A method for controlling an unpowered return and landing of an aircraft

Abstract

The application discloses a kind of aircraft unpowered landing control method, belong to the field of aircraft flight control, the application adopts three-dimensional route collaborative design scheme, and the horizontal plane route is optimized by Dubins curve four-section path, in combination with the slope excess of vertical plane design, significantly improve the path planning ability under complex environment;Adopt spoiler dynamic adjustment lift-drag ratio and segmented throttle control, effectively suppress the speed dispersion caused by model deviation;The control method of the application guarantees the safety of landing at the same time, significantly improves the adaptability of complex scene, model robustness and economy, provides an efficient solution for unpowered landing.

Description

Technical Field

[0001] The present 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 landing technology is a key technology for ensuring a safe landing in the event of a power loss. Significant progress has been made in various fields, including fixed-wing aircraft, helicopters, and other aircraft. In the fixed-wing aircraft sector, researchers focus on trajectory planning, energy management, and guidance and control. Trajectory planning employs methods such as the Dubins trajectory search, combined with optimal control methods and the HP adaptive pseudo-spectral method, to design precise landing trajectories that meet initial and final constraints and aircraft performance requirements, ensuring a safe landing path. Energy management involves adjusting flight attitude and trajectory to precisely control energy consumption, ensuring the aircraft reaches the appropriate speed and altitude upon arrival at the landing point. Furthermore, in the field of guidance and control, advanced systems such as nonlinear guidance laws are being designed to achieve precise control of the aircraft and ensure a precise landing. Research on unpowered landing technology for helicopters focuses on two key areas: autorotation maneuvers and safety improvements. During an autorotation landing, the pilot must skillfully control the rotor and tail rotor to ensure stability during the helicopter's rotation and achieve a safe landing. Furthermore, enhanced helicopter body design, such as the use of crash-resistant structures and cushioning devices, significantly reduces injuries to personnel in the event of a crash, further improving the safety of helicopters undergoing unpowered forced landings. Unpowered forced landing technology in other aircraft fields has also yielded remarkable results. Drones, leveraging advanced sensors and control systems, have achieved autonomous return and landing capabilities. They can autonomously plan their flight path and land safely in the event of an engine failure, significantly reducing the need for and risk of human intervention. The unpowered gliding cabin, with its unique deployment and glider wing design, enhances stability during gliding, providing strong support for scientific experiments and data transmission.

[0003] However, the current unpowered forced landing technology still faces many challenges in practical application. 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, resulting in difficulties in accurate route planning and speed control; the pilot and the automation system do not collaborate smoothly in emergency situations, the decision-making ability of the automation system is limited, and the operation 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 significantly improves the path planning capability in complex environments by optimizing the horizontal plane route through a four-segment path of the Dobbins curve and combining it with the plumb plane slope margin design.

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

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

[0007] S1: After the engine stops in mid-air, the aircraft enters a power-down forced landing, with the lateral guidance mode turned off and the longitudinal guidance mode turned on. The pitch angle is used to control the airspeed, and a new route is calculated at the same time.

[0008] S2: When performing an S-turn to dissipate energy, the aircraft's lateral guidance is heading control to guide the aircraft to turn; the rolling angle is used to control the heading angle to turn, and the track mode is a circular track;

[0009] S3: Initial turn, controlling the aircraft's lateral navigation to follow the turning circle centered at C0, along 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 altitude, the aircraft will level off, and then perform normal taxiing and braking.

[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] Based on the longitude and latitude of the target point, the distance per degree in the longitude and latitude directions is calculated to determine the longitude and latitude and altitude of the AP point. The longitude and latitude and heading angle of point C are calculated for both clockwise and counterclockwise orbits around point C.

[0015] According to the latitude and longitude of the initial point, calculate the latitude and longitude of point C0 when circling point C0 clockwise and counterclockwise 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 for each of the four combined cases, 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, point C, point C0 and the distances of the three segments are the required information for the horizontal route planning.

