There used to be a line in the aircraft.cfg file (back when that was the only cfg...) that controlled prop animation. You could speed it up, slow it down, or even reverse it. I found that line once in the Eviation Alice (its props run in reverse on-screen), but now I can't find it. I'm pretty sure it was in the Engines file though.
Edit: I found the reverse lines, but I don't see anything in the SDK docs about animation speed.