I think you will find that hybrid vehicles only make sense where the peak power required is much larger than the average power.
Automobiles can fit this because of considerable start-accelerate-stop driving in towns. Even at that, I read a road test of the Ford hybrid small SUV today. In-town fuel consumption was quoted as 30 mpg (US), while highway driving was quoted as 26 mpg - all provided by the gasoline engine. In-town the peak power was supplied by electricity, speeds were low, and there was probably a lot of sitting stationary in traffic.
Aircraft have a much less difference between take-off and cruising power requirement. They don't sit idling in traffic
And your suggestion of 2800 watts is
way too small. That's roughly 4 horsepower. What plane will cruise on 4 horsepower? And batteries aren't light.