Swashplateless MAV: valutazione delle prestazioni attraverso l’analisi CFD e confronto con i test sperimentali su banco prova. = Swashplateless MAV: performance evaluation through CFD analysis and comparison with experimental bench tests.

Drones have existed for almost a hundred years, but only nowadays micro air vehicles (MAV) are becoming popular, the reason is that they are becoming smaller, cheaper, and easily available. As well as MAV, also a variety of new technologies are now accessible. All this makes MAVs able to support a wide range of applications: precision farming, inspection of hazardous environments, fire fighting, 3D surveying and mapping. Such vehicles come in a large number of forms including quadrotors, incorporating four lifting rotors, coaxial helicopters, with two counter-rotating blades, or single rotors with a tail rotor. The objective of this work is to make drones smaller and simpler and more inexpensive reducing the number of actuators. Quadrotors, for example, have four actuators to drive the four rotors, even though they are considered under-actuated, the mechanical complexity has to be taken into account. This study aims to analyze an innovative MAV propulsion system designed to be mounted on a MAV that achieves trim control by using two counter-rotating rotors mounted on the same vertical axis. At the state of the art, coaxial MAVs use rotors to generate thrust as well as to regulate the vehicle's pitch and roll. This is achieved through the cyclic control that is the pitch elevation and depression within each revolution. This control technique is made possible thanks to a swashplate and two or more servomotors that actuate the blade pitch axis. To reduce the complexity of this system, some innovative solutions have been found such as the use of piezoelectric actuators, as well as the introduction of an additional outboard propeller or even the addition of a passive stabilizer bar mechanism. In this case study, a controlled cyclic response blade pitch is directly induced by modulating the main drive motor. The system is characterized by a central rotor hub connected to the motor and a couple of identical blades that are attached to the hub by simple pin hinges. The two hinges that link the hub to the blade are not vertical, instead, the top of one of them is inclined inward (positive blade) and the other is inclined outward (negative blade). Thanks to this solution, it is possible to couple the lead-lag motion of the blade tip about the vertical axis, to a pitching motion about the blade’s diameter axis. This system aims to let the blade depress its pitch as it passes some station of the rotor disk and elevates the blade pitch as it passes the station 180° opposite. To achieve a swashplate-like attitude authority and control the flapping rotor’s tip path plane, it is necessary to excite a dynamic response by modulating the torque applied to the motor. The modulation happens by adding a sinusoidal component in phase with the motor rotation and altering the phase offset angle and the amplitude. The result is a variation in lag angle and consequently also in pitch that is similar to conventional cyclic pitch control. In future works, this system will be integrated into a coaxial MAV. On the top motor will be mounted the hinged control rotor, pointing upwards; while a rigid rotor will be mounted to the bottom motor, pointing downwards.