment under energy drive.

[0023] 2. In calculating energy consumption, this invention considers the geometric characteristics and dynamic state changes of the actual flight path of the UAV from the parking point to the FAF point. By calculating the distance to be flown in segments analytically and adjusting energy consumption in conjunction with the air-glide ratio and speed, the accuracy of energy assessment is improved. Simultaneously, this method decomposes the path into three segments: hovering, straight line, and hovering, and explicitly models the turning arc length, more realistically reflecting the actual flight trajectory, which is beneficial for achieving precise guidance decisions driven by energy.

[0024] 3. During the glide return process, this invention dynamically determines the lateral heading control mode, ensuring smooth transitions between the hovering, cutting out, cutting in, and glide phases of the UAV, thus improving the continuity and stability of trajectory tracking. By introducing the distance to be flown and heading angle deviation as mode switching criteria, the adaptability and energy controllability of the guidance system are enhanced, which is beneficial for achieving high-precision navigation in complex glide paths.

[0025] 4. This invention controls the longitudinal control mode during the final glide phase of the return approach, enabling a smooth transition from precise altitude trajectory tracking to stable vertical velocity. This effectively adapts to the dynamic requirements of the terminal approach phase, improving landing safety and flight quality. By switching to vertical velocity hold mode at low altitude, it enhances anti-disturbance capabilities, avoids altitude fluctuations caused by terrain or airflow, and ensures a stable landing.

[0026] 5. During an off-site emergency landing, this invention employs a control strategy combining lateral straight-line tracking and longitudinal pitch angle speed control. This strategy is simple in structure, responds quickly, and effectively guides the UAV along the shortest path to the landing point, improving emergency response efficiency. The longitudinal approach uses a fixed glide speed control to ensure stable energy consumption, avoiding landing risks caused by excessive or insufficient speed, and enhancing the predictability and safety of the emergency landing process. Attached Figure Description

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a schematic diagram of the three-dimensional trajectory of the hollow return field in this invention; Figure 2 This is a top-view schematic diagram of the trajectory of the hollow return field in this invention; Figure 3 This is a three-dimensional perspective view of the flight path of the UAV in this invention; Figure 4 This is a two-dimensional top view of the flight path of the UAV in this invention; Figure 5 This is a diagram showing the energy change during the hollow return process in this invention. Figure 6 This is a diagram showing the local energy changes during the hollow return process in this invention; Figure 7This is a diagram showing the relationship between the current track angle and the target heading angle during the glide return phase of this invention. Figure 8 This is a local relationship diagram between the current track angle and the target heading angle in the air glide return field of this invention; Figure 9 This is a schematic diagram of the FAF point in this invention; Figure 10 This is a schematic diagram of the spiral cutting point and spiral cutting point in this invention; Figure 11 This is a schematic diagram of the hollow sliding glide path in this invention; Figure 12 This is a schematic diagram of the forced landing in this invention. Detailed Implementation

[0028] Example 1 As a basic embodiment of the present invention, the present invention includes a method for guiding the glide return flight path of a fixed-wing unmanned aerial vehicle based on energy planning, comprising the following steps: Step S1. After the UAV experiences an engine shutdown failure, obtain the current optimal air glide return path.

[0029] Step S2. Based on the critical energy supporting the UAV's descent from the FAF point. And the energy consumed by the drone during its flight from the parking spot to the FAF point. Determine the current energy of the drone. Does the requirement for a return to the starting position be met? If yes, proceed to step S3; otherwise, skip step S4 and proceed to step S5.

[0030] The FAF point is the final approach start point for the UAV's air glide return. It is located at the runway entrance, extending along the approach direction and then vertically raised, and is used to guide the UAV to enter a stable glide trajectory with the target air glide ratio.

[0031] Consume energy The calculation method is as follows: , In the formula, The current vacuum speed of the drone, The vacuum velocity of the drone as it glides from the FAF point. , They are constant coefficients, The flight distance for the drone to glide from the parking spot to the FAF point. This is the slip ratio.

