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With the Sensenisch 3-blade ground adjustable prop I recorded the following static WOT RPM:

Elevation (feet MSL) Pitch 1 Pitch 2
920 5200 4950
20 5400 5150

Same prop, engine (912UL) and aircraft, the lower elevation data 13 months later.

The question is this: wouldn't one expect static WOT RPM to be *less* at sea level because the atmosphere is denser and thus there is more drag on the prop? The Bing compensates for atmospheric pressure differences in mixture, right?

Obviously there are other variables (I'm thinking fuel quality) but in theory shouldn't less dense air mean greater static rpm?

Incidentally at Pitch 3 i know see 5010 rpm, which will be my starting point for flight tests.
  • Re: Prop pitch and field elevation

    by » 7 years ago


    Hi Adam,

    There are actually a few variables. At sea level the engine breathes easier and makes more HP than at higher elevations. You lose approx. 3% of the engine for every 1K'.
    Wear within the carbs may allow a tad more fuel. Any maint. done along the way i.e. carb sync. Atmospheric conditions from one time to the other. I wouldn't worry about it. I usually suggest to set the engine WOT rpm at 5600-5650 at a pilot's average altitude because sometimes we fly higher and lower. Since we can't adjust the prop in air we have to pick the best balanced all around rpm.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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