Abstract
This paper presents a nonlinear model of the quadcopter to simulate the actual motion. An aerodynamic model of the rotor is obtained through wind-tunnel tests, which consider the variations in the rotor’s angular velocity, incoming flow speed, and angle of attack of the rotor ( $\alpha _{p}$ ). The quadcopter’s fuselage aerodynamics and mutual interference are simulated using the computational fluid dynamic (CFD) method. The mesh motion method is used to simulate the rotation of the rotor. It can be found that the interference has a significant impact on the aerodynamic load of the fuselage and the thrust and pitch moment of the rear rotor. The mathematical expression of the interference model is given by adopting the idea of the small disturbance hypothesis. The yaw dynamics model is also improved by considering the motor’s dynamics. The quadcopter’s nonlinear model can be obtained by combining the rotor model, fuselage model, motor model, and interference model. Then, flight experiments are done at hovering and forward flight states to verify the established model, and the experiment results are in good agreement with the nonlinear model. Finally, the quadcopter’s characteristic descriptive abilities of different accurate models are discussed to help designers to build a suitable quadcopter model according to the requirements.
Highlights
Quadcopters have been increasingly applied in military and civilian fields due to their simpler mechanical structure and lower cost [1]
A nonlinear model of quadcopter suitable for both hovering and forward flight states is established by wind tunnel tests and computational fluid dynamic (CFD)
Through the analysis of the established model, it is found that the aerodynamic characteristics of the rotor during the forward flight are very different from hovering
Summary
Quadcopters have been increasingly applied in military and civilian fields due to their simpler mechanical structure and lower cost [1]. With the further increase in speed, the characteristics of the quadcopter model have undergone great changes, and those research results are difficult to apply in the forward flight mode. Je et al [18] and Matthew et al [19] pointed out that the aerodynamic interference has a great influence on the aerodynamic model of the rear rotor during the forward flight in both cross configuration and plus configuration quadcopter. The accurate quadcopter models can realistically describe the dynamic characteristics of the quadcopter This helps to verify the robustness of the controller and greatly reduces the cost and risk of the real flight test in the controller design process. The novel models include the thrust and torque, and the hub force, pitching moment and rolling moment, which can be used to describe the rotor’s aerodynamic forces in hovering and forward states.
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