[0018] The plumb line route design specifically includes:

[0019] The slope of each route segment is controlled to be greater than the inverse of the aircraft's maximum lift-to-drag ratio to ensure speed static stability. The slope of the AP-T segment is selected based on the landing gear extended configuration, while the slopes of the AP-T1 arc segment, T1-T0 straight segment, and T0-In arc segment are selected based on the landing gear retracted configuration. The slope of the AP-T segment is greater than the slope of the In-AP segment, and a margin is left to account for the effects of aerodynamic deviation and wind speed.

[0020] Calculate the gliding angle elevation_baseline according to the maximum lift-to-drag ratio of the In-AP segment, and calculate the tangent value of the gliding 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 -1 rad / s.

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

[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 deviation, low efficiency of human-machine collaboration and high cost, a three-dimensional route collaborative design scheme is proposed. The horizontal plane route is optimized through the four-segment path of the Dobbins curve, combined with the plumb plane slope margin design, which significantly improves the path planning capability in complex environments; 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 deviation; 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 This is 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 This 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 in parameters in the first stage of the embodiment of the present invention, where a is forced landing without power, b is mixed control mode, c is not using the mission track, d is the throttle command, e is the airspeed command, and f is the roll angle command;

[0029] Figure 6 Schematic diagram of the changes in parameters in the second stage of the 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 parameter changes in the third stage according to an embodiment of the present invention, a) lateral and heading guidance mode, b) longitudinal guidance mode;

[0031] Figure 8 Schematic diagram of the changes of parameters in the fourth stage of the embodiment of the present invention, where 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] Figure 9 Schematic diagram of the changes in 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 focuses on the unpowered forced landing of a single-engine aircraft after the engine stops in mid-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 mid-air and power-free forced landing are 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 and heading guidance mode is closed. Figure 5As shown, the throttle command = 0.43, the airspeed command = 85m / s, and the roll angle command = 0. The aircraft is kept stable as much as possible and roll is minimized, but the actual roll angle is between -0.5rad and 0.1rad. The longitudinal guidance mode is enabled, and the pitch angle is used to control the airspeed. When the airspeed is too high, the pitch angle is increased to reduce the airspeed. When the airspeed is too low, the pitch angle is decreased to increase the airspeed. The parachute is not cut or opened, and the new route is calculated. After one second, the second stage begins. The formula for controlling the airspeed using the pitch angle is as follows:

[0036] ,

[0037] 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.

[0038] Phase 2: When the S-turn dissipates energy, the aircraft's lateral guidance is used for 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 roll angle is used to control the heading angle to turn. The track mode is circular track. The throttle remains unchanged. Enter the latitude and longitude of point C0, altitude, radius of the C0 circle, glide angle, azimuth and distance to control the aircraft to turn to point In (initial point). After one second, if the altitude is less than the target altitude + 400, it enters the third stage. The formula for using the roll angle to control the heading angle is as follows:

[0039] ,

[0040] 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.

[0041] Phase 3: When turning, the aircraft still follows the turning circle with C0 as the center, and completes the In-T0 arc. Figure 7 As shown in the figure, during this phase, if the longitudinal deviation is less than 0, the longitudinal guidance mode switches from using pitch angle to control airspeed to using pitch angle to control vertical inertial guidance. Simultaneously, the lateral heading guidance mode switches from using roll angle to control yaw angle to using roll angle to control lateral inertial guidance. If the range error is less than 300 or the absolute value of the range error is greater than 5 × radius0 (the circling radius), the aircraft enters the fourth phase.

[0042] Stage 4: Still not using mission track, such as Figure 8 As shown, enter the latitude and longitude of point C, the altitude, and the radius of the HAC circle. Set the track mode to circular, and maintain the throttle constant to reach the AP point. If the longitudinal guidance mode control method was unchanged in the previous stage, deceleration should be achieved in this stage by changing the spoiler reference value to 10°. If the control method was changed in the previous stage, there is no need to deploy the spoilers. If the range error is less than 300m, proceed to the fifth stage.

