can someone tell me an accurate formula to figure out MPH based off prop pitch & diameter, I know it will only be a guesstimate as drag increases with speed. here's what I'm figuring,
8x3 vs 8x4
on the bench with an 8x3 I'm pulling 18,000 rpm so if I take 18000x3 =54000(inches per min)/12= 4500(feet per min)x60=270000(feet per hour)/5280=51.136(MPH)
so if that theory is correct using an 8x4 prop if on the bench I was pulling 13700 RPM the plane would be traveling at the same speed. right? but useing the 8x4 would allow the engine more room to unload in flight. potentially giving the plane a faster top speed, right? if that is correct where does the diameter of the prop come into play? if I could pull 18000 rpm out of a 7x6 what would that do for the speed? what about a 9x3?