Well, guys, I think you should look at this a little differently.  The rotational tip speed pf the prop is at right angles to the forward speed and should be added  vectorially.  As a result, it adds very little.  For example, a 72 inch prop turning 2400 RPM going 180 MPH results in a rotational speed of 6' times pi or 18.85 feet per REV.   Now, the forward speed  in that length of time (1/30 of a second at 2400 RPM) is only 8.8 feet.  Add those vectorially (the two sides of a right triangle) and the result is 20.8 feet per rev,  almost within 10% of using RPM only.