Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Sat, 03 Aug 2002 23:43:36 -0400
Message-ID: <redirect-1681614@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: thrust horsepower
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<<-ATP web site (http://atpcoinc.com) shows 16.6 GPH at 240 HP
but they dont describe the test conditions.>>

That would be a BSFC of 0.48, certainly a new worlds record for a turbine of
that size.  I think it is more likely that the BSFC is 0.7, giving at fuel
flow of 24 GPH at 240 hp.  I assume 7 pounds/gallon for jet fuel - I don't
know what it should be.

<<-what is 50 lbs converted to HP (roughly)? if i understand this
should be added to the SHP when comparing engines.>>

One pound of thrust produces one horsepower at 326 knots TAS, or 375 mph.
However, since the exhaust thrust will go down as the airspeed goes up 50
pounds of static thrust will be less than that at cruise.  I have no idea
what the exhaust velocity might be, but let's assume the 50 pounds of static
thrust goes down to maybe 30 pounds at 230 knots.  That's 21 horsepower, or
about 10% of the shaft horsepower for this engine.  That would improve the
actual BSFC from, say, .7 to .63.  Significant, but not enough to get it
into the recip category.  Another thing to consider is that the air density
at 18,000 feet (the designed "sweet spot" for my ES) is only 57% of the
density at sea level.  The turbine engine will be running at maybe a little
more than that percent of sea level power, where a turbocharged recip will
probably be able to maintain 75% or more power, giving the speed advantage
to the recip.  Why do we think the turbine engine is "fast?"  It is easy and
cheap to overpower the airplane - look at the turbine IVP with - what is
it? - 700 hp.  A turbine engine of 350 hp would probably cost as much so why
not live Grand?  The traditional (certified) way would be to limit the
engine to the pre-existing certified horsepower of maybe 350 and then it
would be flat-rated to about 18,000 feet.  Or for an experimental, just push
the lever forward and climb straight up - you're going to need to get to
altitude quick because it burns so much fuel.

Gary Casey
ES project