Performance Comparison of Quadcopters with Variable-RPM and Variable-Pitch Rotors

Use of variable-pitch rotors was compared against variable-RPM rotors on a 2kg ( 20N) quadcopter. To generate 5N of thrust in hover while maintaining a 2:1 maximum thrust-to-weight ratio, the variable-pitch rotor required 29% more power. At low climb rates the variable-RPM rotor requires less power, but near its maximum rate it required more power than the variable-pitch rotor. The maximum climb rate for the variable-pitch rotor was up to 70% greater than the variable-RPM rotor. A quadcopter equipped with variable-pitch rotors required more power to operate compared to the aircraft with variable-RPM rotors over its operational airspeed range. The variable-pitch quadcopter required 30% more power at best-endurance speed, and had 18% less range than the variable-RPM quadcopter (at maximum-range speed). The 1/ rev root drag shear was 42% larger for the variable-RPM rotor, and the 2/rev H- and Y-forces were 37% and 50% larger. The 2/rev thrust vibration was 6.5% smaller for the variable-RPM rotor, and the hub pitching and rolling moments were 11% and 9% smaller, respectively. Unlike the quadcopter equipped with variable-pitch rotors, the quadcopter equipped with variable-RPM rotors experienced a beating phenomenon in the aircraft-level vibratory loads.

Reference

McKay, M., Niemiec, R., and Gandhi, F., "Performance Comparison of Quadcopters with Variable-RPM and Variable-Pitch Rotors ,"

Proceedings of the AHS Specialists’ Conference on Aeromechanics Design for Transformative Vertical Flight, San Francisco, California, Jan 16-19, 2018.