Heavier fuels (kerosen, a/k/a jet fuel, diesel) have equivalent energy density to petrol, but are far less flamable. You might get a small fire, but not an explosion. And there are a lot of RC aircraft already.
They are noisy, however. Drone buzz now is simply from spinning fans. Adding a reciprocating motor to the mix is all the louder.
The alternative is lighter airframes and solar power. For quads / octos, probably not viable, but for a prop-driven fixed-wing craft, a very small amount of thrust to counter gravity could be quite effective. Expanded polystyrene or similarly light body, solar cells over all horizontal surfaces, and an ultra-lightweighted controls and imaging payload. That would allow for long-duration flights at least in daylight.
The low-energy use would also make battery-powered night flights more viable, certainly beyond 15 minutes.
The motor to run the drones was expensive till they became mass produced and dropped in price. Same for the batteries. DJI Drones aren't exactly cheap either.
also I believe if you want to be pedantic, if it runs on combustion it's a engine. if electric then a motor.
