This is confusing. The heli shown is a gasoline-powered machine, as evidenced by the Tygon fuel line and the 2-stroke gasoline muffler.
As Lownverted has indicated, there is no such thing as an onboard generator for an electric-powered airplane to recharge the main (motor) batteries. If that is the goal, forget it, it ain't happenin'.
If the goal (with an electric-powered airplane) is to recharge the receiver/camera/downlink batteries, forget that as well. The complexity and weight of the generator will be more than offset by using bigger batteries.
So, forget the generator idea altogether.
You wanna stay up a long time? Get an 8-foot Telemaster, put a Zenoah G-20 (with magneto ignition, if you can find one) on it, a 32-oz gas tank, and use a couple of 3200mah 2s lipo batteries with regulators to run the Rx and all the onboard goodies. Float around for a couple hours minimum with the throttle a bit above idle. I am working on just such an airplane now, with a G-20 EI, with a 2850 mah ignition battery.
I already have a 6-foot telemaster (my first UAV project) with UNAV PicoPilot, camera/video downlink. Using two 3700 mah 3s lipos in parallel for main power, I can stay aloft for 20-25 minutes at about 1/3 throttle, which ain't half bad for an electric airplane. I downlink video and record on a laptop computer.
My suggestion is to start with a smaller project to learn how to do systems integration. Sounds simple enough to get an autopilot to work with your airplane. Until you actually try it.[>:]
Bob