RE: Using a DF OS .91 as a prop plane
r-c-guy,
My Rossi 105 DF-engine turned APC 11x8 at only 16800 rpm with a muffled pipe, and I got afraid the prop will explode any time. APC at 11" diameter should never be turned faster than 17300rpm static. The APCs are rpm limited to 190000/diameter. So if your engine is so powerfull then you should only use CF props.
Thanks, Amir