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Hank:
I have flown 53 hours on an Ivoprop Magnum, 3-blade, 68.5 inch propeller
with 90 inches of helical arc (standard pitch for the normal use Ivoprop).
It is truly smooth and quiet but then I have little to compare its
performance to in other Lancairs. I am sure that it is under pitched for
the speeds that Lancairs typically fly but on my 180 hp Lyc, I routinely see
215 to 220 mph at most every altitude up to 13500 (beyond which I'm not
equipped to fly). The important point here is that I am running the engine
at redline of 2750 rpm and choose to not push the engine any faster though I
have inches remaining in both manifold pressure and throttle length. My
airplane has extended wings and weighs 1170# empty, climbs at a sustained
2300 feet per minute and accelerate so rapidly that it scares me. I use the
electric, cockpit-adjustable pitch control mechanism which is quite simple
but has given me some difficulty with stuck gears (fixed at no expense by
Ivo) and worn brushes. Perhaps the most serious difficulty that I
experienced with this equipment is that Ivo has not provided any means by
which to determine where in the pitch position the prop is at any given
time. Instead one has to fly a constant speed and altitude while running
the prop out and in to its limits. If the switch is depressed too long, the
in-line circuit breaker trips stopping further movement-- a rather crude
tell tale of position. I view this propeller as a gear shift only. I have
an exact cruise pitch that I desire and when cruising, I move steadily
towards a full cruise pitch seldomly stopping long in-between.
I like this prop enough to have just recently purchased the brand new
high-pitch model of Magnum which ranges from 45 inches to 105 inches of
pitch (instead of 30 inches to 90) which were designed specifically for the
faster homebuilt planes including Glasair and Lancair. Though I haven't
flown on it yet (fixing a fuel tank leak) it looks great and has visibly
much greater pitch and is sure to improve performance at all ranges.
I have had no problems whatsoever with vibration or breaking the stress tape
that permit Ivoprop users to gauge integrity of the propeller mounting.
However, Ivo does say that his Magnum likes bigger engines including 6 and 8
cylinders because they generally run smoother with less vibration.
When I have about 25 hours on this new propeller, I'll update this
report. Greg Nelson
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
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