Aircraft unpowered returning forced landing control method

Abstract

The invention discloses an aircraft unpowered returning forced landing control method, which belongs to the field of aircraft flight control, adopts a three-dimensional route collaborative design scheme, optimizes a horizontal plane route through a four-section path of a Durbin curve, and is combined with a vertical plane slope margin design, so that the route planning capability in a complex environment is remarkably improved; a spoiler is adopted to dynamically adjust the lift-drag ratio and perform sectional throttle control, so that speed dispersion caused by model deviation is effectively inhibited; according to the control method, the complex scene adaptability, the model robustness and the economical efficiency are remarkably improved while the forced landing safety is guaranteed, and an efficient solution is provided for unpowered forced landing.

Description

Technical Field

[0001] The invention belongs to the field of aircraft flight control, and in particular relates to a method for controlling an aircraft's unpowered return to a landing. Background Art

[0002] Unpowered forced landing technology is a key technology to ensure the safe landing of aircraft in the event of power loss. At present, unpowered forced landing technology has made significant progress in many fields such as fixed-wing aircraft, helicopters and other aircraft. In the field of fixed-wing aircraft, researchers focus on trajectory planning, energy management and guidance control. In trajectory planning, methods such as Dubins trajectory search are used, combined with optimal control methods and hp adaptive pseudo-spectral method to design accurate forced landing trajectories that meet the initial and terminal constraints and aircraft performance requirements, providing path guarantee for safe forced landing. In terms of energy management, by adjusting the flight attitude and trajectory, the energy consumption rate is accurately controlled to ensure that the aircraft has a suitable speed and altitude when it arrives at the forced landing point. At the same time, in the field of guidance control, advanced systems such as nonlinear guidance laws are designed to achieve precise control of the aircraft and ensure accurate forced landing. The research on unpowered forced landing technology of helicopters mainly focuses on two key directions: autorotation maneuver and safety performance improvement. During autorotation landing, the pilot needs to skillfully control the rotor and tail rotor to ensure the stability of the helicopter during the autorotation process, so as to achieve a safe landing. In addition, through the enhanced design of the helicopter body, such as the use of anti-crash structures and buffer devices, the damage to personnel when falling to the ground is significantly reduced, and the safety of the helicopter's unpowered forced landing is further improved. The unpowered forced landing technology in other aircraft fields has also achieved remarkable results. With the help of advanced sensors and control systems, the drone has achieved autonomous return and landing functions. In the event of engine failure, it can autonomously plan the trajectory and land safely, greatly reducing the need and risk of manual intervention. The unpowered gliding cabin has enhanced stability during the gliding process through the unique design of deployment components and glider wing components, providing strong support for scientific experiments and data transmission.

[0003] However, the current unpowered forced landing technology still faces many challenges in practical applications. Complex meteorological conditions such as strong winds, heavy rain and heavy fog, as well as complex terrain such as mountainous areas, not only interfere with the aerodynamic performance and flight stability of the aircraft, but also increase the difficulty of finding a suitable forced landing point; the aerodynamic and weight models of the aircraft have deviations due to factors such as manufacturing and component status, which makes it difficult to accurately implement route planning and speed control; the pilot and the automation system do not collaborate smoothly in emergency situations, the automation system has limited decision-making capabilities and the operating prompts are not intuitive enough, which can easily lead to command conflicts; in addition, from research and development to application, high-precision unpowered forced landing technology requires high investment, including research and development, testing, experiments, and aircraft modification and maintenance costs, which makes it difficult for some units with limited budgets to adopt it. Summary of the invention

[0004] The present invention provides an unpowered return-to-field forced landing control method for an aircraft, which optimizes the horizontal plane route through a four-segment path of the Dobbins curve and combines the plumb plane slope margin design to significantly improve the path planning capability in complex environments.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A method for controlling an aircraft to return to an unpowered forced landing comprises the following steps:

[0007] S1: After the engine stops in the air, the aircraft enters the unpowered forced landing mode, the lateral heading guidance mode is turned off, the longitudinal guidance mode is turned on, the pitch angle is used to control the airspeed, and the new route is calculated at the same time;

[0008] S2: When the S-turn dissipates energy, the aircraft's lateral guidance is heading control to guide the aircraft to turn; the heading angle is controlled by the roll angle to turn, and the track mode is a circular track;

[0009] S3: Initial turn, controlling the aircraft to navigate laterally along the turning circle with C0 as the center, and following the In-T0 arc;

[0010] S4: T0-T1-AP segment flight, the track mode is arc mode, and the aircraft navigation is controlled in the Dobbins circle navigation mode with the HAC circle as the center;

[0011] S5: During AP-T flight, the flight navigation is controlled in a straight line, and spoilers are used to control the airspeed. After descending to a certain height, the aircraft is leveled, and then normal taxiing and braking are performed.

