Why hasn’t the Wankel rotary engine seen more use in aircraft? The Wankel rotary engine seems to have several advantages over traditional reciprocating cylinder-and-piston designs. In general, they have a much higher power-to-weight ratio, less vibration, and drastically reduced rate of catastrophic failure, among many other benefits. I can only find disadvantages related to emissions and fuel efficiency. So my question is, why hasn’t it seen more use in aviation even though it seems very well suited to this application?
They do not have drastically lower rates of failure than comparable piston engines. Their manifest unreliability in automotive applications is one reason they failed so badly in the marketplace. My college materials science TA owned one and had it rebuilt four times. His record for the shortest distance before failure on a zero-timed Mazda rotary engine was 150 miles.
The breakdown mode was failure of the apex seals at the tips of the rotor due to poor lubrication, leading to excessive wear and scoring and the complete destruction of the seals. According to my TA, Mazda went through more than six fundamental redesigns of the apex seal system but never could completely solve the basic problem.