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<< Lancair Builders' Mail List >>
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Ron -
Turbocharged vs. Normally Apsirated Engines -
You might want to approach the problem from the operational point of
view.
Cons: A turbocharged engine won't be any advantage below 10,000 ft, and
may actually be a detriment. You pay a penalty in added weight and
greater fuel consumption at the lower altitudes (you can't lean the
mixture as aggresively as you can with a normally aspirated engine).
Turbocharged engines rarely make it to TBO without replacing a couple of
cylinders along the way. They are more susceptible to shock cooling, so
you can't pull the power out quickly to descend. This means you will
probably want speed brakes. Since turbocharged engines are sensitive to
rapid power changes, they make poor candidates for training, which
typically includes alot of touch-and-goes. You need to let the turbo
cool off and spin down after landing to avoid cooking the oil in the
turbine shaft bearing, which can cause carbon deposits. This means a
couple of minutes of idling before shutting down at the end of every
flight. You will also need an oxygen system and a really good heater up
in the flight levels.
Pros: I took a ride in the factory demonstrator at Sun-n-Fun this year.
With the IO-550, we
were going up 1500 fpm at 140 kts. With cruise power settings, the plane
jumped up to 240kts at 3000 ft. Now for the good part - If the IO-550
could make sea level horsepower at 18,000ft, 240KIAS would work out to
326.4KTAS! Holy cow!!! With speeds like that, who cares about TBO!
-------Rule of thumb for TAS: TAS = [IAS x 2%] x [ALT/1,000 ft] +
IAS---------
In case you couldn't tell, I haven't made my mind up yet, either.
Adam Molny
#62 on the L2K waiting list
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Please send your photos and drawings to marvkaye@olsusa.com.
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