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From: "Gary Casey" <glcasey@adelphia.net>
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Subject: Re: Electrical ignition and airspeed
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<<But there are real problems with this approach.  Which electronic ignition
are you going to use?

  Are you going to manually adjust the E-ignition ?   Or are you going to
depend on someone's idea of a MP based advance curve?

  Need more information.
  Regards,   George>>

Good questions.  I would expect to use the Lightspeed system (take whatever
advance someone has figured out) or my own (I get to pick the advance).

<<I found it at least a little curious that all of the rpm traces from the
chart seemed to converge to the same point on the 0 power line. This is
counterintuitive as I would expect at least some of this friction to vary
with rpm as stated above. It may be that some other loss is dominating the
result or that the Lyco chart is "crap".

Probably the best way to determine what power to use for the non varying
friction is to drive an exemplar engine with an electric motor and measure
the electric power it draws. Anyone have an engine laying around they want
to experiment with? Set it up with WOP and whatever rpm you what to know the
answer for.>>

Yes.  I was referring to the POH extrapolations as being excessive, not
yours.  Yours was really to look at the slope of the POH curves, which seem
to cross zero power at an unrealistic MAP.  And yes, the accepted method of
determining engine friction is to motor the engine.  That still doesn't get
the real friction, as there are effects due to firing pressure that aren't
simulated by a motoring engine.  And yes, the engine needs to be at
operating temperature and all the accessories need to be in place, according
to the SAE standard practice for "as installed" power.  The original way -
and the method that gave indicated torque its name - is to measure the
pressure in the cylinder and from that calculate engine torque.  Then
subtract brake torque and the result is the true friction torque on the
operating engine.  The "indicator" was a mechanical pressure/position
instrument used on reciprocating steam engines.  One of our projects in
school was to acquire and indicator diagram of an operating steam engine
(Yes, I'm old, but that steam engine was old when I was young).

<<See:
http://www.epi-eng.com/ET-PistonExcit.htm
 Grayhawk>>

I'm surprised - a very nice dissertation on instantaneous crank torque.  Not
exactly germane to our discussion, bur surprisingly accurate>>

<<On an IO-550, the frictional losses at 2500 rpm are about 30 HP, at 2700
rpm, they are about 46 HP.
Walter>>

There it is, REAL NUMBERS.  Thanks, Walter.  Friction horsepower is usually
about the square of rpm, which would produce a 17% increase in horsepower
instead of the 53% measured.  Perhaps there is something else there that
makes the friction horsepower rise so quickly.  It's obvious from the
numbers that the way to improve efficiency is to run at the lowest rpm
possible.

I don't know what the rest of you are doing on Christmas eve, but I'm going
flying.

Have a great Holiday,

Gary Casey