Experimental investigation into the dynamic characteristics of a tilting multirotor system

Urban Air Mobility (UAM) promises a transformative leap in urban transportation, with electric vertical take-off and landing (eVTOL) aircraft at the forefront. Pivotal in eVTOL flexibility, especially during transitional flight phases, are tilting rotors. However, these configurations pose challenges in maintaining dynamic stability and controlling vibration, leading to potential resonance issues during transition phases. This study aims to explore experimentally the dynamic interplay between modal characteristics of a tilting multirotor system with operational parameters such as tilt angle and rotational speed of propellers. The key focus is placed on understanding the system-wide implications induced due to changes in tilt angle and rotor speed. This research particularly focuses on how these operation parameters influence resonance, leading to shift in shifts in modal frequencies and damping variations, which are critical in the design and operation of tilting rotors. To scrutinise these characteristics, a dynamically scaled experimental rig is developed. This multirotor test rig facilitates investigations into how variations in rotor tilt angles and rotor speed impact the system’s modal characteristics, including natural frequencies, mode shapes, and damping characteristics. A special emphasis is placed on exploring resonance and its implications under different tilt scenarios and operational speeds. Experimental exploration revealed that natural frequencies decrease with an increase in rotor speed, particularly for higher modes. Whereas, increasing the tilt angle from 0◦ to 90◦ results in a substantial increase in frequency and a reduction in amplitude, especially in the first torsional mode. Furthermore, it is found that the system experiences strong resonance at 3120 RPM, where the second-out-plane bending mode is excited by the first rotor harmonics.