My brother used to have RC airplanes. Gas is messy, and starting even a single prop was a massive pain. Motors are also less laggy, and probably easier to precisely control than engine throttles.

Now, that's for small scale drones flying 15 minutes. For, say, commercial airplanes that can fly 18 hours, energy density becomes a major factor.

Great idea if you have robust controls! Terrible idea if you don't, because a crash can handily result in a fire or an explosion.

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 principle cost is loss of hover capabilities.

Yes, but the motor (turbine) to run kero is more expensive than the motor (piston) to run petrol.

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.

> also I believe if you want to be pedantic, if it runs on combustion it's a engine. if electric then a motor.

I think that might be less general than you think: General Motors hasn't exactly been known for their electric motors the last few decades.

Also see: https://en.wikipedia.org/wiki/Engine

"Motor" is commonly used for rockets too, eg:

https://en.wikipedia.org/wiki/Model_rocket_motor_classificat...

The motor/engine dichotomy is blurry at best.

However "reciprocating engine" has a clear usage preponderance over "reciprocating motor":

https://books.google.com/ngrams/graph?content=reciprocating%...

Given the line of sight limitation for drones, gas power does not add much value. Batteries are usually sufficient to map/photograph the area within range of the operator. Given this limitation, it is often more economical to hire a small plane like a Cessna with an avionics package and a 400 mi range.

Tech Ingredients YouTube channel guys did this. They used two two-stroke RC engines to reduce vibrations, and can apparently get close to 2kW.

Build: https://www.youtube.com/watch?v=1yB49G756OI

Generator tests: https://www.youtube.com/watch?v=7zMPodObo-Y and https://www.youtube.com/watch?v=uf78udpz3aI

Not sure how well it'll work in practice but fun build.

This one is better: https://www.youtube.com/watch?v=wS0Hr2lw604

> With petrol’s energy density, why not make gas powered drones?

They exist and are used for long distance drones.