20 years ago when everyone was driving around Toyota Priuses & they weren't catalytic converter bait, a hybrid airplane would have been the big thing instead of the purely electric airplanes they're trying & failing to build.  The idea is an airplane takes off & lands using batteries while cruising using gas.  The takeoff is a short, inefficient phase which can burn all the battery charge.  The descent & landing can recharge the battery.  The cruising phase would be in the most efficient regime & burn gas.  Most battery charging would be on the ground.  It would need a new kind of piston electric engine.  Maybe the power source could be selected by a clutch, the same way priuses did.

The mane concern is the weight of 2 power plants.  The piston engine wouldn't have enough power for takeoff, in the event the electric motor died.  

In 25 years, all of silicon valley bought PT cruisers, then converted to priuses, then converted to Teslas.  The lion kingdom couldn't imagine buying 3 cars in that time.