[0032] Step S3. Perform a glide return, and assess the drone's current energy level in real time during the glide. Can it return to the FAF point? If yes, dynamically determine its lateral control mode based on the UAV's real-time flight status parameters until it enters the glide path guidance mode; if not, skip step S4 and proceed to step S5.

[0033] Step S4. In the final slide section of the empty slide return, control the longitudinal control mode until grounding, and do not execute step S5.

[0034] Step S5. Switch the target point to the nearest forced landing point to the current location and perform an off-site forced landing; calculate the drone's current energy in real time during the forced landing process. To determine if there is excess energy that requires circling and descending.

[0035] Example 2 As a preferred embodiment of the present invention, the present invention includes a method for guiding the glide return flight path of a fixed-wing unmanned aerial vehicle based on energy planning, comprising the following steps: Step S1. After the UAV experiences an engine shutdown failure, obtain the current optimal air glide return path.

[0036] Step S2. Based on the critical energy supporting the UAV's descent from the FAF point. And the energy consumed by the drone during its flight from the parking spot to the FAF point. Determine the current energy of the drone. Does the requirement for a return to the starting position be met? If yes, proceed to step S3; otherwise, skip step S4 and proceed to step S5.

[0037] The FAF point is the final approach start point for the UAV's air-glide return, located at the spatial position extending along the approach direction from the runway threshold and then vertically raised. It guides the UAV to enter a stable glide trajectory with the target air-glide ratio. Energy consumption. The calculation method is as follows: , In the formula, The current vacuum speed of the drone, The vacuum velocity of the drone as it glides from the FAF point. , They are constant coefficients, The flight distance for the drone to glide from the parking spot to the FAF point. This is the slip ratio.

[0038] Step S3. Perform a glide return, and assess the drone's current energy level in real time during the glide. Can the drone return to the FAF point? If yes, use pitch angle control to control the indicated airspeed, with the target speed being the emergency glide speed; and dynamically determine its lateral control mode based on the drone's real-time flight status parameters until it enters glide descent guidance. If no, skip step S4 and proceed to step S5.

[0039] The real-time flight status parameters of the UAV include the UAV's current flight path angle and the distance between the UAV and the point of approach of the hovering approach circle. Dynamically determining its lateral control mode specifically refers to: Based on the direction of the spiraling circle, the lateral navigation mode is activated using the circular tracking control mode; when the UAV's current track angle... The heading angle between the point of entry and the point of exit. If the deviation meets the preset conditions, the horizontal heading exits the circular tracking control mode and switches to the straight-line tracking control mode; when the distance between the UAV and the point of entry of the circling entry circle meets the corresponding preset conditions, the horizontal heading calls the circular tracking control mode; if the following conditions are met simultaneously, the UAV exits the circular tracking control mode and enters the air glide descent guidance mode: ; in, This is the heading cross angle lead that the UAV must meet when gliding from the FAF point. To determine the altitude lead time at which the drone can descend from the FAF point.

[0040] Step S4. During the final glide phase of the return flight, the lateral navigation is switched to the straight-line tracking control mode, and the longitudinal control mode is maintained until grounding. Specifically, controlling the longitudinal control mode means: during the final glide phase of the return flight, the longitudinal trajectory control mode is used to track the glide path; when the UAV's altitude is less than the leveling altitude Hf, the longitudinal control mode switches to the vertical speed maintenance control mode, and step S5 is no longer executed. The leveling altitude Hf is determined based on the glide ascent / descent rate, the grounding ascent / descent rate limit, and the designed leveling ascent / descent rate curve, ensuring that the UAV has sufficient altitude to control the ascent / descent rate within the grounding limit during the glide.

