COG on round wing?

[Flybyguy]

I am planning on building a plane with a round wing, which is 20'' in diameter. Can anybody tell me where the COG should be?

Thanks,

Brian

[ChrisP]

25% of the way back at the centreline i.e 5'' back from the furthest point forward.
All the 36'' - 40'' styrofoam flying discs with 40 - 60 motors that were so popular in the 1970's were set up this way.