[Mr. K]

thank you!

I even thought about using a big RC airplane engine

I am building an electric helicopter (drone) and want to recharge the batteries in-flight

Any engineers here want to get in on the ground floor of a new company?

[Yo-Yo]

As an RC dabbler, I'd say you're better off just putting in bigger batteries. LiPos cannot be charged while they are in use, and must be charged through the balance port. Also the weight penalty of a gasoline motor and generator would far outweigh the weight of additional LiPos.

But the concept of a motor-generator in a quad copter is intriguing, and I'm sure it's been done before, but since it isn't commercially available, there must not be enough duration or payload to make it better than a LiPo powered quad copter.

As for just a glow powered helicopter, heck, there are literally thousands to choose from on the market already.