Coupled Pitch-Lag Hinge for High Inertia Electric Rotors

As rotor diameter and inertia increases, the quickness of the thrust response to pilot inputs slows, yielding negative implications to handling qualities and limitations on scaling electric propulsion. This study presents a novel approach to alleviating these scaling effects by introducing a pitch-lag coupled hinge to the root of 40" and 50" diameter props. The impacts of chordwise hinge placement and hinge angle are examined and compared to a baseline rigid rotor to provide physical understanding of the rotor dynamics. It is shown that a coupled hinge can be designed to maintain propeller efficiency for a design thrust, while increasing the sensitivity of thrust to rotor speed and the maximum thrust of an RPM-limited rotor. Finally, the dynamic implications of this are tested using a first-order motor model. When a 40" diameter trimmed rotor is set to max throttle, rotors with a coupled hinge angle achieve a 6% higher thrust in 9% less time. The dynamic response improvement scales favorably when the rotor diameter is increased. For the 50" diameter rotor, the introduction of pitch-lag coupling reduces the time constant of the rotor’s thrust response by 32%.