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Thread: HP/Prop pitch ratio??

  1. #41

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    Whenever I see reports of exceptional GPH I wonder if the aircraft is using a tachometer with the proper average RPM for tach time. If one Cub guy uses a 2566 rpm clock and another uses 2300 rpm unit we'd expect the GPH report to vary even where actual consumption is identical. Not saying that's what Nimpo's got going, just saying.

  2. #42
    this would be a title NimpoCub's Avatar
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    Sure wish I understood what you're talking about!
    I replaced the old tach with a new SW aircraft tach, and the RPM readings were identical, so I THINK it's accurate. Also think that over 20 hrs of flight time would give an accurate fuel burn, no? I consistently bought less fuel than the bud's 0320 - 160. (I used the total GPS time from all flights)

    Pleeze advise where the doubt/inconsistency could be??
    Nimpo Lake Logan... boonie SuperCubber
    200mi (300km) from nearest stoplight... just right! - "Que hesitatus fornicatus est"

  3. #43

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    Nimpo,

    Aircraft tachometers report rpm on a direct drive basis so all tachs should indicate rpms accurately but those same tachs record tach time using a reduction unit and there are different tach clocks available for different engines and airframes. For instance, a 185's tach will appear identical to a Cub's tach but the clocks are set to 2566rpm and 2300rpm respectively. If a guy puts a 185 tach in a Cub his tach time will accumulate better than 10% slower while the rpm indications will still register correctly. Tach time is a product of total engine revolutions, not seconds and minutes of operation, and a tach's total revolutions rate is assigned by the average engine operating speed. A similar deviation exists in Hobbs time since some guys start the clock when the engine starts while others use squat switches. In any case there's error potential when comparing per hour rates between airplanes.

  4. #44
    this would be a title NimpoCub's Avatar
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    OK, I see what you meant (suspected that, so I included: "I used the total GPS time from all flights").

    This just confirmed my fuel burn from when I flew 3 hrs to get to Kraploops & Bart poured in 15 gals. I asked him if that was possible, and he said yep. (paraphrased)
    Nimpo Lake Logan... boonie SuperCubber
    200mi (300km) from nearest stoplight... just right! - "Que hesitatus fornicatus est"

  5. #45
    skywagon8a's Avatar
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    Quote Originally Posted by Aviator View Post
    My IO-360 pretty much agrees with this chart when leaned.
    N1PA

  6. #46
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    Click image for larger version. 

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    Last edited by Aviator; 02-28-2015 at 01:46 PM. Reason: finger trouble

  7. #47
    TurboBeaver's Avatar
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    Nimpo,
    I would pitch your prop up to a 44" pitch as it sounds like you have a pretty strong engine, expect it to cost you an extra 50' getting off the water, I bet it climbs out 150' fpm better, and gains you around 3/4 mph, But I would expect to see around say 125 less rpm static.
    I had a 82/44 on a cub that was a 160 narrow deck from an Apache, that we stuck 170 pistons in .
    However it originally had a 82/41 same as you do, it got off good, but thats were it ended, if you didnt run it right up to 2500 for cruise it " dragged its ass in the air..... not cool. SO I put on a new 44 pitch, bingo ! Got off 99% as well, climbed better, cruised little faster, and set right up rock solid at 2350 no tail droopy jazz what so ever, nice tail high Cruise attitude, you will be pleased, (garanteed!)
    E
    Last edited by TurboBeaver; 02-28-2015 at 06:14 PM.

  8. #48
    Aviator's Avatar
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    An oft-overlooked way to get a bit more RPM - and pwr. - for just a few $$ is by getting the front-end dynamically balanced.

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