An investigation of a scalable flight control system for a variable pitch, fuel powered, quad-rotor craft

Abstract

Quadrotor platforms continue to face scalability issues that can be linked to factors such as energy density of polymer battery power sources and the limited efficiency of their fixed pitch propulsion systems. This study employs a dual-method analysis, integrating both experimental and theoretical approaches, to explore the trade-offs between endurance and payload capacity in a quadrotor equipped with a scalable variable pitch rotor system. By applying this development framework, the key objective of this work is to broaden the scope of feasible mission profiles by clarifying the inherent constraints and compromises between endurance and payload capacity and illuminating factors contributing to efficiency. In this pursuit, the first main aspect focused on empirically validating various rotor geometries using test bench system. Data collected is analysed using the computational tool MATLAB, whereas XFOIL simulates airfoil lift and drag characteristics. Rotor performance is then characterised through comparative analysis between experimental data and theoretical predictions made by the Blade Element Momentum Theory (BEMT) rotor model. From comparisons it was found that the BEMT model performance and behaviour remained consistent at varying rotor geometry scales and correlated well with empirical thrust results. It was also found that approximations for power output levels were marginally overestimated at high blade pitch angles – the possible causes of which are further explored in an article published in parallel to this work. [1] The 6-DOF (degrees of freedom) nature of quadrotors in a dynamic environment is then explored using Simulink wherein a flight control system (FCS) architecture is formulated by integrating control laws with a BEMT rotor model. Comparative performance evaluations focusing on dynamic behaviour, thrust generation, and power efficiency are then realised by subjecting a standardised quadrotor airframe with varying rotor geometry and payload capacities to an idealized climb-to-hover (C2H) trajectory. From comparisons of simulation tests, it was significant to find that varying rotor geometry and payloads yielded highly contrasting dynamic behaviours and efficiency performance in terms of thrust generation and power demands. Simulation data also indicated that the B04 rotor configuration was the most energy efficient and enabled superior climb rates and accelerations. By employing figures for simulated hovering power demands, abstracted endurance times are shown to be greatly affected by the energy density and payload constraints between chemical battery systems and carbon fuels. Comparative analysis of rotor performance also revealed that the choice of hardware configuration may necessitate prioritising durability and responsiveness over efficiency. Moreover, mission profiles optimised for high dynamic responsiveness must ensure that FCS sensitivity does not exceed the strength constraints of mechanical subsystems or airframe structure. Collectively, this work successfully established a robust framework for future research and early-stage development of scalable quadrotor platforms can be achieved by integrating variable pitch rotor systems with modularized quadrotor control system architectures. This framework provided key insights into improving quadrotor performance and efficiency, particularly through scalable rotor geometry and payload capacity.