[0041] Step S5. Switch the target point to the nearest forced landing point to the current location and perform an off-site forced landing; calculate the drone's current energy in real time during the forced landing process. The system determines if there is excess energy necessitating a circling descent. When this is determined, the lateral navigation adopts a circular tracking control mode, ensuring the UAV tracks the radius around the landing point. The circle, the current energy of the drone during the forced landing process. Less than or equal to critical energy When the drone exits the circling and descent mode, it adopts a straight-line tracking control mode in the lateral direction, tracks the virtual flight path generated by connecting the drone's position when it exits the circling and descent mode with the forced landing point, and uses an air glide descent method until the drone lands.

[0042] Example 3 In another preferred embodiment of the present invention, the present invention includes a method for guiding the glide return flight path of a fixed-wing unmanned aerial vehicle based on energy planning, comprising the following steps: Step S1. After the UAV experiences an engine shutdown failure, obtain the current optimal air glide return path.

[0043] Step S2. Based on the critical energy supporting the UAV's descent from the FAF point. And the energy consumed by the drone during its flight from the parking spot to the FAF point. Determine the current energy of the drone. Does the requirement for a return to the starting position be met? If yes, proceed to step S3; otherwise, skip step S4 and proceed to step S5.

[0044] The FAF point is the final approach start point for the UAV's air glide return. It is located at the runway entrance, extending along the approach direction and then vertically raised, and is used to guide the UAV to enter a stable glide trajectory with the target air glide ratio.

[0045] Critical energy to support drone descent from FAF point The calculation method is as follows: , In the formula, This is the vacuum speed of the drone as it glides from the FAF point, typically taken as the vacuum speed corresponding to the emergency glide speed.

[0046] Energy consumption of the drone during its flight from the parking spot to the FAF point The calculation method is as follows: , In the formula, The current vacuum speed of the drone, , They are constant coefficients, The flight distance for the drone to glide from the parking spot to the FAF point. This is the slip ratio.

[0047] Current drone energy The calculation method is as follows: , In the formula, denoted as , where is the relative altitude between the drone's current altitude and the FAF point, and g is the acceleration due to gravity.

[0048] like If so, it is determined that the current energy of the drone is sufficient for an air glide return.

[0049] Step S3. Perform a glide return, and assess the drone's current energy level in real time during the glide. Can it return to the FAF point? If yes, dynamically determine its lateral control mode based on the UAV's real-time flight status parameters until it enters the glide path guidance mode; if not, skip step S4 and proceed to step S5.

[0050] Step S4. In the final slide section of the empty slide return, control the longitudinal control mode until grounding, and do not execute step S5.

[0051] Step S5. Switch the target point to the nearest forced landing point to the current location and perform an off-site forced landing; calculate the drone's current energy in real time during the forced landing process. To determine if there is excess energy that requires circling and descending.

[0052] Specifically, the current energy of the drone during the forced landing process. The calculation method is as follows: , In the formula, The current altitude of the drone and The relative height between the points, where g is the acceleration due to gravity; The point is above the forced landing point. The point at that location, and , To force a landing, the radius of the high circle is reduced during the circumduction. This is the slip ratio.

[0053] Example 4 In another preferred embodiment of the present invention, the present invention includes a method for guiding the glide return flight path of a fixed-wing unmanned aerial vehicle based on energy planning, comprising the following steps: Step S1. After the UAV experiences an engine shutdown failure, obtain the current optimal air glide return path.

[0054] The optimal air slide return path can be obtained using existing algorithms. In this embodiment, to simplify the model, a path planning method based on the Dubins method is used. This method generates a spiral exit circle and a spiral entry circle, and the coordinates of the exit point of the spiral exit circle are known. Coordinates of the point of entry of the spiraling tangent circle The heading angle from the exit point to the entry point (the angle with true north, clockwise is positive), and the spiraling directions of the exit and entry circles. The entry circle is selected as the circle closest to the engine stop location (hereinafter referred to as the stop point), with its center located at the FAF point on the stop side, perpendicular to the airport line on the stop point side. ( The FAF point is defined as the position of the circle of entry (radius of the hovering entry circle), extending outward from the line connecting the airport points of the air taxiway. (m), then extend vertically upwards. The point (m) is where the slip ratio is guaranteed. The FAF point diagram is attached to the instruction manual. Figure 9 As shown. A schematic diagram of the spiraling cut-out point and spiraling cut-in point is attached to the instruction manual. Figure 10 As shown.

