DS07 - Société de l'information et de la communication

Design of Autopilot for Convertible Aerial Robots – DACAR

Submission summary

Unmanned aerial vehicles (UAVs), also called drones, have proved to be a very efficient means to address surveillance and inspection applications in both the military and civilian domains. Among the numerous missions that can be achieved with drones, some of them only require to hover or fly in a narrow area. They are best addressed with rotary-wings drones, alike the well-known quadcopter. Other missions require covering long distances or staying in the air for a long time. In this case fixed-wing aircraft is preferred due to its good energy efficiency. In some cases, both hovering capacity and energy efficiency in cruising flight are needed. Examples are numerous and include surveillance missions in a large area with take-off from a narrow zone (ship, natural terrain, cluttered environments, etc), or inspection of several structures far apart from each other. Aircraft dedicated to such applications involve the association of propellers with wing(s), and are sometimes referred to in the literature as tilt-rotor, convertible, hybrid, or compound aircraft, depending on their mechanical structure. For simplicity, all these aircraft will be denoted in the sequel as "Convertible UAVs". The project concerns more specifically Convertible MAVs (Mini Aerial Vehicles), i.e. with Maximum Take-Off Weight less than 30 kg (according to UVS international classification).

The main objective of this proposal is to design autopilots for Convertibles MAVs ensuring energy efficient and robust flight capacities. Several issues have to be addressed:
_ Convertible MAVs are redundant systems that can exploit both rotary wings degrees of freedom (rotors' angular velocities) and fixed wings degrees of freedom (flaps, ailerons, etc) for control. At low flight speed the control essentially boils down to the control of a multi-rotor system. At high speed one may view the vehicle as an airplane and make use of associated control approaches. At intermediate speeds, in particular during transition between low and high speed, other methods must be developed. Controlling such "transitions" is a major difficulty for convertible UAVs.
_ Due to the system's redundant actuation, there exist many possible control modes with different energy efficiency levels. Achieving energy efficient flight in all flight phases is essential to justify the utility of this type of structure.
_ Convertible MAVs can be subjected to fast and strong variations of aerodynamic forces acting on the vehicle, due to the presence of wings. Typical cases include transition between stationary and cruising flights, adverse wind gusts perturbations, or aggressive flight maneuvers. Ensuring a large flight envelope is necessary to guarantee flight safety.
_Flight dynamics models valid in the entire flight domain are difficult to obtain. Main issues include aerodynamic modelling at low Reynolds numbers or large angles of attack, stall modelling, and propellers/wings aerodynamic interactions.

For all these reasons, designing an efficient and robust autopilot for a convertible vehicle remains a challenge. This project aims at providing solutions to this problem. The project relies on two pillars: advanced control and estimation techniques, and extensive field tests. From a theoretical point of view, the project will build on the design of nonlinear control laws and observers. A key issue is the real-time estimation of the main aerodynamic efforts which, as explained above, can be difficult to model precisely. From an experimental point of view, an essential aspect is to register the maximum quantity of flight data so as to provide solid ground for modelling and evaluation. This justifies the development of prototypes with dedicated sensor suites. Therefore, the project includes a strong effort on the development and instrumentation of prototypes.

Project coordination

Pascal Morin (Institut des Systèmes Intelligents et de Robotique)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

I3S Laboratoire d'Informatique, Signaux et Systemes de Sophia Antipolis
ALCORE Technologies SA ALCORE TECHNOLOGIES
ISIR Institut des Systèmes Intelligents et de Robotique

Help of the ANR 662,102 euros
Beginning and duration of the scientific project: - 48 Months

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