RE: Don't forget, your prop is an airfoil
Hi Combat pig, I can't answer any questions regarding that article for you, I didn't write it, just retyping it here. However, I have owned more than one airplane that flew significantly faster than the theoretical speed of the prop said it should be able to. It's not hard to see that though when you consider what an airfoil does, it is creating lift, or in the case of a propeller, thrust. It stands to reason that a propeller SHOULD move forward more than just it's pitch will allow when it is generating lift, same way a wing on an airplane allows it to fly. It would be cool to have somebody who is a professional aerodynamicist be able to explain prop efficiency to us and why they don't follow the "theory". The "theory" does not ever take drag into consideration, yet I don't think there would be anyone denying that a prop that should do 100mph according to theory would need a 0 drag airframe to acheive that (impossible) yet there are plenty of 100mph airframes out there that are flying that speed with props that in theory should only be doing 100mph.
A typical sport engine doesn't unload that much in the air, still not enough in most cases to match a real airspeed with a theoretical prop speed, but there are many airplanes out there that are flying faster than the prop should allow. There is more going on with a prop than a simple screw thread working it's way through the air. Unfortunately I don't understand any of it, I just know what real world experience has shown me.