[0012] In the above steps, the route design of the forced landing process is decomposed into horizontal plane route design, plumb plane route design, and speed robustness design;

[0013] The horizontal plane route design specifically includes:

[0014] According to the longitude and latitude of the target point, the distance corresponding to each degree in the longitude and latitude direction is calculated, so as to find the longitude and latitude and altitude of the AP point, and calculate the longitude and latitude and heading angle of point C in the case of clockwise and counterclockwise orbiting around point C respectively;

[0015] According to the latitude and longitude of the initial point, calculate the latitude and longitude of point C0 in the case of clockwise and counterclockwise orbiting point C0 respectively.

[0016] Calculate the distance of the middle straight line segment, the arc length at the target point, and the arc length at the starting point in the four combined cases respectively, and add them together;

[0017] Comparing the total distances in the four cases, the case with the smallest total distance is the horizontal route planning. In this case, the distances of point C, point C0 and the three sections are the required information for the horizontal route planning.

[0018] The plumb line route design specifically includes:

[0019] The slope of each route is controlled to be greater than the inverse of the maximum lift-to-drag ratio of the aircraft to ensure speed static stability; the slope of the AP-T segment is selected according to the landing gear lowering configuration, and the slopes of the AP-T1 arc segment, T1-T0 straight segment, and T0-In arc segment are selected according to the landing gear retracting configuration; the slope of the AP-T segment is greater than the slope of the In-AP segment, and a margin is left considering the influence of aerodynamic deviation and wind speed;

[0020] Calculate the glide angle elevation_baseline according to the maximum lift-to-drag ratio of the In-AP segment, and calculate the tangent value of the glide angle, that is, , multiplied by the horizontal distance, the height of each descent can be calculated;

[0021] In the AP-T segment, the calculated rise and fall rate is -1rad / s.

[0022] The speed robustness design specifically includes: suppressing speed dispersion by adjusting the lift-to-drag ratio through spoilers; in the process of leveling, first changing the spoiler reference amount to 10°, and then changing the spoiler reference amount to 0° when about to land.

[0023] Beneficial effects: The present invention provides a method for controlling an aircraft's unpowered return to an airfield for forced landing. Aiming at the problems of existing unpowered forced landing technologies in complex weather and terrain, poor adaptability, sensitivity to model deviations, low efficiency of human-machine collaboration and high costs, a three-dimensional route collaborative design scheme is proposed. The horizontal plane route is optimized by using a four-segment path of the Dobbins curve, and the path planning capability in complex environments is significantly improved in combination with the plumb plane slope margin design. The spoiler is used to dynamically adjust the lift-to-drag ratio and segmented throttle control to effectively suppress the speed dispersion caused by model deviations. Through the above innovations, the present invention significantly improves the adaptability to complex scenarios, model robustness and economy while ensuring the safety of forced landing, providing an efficient solution for unpowered forced landing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a route in an embodiment of the present invention;

[0025] Figure 2 This is a flow chart of a control method according to an embodiment of the present invention;

[0026] Figure 3 It is a schematic diagram of the horizontal plane route design process in an embodiment of the present invention;

[0027] Figure 4This is a schematic diagram of a plumb line route in an embodiment of the present invention;

[0028] Figure 5 Schematic diagram of the changes of various parameters in the first stage in an embodiment of the present invention, wherein a is forced landing without power, b is mixed control mode, c is not using the mission track, d is throttle command, e is airspeed command, and f is roll angle command;

[0029] Figure 6 Schematic diagram of the change of parameters in the second stage in an embodiment of the present invention, a is the circular track mode, b is the input latitude, c is the input longitude, d is the input altitude, e is the input azimuth, f is the input glide angle, g is the input distance, and h is the input radius;

