O.K., Claude, I understand now what you are saying. I was under the impression that you said the 48" prop produced a slipstream about 50 mph faster than the airplane was going, and that the 50" prop produced one only 10 or so mph faster, so that confused me. Sorry for the misunderstanding.
Syd Claude Wheelbarger wrote: > > I understand what you are saying about the wider prop wash, but I can't > > understand why it would be wider. > > I do not know either. All I have been able to get in the line of an official > answer from the prop mfgr was that the lower pitch props had a wider > propwash than the higher ones and that it was normal. He just couldn't > explain it to me plainly enough for me to understand why.... (sigh) > > >Also, I can't understand why the 48" pitch > > prop would put out faster moving air than the 50" pitch prop. > > It doesn't, What I am trying to say is that since propwash (regardless of > prop pitch) is higher speed air than the ambient air you are moving through, > the 7148 spreads it out wider and exposes more of the plane to it. It > exposes enough of the plane to encompass the mains and nose gear and the > 7150 doesn't. Put your hand out the window in a glide, hold it there and go > full throttle. Even before the plane can accellerate your hand will feel a > significant drag increase since it is in the propwash. So does any other > part of the plane that is within the propwash. Look at the surface area of > your hand and then imagine the surface area of the gear. If I fly with my > 7148 my gear is included in that additional drag because of the wider "wake" > of the prop. If however I use my 7150 the gear flies through clean air > because it's "wake" is narrower. What made it notable enough for me to share > it with the group was that even though the 48 was supposed to have better > climb than the 50 it didn't because it created enough additional drag on my > gear, MLG lights, and inboard wing area to kill it's own advantage over the > 50. > > Claude
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