I have a goldberg ultimate bipe that has an OS 120 surpass III pumped engine on it and I need to know some prop recomendations for it. I plan to fly IMAC style aerobatics with it and maybe some 3D once I get use to flying it. I have never had a 120 size 4 stroke but have had many 91 size. Let me know what you guy's think.

Rick

Start with a 15-6 or 15-8 that should be close. An APC will give a little better power but a MAS will work fine. The APC does not slow down the airplane like a MAS but this is not an issue with a bipe.

I would go with either a 15x8 or 16x6 APC.