[0043] Phase 5: Now it is aligned with the runway, such as Figure 9 As shown, the track mode is straight line mode, the radius input is 0, the throttle remains unchanged, and the spoiler is used to control the speed. By increasing the resistance to reduce the speed, the speed dispersion caused by the model deviation is suppressed to ensure the static stability of the speed. The spoiler reference amount is 10°. When the altitude is less than 300m, the leveling is carried out. During the leveling process, the spoiler reference amount returns to 0°, the vertical rate instruction is -1m / s, the throttle remains unchanged, and then normal rolling and braking are carried out.

[0044] 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;

[0045] 1. Horizontal route design

[0046] like Figure 1 As shown in Figure 1, the unpowered forced landing route starts from the aircraft's current position In 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 on the initial and final positions and the velocity direction.

[0047] The known conditions for this part are: the latitude and longitude of the leveling point T, the latitude and longitude of the initial point In, the length of AP-T, the radius of the HAC circle, and the radius of the S turn.

[0048] The information required in this section is: the center position C of the HAC circle and the turning direction, the center position C0 of the S turn circle and the turning direction, the straight segment distance T0-T1, the arc segment distance T1-AP, and the short arc distance In-T0.

[0049] like Figure 3 As shown in the figure, the horizontal plane route design specifically includes:

[0050] Based on the longitude and latitude of the target point, the distance per degree in the longitude and latitude directions is calculated to determine the longitude and latitude and altitude of the AP point. The longitude and latitude and heading angle of point C are calculated for both clockwise and counterclockwise orbits around point C.

[0051] Distance per degree in latitude :

[0052] ,

[0053] Distance per degree in longitude :

[0054] ,

[0055] The latitude and longitude of the known target point ( , ),high ,course ,distance and glide angle , calculate the latitude and longitude of the AP point and height :

[0056] ,

[0057] ,

[0058] ,

[0059] Clockwise around HAC (point C), the latitude and longitude of point C and heading angle The calculation is as shown below, r is the radius of circle C,

[0060] ,

[0061] ,

[0062] ,

[0063] Counterclockwise around HAC (point C), the latitude and longitude of point C and heading angle The calculation is as follows:

[0064] ,

[0065] ,

[0066] ,

[0067] According to the latitude and longitude of the initial point ( ),course , calculate the latitude and longitude of point C0 when circling point C0 clockwise and counterclockwise respectively.

[0068] 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;

[0069] ,

[0070] ,

[0071] Counterclockwise around point C0, the longitude and latitude of point C0 As shown in the following formula:

[0072] ,

[0073] ,

[0074] Calculate the distance of the middle straight line segment, the length of the arc at the target point, and the length of the arc at the starting point for each of the four combined cases, and add them together.

[0075] Taking the example of going around point C and point C0 clockwise, 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 circle C and circle C0, in rad,

[0076] ,

[0077] ,

[0078] ,

[0079] Comparing the total distances in the four cases, the case with the smallest total distance is the horizontal route planning. In this case, point C, point C0 and the distances of the three segments are the required information for the horizontal route planning.

[0080] 2. Vertical plane route planning problem

[0081] 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 descending along this descent angle, and the flight speed will stabilize to a certain value.

[0082] 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 4As shown, the slope of the AP-T segment is selected based on the landing gear extended configuration. The slopes of the AP-T1 arc, T1-T0 straight line, and T0-In arc segments can remain consistent and are selected based on the landing gear retracted configuration. The slope selection constraint is the maximum lift-to-drag ratio, so the AP-T segment slope is greater than the In-AP segment slope. Furthermore, a certain margin should be left in the slope selection to account for the effects of aerodynamic deviations, tailwinds, and headwinds.

[0083] In this embodiment, the glideslope angle elevation_baseline is calculated based on the derivative of the maximum lift-to-drag ratio of the In-AP segment, and the tangent value of the glideslope angle is calculated, that is, , which is multiplied by the horizontal distance to obtain the descent height of each section. In the AP-T section, the lifting rate calculated in this embodiment is -1 rad / s.

