Curious why the Wankel engine never took off in general aviation? A lot of the advantages of the Wankel engine seem like they'd be even more important in aviation: high power-to-weight ratio, can fit in small spaces, higher RPMs, no vibration, can use lower-octane fuel, reacts quickly to increased power demand, etc. The disadvantages - poor efficiency, poor emissions, and maintenance issues with the seals - are pretty big, but it seems like they'd be less of a problem with general aviation, where planes are used a fraction of the time that a family car would be and already have significant maintenance expectations.
They didn’t catch on for all the reasons you state:
* High RPMs are bad in a aero engine. There are very few (no?) propellers on GA airplanes which operate above 3k RPM, so you need a reduction gearbox. That cuts into your weight savings and also reduces reliability.
* Vibration isn’t a significant concern for GA airplanes.
* Throttle response is not a significant concern in GA-sized reciprocating engines.
* Poor efficiency is a major problem because 1 lb of extra fuel is 1 lb less payload. All airplanes are limited by takeoff weight. (The 3000 HP-class radials built by Wright and P&W at the end of WWII are some of the most efficient reciprocating engines ever built)
* Maintenance is a huge concern for GA owners because labor costs $200/hr. Airplanes with 1200 TBO engines sell for a noticeable discount to airplanes with 2000 TBO engines.
