Experimental Study into Optimal Configuration and Operation of Two-Four Rotor Coaxial Systems for eVTOL Vehicles

Coaxial rotors are utilized in multirotor aerial vehicles for the added thrust compared to independent rotors while keeping similar area footprints; however, performance losses should be considered. This experimental study analyzes the effects of varying motor duty cycle and propeller pitch values in motor-propeller systems with two to four coaxial rotors. The results demonstrate that in a two-rotor coaxial system, to lessen the adverse effects of a front rotor's backwash and operate at the maximum performance, only the back motor should be operated initially up to 75% duty cycle before using the front motor up to its 75% duty cycle. Additional thrust requirements should be generated from the back rotor and then from the front rotor up to their maximum duty cycles. In two, three, and four-rotor coaxial setups, total thrust output generated is 1.6, 2.1, and 2.5 times the thrust output at system thrust performance of 86%, 76%, and 66%, respectively, of that of an isolated rotor. In a four-rotor coaxial setup, the maximum system performance is achieved when the propeller pitch values gradually increase from the first to the last rotor. The gradual increments in propeller pitch values also result in more uniform thrust sharing among rotors.