Fully Actuated Rotorcraft (FAR)
This work presents the development of a Fully Actuated Rotorcraft (FAR). The FAR is a four-rotor aircraft, similar in structure to a quadrotor except that the FAR is augmented with control surfaces and actuators in a manner that allows the removal of the characteristic coupling between the degrees of freedom of the quadrotor, thus creating a fully actuated aircraft. At the time this research was conducted no record of a fully actuated hovercraft was found in the literature. A fully actuated helicopter has advantages in dealing with disturbances and in maneuverability over other types of helicopters. The aircraft structure developed in this work, its dynamic model and control system are innovative and unique to this work. The work presents a literature review, model development, development of a control system, simulations and experiments. The development of the complete dynamic model of the FAR is based on a Newtonian analysis of the rigid body equations together with an aerodynamic model of the rotors and the control surfaces and an electro-mechanical model to describe the dynamics of the propulsion units. The complete dynamic model was simplified, using approximations and assumptions, and afterwards a planar model was constructed by constraining the simplified model to a plane. The planar model served as a tool for having intuitive insight of the non-linear dynamics of the FAR and in formulating a control system by studying the relatively short and simple mathematical expression of the planar model. The FAR control system was developed in two stages: the first, development of a controller for the simplified planar model using exact feedback linearization techniques; the second, development of a controller for the full spatial model. The design of the controller for the full model development is based on insights gained during the process of developing the control of the planar model. The system equilibrium point was analyzed and a proof of the system stability about the equilibrium point is provided for both stages of the control system development.A computer simulation was developed for testing the closed loop performance of the control system with the non-linear dynamic model of the FAR. The simulation was used to test the behavior of the non-linear dynamic model of the FAR under the effect of the control loop and to test the closed loop system stability in a range of conditions simulating real world flight. The simulator also provided the opportunity to introduce other non-linear properties to the model that were not included in the system’s mathematical analysis. The numeric simulations were performed with a variety of initial conditions and the results reveal the system’s stability in a wide range of flight conditions despite the added non-linear effects.
In the last stage of the research a comprehensive experimental system was developed and a variety of flight tests were carried out demonstrating the feasibility of an aircraft of this kind. The aim of the experiment system is to demonstrate the operation of the controller on a real operational platform; it also provides the ability to perform measurements for identifying aircraft parameters. The experiments enable a comparison of the analytical model simulation and the experimental system and to conduct a comparison between a conventional quadrotor aircraft and FAR. The experiments results also reveal the control system’s performance under a variety of disturbances (perturbations) in location and orientation of the aircraft. Further more, the experimental system demonstrates the features differentiating a real system from an ideal or simulated system such as the effect of the actuator properties (dynamics, range), software response time and sampling rate on system performance. The experiments results validate the analysis conducted, the results are similar to the results achieved simulation and confirm that the controller stabilizes the system in the range of configurations in which the flight experiments were performed. The research results demonstrate that it is feasible to build an aircraft which is fully actuated in a position and orientation range wide enough to have an operational advantage over other aircrafts. The research provides insights into the FAR structure, its technical characteristics and analytical details that need to be taken into account during the design and construction of a fully actuated rotorcraft.