Well, in FSX the prop disk rotation isn't quite smooth. I call it a "hiccup": propeller disk spins round and from time to time flutters. To observ this try the stock DC3, Military Surplus skin. The black propellers in this skin demonstrates the "hiccup" very good. Or rather bad.
We decided to make the propeller disks solid to avoid this effect.
BTW the solid disks are what we observe in real life using naked eye.
MS developers have left some notes in the SDK about need for better solution with regard to propeller rotations.
Similar notes refer to wheel rotations. Tires like to stop their spining right away the aircraft is in the air, even 1 inch above the ground. I managed to fix this at some degree but what I do expect is official FSX update. Let's hope we will get it fixed soon.
PS. Yes, I know the FS9 converted aircrafts don't have this problem. Don't ask me