Cycloidal Rotor Airplane: The Cycloplane

I'll just get right to the point: Why? Don't propellers work fine? How does a cyclorotor even produce useful thrust? You're probably asking these questions, and they were the same questions I asked myself when I started this project. The short answer is: building a cycloidal rotor airplane is a fun opportunity to explore something that's never really been done before with the chance of learning something really interesting along the way.

What is a Cyclorotor?

A cyclorotor is a type of propulsion system consisting of blades that rotate around an axis parallel to their span, or length. The blades pitch once per revolution to maintain a positive angle of attack relative to their rotational velocity so they can produce a net thrust in a single direction. What does all this really mean? It means you get thrust + the blades experience the same air velocity across the entire blade.

Regular propellers need special twist and and taper so that they can generate a relatively uniform thrust over their entire disk area. Figuring out this exact twist and taper for the highest efficiency can be tricky, but the cyclorotor blades see the same air velocity over their entire length, so the blade design can be much simpler. The rotational and high frequency pitching nature of the cyclorotor also allows for much higher blade angle of attack before stalling, which takes advantage of some dynamic stall black magic (I'll save you the details...). Higher angle of attack means lower rotational speed for the same thrust, which means lower noise.

With all of that said, the cyclorotor still has a long way to go before it can out-compete the propeller in terms of performance. Simple thrust tests show that the propeller outperforms my unoptimized cyclorotor design (though, I'm sure an unoptimized 3D printed propeller would also do much worse than a mass-produced injection molded propeller). There are many places where mechanical losses from the cyclorotor can be improved, and I'm sure there's an optimal blade size and shape that I haven't quite discovered yet.

The Cycloplane

I wanted a platform that I knew would fly, so I went with a simple slow-stick style airplane with two cyclorotors on the front. Apparently, I wasn't the first to come up with this idea:

The 'Schroeder S1 Cyclogyro' was dreamed up in the 1930's, but unfortunately never saw flight. This gave me even more reason to see this project through to a successful flight and show that cyclorotors have potential as an alternative propulsion system with unique benefits. But it's safe to say that your airplanes are better off with propellers... for now.

Be sure to watch the video to see how my cycloplane flew, and there might just be an explosive surprise at the end:

https://www.youtube.com/watch?v=iCEGgSJTXvc