Is it possible to use ardupilot to control quadcopter with 4 gasoline engine?

Hmmmm.I’ve got a couple of old Syma S33 coaxials which I could butcher mercilessy.

All I need is time.

I have one of those too. It is a different concept though. It uses a flybar and the top rotor for stabilization of the head, and a fixed pitch design.

A coaxial with CCPM mixing, I’m pretty sure, the tandem heli code in 3.6-dev can fly. Pitt did it with his synchrocopter and it is pretty much the same concept except the rotors being inline with a coax. Once you get away from the multirotor concept of throttling motors for stabilization, and think outside the box a bit, combustion engine power becomes more practical. Here is a turbine powered coax UAV, although I do not know what software is being used to fly it:

Being the above coax is from 2006, which was pretty much before the electronic stabilization systems we have now came along, it might not use any electronic stabilization at all. And was built using twin flybar heads. I could not really see the flybar linkages in the video, but I think that’s what it might be.