Research On Flight Control Of Ducted Tiltrotor Aircraft

The ducted tiltrotor aircraft is a new configuration of rotorcraft which provides lift force,thrust and controls through the thrust vector.The ducted tiltrotor aircraft has the characteristics including vertical-take-off-and-landing,high maneuverability in low-altitude flight and hovering flight,It also has the advantages of fixed-wing aircraft such as long range,long endurance and high cruise speed.This thesis takes the small-scaled ducted tiltrotor as the research object.Firstly,the general configuration and flight principle of the ducted tiltrotor aircraft were analyzed.Based on the blade element theory,the rotor aerodynamics model is derived,and the quasi-steady nonlinear aerodynamic model of the wing and the fuselage is established.A 6 Degree of freedom(6DoF)nonlinear flight dynamics model was implemented under the MATLAB/Simulink environment.The flight dynamical characteristics of the ducted tiltrotor aircraft were analyzed which lays a foundation for the design of control law.Secondly,the control strategy of small-scaled ducted tiltrotor in all three flight modes was proposed.The cascade PID control was adopted to track the attitude and speed command.The autonomous take-off-and-landing control strategy in helicopter mode was derived.The smooth transition between the different flight modes was accomplished by using the controller switching technique,and the flight simulation verification of all three flight modes was carried out.Thirdly,according to the requirements of the flight control system,a flight control system using high-precision commercial strapdown inertial navigation system as the primary sensor was built.In order to improve the reliability of the flight control system,an extra set of redundant sensors was used as the failsafe in case of the malfunctions of the commercial strapdown inertial navigation system.As for the software,according to the priority of the task,the task scheduling sequence was improved,which makes the software system always in the optimal operating condition.Finally,the flight test of the small ducted tiltrotor was carried out,which includes flight modes of stability augmentation,altitude hold,position hold and autonomous take-off and landing.The data show that the controllers in both inner and outer loops possess good performance.Autonomous navigation positioning accuracy and flight trajectory tracking control law can meet the requirements of the mission.