Optimization method for optimal short-distance takeoff strategy of vertical / short-distance takeoff and landing aircraft

Abstract

The invention discloses an optimization method for an optimal short-distance takeoff strategy of a vertical / short-distance takeoff and landing aircraft, and the method comprises the steps: firstly building a vertical / short-distance takeoff and landing aircraft longitudinal dynamic model and a ground stress model which consider the dynamic state of an actuator, and augmenting the dynamic state of the actuator to an aircraft motion equation; secondly, the minimum ground clearance speed is solved through a constrained balancing algorithm, the speed serves as a take-off criterion, and a fixed-value take-off strategy is obtained through theoretical derivation and serves as a dynamic optimization initial value; the optimal short-distance takeoff problem is converted into an unconstrained nonlinear programming problem with fixed final state time, and a dynamic optimization takeoff strategy is solved in combination with a numerical optimization method; and finally, carrying out sensitivity analysis on the thrust-weight ratio, the thrust distribution ratio and the gravity center position to obtain an influence rule of each factor on the takeoff distance. The method has the advantages of being high in strategy optimization efficiency, short in takeoff distance and high in engineering guidance, the rapid starting capability of the vertical / short-distance takeoff and landing aircraft is remarkably improved, and technical support is provided for control of the short-distance takeoff and landing stage of the vertical / short-distance takeoff and landing aircraft.

Description

An optimization method for the optimal short takeoff strategy of vertical / short takeoff and landing aircraft. Technical Field

[0001] This invention relates to the field of flight control and trajectory optimization technology, and in particular to an optimization method for the optimal short takeoff strategy of vertical / short takeoff and landing aircraft. Background Technology

[0002] Vertical / short takeoff and landing (V / STOL) aircraft combine the high aerodynamic efficiency of fixed-wing aircraft with the flexible takeoff and landing capabilities of rotorcraft. They can take off and land in confined spaces and have broad application prospects in scenarios such as carrier-based operations and special mission delivery. Short takeoff is the core advantage of this type of aircraft, which can effectively improve payload and flight safety compared to vertical takeoff.

[0003] Currently, research on short takeoff strategies for vertical / short takeoff and landing (VTOL) aircraft largely focuses on trajectory optimization to minimize energy or power consumption. Research on optimization strategies for the shortest takeoff distance is limited and has significant limitations: First, traditional research does not consider modeling and constraining the dynamic characteristics of actuators, resulting in optimized strategies that may not be compatible with actual actuator bandwidth, leading to low engineering feasibility. Second, existing strategies are mostly fixed-value schemes with fixed thrust deflection angles, failing to incorporate dynamic optimization based on changes in the aircraft's state during takeoff, thus lacking clear strategic advantages. Third, analyses of factors influencing takeoff distance are mostly qualitative descriptions, lacking quantitative sensitivity analysis, making it difficult to provide precise engineering guidance.

[0004] Therefore, there is an urgent need for an optimal short takeoff strategy optimization method for vertical / short takeoff and landing (VTOL) aircraft that takes into account actuator dynamic constraints, enables dynamic strategy optimization, and has engineering guidance, in order to solve the above-mentioned technical problems. Summary of the Invention

[0005] The main objective of this invention is to provide an optimization method for the optimal short takeoff strategy of vertical / short takeoff and landing (VTOL) aircraft, which solves the problems of traditional short takeoff strategies not considering actuator dynamics, having limited optimization effects, and lacking engineering guidance.

[0006] Another objective of this invention is to propose an optimization system for the optimal short takeoff strategy of vertical / short takeoff and landing (VTOL) aircraft.

[0007] To achieve the above objectives, a first aspect of the present invention proposes an optimization method for the optimal short takeoff strategy of a vertical / short takeoff and landing (V / STOL) aircraft, comprising:

[0008] S1. Establish a longitudinal dynamics model and a ground force model for a vertical / short takeoff and landing (VTOL) aircraft that consider actuator dynamics, and extend actuator dynamics to the aircraft's equations of motion to construct a coupled dynamics calculation framework that includes aerodynamics, propulsion, actuators, and ground constraints. S2. Based on the aircraft's longitudinal dynamics model, use a constrained trim algorithm to solve for the minimum takeoff speed. Use the solution as the takeoff criterion for short takeoff and output terminal speed constraints. S3. Based on the aircraft's longitudinal dynamics model and the ground force model, and combined with the minimum takeoff speed, theoretically derive a fixed-value short takeoff strategy and use this strategy as the initial value for dynamic optimization. S4. Based on the coupled dynamics calculation framework and the initial value of the fixed-value strategy, transform the optimal short takeoff problem into an unconstrained nonlinear programming problem with a fixed final state time. Output a dynamically optimized short takeoff strategy through numerical optimization. S5. Based on the constructed complete optimization system, conduct sensitivity analysis on three influencing factors: thrust-to-weight ratio, thrust distribution ratio, and center of gravity position. Obtain the influence of each factor on the short takeoff distance and form engineering guidance data.

[0009] In one embodiment of the present invention, the longitudinal dynamics model includes the nonlinear relationship between the thrust component, aerodynamic component and pitching moment of the aircraft propulsion system, the ground force model equates the nose and main landing gear to the centerline force model, and the actuator dynamics are modeled using a first-order inertial element.

[0010] In one embodiment of the present invention, the constraints of the constrained trim algorithm include airframe velocity constraints, pitch angle constraints, and actuator travel constraints. With minimum airspeed as the objective function, the trim state under a fixed angle of attack climb is solved to obtain the minimum takeoff speed. The derivation of the fixed-value short takeoff strategy satisfies the pitch stability constraint that the front wheels do not leave the ground at the start and end points and the rear wheels do not leave the ground at the end point. The optimal lower bound of the longitudinal deflection angle of the 3BSM vector nozzle is determined, and the corresponding takeoff distance is obtained by integrating the dynamic equations.

