Why are there no quadcopters on combustible fuel?

Question

Robotics

It would be more powerful and stay in the air longer. For example, the US Army has an RQ-16 drone that flies for 40 minutes. With a weight of 6.6 kilos.

Answer 1

The problem is weight and size. For electric motors, this problem does not exist - a microscopic engine from a silent cooler is (roughly speaking) just a greatly reduced copy of an electric car's electric drive. For piston engines, everything is different - the pressure in the cylinder must be large enough, therefore the cylinder walls must be strong enough, therefore massive enough. Therefore, the creation of miniature (and light) piston engines is a serious engineering problem. In practice, such engines turn out to be either too uneconomical or too expensive (when using heavy-duty materials).
Here, for example, almost a chapel of miniaturization for mass production - 25 cm2. It is worth paying attention to the weight - 730 grams, and the price - $195. Now let's remember that the engine is just one of the many parts of an aircraft and try to imagine how much a UAV with this engine can cost, taking into account the typical price ratios (models) of air (and ground) vehicles and their engines.