Relative Rotor Phasing for Vibratory Load Minimization for a Coaxial Multicopter

This study focuses on vibration reduction for a coaxial multicopter with 2-bladed, synchronized RPM, variable-pitch
rotors through the use of rotor phasing. The study also examines the effect of aerodynamic interference between
the rotors of a coaxial pair on the vibration predictions. A set of seven multi-rotor phase parameters are defined—a
crossover azimuth for each the four coaxial pairs along with three aircraft level modes—pitch phasing, roll phasing, and
differential phasing. The phase modes are examined in both a cross- and plus-configuration multicopter. Irrespective
of whether interference was included or not, crossover azimuth of 0° tends to minimize the 2/rev lateral loads, while
moderate values of crossover azimuth reduces the 2/rev longitudinal loads, for a coaxial rotor pair. For minimizing
overall vibratory moments at the C.G., crossover azimuth corresponding to minimum 2/rev thrust is chosen for all the
coaxial rotor pairs. It was observed that when interference is not included in the model, vibrations at the aircraft level
are almost zero for pitch phasing and very low for the roll phase mode. However, when interference is included pitch
phase is no longer a free parameter. With interference modeled, the 2/rev forces for the cross-configuration are ∼65%
lower than the plus-configuration, while the 2/rev moments are ∼70% lower.