[0011] In one embodiment of the present invention, the method of transforming a constrained dynamic optimization problem with free final state time into an unconstrained problem with fixed final state time includes: processing the free final state time by time normalization, mapping the bounded control quantity to the full real number domain using the Sigmoid function, and introducing a penalty function to eliminate system state and performance constraints.

[0012] In one embodiment of the present invention, the sensitivity analysis includes: defining a normalized sensitivity coefficient to quantify the dimensionless ratio of the rate of change of a single parameter to the rate of change of takeoff distance, and establishing a unified measurement benchmark for the degree of parameter influence; based on the standard takeoff distance benchmark value and standard parameter combination under standard settings, calculating the takeoff distance after disturbances of thrust-to-weight ratio, thrust distribution ratio, and center of gravity position, and substituting them into the normalized sensitivity coefficient formula to obtain the sensitivity values ​​of each factor; comparing the sensitivity values ​​of the three factors to conclude that the takeoff distance under standard settings has the highest sensitivity to thrust-to-weight ratio and the lowest sensitivity to thrust distribution ratio, forming engineering guidance data for prioritizing parameter adjustments.

[0013] In one embodiment of the present invention, S1 further includes: establishing a longitudinal dynamic model to characterize the nonlinear relationship between the thrust component, aerodynamic component, and aerodynamic pitching moment of the propulsion system, and outputting the basic equations of motion with the forward velocity, vertical velocity, pitching angular velocity, north coordinate, and down coordinate of the engine system as state variables; establishing a ground force model, equating the dual main landing gear to a single landing gear on the centerline, and establishing the balance relationship between the support force of the front and main landing gear and the pitching moment based on the output pitching moment and vertical force data, and calculating the ground contact force constraint conditions; establishing an actuator dynamic model, for the four control quantities of elevator deflection angle, thrust distribution ratio, 3BSM vector nozzle longitudinal deflection angle, and lift fan thrust vector deflection angle, using a first-order inertial element for modeling and amplifying the actuator bandwidth parameter to form the joint equations of motion, ensuring that the subsequent optimization results meet the actuator dynamic constraints.

[0014] In one embodiment of the present invention, S2 further includes: setting a trim state for the aircraft to climb at a fixed angle of attack, and determining the forward velocity, vertical velocity, pitch angle, and actuator travel constraints of the aircraft as constraint data for trim calculation; using minimum airspeed as the objective function, and combining the established trim state and constraint data, constructing a mathematical model of a constrained optimization problem; solving the constructed optimization problem through a sequential quadratic programming algorithm to obtain the minimum airspeed that satisfies all constraints, and using it as the minimum takeoff speed to ensure that the aircraft has a safe climb capability after lifting off the ground.

[0015] In one embodiment of the present invention, S4 further includes: processing the free final state time by time normalization and converting it into a variable to be optimized, so as to eliminate the final state time degree of freedom and achieve fixed time domain mapping; using the Sigmoid function to map the bounded control quantity to the full real number domain to eliminate actuator travel constraints, and introducing a penalty function to handle system state and performance constraints, constructing an objective function with a penalty term; solving the unconstrained optimization problem by combining the quasi-Newton method with gradient calculation to obtain a dynamically optimized short-distance takeoff strategy.

[0016] In one embodiment of the present invention, S3 further includes: fixing the elevator deflection angle to neutral, the propulsion system thrust to high state, and the lift fan thrust vector deflection angle to maximum back deflection angle, to form a constant control command set; solving for the optimal lower bound of the longitudinal deflection angle of the 3BSM vector nozzle by means of pitch stability constraints at the start and end points where the front wheels do not leave the ground and the rear wheels do not leave the ground, to meet the pitch stability requirements during the takeoff phase; substituting the determined fixed control quantity and the obtained optimal lower bound into the longitudinal dynamic equation, and integrating the dynamic equation to obtain the takeoff distance corresponding to the fixed strategy, providing a reasonable initial value for subsequent dynamic optimization.

[0017] To achieve the above objectives, a second aspect of the present invention proposes an optimization system for the optimal short takeoff strategy of a vertical / short takeoff and landing (VTOL) aircraft, comprising: a modeling module for establishing a longitudinal dynamics model of the VTOL aircraft and a ground force model considering actuator dynamics, and extending the actuator dynamics to the aircraft's equations of motion to construct a coupled dynamics calculation framework including aerodynamics-propulsion-actuator-ground constraints; a minimum takeoff speed solution module for solving the minimum takeoff speed of the aircraft based on the longitudinal dynamics model of the aircraft using a constrained trim algorithm, using the solution result as the takeoff criterion for short takeoff, and outputting terminal speed constraint conditions; and a fixed-value strategy initial value module for... Based on the dynamic model and ground force model, combined with the minimum takeoff speed, a fixed-value short takeoff strategy is theoretically derived and used as the initial value for dynamic optimization. The dynamic optimization solution module is used to transform the optimal short takeoff problem into an unconstrained nonlinear programming problem with a fixed final state time based on the coupled dynamics calculation framework and the initial value of the fixed-value strategy. The dynamically optimized short takeoff strategy is output through numerical optimization solution. The sensitivity analysis module is used to conduct sensitivity analysis on three influencing factors, namely thrust-to-weight ratio, thrust distribution ratio, and center of gravity position, based on the constructed complete optimization system. The module obtains the influence law of each factor on the short takeoff distance and forms engineering guidance data.

