When the wankle was first mfg I flew two or three of them. They are really smooth. So smooth that I held one with my hands while we started it and ran it at idle only. Try that with a piston engine. The Wankle was .40 with the equivalent power of a .30. It burned an excessive amount of fuel. It is very heavy. I think the wankle was originally designed in Germany. When they gave up the Japanese bought the right to produce it. They finally gave up. The engine was too expensive to mfg. They remedied the fuel economy but more expense and weight.
That is about all I know.
Lee