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At 12:31 AM 2/23/2006, WRB wrote:
The C-90 is a 90 hp engine rated at 95 hp for one minute (take-off). I
believe the prop would have to be pretty close to a "climb" pitch for the
engine to turn necessary rpm to develop 95 hp in a cruise-climb
configuration.
It's not that simple. A prop that would allow you to turn 2625 RPM
(the rpm at which the 95 hp rating is achieved) would be way beyond
extreme cruise and would only allow something like 50% power in level
cruise before it overspeeded. Such a prop would not meet the static
RPM requirements and as such would be an unairworthy combination. To
say nothing of the 75mph top cruise speed...
TCDS A-787 lists 2475 as the RPM limit for the C90
installation. Period, end of statement.
On other aircraft using the C90 that do have provisions for the 95 hp
takeoff limit, the ONLY prop for which this is allowed (generally-
there may be exceptions) is the Beech Roby adjustable prop. That
prop is not certified for use on a C90 equipped "ercoupe". Bottom
line, without a field approval and the Beech prop, the 95 hp takeoff
limit is out of reach.
...The two engines are mechanically identical except for the
recommended rpm limits, which Erco
ignored.
I don't know where you get that idea from. The TCDS clearly states
"Engine Limits: For all operations, 2275 RPM (75 hp)." Further
more, the static RPM limits prohibit use of a prop that would allow
operation significantly above 2275 in all circumstances except a dive.
What Fred may have done in the privacy of his own home does not in
any way overrule the published limitations.
John Cooper, A&P
Skyport Services
PO Box 249
4996 Delaware Tnpk
Rensselaerville, NY 12147
518 797-3064
Fax 518 797-3865
www.skyportservices.net
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