[0018] The optimization method and system for the optimal short takeoff strategy of vertical / short takeoff and landing (VTOL) aircraft in this invention ensures the engineering feasibility of the strategy by establishing a multi-dimensional model that considers actuator dynamics; improves the efficiency and effectiveness of strategy optimization through a hierarchical scheme of "fixed initial strategy value + dynamic optimization solution"; and enhances engineering guidance through quantitative sensitivity analysis. Compared with the traditional fixed-value deflection strategy, the takeoff distance is significantly shortened, and the rapid takeoff capability of the aircraft is significantly improved.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, in which: Figure 1 is a flowchart of an optimization method for an optimal short takeoff strategy for a vertical / short takeoff and landing (VTOL) aircraft provided by an embodiment of the present invention; Figure 2 is a simplified model diagram of a VTOL aircraft and its propulsion system provided by an embodiment of the present invention; Figure 3 is a ground force model diagram of a VTOL aircraft during the short takeoff phase provided by an embodiment of the present invention; and Figure 4 is a structural diagram of an optimization system for an optimal short takeoff strategy for a VTOL aircraft provided by an embodiment of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] The following describes, with reference to the accompanying drawings, an optimization method and system for the optimal short takeoff strategy of a vertical / short takeoff and landing (VTOL) aircraft according to an embodiment of the present invention.

[0024] To address the aforementioned limitations in the background technology, current research on short takeoff strategies for vertical / short takeoff and landing (VTOL) aircraft primarily focuses on trajectory optimization to minimize energy or power consumption, with limited research on optimization strategies for the shortest takeoff distance. Furthermore, existing strategies often fail to consider the dynamic characteristics and constraints of actuators, resulting in strategies that cannot adapt to actual actuator bandwidth and have low engineering feasibility. Existing strategies are mostly fixed-value schemes with fixed thrust deflection angles, failing to incorporate dynamic optimization based on aircraft state changes during takeoff, thus offering limited strategic advantages. Additionally, analyses of factors influencing takeoff distance are largely qualitative descriptions, lacking quantitative sensitivity analysis and failing to provide precise engineering guidance. Therefore, this invention provides a... An optimization method for the optimal short takeoff strategy of vertical / short takeoff and landing (VTOL) aircraft is proposed. This method first establishes a longitudinal dynamics model of the VTOL aircraft and a ground force model considering actuator dynamics, and then extends the actuator dynamics to the aircraft's equations of motion. A constrained trim algorithm is then used to solve for the minimum takeoff speed, which is used as the takeoff criterion. A fixed-value takeoff strategy is theoretically derived as the initial value for dynamic optimization. The optimal short takeoff problem is then transformed into an unconstrained nonlinear programming problem with a fixed final-state time. Numerical optimization methods are used to solve the dynamically optimized takeoff strategy. Finally, sensitivity analyses are conducted on thrust-to-weight ratio, thrust distribution ratio, and center of gravity position to obtain the influence of each factor on takeoff distance. Compared to traditional fixed thrust deflection takeoff strategies, this method has advantages such as high optimization efficiency, short takeoff distance, and strong engineering guidance, significantly improving the rapid sortie capability of VTOL aircraft and providing technical support for their short takeoff control. This addresses several issues in related technologies, including: low engineering feasibility due to the lack of modeling and constraints on actuator dynamics for short takeoff strategies of vertical / short takeoff and landing (VTOL) aircraft; the failure to dynamically optimize fixed thrust deflection angles by incorporating changes in aircraft state during takeoff, resulting in unclear strategic advantages; and the lack of quantitative sensitivity analysis of factors influencing takeoff distance, hindering precise engineering guidance. Taking a thrust vectoring VTOL aircraft as an example, the optimization steps for the optimal short takeoff strategy are as follows: This embodiment provides an optimization method for the optimal short takeoff strategy of a VTOL aircraft. As shown in Figure 1, it includes: S1, establishing a longitudinal dynamics model of the VTOL aircraft and a ground force model considering actuator dynamics, and extending the actuator dynamics to the aircraft's equations of motion to construct a coupled dynamics calculation framework encompassing aerodynamics, propulsion, actuators, and ground constraints.

[0025] It is understandable that the longitudinal dynamics model includes the nonlinear relationship between the thrust component, aerodynamic component, and pitching moment of the aircraft propulsion system, the ground force model equates the nose and main landing gear to the centerline force model, and the actuator dynamics are modeled using a first-order inertial element.

[0026] Specifically, the longitudinal dynamics model needs to characterize the nonlinear relationships of propulsion system thrust (including 3BSM vector nozzle, lift fan, and roll nozzle thrust), aerodynamic forces (lift and drag), and aerodynamic pitching moment. Its state variables include the aircraft system's forward velocity, vertical velocity, pitch angular velocity, north coordinate, and down coordinate. The ground force model equates the dual main landing gear to a single landing gear on the centerline, establishing a balance between the support forces of the nose and main landing gear and the pitching moment. The actuator dynamics model uses a first-order inertial element to model the elevator deflection angle, thrust distribution ratio, 3BSM vector nozzle longitudinal deflection angle, and lift fan thrust vector deflection angle, extending it to the aircraft's equations of motion to ensure that subsequent optimization results meet the actuator bandwidth constraints.

[0027] In one embodiment, the vertical / short takeoff and landing (VTOL) aircraft propulsion system can be understood as an advanced aviation propulsion technology that combines the characteristics of fixed-wing and rotary-wing aircraft. The thrust vectoring type achieves the switching between short takeoff, vertical landing and high-speed forward flight modes by adjusting the thrust direction through the thrust vectoring nozzle.

