On Sat Dec 3 20:43 , David Vance sent:
You might recall my post asking whether the average Musketeer could attain
2700 rpm at 8000 feet. The reason behind the question is that the PFS
exhaust is supposed to provide an extra 200 rpm at cruise altitude.
Obviously if the average Mouse can already attain redline rpm at altitude,
there is no need for a fancy exhaust system.
---
Hmmm - my Sport is only 150HP, and it has the original 58" prop.
Level at about 5,500 ft, the engine pulls about 50 RPM over redline (2,700 RPM)
at wide open throttle (WOT.) I have a 4-cylinder graphic engine analyzer, and
the mixtures are very even. I bought an electronic tach, and my mechanical tach
is pretty close.
If I pull back the throttle that little bit to bring the RPMs back to the
redline, the mixtures become very uneven.
So, over several months last year, we all talked about what that meant, and what
could be done. Obviously, I could get the prop twisted a little bit - out to
60", but that would make the climb even 'less' than what I get now.
There's some 'documentation' that indicates that I should actually change the
prop to 56" or less, or reduce the GW to 2,000 lbs to get better climb. NOT an
option.
So, the picture is, if I had more HP, or if the plane was 'sleeker' the same prop
would be overrevving MORE than before, and I'd have to pull the throttle back
even more.
So it seems to me, I can't go any faster than the plane will fly now, even if I
had more horsepower or a sleeker plane, cause I'd have to pull the throttle back
to keep from over-revving, with the associated uneven mixtures.
Jeff, what did you do with your prop?
Bill Howard
BeechSportBill
N1927W 1973 Sport 150
Beech Aero Club NorthWest Region Director
P.S. A little birdy told me the prop was OK out to 2,800 RPM, and I know that the
engine actually LIKES to run WOT (SMOOTH!,) as long as I'm not heading downhill
aand go any farther over that 2,750 in level flight.
---- Msg sent via @bmi.net Mail v4 - http://www.bmi.net
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