Bigger RC helicopters and RC planes are often fuel powered >internal combustion Thing with this is that now you need: a) Fuel tank plus a pump b) A combusti

Bigger RC helicopters and RC planes are often fuel powered >internal combustion Thing with this is that now you need: a) Fuel tank plus a pump b) A combustion chamber c) Gears or a way to mechanically regulate fuel flow ...of which b and c probably need to be metal. For light & small drones you're not necessarily winning here on weight