Cheesy Question
 

Sorry for the noobie question but what is the mathematical name( if there is one) for the rotor? Fat triangle? Puffy triangle?:)

Good question! I think the path the rotor describes is called a trochoid, but I don't know about the rotor shape itself. Obese triangle?!

Hmm... convex faced triangle maybe? The compression ratio will change with the convexity of the triangle faces but the displacement will not. Similarly, the volume of the recesses or "bathtubs" on the rotor faces will change the compression ratio but not the displacement.

I'm sure there is a name for it, but it escapes me. Somewhere at home I have a reprint of the technical paper on the rotary engine that Kenichi Yamamoto presented to the SAE all those years ago. I'll see if I can dig it up.

Thanks very much you guys!

I thought it was epitrochoid...that's what I've always called it

I believe you're correct. For more information that you probably wanted, look here.

But that's the shape of the rotor housing, not the rotor itself, which was the original question. :)

Damn, guess I had it backwards...oops.