I guessing that it's disadvantages were enough that it never appealed
to big auto makers to work on them. Wankel itself was unable to make
it a success and it's hard to argue that Mazda has either.

How can you say that Mazda hasn't made this successful? Sure, the initial
introduction had it's share of problems, but since the RX-7 made the
re-introduction of the rotary here in the US, the engine has been as
troublefree as any engine produced. Emissions was one of the biggest
problems, but the newly redesigned Renesis engine cleaned that up, as well
as taming a bit of the bark, and overly hot exhaust. Fuel consumption in
aircraft use does not seem to be any worse than any other engine of the same
power range. The truth is that other manufacturers tried the rotary, but
didn't feel like it was worth developing, since they were perfectly happy to
churn out piston engines. Only Mazda seems to have had the willingness to
stick with it, and make it successful.

But converting such an engine for use in an airplane is
not without it's challenges.

Corky Scott

What challenges does it present, that aren't shared by any other auto
engine? Heck, it already has dual ignition. These days, two rotor engines
are not nearly the challenge that some engines would be, because Tracy Crook
sells engine controllers, monitors, and gear drives. Conversion Concepts
makes excellent mounts. About the only thing missing is an off the shelf
intake, and exhaust, which aren't far behind.

Cheers,
Rusty
13B powered RV-3 flying (2500+ fpm climb, 200 mph cruise)
Kolb Slingshot being converted from 912S to single rotor almost as I type