[0028] As shown in Figure 2, the power system of a thrust vectoring vertical / short takeoff and landing aircraft consists of: the main engine and its three-bearing thrust vectoring nozzle (LN), lift fan (LF), and left and right roll nozzles (LRCS / RRCS). These are the forward positions of the points of action of the lift fan, the rolling nozzle, and the three-bearing vector nozzle, respectively. and These are the vertical positions of the points of action of the lift fan and the three-bearing vector nozzle, respectively.

[0029] In the case of low speed (the following descriptions all fall under this case), the vertical component of the thrust vector of the three-bearing nozzle, the vertical component of the thrust vector of the lift fan, and the thrust generated by the left and right roll nozzles provide vertical lift; the horizontal component of the thrust vector of the three-bearing nozzle and the horizontal component of the thrust vector of the lift fan provide forward thrust; the thrust difference between the left and right roll nozzles generates a roll moment to adjust the aircraft's roll attitude; the thrust ratio between the lift fan and the three-bearing vector nozzle and the deflection of their thrust vectors generate a pitch moment to adjust the aircraft's pitch attitude; and the lateral deflection of the three-bearing vector nozzle generates a yaw moment to adjust the aircraft's yaw attitude.

[0030] Figure 3 is a ground force model of a vertical / short takeoff and landing aircraft during the short takeoff phase provided in an embodiment of the present invention. In this model, the dual main landing gears are equivalent to a single landing gear on the center axis, and the elastic characteristics of the landing gear are not considered. and These are the ground support forces acting on the nose landing gear and the main landing gear, respectively. and These are the total pitch moments at the nose landing gear and main landing gear, respectively. and These are the forward positions of the stress points of the nose landing gear and main landing gear (relative to the center of gravity; the same applies to the distance variables below). and These are the vertical positions of the stress points of the nose landing gear and main landing gear, respectively. It is the coefficient of friction of the ground.

[0031] In this embodiment of the invention, the ground coordinate system is set as the Northeast-East (NED) coordinate system, and the origin of the body coordinate system coincides with the center of gravity of the aircraft.

[0032] In actual implementation, the longitudinal model of a thrust-vectoring short takeoff and landing (STOVL) aircraft can be established using the following formula: (1) Among them, It is the speed of the aircraft's airframe system. It is the pitch angle. It is the pitch angular velocity. It is the angle of attack. It's the quality of the aircraft. It is the pitch moment of inertia. It is gravitational acceleration. It represents the displacement in the aircraft's ground coordinate system. and These are the representations of the forces and torques generated by the propulsion system in the body coordinate system, calculated as follows: (2) Among them, The thrust generated by the three-bearing vector nozzle exist The component of the force on the axis; It is the thrust generated by the lift fan. exist The component of the force on the axis; The thrust generated by the three-bearing vector nozzle exist The component of the force on the axis; It is the thrust generated by the lift fan. exist The component of the force on the axis; It is the thrust of the left and right rolling nozzle. The sum is in The component of the force on the axis; The thrust vector of the three-bearing vector nozzle is in Projection of a plane and The included angle of the axis; It is the thrust vector of the lift fan and The included angle of the axis. and These are aerodynamic lift, aerodynamic drag, and aerodynamic pitching moment, calculated as follows: (3) Among them, It is air density. It's airspeed. and These are wing area and mean aerodynamic chord length, respectively. It is the elevator deflection angle; It is an aerodynamic coefficient related to the angle of attack, obtained by appropriately adjusting the aerodynamic data of the NACA 0012 airfoil; It is an aerodynamic coefficient related to pitch angular velocity; These are aerodynamic coefficients related to the elevator deflection angle; the last six aerodynamic coefficients were calculated using the vortex lattice method. These are the actual values ​​of four control quantities: elevator deflection angle, thrust distribution ratio, longitudinal deflection angle of the three-bearing vector nozzle, and lift fan thrust vector deflection angle. These are the instruction values ​​for four control variables. The diagonal elements are the bandwidths of the four control variables: (4) Derive the landing gear support force based on the principle of torque balance: (5) When At that time, it is considered that the aircraft has lifted off the ground, and the supporting force at this time... .

[0033] Through the above technical solution, the embodiments of the present invention can realize coupled modeling of "aerodynamics-propulsion-actuator-ground constraints" during the short takeoff phase of an aircraft, solving the problem that the strategy cannot be implemented due to the neglect of actuator dynamics in traditional models, and providing high-precision dynamic support for subsequent optimization.

[0034] S2, based on the longitudinal dynamics model of the aircraft, uses a constrained trim algorithm to solve for the minimum takeoff speed of the aircraft, and uses the solution as the takeoff criterion for short takeoff, and outputs the terminal speed constraint conditions.

[0035] Understandably, the constraints of the constrained trim algorithm include aircraft system velocity constraints, pitch angle constraints, and actuator travel constraints. With the minimum airspeed as the objective function, it solves the trim state of the aircraft under a fixed angle of attack climb state to obtain the minimum takeoff speed.

[0036] Specifically, a trim state is set for the aircraft to climb at a fixed angle of attack (e.g., 5°). The constraints include the aircraft's forward velocity, vertical velocity, pitch angle, and actuator travel constraints. The objective function is to minimize airspeed. The trim state is solved using a sequential quadratic programming algorithm to obtain the minimum takeoff speed, ensuring that the aircraft has a safe climb capability after lifting off the ground.

