Research On Aircraft Trajectory Planning Based On Differential Flatness Theory

Trajectory planning, as an integral part of the mission planning technology, can help to improve the aircrafts' flying qualities to meet the established mission requirements, and effectively enhance the success rate of combat aircraft attacking. Being an optimal control problem, aircraft trajectory planning is restrained by differential equations, algebraic equations and inequalities, and it aims to find the functional extremum. Consequently, the immediate solution is difficult to imagine.In order to reduce the complexity of the problem, the thesis introduces the differential flatness theory to serve the dynamical equations, the nonholonomic constraint, and proposes a hierarchical programming approach. With the basis of template route planning based of B-spline curve, the optimal control problem were changed into a general nonlinear programming problem and got the solution in the framework of the differential flatness theory, which guaranteed the enforceability of the generated trajectory. The main contents are as follows:1. Problem analysis and modeling. With the analysis of the aircraft combat mission and the summary of the constraints of the trajectory planning involved, the thesis proposed the objective functions of the trajectory planning. On this basis, the trajectory planning problem was modeled as a general nonlinear programming one, comprising the aircraft dynamic model, described by the overload and roll angle as the decision variables, and the threat model, etc., which constituted the constraints of the trajectory planning, and laid the foundation for further study of the method of trajectory planning.2. Template route planning technology. Having analyzed the commonly-used tactical motivation of the aircraft combat missions against the ground, the paper extracted a series of basic maneuver and the general pattern of air-to-ground combat (i.e. tactical template). Two typical tactical templates were selected to execute the maneuver decomposing and numerical value description. Then the template route planning based on the B-spline curve was studied, and a collision free route planning algorithm was put forward, which could satisfy the terminal constraints and provide the technical support for the following trajectory generation.3. Trajectory generation based on the Differential Flatness Theory. The aircraft trajectory planning with nonholonomic constraints was discussed and the trajectory generating procedures, based on differential flat trajectory, were presented. In addition, the flat output was determined by judging the flatness of the aircraft dynamics and the kinematics model. Based upon its template path planning, B-spline curve was used as the flat output in a parametric way, transforming the optimal control problem into a general nonlinear programming problem, which ensured the generating trajectory enforceable, and reduced the difficulty of the problem solution. Through the application in the project, this method is able to satisfy the nonholonomic constraints of the aircraft, terminal constraints and other constraints, and combine the tactical and the techniques intelligently. As a result, it may solve the problem of aircraft trajectory planning effectively in the air-to-ground attacking mission.