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Heidi Johnson wrote:
20% [or rather 80% efficent] isn't really that huge, I think the norm for a run of the mill fixed prop is in the range of about 85%, Paul Lipps posted a note someplace just recently saying his props's
are just over the 90% [ I think] so.. it's a decent [conservative] ball-park number anyway..
Jarrett Johnson
It's a notoriously difficult number to nail down, because it depends on how fast the engine is turning and how fast the airplane is moving. The figure is 0% during the run-up. Go to altitude and pull throttle in a dive, the figure can shoot up to over 100% (right after the wings come off). I would think a conscientous manufacturer like Catto would quote a typical figure that would include a balance of climb and WOT cruise performance, the former being low and the latter much higher.
When it's all rolled up though, I don't think the numbers that Joe is quoting are all that far off. If he was getting 80% efficiency, it would indicate the prop is pitched at 91". If he were reaching 95%, the prop would be pitched at 77". Add in a few other fudged factors, like where the pitch was measured as Joe has already mentioned, and everything looks fairly reasonable.
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,|"|"|, Ernest Christley |
----===<{{(oQo)}}>===---- Dyke Delta Builder |
o| d |o www.ernest.isa-geek.org |
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