[0084] 3. Speed ​​robustness of unpowered forced landing

[0085] If the initial energy level is appropriate, the aircraft can fly stably along the three-dimensional Dubins curve to the level-off point. However, due to the accuracy of the aircraft's aerodynamic / weight model, the indicated flight speed will exhibit some dispersion. This solution suppresses speed dispersion by adjusting the lift-to-drag ratio with spoilers. Controlling the spoiler reference angle solves the speed stability issue during a power-off landing. In this invention, during the level-off process, the spoiler reference angle is initially set to 10°, and then returned to 0° just before landing.

[0086] The specific method of spoiler speed control is as follows: the UAV's speed is controlled by a proportional-integral control method, the deviation signal between the UAV's target speed and the current flight speed is converted into an acceleration command for the UAV, and then the engine throttle command 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 engine throttle command and the size of the spoiler deflection simultaneously, high-precision speed control is achieved.

[0087] The proportional integral control method is used to control the speed of the UAV as follows:

[0088] ,

[0089] ,

[0090] in, is the airspeed, is the airspeed command, The natural frequency of the model of the speed command, The transient 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 deviation signal, is the first-order derivative of the speed deviation signal, The second derivative of airspeed, The first derivative of airspeed, is the proportional gain, is the integral gain.

[0091] 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 spoiler deceleration capability.

[0092] 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 are all within the scope of protection 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 mid-air, the aircraft enters a power-down forced landing, with the lateral guidance mode turned off and the longitudinal guidance mode turned on. The pitch angle is used to control the airspeed, and a new route is calculated at the same time. S2: When performing an S-turn to dissipate energy, the aircraft's lateral guidance is heading control to guide the aircraft to turn; the rolling angle is used to control the heading angle to turn, and the track mode is a circular track; S3: Initial turn, controlling the aircraft's lateral navigation to follow the turning circle centered at C0, along 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 linear, with spoilers used to control airspeed. After descending to a certain altitude, the aircraft will level off, followed by normal roll and braking. The unpowered landing route starts from the aircraft's current position In 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 segment T0-T1, the arc segment T1-AP, and the straight segment AP-T. The plumb line route design specifically includes: The slope of each route segment 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 extended 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 retracted 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 based on 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.

2. The method for controlling an aircraft's unpowered return landing according to claim 1, wherein: 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, wherein: 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, wherein: The horizontal plane route design of the unpowered forced landing route specifically includes: According to the latitude of the target point Calculate the distance per degree in the longitude and latitude directions to determine the longitude and latitude and altitude of the AP point. Calculate the longitude and latitude and heading angle of point C for both clockwise and counterclockwise orbits around point C. Distance per degree in latitude : ， Distance per degree in longitude : ， Known latitude and longitude of the target point 、 ,high ,course ,distance and glide angle , calculate the latitude and longitude 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: ， ， ， When going counterclockwise around point C, 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 latitude and longitude 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 in the following formula: ， ， Counterclockwise around point C0, the longitude and latitude of point C0 As shown in the following formula: ， ， 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 for each of the four combined cases, and add them together. Comparing the total distances in the four cases, the case with the smallest total distance is the horizontal plane route planning. In this case, the distances of point C, point C0 and the three segments are the required information for the horizontal plane route planning.

5. The method for controlling an aircraft's unpowered return landing according to claim 1, wherein: The specific method of using spoilers to control airspeed in S5 is: the proportional-integral control method is used to control the speed of the UAV, and the deviation signal between the UAV's target speed and the current flight speed is converted into the UAV's acceleration command. Then, the engine throttle command and the size of the spoiler deflection are given according to the engine thrust characteristics and the deceleration capability of the spoiler. By simultaneously adjusting the engine throttle command and the size of the spoiler deflection, high-precision speed control is achieved.

6. The method for controlling an aircraft's unpowered return landing according to claim 5, wherein: 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 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 deviation signal, is the first-order derivative of the speed deviation signal, The second derivative of airspeed, The first derivative of airspeed, is the proportional gain, is the integral gain.

7. The method for controlling an aircraft's unpowered return landing according to claim 5, wherein: The base angle of the spoiler is 10°, and it should be leveled when the altitude is less than 300m.

8. The method for controlling an aircraft's unpowered return landing according to claim 7, wherein: When landing is imminent, the spoiler reference value returns to 0°.

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