i have a cap 580 with a saito .82 engine. im currently running a13x7 pop and would like to upgrade a little... What prop do you reccomend i use for solid aerobatics and mild 3D flight???

A 6" pitch blade could do better, maybe APC 14x6 or graupner/vess 14x6,if you are using MA,drop it and try something else. props will make ALL the diff.

I'm running an OS .75 AX spinning a 14x5 ACP

Try an APC 13x4 W prop. The wide blade will give you more thrust for aerobatics but slow your stop speed (not that you want to use this thing as a racer).

I ran a 13x4 on my YS-63 powered Cap-580 and it was outstanding. The .82 might even pull a 15x4.

I need some advice: I have a YS91 engine and I want to see if I buy this plane, could I use the YS91 or is it too big for it? I just don't want to spend more money on a new engine if I can use the one I have...

Any comments or suggestions will be appreciated.

Thank you

Modern YS are lighter than most other 4 strokes. if your .91 weighs in similar to the saito .82, and pysically fits, go for it. Its not a good 3D plane, if that is what you want, put the YS on one of the popular profiles instead

Thank you for responding! The YS91 weighs about 150 grm more than the Saito .82 ... Also, it a bit bigger in dimension, a couple of mm here and there, but not too much bigger, I think it should just fit in the cowling. Also, maybe I can put one of the servos back in the tail to counteract the extra weight in front... that way the plane is not too nose heavy.