[0055] Step S2. Based on the critical energy supporting the UAV's descent from the FAF point. And the energy consumed by the drone during its flight from the parking spot to the FAF point. Determine the current energy of the drone. Does the requirement for a return to the starting position be met? If yes, proceed to step S3; otherwise, skip step S4 and proceed to step S5. Specifically, if... If so, it can be determined that the drone is capable of returning to the field via air glide.

[0056] The total energy per unit after the drone stops includes only kinetic and potential energy, namely: , In the formula, The current vacuum speed of the drone, Let g be the relative altitude between the drone's current altitude and the FAF point, and g be the acceleration due to gravity. The critical energy supporting the drone's descent from the FAF point consists of kinetic energy and potential energy. Here, since the zero potential energy surface selected when determining the energy is the horizontal plane where the FAF point is located, the potential energy is zero. Therefore, the critical energy... for: .

[0057] in, This is the vacuum speed of the drone as it glides from the FAF point, typically taken as the vacuum speed corresponding to the emergency glide speed.

[0058] The energy consumed by the drone during its flight from the parking point to the FAF point due to factors such as air friction is: , In the formula, , These are constant coefficients, which are related to the aerodynamic characteristics of the UAV. The flight distance for the drone to glide from the parking spot to the FAF point. This is the slip ratio.

[0059] for The calculation can be broken down into three parts: spiraling and cutting out the circular part. Line tracking section , spiraling into the circular part The flight path angle of the UAV at the moment of stopping is known to be... The heading angle from the point of exit to the point of entry is The direction of rotation of the spiraling exit circle, the direction of rotation of the spiraling entry circle, and the airport heading angle of the landing direction. .

[0060] The calculation formula is as follows: , In the formula, To cut out the radius of the circle by spiraling, if ,but ,otherwise .

[0061] If the spiral cutting out of the circle is in a counterclockwise direction, then This is the azimuth angle in radians of the aircraft's current track angle rotated counterclockwise to the point of entry / exit; if the rotation direction of the tracing circle is clockwise, then... It is the heading angle in radians when the aircraft's current track angle is rotated clockwise to the point from the exit point to the entry point.

[0062] The calculation formula is as follows: .

[0063] The calculation formula is as follows: , In the formula, For the radius of the spiraling tangent circle, if ,but ,otherwise If the spiraling direction of the tangent circle is counterclockwise, then This is the radian value of the airport's heading angle, rotated counterclockwise from the exit point to the entry point, towards the landing direction; if the direction of the spiraling entry circle is clockwise, then... The heading angle is the airport heading angle in radians that is rotated clockwise from the point of entry to the point of exit to the landing direction.

[0064] but Approximate as .

[0065] Step S3. Perform a glide return, and assess the drone's current energy level in real time during the glide. Can it return to the FAF point? If yes, dynamically determine its lateral control mode based on the UAV's real-time flight status parameters until it enters glide path guidance. If not, skip step S4 and proceed to step S5.

[0066] Specifically, if the UAV has sufficient real-time energy to glide back to the field after a malfunction, the control mode of circular tracking is called according to the lateral direction of the circling cut-out circle, so that the UAV tracks the circling cut-out circle generated by the flight path, and the longitudinal speed is controlled by the pitch angle, with the speed target being the emergency glide speed.

[0067] When the drone's current flight path angle The heading angle between the point of entry and the point of exit. satisfy: Then, circular tracking will exit. The angular lead for exiting circular tracking can generally be taken as the roll angle during stable circling divided by the roll rate when exiting circling, and then multiplied by the yaw rate during stable circling.

