As we have said, find some glow power flier help.

Your 72 meg radio is fine , no reason not to use it. I fly them all the time, just DON'T forget the freq. pin.

I think I would try a 10x6 or 10x5 prop on that 40, but I would do some testing before flying it.

4 minutes would be an electric flight. You can probably get closer to 10 minutes and if the throttle hangs up you will probably think you are up there for a hour. ENJOY !!! RED