[0037] In one embodiment, the core of solving the minimum takeoff speed is to obtain the minimum safe airspeed while ensuring stable climb after the aircraft lifts off the ground, so as to avoid the risk of altitude loss due to excessively low takeoff speed. At the same time, this speed is also the core criterion for subsequent takeoff strategy optimization.

[0038] Specifically, the embodiment of the present invention can achieve the solution of minimum takeoff speed through the following scheme: First, define the trim state and set the aircraft angle of attack. pitch angular velocity acceleration Satisfying the force and torque balance constraints: (6) Among them, These are the forward and vertical components of the resultant force in the body coordinate system. It is the total pitching moment.

[0039] Then, constraints are set, and decision variables include the forward velocity, vertical velocity, pitch angle, elevator deflection angle, thrust distribution ratio, longitudinal deflection angle of the three-bearing vector nozzle, and thrust vector deflection angle of the lift fan; and the thrust of the fixed propulsion system is fixed.

[0040] Finally, at airspeed The objective function is minimized, and a sequential quadratic programming algorithm is used to solve the balancing problem to ensure that there is no risk of altitude loss after the aircraft lifts its wheels.

[0041] Through the above technical solution, the embodiments of the present invention can obtain the minimum take-off speed that balances safety and optimization, compared with traditional take-off criteria. The speed calculation method retains the safety margin for wheel lifting while ensuring the optimal takeoff speed, providing a reliable basis for the boundary constraints of subsequent takeoff strategies.

[0042] S3, based on the aircraft longitudinal dynamics model and the ground force model, combined with the minimum takeoff speed, theoretically derives a fixed-value short takeoff strategy, and uses this strategy as the initial value of the fixed-value strategy for dynamic optimization.

[0043] Understandably, the derivation of the fixed-value short takeoff strategy satisfies the pitch stability constraint that the front wheels of the starting point and the ending point do not leave the ground, and the rear wheels of the ending point do not leave the ground. The optimal lower bound of the longitudinal deflection angle of the 3BSM vector nozzle is determined, and the corresponding takeoff distance is obtained by integrating the dynamic equations.

[0044] Specifically, with the elevator deflection angle set to neutral, the propulsion system thrust set to high, and the lift fan thrust vector deflection angle set to maximum rear deflection, the optimal lower bound of the 3BSM vector nozzle longitudinal deflection angle is solved by using pitch stability constraints where the front wheels do not leave the ground at the start and end points and the rear wheels do not leave the ground at the end point. The takeoff distance corresponding to the fixed-value strategy is obtained by integrating the dynamic equations, providing a reasonable initial value for subsequent dynamic optimization.

[0045] The core of the fixed-value strategy implemented in this invention is to determine the constant value instructions for each control variable while ensuring pitch stability during the taxiing phase. This strategy has the advantages of convenient control and easy engineering implementation. At the same time, its calculation results can be used as the initial values ​​for dynamic optimization, thereby improving the convergence efficiency of the optimization algorithm.

[0046] Specifically, this embodiment refers to the F-35B flight verification data and fixes the control variables as follows: elevator neutral, maximum non-afterburning thrust, maximum lift fan back deflection (to reduce pitching moment and maximize forward acceleration), and thrust distribution ratio. To ensure that the aircraft landing gear does not leave the ground during the takeoff phase, i.e., pitch does not become unstable, the following constraints must be met: (1) The nose wheel does not leave the ground when the takeoff begins: (2) The front wheels did not leave the ground before reaching the ground speed: (3) The rear wheels did not leave the ground before reaching the ground speed: Substituting the constraints into the ground force model, the solution is obtained. The optimal lower bound is obtained by substituting all fixed control variables into the longitudinal motion equation and using the fourth-order Runge-Kutta integral approximation to solve the taxiing process, thus obtaining the takeoff distance at which the aircraft reaches its minimum takeoff speed under the fixed-value strategy.

[0047] Through the above technical solution, this embodiment can obtain a fixed-value short takeoff strategy that combines stability and engineering practicality. The result can be directly applied to actual flight missions and can also provide a realistic initial solution for dynamic optimization, solving the problem of slow convergence caused by unreasonable initial values ​​in traditional dynamic optimization.

[0048] S4, based on the coupled dynamics calculation framework and fixed initial values ​​of the strategy, transforms the optimal short takeoff problem into an unconstrained nonlinear programming problem with a fixed final state time, and outputs a dynamically optimized short takeoff strategy through numerical optimization.

[0049] It is understandable that ways to transform a constrained dynamic optimization problem with a free final state time into an unconstrained problem with a fixed final state time include: normalizing the free final state time, using the Sigmoid function to map bounded control variables to the entire real number domain, and introducing a penalty function to eliminate system state and performance constraints.

[0050] Specifically, firstly, the free final state time is normalized to transform it into a variable to be optimized; secondly, the bounded control quantity is mapped to the real number domain using the Sigmoid function to eliminate actuator travel constraints; then, a penalty function is introduced to handle system state and performance constraints (such as landing gear support force constraints and actuator speed constraints) to construct an objective function with a penalty term; finally, the optimization problem is solved by combining the quasi-Newton method with gradient calculation (central difference approximation, Runge-Kutta integral) to obtain a dynamic optimization strategy.

[0051] The core of solving the dynamic optimization strategy in this embodiment of the invention is to eliminate the influence of constraints and free final state time by transforming the problem, improve the solution efficiency of the optimization algorithm by gradient calculation, and finally obtain a dynamic optimization strategy that is better than the fixed value strategy.

