Thanks for the informed response, bob27. So is it possible to come up with another powerplant that will not impose the mass penalty of a Stirling engine?
What about a turbine? A turbine is certainly more lightweight than a piston engine, because it operates in a steady state mode. There are microturbines used in R/C model aircraft, and even in UAV drones too. For example:
Couldn’t this approach be used to improve paramotors?