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White Paper: Modeling and Controlling a Tandem Helicopter Drone

For the last fifteen years, the drone market has been booming, thanks in part to academic research.

Drones can usually be found as miniature helicopters, multicopters, or planes, depending on the tasks they are expected to carry out. A task that today’s drones struggle to accomplish is the transportation of goods — which is receiving a growing interest from the commercial and industrial sectors. It is in this context that the CARIC AUT703 TRL4+ research and development project was born.

Laliberté, F. (2017). Modélisation et commande d'un drone hélicoptère tandem (Masters thesis, École Polytechnique de Montréal).

This project brings together industrial and academic partners in the aim to develop a tandem helicopter drone. This configuration offers recognized advantages for payload transport, including its robustness to weight, balance and inertia changes. This master’s thesis covers the modelling and control of the tandem helicopter drone considered in the framework of the CARIC project, the LX300. The goal of this research is to model a tandem helicopter, a configuration that is often neglected in the literature, and to synthesize a fixed-structure controller that stabilizes the rotorcraft over its entire flight envelope while being robust to the variations caused by the payload. The modelling of the drone is first realized using a conventional approach for helicopters. However, particular attention is paid to the modelling of the influence of an unbalanced payload, the aerodynamic interaction between the two rotors, and the design specific to the rotors under consideration. The dynamics of the rotors is fully modelled in order to be able to simulate their finer behaviours, then a simplification is applied in order to allow the trimming and the linearization of the system. This simplification leads to equations that are very close to what is currently found in the literature, with the additions brought by the tandem configuration and by the unique rotors under consideration. The stabilization loops of the drone are then synthesized ensuring robustness to variations in weight, balance and inertia for all the expected flight conditions. Since the controller architecture is imposed by the selected embedded platform, the structured H1 method with gain scheduling is favoured in order to achieve the objectives of performance and robustness. This method being sensitive to the initial conditions, a multi-step approach is used in order to gradually increase the complexity of the problem to be solved. This approach also allows the validation of the selected requirements, before using them for the complete synthesis. The controller is finally validated on the complete nonlinear model, and then on a high fidelity simulator for different types of manoeuvres, according to the presented implementation.