[0052] Specifically, the problem transformation and solution process of this invention embodiment is as follows: Optionally, the following optimization objective function is available: (7) Among them, These are the weight coefficients of the objective function; This is the final state time. The first term represents the actual final velocity. With expected terminal velocity The difference; the second item represents the takeoff distance. To ensure the rationality of the desired strategy, necessary constraints need to be introduced. The first type is the range constraint of the actuator, including: (1) elevator deflection angle; (2) thrust distribution ratio; (3) longitudinal deflection angle of the three-bearing vector nozzle; (4) thrust vector deflection angle of the lift fan; The second type is the system state and performance constraint, including: (5) pitch angle: (6) Height: Initial center of gravity height; (7) Support force: (8) Elevator deflection rate; (9) Three-bearing vector nozzle longitudinal deflection rate; (10) Lift fan thrust vector deflection rate; (11) Thrust distribution ratio change rate.

[0053] Furthermore, the optimization problem of the optimal short takeoff strategy can be expressed as the following constrained dynamic optimization problem with final-state time freedom: (8) Among them, This represents the first type of constraint; This represents the second type of constraint.

[0054] First, we handle the free final state time and define... The system dynamics equations are transformed into: (9) Next, the two types of constraints are handled separately. For the first type of constraint, the Sigmoid function is introduced to map the bounded variable to the entire real number field: (10) Among them, Represents the original control quantity; This represents the corresponding control quantity after the transformation; This represents the upper and lower bounds of the original control variable. The same method can be used to transform the final state time: (11) Among them, Represents the final state time after the transformation; This represents the upper and lower bounds of the final state time. Clearly, for any... The range constraints of the actuator and final state time are naturally satisfied. For the second type of constraint, the constraint body is mapped to a function using the sum of squares form. And a penalty function is introduced to eliminate inequality constraints. : (12) Among them, This determines the segmented interval of the penalty function. When When the time is equal to 0, the penalty function changes from an inverse proportional function to a quadratic function, making the penalty function defined over the entire real number domain and exhibiting good smoothness.

[0055] Finally, based on the above processing, equation (8) can be written as a new objective function with a penalty term: (13) Among them, This represents the penalty term corresponding to the second type of inequality constraint; Represents the penalty coefficient, when When, equation (13) is equivalent to equation (8); This represents the weighting coefficient of each penalty item.

[0056] Furthermore, the new unconstrained dynamic optimization problem with fixed final-state time is as follows: (14) The gradient of equation (13) is calculated according to the chain rule. The partial derivative of the state with respect to the control quantity is approximated by the central difference method. The integral term is approximated by the fourth-order Runge-Kutta integral. Finally, the dynamic optimization strategy is obtained by iterative solution using the quasi-Newton method. The corresponding take-off distance is significantly shorter than that of the fixed value strategy.

[0057] Through the above technical solutions, the embodiments of the present invention can obtain a dynamic optimization strategy that takes into account both optimality and constraint satisfaction. Compared with the traditional fixed thrust deflection scheme, its takeoff distance is significantly shortened, and the technical pain points of difficult solution and slow convergence of constrained dynamic optimization problems are solved at the same time.

[0058] S5, based on the constructed complete optimization system, conducts sensitivity analysis on three influencing factors: thrust-to-weight ratio, thrust distribution ratio, and center of gravity position, to obtain the influence law of each factor on short takeoff distance and form engineering guidance data.

[0059] Understandably, the sensitivity analysis was achieved by defining a normalized sensitivity coefficient, which led to the conclusion that, under standard settings, takeoff distance is most sensitive to thrust-to-weight ratio and least sensitive to thrust distribution ratio.

[0060] Specifically, a normalized sensitivity coefficient is defined to quantify the dimensionless ratio of the rate of change of a single parameter to the rate of change of takeoff distance, establishing a unified benchmark for measuring the degree of parameter influence. Based on the benchmark takeoff distance value under standard settings and the standard parameter combination, the takeoff distance after disturbances in thrust-weight ratio, thrust distribution ratio, and center of gravity position are calculated respectively, and substituted into the normalized sensitivity coefficient formula to obtain the sensitivity values ​​of each factor. By comparing the sensitivity values ​​of the three factors, it is concluded that the takeoff distance under standard settings has the highest sensitivity to thrust-weight ratio and the lowest sensitivity to thrust distribution ratio, forming engineering guidance data for prioritizing parameter adjustments.

[0061] This embodiment defines a normalized sensitivity coefficient, adjusts the single factor parameter respectively, calculates the rate of change of the corresponding takeoff distance, and concludes that the takeoff distance is most sensitive to thrust-to-weight ratio and least sensitive to thrust ratio under standard settings, providing guidance for engineering practice.

[0062] The core of the sensitivity analysis in this invention is to quantify the impact of each key parameter on takeoff distance and clarify the priority of parameter adjustment, thereby providing accurate technical basis for actual operations such as aircraft weight distribution and thrust allocation.

[0063] Specifically, the normalized sensitivity coefficient is defined in this embodiment of the invention: (15) Among them, This indicates the change in takeoff distance; This indicates the optimal short takeoff distance under standard settings; This indicates the amount of change in the three parameters; This indicates the values ​​of the three parameters under standard settings.

[0064] Optionally, the embodiments of the present invention perform sensitivity analysis on three factors: thrust-to-weight ratio, thrust distribution ratio, and center of gravity position, respectively, to clarify the priority of each parameter's influence on takeoff distance (thrust-to-weight ratio > center of gravity position > thrust distribution ratio), providing quantitative engineering guidance for parameter adjustment in actual flight missions and solving the problem of lack of practicality in traditional qualitative analysis.

