> -----Original Message----- > From: Ken Carnahan <[EMAIL PROTECTED]> > >I may want to trade 71-48 for a 52 thants Ken C > -------Claude Wheelbarger wrote: > Ken > I was flying with a 48 in my 85hp 415-C and the engine would just reach > redline in level flight. Went to the 71-50 and it would only turn up to > about 2400 full throttle cruise and it took 250 more feet on takeoff roll > and I lost 100fpm on climb. and gained only 4mph on average. Borrowed a > 71-52 from my local IA and could barely get off the ground. I went from a > 2200 runup with the 48 to barely 2000 rpm with the 52 and could only turn up > about 2250 in level flight.
Claude and Ken,
My experience in an Alon with a C90 differs significantly
(in RPM) with the one reported by Claude and should not be
the result of only 5HP difference. I own both a 71-48 and a
71-52, both recently overhauled, so I know their actual
pitch - the 48 is right on and the 52 is almost a 53. I
also overhauled my tach and checked it in flight against an
electronic prop tach.
Static (runup) RPM with the two props runs around 2250 (48)
and 2150 (52) which are in the range given in the manual.
The "52" does result in 100-200 feet more ground roll and
100-150fpm less climb at sea level. The 52 gives
approximately 4-6MPH more airspeed. However, maximum
airspeed (at 5000ft) is limited by redline RPM of the C90
(2475RPM). I have to throttle back only slightly with the
71-52 prop to stay below redline, wheras the 71-48 will
greatly overspeed if not throttled back.
I use the 71-48 all summer and for mountain flying while the
71-52 is on during the winter for a little more speed.
Regarding C85, C90, and O200 engines, the horsepower
developed by each appears to be produced by going to
successively higher RPM, not as a result of more torque. So,
unless you use a prop which is pitched to obtain a higher
RPM, you won't get anymore takeoff umph by upgrading engines
- the O200 is approved only with a shorter prop that turns
faster, so it has more takeoff performance (it is not faster
at cruise). The C90 is actually rated at 95HP at 2625RPM for
takeoff, but without a really fine pitch prop (or a constant
speed prop - wouldn't that be nice?), you can't develop that
RPM so you can't develop 100% power.
Remember that changing the prop requires a log entry signed
off by a mechanic. Because you are trying to get all you can
out of the engine, you should check your tach for accuracy.
David Smoler | __ | San Jose, CA
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Alon A-2 | \____/ | N6359V
s/n A35 () () () based at RHV
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