[0068] After exiting, the lateral navigation control mode switches to the straight-line tracking control mode, enabling the UAV to track the virtual flight path generated by connecting the exit point and the entry point. The longitudinal speed is controlled by the pitch angle, with the target speed being the emergency glide speed.

[0069] If the drone's approach point is within the circling circle, the flight distance is... hour( This is a constant coefficient, related to the turning characteristics of the drone; the faster the roll rate... (The smaller the value, the larger the value). Based on the spiraling direction of the spiraling entry circle, the control mode of circular arc tracking is invoked to enable the UAV to track the generated spiraling entry circle.

[0070] Because the entire glide process uses pitch angle control for airspeed, and the target speed is the speed of the UAV when it descends from the FAF point, the kinetic energy at the point of entry will not differ significantly. The main consideration is the difference in decision-making caused by the magnitude of potential energy. If the UAV's energy is too high at the point of entry (i.e., too high potential energy or too high altitude), the UAV continues to descend along the circling entry disc. Once the altitude is appropriate, it can begin to determine whether it can glide from the FAF point, based solely on the UAV's current flight path angle. Airport heading angle relative to landing direction If the difference is less than an appropriate angle, the vehicle can glide from the FAF point towards the airport. When the following conditions are met simultaneously, the circular tracking will be discontinued, and the vehicle will enter air glide guidance:

[0071] in, This is the heading cross angle lead that the UAV must meet when gliding from the FAF point. As an option for drones with longer landing runways or higher deceleration performance during landing, To determine the altitude lead time for a drone to glide from the FAF point, it is generally taken as half the descent altitude of the drone after one full gliding circle. This can further improve the reliability of a safe landing during the glide return.

[0072] If, during the drone's circling and descent around the entry circle, it first passes over the FAF, the calculated... The value may jump, and the calculation is based on the first half-circle of the drone's flight. It will be at least half the actual flight distance, but due to the limitation of the heading angle, this situation will not cause the drone to exit the hovering and descend at the wrong time.

[0073] Step S4. During the final glide phase of the return glide, maintain longitudinal control mode until grounding. Specifically, during the final glide phase of the return glide, switch to straight-line tracking control mode in the lateral direction to correct the UAV's side offset, and use altitude trajectory control in the longitudinal direction to track the glide glide path. The glide glide path is defined as follows: Taking the instantaneous position of the UAV as it exits its circling and descends altitude phase and begins its glide phase as the reference point, the point projected onto the vertical plane containing the two airport reference points is designated as point A. The projection of A onto the airport's horizontal plane is taken as the origin O. The intersection of the vertical plane containing the two airport points and the airport's horizontal plane is used as the X-axis, with the positive direction of the X-axis being the direction of the airport where the UAV lands, and the positive direction of the Y-axis being the positive direction of the sky, H. Using A as the starting point of the glide phase... The intersection point P of the glide slope angle and OX is shown in the instruction manual. Figure 11 As shown.

[0074] In the above coordinate system, when the drone's altitude is less than the leveling height Hf, the longitudinal control mode is switched to vertical velocity hold, allowing the drone to glide at an appropriate descent rate until it touches down, at which point step S5 is no longer executed. The leveling height Hf is determined based on the descent and ascent / descent rates, the grounding ascent / descent rate limit, and the designed leveling ascent / descent rate curve, ensuring that the drone has sufficient altitude to control its descent and ascent / descent rates within the grounding limit.

[0075] Step S5. Switch the target point to the nearest forced landing point to the current location and perform an off-site forced landing. During the forced landing, calculate the drone's current energy in real time. To determine if there is excess energy that requires circling and descending.

[0076] Specifically, if during the glide return process, it is determined that the UAV's current energy is insufficient to glide to the FAF point, the target point is switched to the nearest emergency landing point for an off-site emergency landing. The emergency landing point should be selected around the mission flight path to avoid the UAV being unable to reach a point that is too far away. The lateral navigation uses a straight-line tracking control mode, allowing the UAV to track a virtual flight path generated by connecting the UAV's position at the moment of emergency landing with the emergency landing point. The longitudinal navigation uses a pitch angle control mode with the target speed being the emergency glide speed. After the off-site emergency landing, the determination of whether the UAV's current energy meets the requirements for glide return is no longer made; instead, the UAV's current energy during the emergency landing process is assessed in real time. Does the off-site emergency landing have enough energy to require circling and descending?

