I flew mine two weeks ago with an OS 70 4-Cycle swinging an 13x7 prop... plenty of authority... some yaw on full power climbs. I'll adjust the thrust line with washers to correct. Flies great at 1/2 throttle. No problem with the landings 1/4 power until the main wheels touch... power off to slow down until the tail drops... full aft stick to hold the tail down until parked.

Only complaint is the fiberglass pants... minor off field landing after engine died... wheel pants caught the grass and the plane tipped up and crushed the pants... fixed with some work.

I would not fly this plane with a smaller engine but based on the power difference a 52 would be plenty. I just wanted the extra power. I have pictures posed: http://www.webmasterphoto.com/geebee

I'll be flying mine with a buddy who has the same kit with an OS 52 4-cycle on the weekend of May 17th. I'll post some video clips of the flying for high bandwidth readers to see the comparison.