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I was able to spend some time at the Innodyne tent
and examining the twin engine unit on display in the Lancair tent.
There was also a high wing on the flight line with the engine installed
and (apparently) flying. From what I could see from the outside, it
seems like an attractive alternative, if you have money to burn.
The engine has a single stage centrifugal turbine and compressor.
Imagine a big turbocharger (apologies to Innodyne engineers). On
interrogation, the Innodyne representative claimed an overall
compression ration of 4.5 to 1 and a fuel burn of 8 gallons per hour
per one hundred horsepower. Later in the conversation he mentioned
that the horsepower was rated at sea level but the fuel burn was from a
9,000' MSL test flight so the fuel burn claim is significantly
underestimated. If you calculate the horsepower derating based on the
density delta from 0 to 9,000' MSL you will have 76 horsepower where
you once had 100 so you now have 8 gallons per hour per 76 horsepower
or (given 8 lbs per gallon for Jet-A) 64 lbs per hour per 76 horsepower
or 0.84 pounds per horsepower hour. My Lycoming running at 75% power
and 150 deg F rich of peak burns 0.47 pounds per horsepower hour. To be
fair, there are 15% more pounds in a gallon of Jet-A than a gallon of
100LL and Jet-A is ~10% cheaper so the fuel consumption of the Innodyne
only 116% of the Lycoming comparing dollars per hour. All this assumes
that the horsepower number was not overstated and the fuel consumption
was not understated, in the best OSH tradition. Of course my
calculations are very rough estimates.
For a sanity check we can review the performance of a similar engine
made by Solar, the T62, you will find the overall compression ration
listed as 3.5 with a BSFC of 1.3 Lb/HpHr. Is it reasonable to expect
a 35% reduction in fuel consumption? The laws of thermodynamics are
very difficult to break.
Turbine (and IC) engines benefit from size such that bigger is more
efficient. A twin pack of smaller, less efficient engines, will not be
as efficient as a single larger engine.
I am encouraged by the advent of engine alternatives. I am also hopeful
that accurate data will be forthcoming so that a reasoned performance
comparison can be performed.
Show me the data......Until then "Caveat Emptor".
Regards
Brent Regan
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