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<< Lancair Builders' Mail List >>
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In a message dated 8/30/2001 8:23:08 PM Pacific Daylight Time,
AVIDWIZ@aol.com writes:
<< The benefit is increased horsepower (400 HP) and a smoother engine. >>
Just some thoughts to contemplate re the subject matter:
For the sake of discussion, lets conjecture that they REALLY CAN increase the
power output to 400 HP. Since this is not a geared engine, they would (I
assume) be increasing the power to 400 HP at 2700 RPM.(??) That being the
case, then there would need to be a significant increase in volumetric
efficiency, probably accomplished mostly through increasing operational MAP,
which (unless intercooler efficiency is dramatically increased) results in
higher inlet air temperature, resulting in much-reduced detonation margins.
Increase the intercooler capacity and you get higher cooling drag.
On "flow-balancing": In-house testing has shown that the big LycoNental heads
flow very impressively out-of-the-box. SMALL flow increases can be achieved
without detrimental effects; large flow increases are often at the expense of
flow "quality" (velocity profile), and often with a net decrease in power
produced. Other field experience has shown that any significant metal removal
around the valve areas CAN lead to dramatically-reduced valve and
cylinder-head life.
The in-service reliability of the 350 HP version of this engine is, according
to the reports of Lancair owners alone, something less than acceptable, both
from heat rejection and structural standpoints.
So can it be reasonably deduced that reliability will be in any way increased
by such a theoretical increase in demands on an already overtaxed engine?
Note that the GTSIO's make from 375 to 435 HP, and in certified aircraft
service, typically achieve 600 to 800 hours between top overhauls, largely
due to the inability to reject the heat produced at those power levels.
In the flight levels, 227 HP (65% of 350) can cause CHT and valve-life
concerns. If that's the case, how will the same engine with the same cowling
dissipate the heat produced at 260 HP (65% of 400). And if you change the
cowling for more cooling, you've probably added more cooling drag, and the
airplane might even go slower. (If airframe total drag remains constant,
speed increases with the cube root of power increase.) (I'd really like
to see some hard data on how many people ACTUALLY fly their engines at 65%,
and for what time-fraction.)
Remember, the calibration of the dyno is very critical. If you want to see
500 HP from your lawnmower engine, just give me a little time to change the
dyno calibration and you can see it. Is it real? You be the judge.
The reliability issues (heat-rejection) are real, even with a modest increase
at 2700 RPM (225 HP from a claimed 200 HP Lyc IO-360; 335 HP from a claimed
300 HP Lyc IO-540). And, don't forget that you can get a 10 HP increase from
a 300 HP IO-540 simply by jacking the prop governor limit up 100 RPM.
Bottom line: be cautious and be cynical about claimed HP increases, and
consider the effect that those increases (if they actually occur) can have on
the reliability of an already-questionable reliability situation.
Jack Kane
EPI, Inc.
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LML website: http://www.olsusa.com/mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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