[0077] Current energy of the drone during the forced landing process The calculation method is as follows: , In the formula, The current altitude of the drone and The relative height between the points, where g is the acceleration due to gravity; The point is above the forced landing point. The point at that location, and , To force a landing, the radius of the high circle is reduced during the circumduction. This is the slip ratio. Generally, the turning radius is set to be more than twice the maximum usable roll angle to ensure that the drone can align with the emergency landing point after exiting the hovering and descending, while also ensuring the critical energy required to exit the hovering at that radius. Just enough time to fly to the emergency landing point.

[0078] For the energy consumption calculation formula during the air glide landing process It can be directly approximated as the planar distance between the current position of the drone and the forced landing point.

[0079] If the distance to the emergency landing point is less than or equal to At that time, if the energy satisfies: Then, the horizontal heading adopts the circular tracking control mode, so that the UAV tracks the radius around the forced landing point as... The circle, when the drone's current energy is less than or equal to the critical energy. When the drone exits its circling and descent mode, it adopts a straight-line tracking control mode for lateral navigation. The virtual flight path is generated by connecting the drone's position when it exits the circling and descent with the forced landing point. It then uses a glide descent method until the drone lands. This is a constant coefficient, related to the time required to establish the rotation and roll angle; The current ground speed of the drone is [value] m / s. A diagram of the forced landing is attached to the instruction manual. Figure 12 As shown.

[0080] Example 6 As a specific embodiment of the present invention, the present invention includes a fixed-wing unmanned aerial vehicle (UAV) air-glide return trajectory guidance method based on energy planning. This embodiment adopts the following assumption: UAV air-glide ratio... , ,but The lead time for the drone to cut out from the circling cutting circle is set as follows: The heading cross angle lead for gliding from the FAF point is The radii of both the spiral out-of-circle and spiral in-circle are set to 600m. The coordinates of the runway endpoints are A(99.768368°, 40.3°) and B(99.768368°, 40.315°). The vacuum velocity of the UAV during its descent from the FAF point is taken as follows. The normal flight path and landing path of the drone are as shown in the instruction manual. Figure 3 Included with instruction manual Figure 4 As shown, route 1 is the mission route and route 7 is the landing route.

[0081] At 800 seconds, the drone engine is shut down, thus initiating the air glide return procedure. The entire flight trajectory is shown in the attached manual. Figure 1 Included with instruction manual Figure 2 As shown.

[0082] From the instruction manual Figure 2 It can be seen that the tracking effect of the generated air glide path is good after the UAV experiences engine failure (after the stopping point), as shown in the instruction manual. Figure 1 It can be seen that when the drone was tracking the circling entry circle, due to excessive energy, it circled the circle once to meet the descent conditions before beginning its descent. The energy changes of the drone throughout the process are shown in the attached manual. Figure 5 Included with instruction manual Figure 6 As shown.

[0083] From the instruction manual Figure 5 Included with instruction manual Figure 6 As can be seen, at the current air glide phase, the drone has not yet entered the air glide return phase when it is 0; at 100, the drone flies around the exit circle; at 200, the drone flies along the line connecting the exit and entry points; at 300, the drone circles around the entry circle and descends in altitude; and at 400, the drone begins its air glide descent from the FAF point. The energy consumed during the air glide return process is significant. There are two transitions. The first is when the drone passes over the FAF point. The calculation is refreshed; the second refresh occurs after the drone completes its first half-circle. The settings were refreshed again, but none of these changes affected the drone's correct decision to exit the circling and descend. During the glide return process, the relationship between the drone's current track angle and the target heading angle is shown in the attached manual. Figure 7 Included with instruction manual Figure 8 As shown.