[0030] Figure 7 Schematic diagram of the change of various parameters in the third stage in an embodiment of the present invention, a is the lateral heading guidance mode, b is the longitudinal guidance mode;

[0031] Figure 8 Schematic diagram of the change of parameters in the fourth stage in the embodiment of the present invention, wherein a is the input latitude, b is the input longitude, c is the input altitude, d is the input azimuth, e is the input glide angle, and f is the spoiler reference value;

[0032] Fig. 9 Schematic diagram of the change of parameters in the fifth stage in an embodiment of the present invention, wherein a is a straight track mode, b is an ascending and descending rate, c is a spoiler reference value, and d is a brake command. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0034] This embodiment is about the unpowered forced landing of a single-engine aircraft after the engine stops in the air, such as Figure 1 As shown in the figure, the unpowered forced landing route starts from the current position In of the aircraft and ends at the leveling point T. It is composed of a set of Dobbins curves consisting of the arc segment In-T0, the straight line segment T0-T1, the arc segment T1-AP, and the straight line segment AP-T. This curve can satisfy the constraints of the initial and final positions and the speed direction. Figure 2 As shown in the figure, the engine shutdown in the air without power forced landing is divided into the following five stages:

[0035] Phase 1: After the engine stops in the air, enter the unpowered forced landing, do not use the original mission track, the mixing mode is the control rate cross-linking mixing, and the lateral heading guidance mode is closed. Figure 5As shown, the throttle command = 0.43, the airspeed command = 85m / s, the roll angle command = 0, try to ensure the stability of the aircraft, try not to roll, but the actual roll angle is between -0.5rad-0.1rad, the longitudinal guidance mode is turned on, and the pitch angle is used to control the airspeed. When the airspeed is too high, the airspeed is reduced by increasing the pitch angle. When the airspeed is too low, the airspeed is increased by reducing the pitch angle. Do not cut the parachute, do not open the parachute, and calculate the new route at the same time. Enter the second stage after one second; the formula for controlling the airspeed with the pitch angle is as follows: , in, is the acceleration due to gravity, is the pitch angle gain, is the pitch angle command, is the airspeed command, is the actual airspeed.

[0036] Phase 2: When the S-turn dissipates energy, the aircraft's lateral guidance is heading control, guiding the aircraft to turn so that the HAC circle is in the 3-9 o'clock direction, and the mission track is still not used, such as Figure 6 As shown, the rolling angle is used to control the heading angle to turn, the track mode is arc track, the throttle remains unchanged, and the latitude and longitude, altitude, C0 circle radius, glide angle, azimuth and distance of point C0 are input to control the aircraft to turn to point In (initial point). After one second and the altitude is less than the target altitude + 400, it enters the third stage; the formula for controlling the heading angle with the rolling angle is shown as follows: , in, is the roll angle command, is the ground speed, is the acceleration due to gravity, It is the heading angle deviation proportional control gain in the roll angle correction side deviation mode. is the yaw angle command, is the yaw angle, is the heading angular rate of the planned route.

[0037] Phase 3: When turning, the aircraft still follows the turning circle with C0 as the center, completing the In-T0 arc. Figure 7 As shown in the figure, in this stage, if the longitudinal deviation is less than 0, the longitudinal guidance mode changes from using the pitch angle to control the airspeed to using the pitch angle to control the vertical inertial navigation, and the lateral heading guidance mode changes from using the roll angle to control the yaw angle to using the roll angle to control the lateral inertial navigation. The fourth stage is entered when the distance error is less than 300 or the distance error is greater than the absolute value of 5×radius0 (circling radius).

[0038] Stage 4: Still not using mission tracks, such as Figure 8As shown, input the latitude and longitude of point C, altitude and radius of the HAC circle, the track mode is arc mode, the throttle remains unchanged, and then turn to the AP point. If the control method of the longitudinal guidance mode has not changed in the previous stage, then in this stage, the spoiler reference amount should be changed to 10° to slow down. If the control method has been changed in the previous stage, there is no need to open the spoiler. If the distance error is less than 300m, enter the fifth stage.

