I used to fly a OMP yak 65 with a 91fx engine. The prop was an APC 15x4w. Now this engine is damaged and I am replacing it with an OS 91 four stroke that I had laying around. Whats the equivalent prop for this engine for similar performace? I would not mind buuying a new engine whats recommended in the new 2 strokes? Perhaps a 120AX? Not been flying glow for almost 2 years so little out of touch with it.

The 91 4S would be a little weak on the 65 yak but the new 120 ax would be the ultimate ticket! I have my eye on a 120 ax myself. As for props on the 91 4s I'm not sure but would guess maybe a 14-4 to 14-6 might be good.

Mike whats the recommended prop for the 120AX?

i was wondering the same thing. i just ordered the O.S. 120AX of my new yak 65 arf and im not sure what prop would yank this plane around really nice for some sick 3D.

Believe it or not the new 120 AX will swing a 17-6 with authority. That's what I'm using on my setup. Huge difference from the .91 FX.

Mike, what prop would you use on the Yak with a YS 110? How dose the OS 120 compair to the YS 110 for 3D?

I use a 16-4W with 20% fuel on my YS 110 and Fusion combination. I get instant throttle response with this setup. Many folks also use the 16-6 with the YS 110 and like that combo a lot as well. Many of those folks do run 30% nitro as well. Hard to compare but I'd say the OS has more total thrust but the YS has faster throttle response.

AFSalmon, I read on an earlier post you were using a 17-6 with the O.S. 120ax. Have you changed or was this a typo. I'm fixing to order some props for my 120ax Yak combo.

You are correct! I did make a typo above and just corrected that. I use the APC 17-6 prop on my OS120 AX. I have found though that a lighter high quality wood prop such as the Vess 17-6 performs much better than the heavier nylon props.

Mine flies nicely on an APC 17x6 with a 120 AX. Bags of thrust and a pretty good throttle response. The engine is still new so I am running rich and have yet to play with the slow running settings.

ys 110 16x5 30% nitro on my fusion . same thing going on the yak 55 (omp)