ORIGINAL: combatpigg
Mark, thanks for hanging in there with me, but I don't think we are on the same page yet.....If this scenario can be played in mathematical reverse, a plane traveling 200 mph with a spinning prop would be going faster than a 200 mph plane with a prop that is not moving. If the seperate motions are additive, what I propose must be true, but I surely know that this is non-sense!
Ah! Now I get it. The fact that the prop is spinning has no effect on the plane's speed. We were talking about prop TIP speed and that it is a composite of the rotational speed and the forward motion of the aircraft. How fast the spinning prop will pull the airframe has to do with RPM, pitch, drag, etc. The prop is rotating only because that is how it makes thrust to move the airframe through the air. The fact that the tip is moving faster than the airframe does not make the plane go faster.
What you need to do is shift your reference point to see this. If you are sitting on the nose of the plane, you see the air coming at you at whatever speed the plane is going. Now imagine you are sitting on the tip of the prop. You will see the air coming at you with the velocity from the rotation, plus the velocity from the forward motion. The only trick is that the two velocities are at right angles to one another (one forward, one in the prop plane), so they do not add directly together, but end up combining to make an angle. Think of a north wind being added to an equal velocity east wind. You end up with a wind direction of north-east and the total wind velocity will not be twice either, but actually 1.414 times one velocity, acting at 45 degrees (the north-east direction).
The question really was, can a prop turn TOO fast? And the answer is YES. When the prop tips start to close in on the speed of sound the efficiency falls off and it gets hard to make more thrust regardless of how much power you throw at it.
Mark
*edited because I can't type...*