Holzsager, Jonathan Elliot. The effects of coaxial propellers for the propulsion of multirotor systems. Retrieved from https://doi.org/doi:10.7282/T3D79FJ6
DescriptionMultirotor vehicles offer access to the skies for users across all walks of life and industry due to their simplicity, availability, and low cost. Although advancements continue, developers are slowed by the limits of available propulsion systems. Coaxial rotors stack propellers over one another to provide more thrust without increasing a vehicle’s footprint nor battery voltage. Previous investigations studied the thrust lost to coaxial rotor systems, wherein downstream propellers produced less thrust than their predecessors. This experimental study examines the effects of propeller spin direction, separation distance, motor speed, and propeller pitch to explore different methods of recuperating thrust losses. During testing, each propeller’s thrust, current draw, and rotational speed was measured. Results show that for 13-inch propellers, reducing the distance between the planes of rotation from 8 to 2 inches produced variations up to 123 grams of thrust, representing a 4.5% improvement. Controlling the motors’ speeds independently confirmed that a coaxial pair will provide thrust most efficiently if the back (downstream) motor is operated at a higher throttle setting than the front (upstream) motor. Similarly, a coaxial pair will provide more thrust if the back propeller’s pitch is higher than the front propeller’s pitch. This was applied to the effect that the back propeller in a coaxial pair provided 119% of the thrust of the front propeller. This allowed for a coaxial pair’s thrust to range between 1790 and 2530 grams, allowing for a 41% increase in thrust from the worst case to the best case. When varying propeller pitch was applied to six different arrangements of four propellers, maximum thrusts ranged between 2960 and 4010 grams. One of these coaxial quadruplets was tested to provide a total of 401% of the thrust of its front propeller.