I agree with Dan. Most of my Flite Streak Jr.'s have had Max .15 steel fins. I have also Tried a Webra Mk-1 diesel that performed well, and one that first had a Rivers Silver Streak, then a FROG .21. The Rivers and the FROG were too heavy and the plane only flew round and round...FAST. I did not want to add weight to balance it so I opted to rebuild the mounts and install a smaller engine. It's still around and currently has a Fox .15X in it.

My FS Jr's are for sport flying so they are built with kit wood, with no effort to lighten them.

One of the problems is that engines have increased so much in power that old 1/2A planes are not large enough for today's 1/2A engines. This ripples up and for a modern .15, a profile Peacemaker is a better match than a FS Jr, IMHO.

George