I carve my prop as needed from a long time.
But I still have this question. For example, I use an APC 10X9 on my OS.55AX with ultratrusth muffler (Viper 500). I want to try a 9.5X9. Do I simply cut tips by a 1/4, or I carve the prop and tip etc.... to look like an original prop?

Would it be efficiency as a real APC 9.5X9 (I know, it not exist)?

I would cut them off neatly and square, then clean the cut face and edges with 600 grit paper. I use it wet. Rebalance and test. A square tip is not all that bad for efficiency. You will lose a tiny bit of efficiency but maybe not enough to care. The more you clip off the more you can hurt the efficiency if you do not properly reshape and verify the pitch with a gauge. But to reshape the tips you must know what you are doing, otherwise your effort may cause more trouble than good. If the 1/4" off is not enough, try a 9-9 or maybe 9-10 (?) prop to see if you are going the right direction.

Just my thoughts.

MJD

Thanks for the answer. Ok square at tip.

I will tach my original APC 10X9 firts and reduce the diameter by 1/4" at the time. I want something like 14 000 - 14 500 on ground. If finally the diameter is 9", I will order some.

I use Ultrathrust racing muffler on my OS.55AX. The engine at the moment don't rev enough, It takes a lot of time to the engine to go on tune and gets extra rpm... I will help him a bit!

There are guys running 10 to 15% on the same plane, engine and tuned muffler as you. They have been using the APC 10X9 and 10X10 with the best results with the latter.
It should be turning that prop just south of 14K. A Viper or cleaner plane is about the only time that engine/muffler combo will use a 10X10 effectively(almost too much prop). On most sport planes the 55AX's sweet spot is 14,300 on the ground with stock or tuned muffler. This engine develops the most power at 14,600 due to port timing and falls off radically after that, so if you can get everything together at terminal speed at that point, RPM, prop, pipe/muffler etc. you know you are there.