[0084] During the drone's circular flight around the target path, the absolute value of the difference between the current path angle and the target path angle is less than... At t=1446s, the absolute value of the difference between the current track angle and the target track angle is less than 1446s. If both the heading cross angle and energy criteria are met, exit the circling and descend, and enter the glide descent.

[0085] In summary, any other corresponding modifications made by those skilled in the art after reading this invention document, without requiring creative mental effort, based on the technical solutions and concepts of this invention, are all within the scope of protection of this invention.

Claims

1. A method for guiding the glide return flight path of a fixed-wing unmanned aerial vehicle based on energy planning, characterized in that: Includes the following steps: Step S1. After the UAV experiences an engine shutdown failure, obtain the current optimal air glide return path; Step S2. Based on the critical energy supporting the UAV's descent from the FAF point. And the energy consumed by the drone during its flight from the parking spot to the FAF point. Determine the current energy of the drone. Does the requirement for a return to the starting position be met? If yes, proceed to step S3; otherwise, skip step S4 and proceed to step S5. The FAF point is the final approach start point for the UAV's air glide return, located at the spatial position after extending along the approach direction from the runway threshold and then vertically lifting; energy consumption. The calculation method is as follows: ， In the formula, The current vacuum speed of the drone, The vacuum velocity of the drone as it glides from the FAF point. , They are constant coefficients, The flight distance for the drone to glide from the parking spot to the FAF point. The slip ratio is the empty slip ratio. Step S3. Perform a glide return, and assess the drone's current energy level in real time during the glide. Can it return to the FAF point? If yes, dynamically determine its lateral control mode based on the UAV's real-time flight status parameters until it enters the air glide descent guidance mode. If no, skip step S4 and proceed to step S5. Step S4. In the final slide section of the empty slide return, control the longitudinal control mode until grounding, and do not execute step S5; Step S5. Switch the target point to the nearest forced landing point to the current location and perform an off-site forced landing; calculate the drone's current energy in real time during the forced landing process. To determine if there is excess energy that requires circling and descending.

2. The method for guiding the return flight path of a fixed-wing UAV based on energy planning according to claim 1, characterized in that: Current drone energy The calculation method is as follows: ， In the formula, The current vacuum speed of the drone, The relative altitude between the drone's current altitude and the FAF point, where g is the acceleration due to gravity; Critical energy to support drone descent from FAF point The calculation method is as follows: ， In the formula, The vacuum velocity of the drone as it descents from the FAF point.

3. The method for guiding the air glide and return flight path of a fixed-wing UAV based on energy planning according to claim 2, characterized in that: The method for calculating the flight distance D of the drone from the parking point to the FAF point is as follows: ， ， ， ， like ,but ,otherwise ; like ,but ,otherwise ; In the formula, To cut out the circular part by spiraling, For the linear tracking section, To spiral into the circular section, To cut out the radius of the circle by spiraling, This is the heading angle in radians, measured by rotating the aircraft's current track angle counterclockwise or clockwise to the point where the exit point points towards the entry point. The flight path angle of the drone at the moment of parking. The heading angle from the point of entry to the point of exit. The radius of the spiral tangent circle, The coordinates of the exit point of the spiraling exit circle are the airport's heading angle in radians, rotated counterclockwise or clockwise towards the landing direction. The coordinates of the point of entry of the spiraling tangent circle are: .

4. The method for guiding the air glide return flight path of a fixed-wing UAV based on energy planning according to claim 1, characterized in that: The real-time flight status parameters of the UAV in step S3 include the current flight path angle of the UAV and the distance to be flown between the UAV and the entry point of the circling entry circle.