[0065] The optimization method for the optimal short takeoff strategy of vertical / short takeoff and landing (VTOL) aircraft proposed in this embodiment of the invention first establishes a longitudinal dynamics model of the VTOL aircraft and a ground force model considering actuator dynamics, and then extends the actuator dynamics to the aircraft's equations of motion. Next, a constrained trim algorithm is used to solve for the minimum takeoff speed, which is then used as the takeoff criterion. A fixed-value takeoff strategy is theoretically derived as the initial value for dynamic optimization. The optimal short takeoff problem is then transformed into an unconstrained nonlinear programming problem with a fixed final-state time. Numerical optimization methods are then used to solve the dynamically optimized takeoff strategy. Finally, sensitivity analyses are conducted on the thrust-to-weight ratio, thrust distribution ratio, and center of gravity position to obtain the influence of each factor on the takeoff distance. Compared with traditional fixed thrust deflection schemes for takeoff strategies, this method has the advantages of high strategy optimization efficiency, short takeoff distance, and strong engineering guidance, significantly improving the rapid sortie capability of VTOL aircraft and providing technical support for their short takeoff phase control. This solves several problems in related technologies, such as: low engineering feasibility due to the lack of modeling and constraints on the dynamic characteristics of actuators for short takeoff strategies of vertical / short takeoff and landing aircraft; lack of dynamic optimization of fixed thrust deflection angle schemes in conjunction with changes in the aircraft's state during takeoff, resulting in unclear strategic advantages; and lack of quantitative sensitivity analysis of factors affecting takeoff distance, making it difficult to provide accurate engineering guidance.

[0066] To implement the methods of the above embodiments, the present invention also provides an optimization system for the optimal short takeoff strategy of a vertical / short takeoff and landing (VTOL) aircraft, as shown in Figure 4. The system includes: a modeling module 100, used to establish a longitudinal dynamics model of the VTOL aircraft considering actuator dynamics and a ground force model, and to extend the actuator dynamics to the aircraft's equations of motion to construct a coupled dynamics calculation framework including aerodynamics-propulsion-actuator-ground constraints; a minimum takeoff speed solution module 200, used to solve for the minimum takeoff speed of the aircraft based on the longitudinal dynamics model using a constrained trim algorithm, using the solution result as the takeoff criterion for short takeoff, and outputting terminal speed constraints; and a fixed-value strategy initial value module 30. The first module, 0, is used to theoretically derive a fixed-value short takeoff strategy based on the aircraft's longitudinal dynamics model and ground force model, combined with the minimum takeoff speed. This strategy is then used as the initial value for the fixed-value strategy in dynamic optimization. The second module, 400, is used to transform the optimal short takeoff problem into an unconstrained nonlinear programming problem with a fixed final state time based on the coupled dynamics calculation framework and the initial value of the fixed-value strategy. The dynamic optimization strategy is then output through numerical optimization. The third module, 500, is used to conduct sensitivity analysis on three influencing factors—thrust-to-weight ratio, thrust distribution ratio, and center of gravity position—based on the constructed complete optimization system. This analysis aims to obtain the influence of each factor on the short takeoff distance and generate engineering guidance data.

[0067] The optimization system for the optimal short takeoff strategy of vertical / short takeoff and landing (VTOL) aircraft in this embodiment of the invention has the advantages of high strategy optimization efficiency, short takeoff distance, and strong engineering guidance compared with the traditional fixed thrust deflection scheme takeoff strategy. It can significantly improve the rapid takeoff capability of VTOL aircraft and provide technical support for the control of its short takeoff phase.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0069] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0070] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. An optimization method for the optimal short takeoff strategy of a vertical / short takeoff and landing (V / STOL) aircraft, characterized in that, include: S1. Establish a longitudinal dynamics model and a ground force model for a vertical / short takeoff and landing (VTOL) aircraft that consider actuator dynamics, and extend actuator dynamics to the aircraft's equations of motion to construct a coupled dynamics calculation framework that includes aerodynamics, propulsion, actuators, and ground constraints. S2. Based on the aircraft's longitudinal dynamics model, use a constrained trim algorithm to solve for the minimum takeoff speed. Use the solution as the takeoff criterion for short takeoff and output terminal speed constraints. S3. Based on the aircraft's longitudinal dynamics model and the ground force model, and combined with the minimum takeoff speed, theoretically derive a fixed-value short takeoff strategy and use this strategy as the initial value for dynamic optimization. S4. Based on the coupled dynamics calculation framework and the initial value of the fixed-value strategy, transform the optimal short takeoff problem into an unconstrained nonlinear programming problem with a fixed final state time. Output a dynamically optimized short takeoff strategy through numerical optimization. S5. Based on the constructed complete optimization system, conduct sensitivity analysis on three influencing factors: thrust-to-weight ratio, thrust distribution ratio, and center of gravity position. Obtain the influence of each factor on the short takeoff distance and form engineering guidance data.

2. The method according to claim 1, characterized in that, The longitudinal dynamics model includes the nonlinear relationship between the thrust component, aerodynamic component, and pitching moment of the aircraft propulsion system. The ground force model equates the nose and main landing gear to the force model along the central axis. The actuator dynamics are modeled using a first-order inertial element.

3. The method according to claim 1, characterized in that, The constraints of the constrained trim algorithm include airframe velocity constraints, pitch angle constraints, and actuator travel constraints. With minimum airspeed as the objective function, the trim state under a fixed angle of attack climb condition is solved to obtain the minimum takeoff speed. The derivation of the fixed-value short takeoff strategy satisfies the pitch stability constraint that the front wheels do not leave the ground at the start and end points and the rear wheels do not leave the ground at the end point. The optimal lower bound of the longitudinal deflection angle of the 3BSM vector nozzle is determined, and the corresponding takeoff distance is obtained by integrating the dynamic equations.

