Compared to airplanes, helicopters are very complex. An airplane’s rotors only need to vary in how much forward thrust they’re providing, which can be adjusted by changing their speed or the pitch angle of the rotor blades. A helicopter’s main rotor needs to be able to do that and simultaneously adjust the relative pitch angles of the blades at specific points in order to move the aircraft forward, backwards, left, and right. That is handled by a clever mechanism called a swashplate. Tom Stanton recently constructed a drone-helicopter hybrid that ditches the swashplate altogether in favor of a “virtual swashplate.”
Stanton didn’t invent this virtual swashplate concept, which he came across after seeing an aircraft made by James Paulos and Mark Yim at the University of Pennsylvania. That drone-like aircraft is able to fly using just two rotors, neither of which has a conventional swashplate. Instead, the rotors are mounted on special hinges that force the blade pitch angles to change in response to acceleration — either speeding up or slowing down. By controlling the exact moment at which the rotor accelerates, the movement of the aircraft can be steered in the same way that a normal helicopter is via a swashplate.
The hybrid aircraft that Stanton built takes advantage of that in a surprisingly practical way. His design has only two motors: one for the main rotor and one for the tail rotor that counteracts the torque of the main rotor. The main rotor does not have a swashplate or the servo motors usually associated with them in RC helicopters. Instead, the rotor blades are attached to 3D-printed hinges that alter the pitch just like those designed by Paulos and Yim. The main rotor’s motor is equipped with a sensor that lets the controller know its position twice every rotation. By very precisely controlling the motor speed throughout each rotation — from very quick to nearly stopped — Stanton can change the blade pitch angles at the exact point necessary to steer the aircraft. It is amazing to watch and an ingenious implementation of physics, resulting in a surprisingly practical way to fly.