RVator,

I also have Balsa USA Stick 40 with strip ailerons with the tri gear.
I also fly off of grass. I started out with a OS 40 LA. Not enough power and a crappy engine IMO.

I do think you need a 46.

I tried the Tower 46's, good power but harder to tune and they did not want to shut off. Even when the carb was completely closed it would still run.

I now buy Thunder Tiger Pro 46's.

I like these engines and you can easily use them in your next plane.

I have them on a Sport and a Somethin' Extra.

Good Luck

Bill