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Date: Fri, 09 Sep 2005 20:41:33 -0400
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From: "Mike Hutchins" <210flyer@earthlink.net>
Subject: RE: Another way to look at the Innodyne
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Hi Dan,

 

I think your fuel flow assumptions are overly optimistic. In addition, the
power output of the turbine will degrade with altitude just like a normally
aspirated piston engine. The exception is if the turbine has a power limit
at lower altitudes, often due to inter-turbine temperatures, then it will
behave more like a turbonormalized engine where it will produce rated power
up to some critical altitude and then degrade with additional altitude.

 

As Gary points out, your fuel flow estimate requires a BSFC of 0.38 (using a
Jet A density of ~ 6.9Lbs/Gal) which is very unlikely. In comparison, the
Walter only achieves a BSFC around 0.67 Lbs/Hp/Hr. Using this figure, your
Innodyne 255TE will be sucking down 24 gal/Hr. On their website, Innodyne
reports a flight average fuel consumption of 7 Gal/100 Hp/Hr which equates
to an average BSFC of 0.48 Lbs/HP/Hr. This would amount to 17.7 GPH at
takeoff and would decrease to 12.4 GPH at 12,000' which would be equivalent
to 70% power, assuming the engine is not derated. I think the new Williams
engines, such as the FJ33 and FJ44 are achieving BSFCs around 0.55 (though I
can't confirm the BSFC figure), which is almost 15% higher than the Innodyne
BSFC yet 18% lower than the Walter BSFC. Using the 0.55 value, your fuel
flows would be ~ 20 GPH at full power and ~ 14 GPH at 12,000' and maximum
power of 70% (or ~180HP). Like Gary, I think these numbers will hit closer
to the mark when Innodyne publishes the BSFC for its production turbines.

 

Also, don't forget that Jet-A weighs about a pound more per gallon than
100LL, so your useful load with full fuel will be less, offsetting some of
the weight saved from the lighter engine.

 

We're getting closer to a practical turbine engine for GA aircraft, and
certainly Innodyne may be the closest when it comes to the smaller SHP
engines. Unfortunately, I think it may be many years before we see a turbine
that rivals the efficiency of our "modern" piston aircraft engines.

 

Best Regards,

Mike


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<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>Hi Dan,<o:p></o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>I think your fuel flow assumptions are overly optimistic. In =
addition,
the power output of the turbine will degrade with altitude just like a =
normally
aspirated piston engine. The exception is if the turbine has a power =
limit at
lower altitudes, often due to inter-turbine temperatures, then it will =
behave
more like a turbonormalized engine where it will produce rated power up =
to some
critical altitude and then degrade with additional =
altitude.<o:p></o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>As <st1:City w:st=3D"on"><st1:place =
w:st=3D"on">Gary</st1:place></st1:City>
points out, your fuel flow estimate requires a BSFC of 0.38 (using a Jet =
A
density of ~ 6.9Lbs/Gal) which is very unlikely. In comparison, the =
Walter only
achieves a BSFC around 0.67 Lbs/Hp/Hr. Using this figure, your Innodyne =
255TE
will be sucking down 24 gal/Hr. On their website, Innodyne reports a =
<i><span
style=3D'font-style:italic'>flight average</span></i> fuel consumption =
of 7
Gal/100 Hp/Hr which equates to an <i><span =
style=3D'font-style:italic'>average</span></i>
BSFC of 0.48 Lbs/HP/Hr. This would amount to 17.7 GPH at takeoff and =
would
decrease to 12.4 GPH at 12,000&#8217; which would be equivalent to 70% =
power,
assuming the engine is not derated. I think the new Williams engines, =
such as
the FJ33 and FJ44 are achieving BSFCs around 0.55 (though I can&#8217;t =
confirm
the BSFC figure), which is almost 15% higher than the Innodyne BSFC yet =
18%
lower than the Walter BSFC. Using the 0.55 value, your fuel flows would =
be ~ 20
GPH at full power and ~ 14 GPH at 12,000&#8217; and maximum power of 70% =
(or ~180HP).
Like <st1:City w:st=3D"on"><st1:place =
w:st=3D"on">Gary</st1:place></st1:City>, I
think these numbers will hit closer to the mark when Innodyne publishes =
the
BSFC for its production turbines.<o:p></o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>Also, don&#8217;t forget that Jet-A weighs about a pound more =
per
gallon than 100LL, so your useful load with full fuel will be less, =
offsetting some
of the weight saved from the lighter =
engine.<o:p></o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>We&#8217;re getting closer to a practical turbine engine for GA
aircraft, and certainly Innodyne may be the closest when it comes to the
smaller SHP engines. Unfortunately, I think it may be many years before =
we see
a turbine that rivals the efficiency of our &#8220;modern&#8221; piston
aircraft engines.<o:p></o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>Best Regards,<o:p></o:p></span></font></p>

<p class=3DMsoPlainText><font size=3D2 face=3D"Courier New"><span =
style=3D'font-size:
10.0pt'>Mike<o:p></o:p></span></font></p>

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