bstratt
Cleared for Takeoff
Learning about leaning in the Arrow and once again there is conflicting info.
POH says 10.2gph = 75% power, 9.2gph = 65% power. No adjustment in fuel flow for altitude. It also says 75% power cannot be achieved at 5,000 ft but at 4,000 is 24.4 inches.
My normal flights aren't long enough to really experiment but on the 5 hour flight to Norfolk, trimmed up at 6,000 ft, I had the time to do some.
The plane does not have an engine analyzer or even a digital EGT/CHT probe, just the old "needle", so leaning to find peak is an exercise. It does have a fuel flow meter. First discrepancy, fuel flow meter shows 10gph in the bottom of the 65% range and 14gph in the 75% range. So for 75% is it 10.2 or 14.0? The 10.2 book 75% equates to a low, 65% on the fuel flow.
Trying to find best power, I levelled off at 6,000 ft - full throttle was about 24 inches which I figured had to be close to the 75% power range. Pulled the fuel flow back to 9 gph indicated and waited 5 minutes to see where things steadied out, then 9.5, then 10, then 10.5. Best speed was at 10gph, with 10.5 slowing us down a bit. From this it appears the 10.2 book figure is accurate but this was at 6,000 ft. Would 14 be more accurate at sea level?
Without an engine analyzer, which fuel flow number would you start with?
Do you go with the book? The fuel flow? Or just lean for best speed?
POH says 10.2gph = 75% power, 9.2gph = 65% power. No adjustment in fuel flow for altitude. It also says 75% power cannot be achieved at 5,000 ft but at 4,000 is 24.4 inches.
My normal flights aren't long enough to really experiment but on the 5 hour flight to Norfolk, trimmed up at 6,000 ft, I had the time to do some.
The plane does not have an engine analyzer or even a digital EGT/CHT probe, just the old "needle", so leaning to find peak is an exercise. It does have a fuel flow meter. First discrepancy, fuel flow meter shows 10gph in the bottom of the 65% range and 14gph in the 75% range. So for 75% is it 10.2 or 14.0? The 10.2 book 75% equates to a low, 65% on the fuel flow.
Trying to find best power, I levelled off at 6,000 ft - full throttle was about 24 inches which I figured had to be close to the 75% power range. Pulled the fuel flow back to 9 gph indicated and waited 5 minutes to see where things steadied out, then 9.5, then 10, then 10.5. Best speed was at 10gph, with 10.5 slowing us down a bit. From this it appears the 10.2 book figure is accurate but this was at 6,000 ft. Would 14 be more accurate at sea level?
Without an engine analyzer, which fuel flow number would you start with?
Do you go with the book? The fuel flow? Or just lean for best speed?