ORIGINAL: priyasman
Pitch speed for a 6" pitch prop @ 15,500 rpm is about 93 mph, and 102 mph @ 17,005rpm. RPM x pitch=speed approximately, and that's with 100% prop efficiency. Where did you mount the pitot tube?[sm=confused.gif]
put the calculator away.... pitch is not the only factor with prop performance. (I will not go into a course on prop design here, but this is true).
Common example: Many 424 sport Q-500 aircraft are well documented at flying up around 110-120 mph in level flight - that, with a TT40 Pro engine, turning a 9x6 prop, with ground static rpm around 16,300. Figure with the required stock, untuned muffler, it unloads to appx 17,000 in a straight line level flight.
Sanity check here.... a good 424 combination can fly 10 laps (2 mile course) in about 1:20 (somtimes as low as 1:15). That is 80 seconds, or 1.33 minutes, for what is essentially (due to the way you fly it) 2.5 miles of flight path. That comes to about an average 112 mph, on the race course, turning, slowing, and accellerating every 3-4 seconds. So one would expect, in clean, trimmed, level flight over an extend distance, that approaching 120 mph is not unreasonable (and has indeed been varified)
Doing a simple pitch/rpm regression - 120 mph is 2 miles/min; 10560 ft/min ; 126720 in/min. That divided by 6" pitch, would regress back to 21,120 rpm. And I think we know that the TT40 is not turning that, even on a really good day
So the logical conclusion, in this simplified example at least, is that the prop is doing more than "pushing" the plane forward 6" with each prop revolution.