"ELIPPSE" wrote in message
ups.com...

Robert Bates wrote:
I was reading on a site about someone running a Chevy LS1 that was
derated
to 320hp and bone stock that was running 10.9 gal/hr at cruise. Does
anyone
have experience with these engines? If it is accurate, that is quite
a
savings over Lycoming and Continentals of that HP.

Hi, Robert!
Typically, the SFC of 4-stroke IC engines, liquid or air-cooled, is
0.5lb/hp-hr at best power mixture of about 12.5:1 A-F. Leaned for max
economy this will range from O.45 to 0.38 depending upon the engine.
Those that have 0.38 are very efficient. Some new Continentals or
Lycomings are getting this value leaned for best economy. The 10.9
gal/hr says that this engine, if it's leaned for best economy, is
producing between 148hp and 168hp, or about 50% power. "Cruise" is an
ambiguous designator, and doesn't really convey any information about
the engine's operating parameters! Be careful of these kind of claims!
So to get a good estimate of an engine's full-throttle, max. power
output, divide the fuel flow in gallons/hour by 0.5 then multiply this
by the weight of the fuel, which for av-gas averages about 5.85lb/gal.
Paul

Hmmmmm... Interesting...

Since I can't seem to get started on a real airplane project, due to
currently living in a condominium (aaarrrggghh!!!) and not being ready to
spend money on both hangar rent and the project, I've been reduced to
*fantasy* airplanes on a doodle pad...

What makes this interesting is: If I assume that I will do everything
practical to aerodynamically clean up the airframe, take full advantage of
the reduced ram air pressure requirement for a liquid cooling system, use a
fixed pitch prop, and still use the age-old formula of 0.2G static thrust to
allow for successful grass field operation; then I end up with a projection
of 50% power at cruising speed and altitude and 100% rpm as configured for
the application.

Therefore, someone using a constant sped prop and the same cruising speed,
which is conservative operation of the engine, should almost exactly match
Elippse's calculated numbers.

With my fixed pitch prop, I would expect slightly poorer fuel flow numbers,
although that alone would never pay for the constant speed prop.

Remember, however, that the example given was for a STOL aircraft where the
constant speed prop is used to gain much greater static thrust (a/k/a runway
acceleration). So long as we both use conservative numbers for maximum rpm,
and well designed drive systems, both engines should be extremely reliable.

Peter

p.s.: My alternative doodles with _standard_ aircraft engines end up
cruising at about 60% of maximum power as configured. That can be raised to
between 65% and 70% by using a smaller diameter prop and higher rpm, as
advocated by Steve Witman and others. That means winding the engine up to
110% to 115% on take off and initial climb.