4. The method according to claim 1, characterized in that, Methods to transform a constrained dynamic optimization problem with a free final state time into an unconstrained problem with a fixed final state time include: normalizing the free final state time, using the Sigmoid function to map bounded control variables to the entire real number domain, and introducing a penalty function to eliminate system state and performance constraints.

5. The method according to claim 1, characterized in that, The sensitivity analysis includes: defining a normalized sensitivity coefficient to quantify the dimensionless ratio of the rate of change of a single parameter to the rate of change of takeoff distance, and establishing a unified benchmark for measuring the degree of parameter influence; based on the benchmark takeoff distance value under standard settings and the standard parameter combination, calculating the takeoff distance after disturbances to the thrust-to-weight ratio, thrust distribution ratio, and center of gravity position, and substituting them into the normalized sensitivity coefficient formula to obtain the sensitivity values ​​of each factor; comparing the sensitivity values ​​of the three factors to conclude that the takeoff distance under standard settings has the highest sensitivity to the thrust-to-weight ratio and the lowest sensitivity to the thrust distribution ratio, forming engineering guidance data for prioritizing parameter adjustments.

6. The method according to claim 1, characterized in that, S1 further includes: establishing a longitudinal dynamic model to characterize the nonlinear relationship between the thrust components, aerodynamic components, and aerodynamic pitching moment of the propulsion system, and outputting the basic equations of motion with the forward velocity, vertical velocity, pitching angular velocity, north coordinate, and down coordinate of the engine system as state variables; establishing a ground force model, equating the dual main landing gear to a single landing gear on the centerline, and establishing the balance relationship between the support force and pitching moment of the nose and main landing gear based on the output pitching moment and vertical force data, and calculating the ground contact force constraint conditions; establishing an actuator dynamic model, using a first-order inertial element to model the four control quantities—elevator deflection angle, thrust distribution ratio, 3BSM vector nozzle longitudinal deflection angle, and lift fan thrust vector deflection angle—and amplifying the actuator bandwidth parameters to form the joint equations of motion, ensuring that subsequent optimization results meet the actuator dynamic constraints.

7. The method according to claim 1, characterized in that, S2 further includes: setting the trim state of the aircraft climbing at a fixed angle of attack, and determining the forward velocity, vertical velocity, pitch angle, and actuator travel constraints of the aircraft as the constraint data for trim calculation; using the minimum airspeed as the objective function, and combining the established trim state and constraint data, constructing a mathematical model of a constrained optimization problem; solving the constructed optimization problem through a sequential quadratic programming algorithm to obtain the minimum airspeed that satisfies all constraints, and using it as the minimum takeoff speed to ensure that the aircraft has a safe climb capability after lifting off the ground.

8. The method according to claim 1, characterized in that, S4 further includes: processing the free final state time through time normalization, transforming it into a variable to be optimized, so as to eliminate the final state time degree of freedom and achieve fixed time domain mapping; using the Sigmoid function to map the bounded control quantity to the full real number domain to eliminate actuator travel constraints, and introducing a penalty function to handle system state and performance constraints, constructing an objective function with a penalty term; solving the unconstrained optimization problem by combining the quasi-Newton method with gradient calculation to obtain a dynamically optimized short-distance takeoff strategy.

9. The method according to claim 1, characterized in that, S3 further includes: fixing the elevator deflection angle to neutral, the propulsion system thrust to high state, and the lift fan thrust vector deflection angle to maximum back deflection angle, to form a constant control command set; solving for the optimal lower bound of the longitudinal deflection angle of the 3BSM vector nozzle by using pitch stability constraints where the front wheels do not leave the ground at the start and end points and the rear wheels do not leave the ground at the end point, to meet the pitch stability requirements during the takeoff phase; substituting the determined fixed control quantity and the obtained optimal lower bound into the longitudinal dynamic equation, and integrating the dynamic equation to obtain the takeoff distance corresponding to the fixed strategy, providing a reasonable initial value for subsequent dynamic optimization.

10. An optimization system for the optimal short takeoff strategy of a vertical / short takeoff and landing (V / STOL) aircraft, characterized in that, The system includes: a coupled model construction module, used to establish a longitudinal dynamics model and a ground force model for vertical / short takeoff and landing (VTOL) aircraft that consider actuator dynamics, and to extend actuator dynamics to the aircraft's equations of motion to construct a coupled dynamics calculation framework that includes aerodynamics, propulsion, actuator, and ground constraints; a minimum takeoff speed trim calculation module, used to solve for the minimum takeoff speed of the aircraft based on the longitudinal dynamics model using a constrained trim algorithm, and to use the solution as the takeoff criterion for short takeoff, and to output terminal speed constraints; a fixed-value strategy theoretical derivation module, used to theoretically derive a fixed-value short takeoff strategy based on the aircraft's longitudinal dynamics model and ground force model, combined with the minimum takeoff speed, and to use this strategy as the initial value for a dynamically optimized fixed-value strategy; and a dynamic optimization problem solving module, used to transform the optimal short takeoff problem into an unconstrained nonlinear programming problem with a fixed final state time based on the coupled dynamics calculation framework and the initial value of the fixed-value strategy, and to output a dynamically optimized short takeoff strategy through numerical optimization. The multi-parameter sensitivity analysis module is used to conduct sensitivity analysis on three influencing factors—thrust-to-weight ratio, thrust distribution ratio, and center of gravity position—based on the constructed complete optimization system, to obtain the influence law of each factor on short takeoff distance and form engineering guidance data.

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