> > Claude, I agree that the prop wash air is moving faster that the clean air > outside the prop wash. It's just that you seem to report that the 48" pitch > prop creates more thrust than the 50" pitch prop that has me wondering. Any > aeronautical engineers out there? > > Syd > I really suck at this... like an electrolux on fast forward (grin) I don't know which creates more thrust. My direction was that the propwash from the 48 spread out much wider and much sooner exposing more of my plane to it than that of the 50 pitch. It included my nose gear and mains along with more of the wing than the 50 did. Enough so that the increased drag on the exposed parts and killed it's climbing advantage over that of the 50 on my particular plane. We re-ran the same tests on J.T Hartzler's coupe on Saturday. He has the same MLG lights but we skipped the pitot static tests and just looked at max cruise speed with and without his MLG lights and snubber cable. He saw a 3mph gain overall (indicated) by pulling the cable and lights with my 7150. However with his 7148 he got a 5-7 mph gain max cruise with the goodies removed. Also finally got a reply from mccauley. They said it's not just their prop and that's normal. He said to look at the wake of a boat with a pulling prop and one with a speed prop. A flatter pitched prop almost always has a wider dispersion angle and that "rounding the tip alleviates some of this problem" (wow) However this leaves the rounded part doing less work even if it is moving the fastest and then you have to increase the length to compensate.
Gald I'm in electronics instead of engineering. Claude PS That sensenich I liked so well had those round tips...
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