46 size engines work really well on an Avistar. Gives you extra oomph if you need it and the larger prop can act as a brake for landing with the engine at idle. I own mostly OS engines and really like them but I have helped lots of new flyers with Thunder Tiger engines and have found them to be just as easy to tune and also have good reliable power! The new 46AX series is a quieter version of the FX series and it has a touch more power. It would be a really nice power plant for the Avistar. [8D]