[0039] Stage 5: Now you are aligned with the runway. Fig. 9 As shown, the track mode is straight line mode, the radius input is 0, the throttle remains unchanged, the spoiler is used to control the speed, the speed is reduced by increasing the resistance, the speed dispersion caused by the model deviation is suppressed, and the speed static stability is ensured; the spoiler reference value is 10°, when the altitude is less than 300m, leveling is performed. During the leveling process, the spoiler reference value returns to 0°, the ascent and descent rate instruction is -1m / s, the throttle remains unchanged, and then normal taxiing and braking are performed.

[0040] The above-mentioned fixed-point forced landing process is decomposed into the control of three sub-problems: horizontal plane route design, plumb plane route design, and speed robustness design;

[0041] 1. Horizontal route design

[0042] like Figure 1 As shown in the figure, the unpowered forced landing route starts from the current position In of the aircraft and ends at the leveling point T. It is composed of a set of Dobbins curves consisting of arc segment In-T0, straight line segment T0-T1, arc segment T1-AP, and straight line segment AP-T. This curve can satisfy the constraints of the initial and final positions and the speed direction.

[0043] The known conditions for this part are: the longitude and latitude of the leveling point T, the longitude and latitude of the initial point In, the length of AP-T, the radius of the HAC circle, and the radius of the S turn.

[0044] The information required in this part is: the center position C of the HAC circle and the turning direction, the center position C0 of the S turn and the turning direction, the straight segment distance T0-T1, the arc segment distance T1-AP, and the short arc distance In-T0.

[0045] like Figure 3 As shown in the figure, the horizontal plane route design specifically includes:

[0046] According to the longitude and latitude of the target point, the distance corresponding to each degree in the longitude and latitude direction is calculated, so as to find the longitude and latitude and altitude of the AP point, and calculate the longitude and latitude and heading angle of point C in the case of clockwise and counterclockwise orbiting around point C respectively;

[0047] Distance per degree in latitude : ,

[0048] Distance per degree in longitude : ,

[0049] The latitude and longitude of the target point are known ( , ),high ,course ,distance and the glide angle , calculate the longitude and latitude of the AP point and height : , , ,

[0050] Clockwise around HAC (point C), the longitude and latitude of point C and heading angle The calculation is as shown below, r is the radius of circle C, , , ,

[0051] Counterclockwise around HAC (point C), the longitude and latitude of point C and heading angle The calculation is as follows: , , ,

[0052] According to the latitude and longitude of the initial point ( ),course , calculate the longitude and latitude of point C0 when traveling around point C0 clockwise and counterclockwise respectively.

[0053] Go clockwise around point C0, the longitude and latitude of point C0 As shown in the following formula, is the radius of the C0 circle; , ,

[0054] Counterclockwise around point C0, the longitude and latitude of point C0 As shown below: , ,

[0055] The distance of the middle straight line segment, the arc length at the target point, and the arc length at the starting point are calculated for each of the four combined cases, and then added together.

[0056] Take the example of going clockwise around point C and clockwise around point C0 to calculate the distance of the middle straight line segment. , the arc length at the target point and the arc length at the starting point , and add them together to calculate the total distance ,in is the center angle of the path in the C circle and the C0 circle, in rad, , , ,

[0057] Comparing the total distances in the four cases, the case with the smallest total distance is the horizontal route planning. In this case, the distances of point C, point C0 and the three sections are the required information for the horizontal route planning.

[0058] 2. Vertical plane route planning problem

[0059] There is a classic conclusion about the speed stability of unpowered descent: the unpowered descent angle corresponds to the inverse of the aircraft's lift-to-drag ratio. Therefore, if the descent angle is greater than the inverse of the aircraft's maximum lift-to-drag ratio in this configuration, the aircraft has speed static stability, that is, the aircraft will not stall when descenting along this descent angle, and the flight speed will stabilize to a certain value.

[0060] Applying it to the plumb line trajectory design of the three-dimensional Dubin curve for the unpowered forced landing route, the principle is that the slope of each segment must be greater than the inverse of the maximum lift-to-drag ratio of this configuration. Figure 4 As shown in the figure, the slope of the AP-T segment is selected according to the landing gear retracted configuration. The slopes of the AP-T1 arc segment, T1-T0 straight segment, and T0-In arc segment can remain consistent and are all selected according to the landing gear retracted configuration. The selection limit of the slope is the maximum lift-to-drag ratio, so the slope of the AP-T segment is greater than the slope of the In-AP segment. At the same time, considering the influence of aerodynamic deviation, headwind and tailwind, etc., a certain margin should be left when selecting the slope.

