AHhhh..........but props and turbines are 2 different concepts whereas props bite the air and turbines compress the air. This is why props are more efficient at sea level and turbines are more efficient at altitude. And I thought P factor was torque. Oh yea, I remember... P factor is that first big drop on a roller coaster . Removal of blade tips prevents them from going supersonic thereby getting more rpm. This doesnt mean you can snip you blade tips(unless you put it in a shroud!). The new blade designs used on the highly efficient turboprops(pushers!) are the ultimate way to go. Our subs use the same design.