I have seen RC helicopter powered by 2-stroke gasoline engine. I wonder why there isn't any Drone use that engine, it basically provide more fly time, more lift power and short "charge" hours.
The first commercially available one I know of (no longer produced):
http://www.curtisyoungblood.com/legacy-product-support-curti...
A knock-off of the Stingray:
http://www.hobbyking.com/hobbyking/store/__77122__Assault_Re...
A big exception: this thing is massive and works with nitro and 2-stroke engines:
http://www.curtisyoungblood.com/legacy-product-support-curti...