[0061] In this embodiment, the glide angle elevation_baseline is calculated according to the derivative of the maximum lift-to-drag ratio of the In-AP segment, and the tangent value of the glide angle is calculated, that is, , which is multiplied by the horizontal distance, the descending height of each section can be obtained. In the AP-T section, the lifting rate calculated in this embodiment is -1rad / s.

[0062] 3. Speed ​​robustness of unpowered forced landing

[0063] If the initial energy height is appropriate, the aircraft can stably fly along the above three-dimensional Dubins curve to the leveling point. However, due to the accuracy of the aircraft aerodynamic / weight model, the flight speed will have a certain dispersion. This solution suppresses speed dispersion by adjusting the lift-to-drag ratio through spoilers. The speed stability problem of unpowered forced landing is solved by controlling the spoiler reference amount. In the present invention, during the leveling process, the spoiler reference amount is first changed to 10°, and then the spoiler reference amount is changed to 0° when landing is about to begin.

[0064] The specific method of spoiler speed control is: the speed of the UAV is controlled by proportional integral control method, the target speed of the UAV and the current flight speed deviation signal are converted into the acceleration command of the UAV, and then the throttle command of the engine and the deflection size of the spoiler are given according to the engine thrust characteristics and the deceleration ability of the spoiler. By adjusting the throttle command of the engine and the deflection size of the spoiler at the same time, high-precision speed control is achieved together;

[0065] The proportional integral control method is used to control the speed of the drone as follows: , , in, is the airspeed, is the airspeed command, The natural frequency of the model of the speed command, The transient characteristics and steady-state characteristics of the speed command model are determined by the damping ratio of the speed command model, is the transfer function identifier, is the new speed deviation number, is the second-order derivative of the speed error signal, is the first-order derivative of the speed error signal, The second derivative of airspeed, The first derivative of airspeed, is the proportional gain, is the integral gain.

[0066] Calculated Finally, combined with the UAV's engine thrust model, the engine throttle command and the size of the spoiler deflection are given according to the UAV's engine thrust characteristics and the spoiler's deceleration capability.

[0067] The above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make corresponding changes and adjustments to the technology of the present invention without departing from the basic principles of the present invention. These changes and adjustments all fall within the protection scope of the present invention.

Claims

1. A method for controlling an aircraft's unpowered return landing, characterized in that: The following steps are involved: S1: After the engine stops in the air, the aircraft enters the unpowered forced landing mode, the lateral heading guidance mode is turned off, the longitudinal guidance mode is turned on, the pitch angle is used to control the airspeed, and the new route is calculated at the same time; S2: When the S-turn dissipates energy, the aircraft's lateral guidance is heading control to guide the aircraft to turn; the heading angle is controlled by the roll angle to turn, and the track mode is a circular track; S3: Initial turn, controlling the aircraft to navigate laterally along the turning circle with C0 as the center, and following the In-T0 arc; S4: T0-T1-AP segment flight, the track mode is arc mode, and the aircraft navigation is controlled in the Dobbins circle navigation mode with the HAC circle as the center; S5: During AP-T flight, the flight navigation is controlled in a straight line, and spoilers are used to control the airspeed. After descending to a certain height, the aircraft is leveled, and then normal taxiing and braking are performed.

2. The method for controlling an aircraft's unpowered return landing according to claim 1, characterized in that: The pitch angle used to control the airspeed in S1 is expressed as: ， in, is the acceleration due to gravity, is the pitch angle gain, is the pitch angle command, is the airspeed command, is the actual airspeed.

3. The method for controlling an aircraft's unpowered return landing according to claim 1, characterized in that: In S2, the rolling angle is used to control the heading angle to turn as follows: ， in, is the roll angle command, is the ground speed, is the acceleration due to gravity, It is the heading angle deviation proportional control gain in the roll angle correction side deviation mode. is the yaw angle command, is the yaw angle, is the heading angular rate of the planned route.

