ORIGINAL: anotherhobby
Putting the 52 4S in the avistar is not intended to add more power (46ax) but really a preference in sound and a slightly extended flight time. I am more concerned with a slight power loss. Am I correct in thinking it will climb better with a 4S but lose a little speed?
The flight characteristics can be maintained if you prop the engine similarly to your .40 LA. This could be a challenge, however, as the recommended break-in prop for the RFS .52 is 12x5, and this could cause ground clearance issues for you.
This engine is slightly heavier than the .40 LA also, but only by a couple of ounces.
Have you considered that you might improve the sound quality and flight times of your Avistar by switching to a ball-bearing .36 engine? This could also lead to an improvement in power if choose a Thunder Tiger Pro .36, for example.