just prchased a cap 580 flatout and would like to know of a good set of servo`s that are compatable with a jr radio .

Hitec's are good and work with Jr.

FERNANDO

I just bought a used Morris the Knife , it had a ST 51 2s , I'm putting in OS 50 2s , the plans don't show where the cg is . Do you have any ideas where to start ?

I don't know that plane but generally most all conventional planes have CG in vicinity of 25-30% back from ld.edge at fuse. Start with that then after flying can if needed move it by shifting things some. For 3D they usually do better with CG back a bit from there.