5. The method for guiding the air glide and return flight path of a fixed-wing UAV based on energy planning according to claim 4, characterized in that: Based on the real-time flight status parameters of the UAV, its lateral control mode is dynamically determined, specifically: Based on the direction of the spiraling circle, the lateral navigation mode is activated using the circular tracking control mode; when the UAV's current track angle... The heading angle between the point of entry and the point of exit. If the deviation meets the preset conditions, the horizontal heading exits the circular tracking control mode and switches to the straight-line tracking control mode; when the distance between the UAV and the point of entry of the circling entry circle meets the corresponding preset conditions, the horizontal heading calls the circular tracking control mode; if the following conditions are met simultaneously, the UAV exits the circular tracking control mode and enters the air glide descent guidance mode: ； in, This is the heading cross angle lead that the UAV must meet when gliding from the FAF point. The airport heading angle for the landing direction. To determine the altitude lead time at which the drone can descend from the FAF point.

6. The method for guiding the air glide and return flight path of a fixed-wing UAV based on energy planning according to claim 5, characterized in that: When determining the current energy of the drone It can return to the FAF point. During the air gliding process, the longitudinal speed is controlled by the pitch angle, and the speed target is the emergency air gliding speed.

7. A method for guiding the glide and return flight path of a fixed-wing UAV based on energy planning according to claim 1 or 6, characterized in that: The longitudinal control mode specifically refers to the following: during the final glide phase of the glide return, the longitudinal control mode adopts the altitude trajectory control mode to track the glide glide line; when the UAV altitude is less than the flattening altitude Hf, the longitudinal control mode switches to the vertical speed maintenance control mode.

8. The method for guiding the air glide return flight path of a fixed-wing UAV based on energy planning according to claim 7, characterized in that: The glide path specifically refers to: taking the instantaneous position point of the UAV exiting its hovering and descent phase and beginning its glide phase as a reference, projecting the orthographic projection of this point onto the vertical plane determined by the two airport reference points. The resulting projection point is denoted as point A. A local rectangular coordinate system is established using the orthographic projection of point A onto the airport's horizontal plane as the origin O. The intersection of the vertical plane containing the two airport reference points and the airport's horizontal plane is used as the X-axis, with the positive direction of the X-axis being the airport direction of the UAV's landing, and the positive direction of the Y-axis being the positive direction of the sky (H). Point A is taken as the starting point of the glide, and a preset glide angle is used... Construct a downward-sloping glide path starting from point A, and denote the intersection of the glide path and the OX axis as point P.

9. A method for guiding the glide and return flight path of a fixed-wing UAV based on energy planning according to claim 8, characterized in that: During the final glide phase of the return glide, the lateral navigation mode is switched to straight-line tracking control.

10. A method for guiding the air glide and return flight path of a fixed-wing UAV based on energy planning according to claim 1 or 6, characterized in that: During the emergency landing process, the lateral direction adopts the straight-line tracking control mode, which enables the UAV to track and call the virtual flight path generated by connecting the UAV's position at the moment of emergency landing with the landing point. The longitudinal direction adopts the pitch angle control speed mode, and the speed target is the emergency glide speed.

11. The method for guiding the return flight path of a fixed-wing UAV based on energy planning according to claim 10, characterized in that: Current energy of the drone during the forced landing process The calculation method is as follows: ， In the formula, The current vacuum speed of the drone, The current altitude of the drone and The relative height between the points, where g is the acceleration due to gravity; The point is above the forced landing point. The point at that location, and , To force a landing, the radius of the high circle is reduced during the circumduction. This is the slip ratio.

12. The method for guiding the air glide return flight path of a fixed-wing UAV based on energy planning according to claim 11, characterized in that: If the distance to the emergency landing point is less than or equal to At that time, the energy is satisfied: The lateral navigation uses a circular arc tracking control mode, enabling the UAV to track the radius around the forced landing point. The circle, awaiting the current energy of the drone Less than or equal to critical energy When the drone exits its circling and descent phase, it adopts a straight-line tracking control mode in the lateral direction, tracking the virtual flight path generated by connecting the drone's position when it exits the circling and descent phase with the forced landing point, and then using an air glide descent method until the drone lands; among these... The constant coefficient, This represents the current ground speed of the drone.

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