Dynamic stability and flight control of biomimetic flapping wing micro air vehicle based on multibody dynamics

Abstract

Since the demand for biomimetics-based aerospace systems is surging rapidly for the past few years, Flapping-wing Micro Air Vehicles (FWMAVs) are not an exception to these necessities. With the growing advancements in science and technology, scientists have realized that nature-inspired designs generally produce optimal solutions at minimal cost. One of the key bioinspired-based aerospace systems is an insect-like FWMAV that is considered quite impressive owing to its efficient flight utilizing complex aerodynamics. As real insects generally do the optimum flight, engineers are doing their best to explore the aerodynamics, kinematics, flight dynamics, and control to better mimic their flight. However, mimicking insects’ flight using FWMAVs has limited functionality considering the difficulty in understanding its complex aerodynamics and applying control. Many studies have been conducted to characterize the stability of insect-like FWMAVs

however, they have limitations based on different areas such as the fidelity of the aerodynamic model, assumptions taken to modify the flight mechanics equations, wing kinematics adopted, rigid or flexible model used, and the type of trim search algorithm adopted. The present study considers a hawkmoth-scaled FWMAV model for characterizing its stability using a multibody dynamics simulation environment that involves fully coupled nonlinear equations of motion. The simulation environment incorporates a quasi-steady aerodynamic model, real and simplified hawkmoth wing kinematics and morphological data, kinematic constraints, and finally a gradient-based trim search algorithm. The complete simulation is run for five different speeds involving equal intervals from 0 to 1 m/s, and 6 Degrees of Freedom (6-DOF) stability is characterized based on it. The FWMAV model shows unstable behavior both in longitudinal and lateral directions (slightly damped) based on the results of the trim search. The longitudinal direction instability is mainly related to the forward-backward direction velocities coupled with the pitching rate that results in unstable oscillatory modes. On the other hand, lateral instability augments as sideways velocity pairs with rolling and yawing rates. Firstly, the influence of body to wings mass ratio on longitudinal and lateral dynamic stabilities is investigated. Since longitudinal unstable oscillatory mode’s influence increases with speed, this study focuses on longitudinal motion control. LQR controller is implemented first to control the speed of linear FWMAV system using integral action. Next, the controller is implemented for 3-DOF motion control of the nonlinear model at five different speeds. Then, reference velocity profile tracking, involving hovering, acceleration, constant speed, and deceleration phases, is achieved for the non-linear model. Finally, various reference trajectories tracking is achieved by implementing a dual loop control technique.