4. The method for controlling an aircraft's unpowered return landing according to claim 1, characterized in that: The unpowered forced landing route starts from the current position In of the aircraft and ends at the leveling point T. It is composed of a set of Dubin curves consisting of the arc segment In-T0, the straight line segment T0-T1, the arc segment T1-AP, and the straight line segment AP-T.

5. The method for controlling an aircraft's unpowered return landing according to claim 1 or 4, characterized in that: The horizontal plane route design of the unpowered forced landing route specifically includes: According to the longitude and latitude of the target point, the distance corresponding to each degree in the longitude and latitude direction is calculated, so as to find the longitude and latitude and altitude of the AP point, and calculate the longitude and latitude and heading angle of point C in the case of clockwise and counterclockwise orbiting around point C respectively; Distance per degree in latitude : ， Distance per degree in longitude : ， The latitude and longitude of the known target point , ,high ,course ,distance and the glide angle , calculate the longitude and latitude of the AP point and height : ， ， ， If you go around point C clockwise, the longitude and latitude of point C are and heading angle The calculation is as follows: ， ， ， If you go around point C counterclockwise, the longitude and latitude of point C are and heading angle The calculation is as follows: ， ， ， Where r is the radius of circle C; According to the latitude and longitude of the initial point ,course , calculate the longitude and latitude of point C0 when circling point C0 clockwise and counterclockwise respectively; Go clockwise around point C0, the longitude and latitude of point C0 As shown below: ， ， Counterclockwise around point C0, the longitude and latitude of point C0 As shown below: ， ， in, is the radius of the C0 circle; Calculate the distance of the middle straight line segment, the arc length at the target point, and the arc length at the starting point in the four combined cases respectively, and add them together; Comparing the total distances in the four cases, the case with the smallest total distance is the horizontal route planning. In this case, the distances of point C, point C0 and the three sections are the required information for the horizontal route planning.

6. The method for controlling an aircraft's unpowered return landing according to claim 1 or 4, characterized in that: The plumb line route design of the unpowered forced landing route specifically includes: The slope of each route is controlled to be greater than the inverse of the maximum lift-to-drag ratio of the aircraft to ensure speed static stability; the slope of the AP-T segment is selected according to the landing gear lowering configuration, and the slopes of the AP-T1 arc segment, T1-T0 straight segment, and T0-In arc segment are selected according to the landing gear retracting configuration; the slope of the AP-T segment is greater than the slope of the In-AP segment, and the influence of aerodynamic deviation and wind speed is considered, leaving a margin; the glide angle elevation_baseline is calculated according to the maximum lift-to-drag ratio of the In-AP segment, and the tangent value of the glide angle is calculated, that is, , multiplied by the horizontal distance, the height of each descent can be calculated.

7. The method for controlling an aircraft's unpowered return landing according to claim 1 or 4, characterized in that: The specific method of using spoilers to control airspeed in S5 is: the speed of the UAV is controlled by a proportional-integral control method, the target speed of the UAV and the current flight speed deviation signal are converted into an acceleration command of the UAV, and then the throttle command of the engine and the size of the spoiler deflection are given according to the engine thrust characteristics and the deceleration capability of the spoiler. By adjusting the throttle command of the engine and the size of the spoiler deflection at the same time, high-precision speed control is achieved together.

8. The method for controlling an aircraft's unpowered return landing according to claim 7, characterized in that: The proportional integral control method is used to control the speed of the drone: ， ， in, is the airspeed, is the airspeed command, The natural frequency of the model of the speed command, The transient characteristics and steady-state characteristics of the speed command model are determined by the damping ratio of the speed command model, is the transfer function identifier, is the new speed deviation number, is the second-order derivative of the speed error signal, is the first-order derivative of the speed error signal, The second derivative of airspeed, The first derivative of airspeed, is the proportional gain, is the integral gain.

9. The method for controlling an aircraft's unpowered return landing according to claim 7, characterized in that: The base angle of the spoiler is 10°, and it should be leveled when the altitude is less than 300m.

10. The method for controlling an aircraft's unpowered return landing according to claim 9, characterized in that: When approaching landing, the spoiler reference value returns to 0°.

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