we import from china containers with parts for electric bicycles. batteries motors etc. all high quality. also, just for fun, we bought once a few small ICE engines as kit for bicycles. very low quality, lot of noise and smell, unusable in town but for outside with 1 kg fuel it goes faster and further than an electric engine with a battery pack of a few kg... (engines have almost the same weight. ). Although the ice produce more, much more heat it doesn't lead to failure, while the electric one produce less heat, it is causing much failures. but back to planes, a battery less system means you need to add an ice and generator . a combination ice+generator+battery pack+electric engines could be good as the ice+generator can be lighter and deliver less power than the electric engines need ,the battery pack can add the needed power. but the less weight of the ice+generator is lost by the extra weight of the battery pack. in a car who needs a lot of power to accelerate and much less at cruising speed ( although in a Lexus the ice jumps in for extra power with direct drive next to generator and cruising does it almost only on battery. very sophisticated and for a big car (for european/middle east) it uses very little fuel.but airplanes cruise at relative high power setting so the benefit is far less and i doubt the propulsion will generate energy back to the battery when the pilot put his foot on the brakes. (joke). my whole point is its an other technical world i know even less about than conventional ICE-s so I only can look at it with common sense and logic. IMHO and experience that's always a good start.