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From: Walter Atkinson <walter@advancedpilot.com>
Subject: Re: [LML] Re: Electrical ignition and airspeed
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On an IO-550, the frictional losses at 2500 rpm are about 30 HP, at=20
2700 rpm, they are about 46 HP.

Walter


On Dec 23, 2004, at 11:11 AM, REHBINC@aol.com wrote:

In a message dated 12/23/2004 9:40:30 AM Eastern Standard Time,=20
glcasey@adelphia.net writes:
<<In reviewing the WOT performance curves for O-360-A, I note that they
converge to 0 power at 59,000 ft. This would equate to around 0.24 inHg=20=

at 0
C.>>

An interesting observation.=A0 However, one problem that I have observed=20=

in
looking at POH performance is that in some cases it looks like the data=20=

was
excessively extrapolated.=A0 Like they made a couple of measurements and=20=

then
just filled out the rest of the chart.=A0 In the case you bring up the=20=

offset
in manifold pressure readings is only 0.24 inches.=A0 Sounds more like=20=

someone
was extrapolating to zero rather than giving actual data, as I don't=20
see how
the friction horsepower could be so low as to account for only .24=20
inches of
manifold pressure.=A0 I previously guessed 4, which is probably on the=20=

high
side.=A0 2 or 3 might be more reasonable.

Gary Casey
Gary,
=A0
There certainly is a fair amount of interpolation/extrapolation in=20
these performance curves and I confess that I added additional=20
extrapolation to get down to the 0 power condition. Further, I agree=20
that the frictional power loss at full power is substantially greater=20
than 0.24 inches. In fact it is probably in the neighborhood of=A06 or=20=

7=A0inches. But, the majority of the frictional loss varies with the=20
engine speed and load. For instance, the bearings and the ring/cylinder=20=

interface are hydrodynamic and their power consumption will vary with=20
the cube of engine speed. Their power consumption=A0will also vary=20
directly with the cylinder pressure and hence, this portion should be a=20=

constant fraction of the MAP. I was only trying to get an idea of the=20
fraction of power that is independent of engine load.
=A0
I found it at least a little curious that all of the rpm traces from=20
the chart=A0seemed to converge to the same point on the 0 power line.=20
This is counterintuitive as I would expect at least some of this=20
friction to vary with rpm as stated above. It may be that some other=20
loss is dominating the result or that the Lyco chart is "crap".
=A0
Probably the best way to determine what power to use for the non=20
varying friction is to drive an exemplar engine with an electric motor=20=

and measure the electric power it draws. Anyone have an engine laying=20
around they want to experiment with? Set it up with WOP and whatever=20
rpm you what to know the answer for.

--Apple-Mail-6-961635010
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	charset=ISO-8859-1

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


Walter



On Dec 23, 2004, at 11:11 AM, REHBINC@aol.com wrote:


<fontfamily><param>Arial</param><x-tad-bigger>In a message dated
12/23/2004 9:40:30 AM Eastern Standard Time, glcasey@adelphia.net
writes:</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger><<<<In reviewing the WOT
performance curves for O-360-A, I note that =
they</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>converge to 0 power at
59,000 ft. This would equate to around 0.24 inHg at =
0</x-tad-bigger></fontfamily>

=
<fontfamily><param>Arial</param><x-tad-bigger>C.>></x-tad-bigger></fontfam=
ily>


<fontfamily><param>Arial</param><x-tad-bigger>An interesting
observation.=A0 However, one problem that I have observed =
in</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>looking at POH
performance is that in some cases it looks like the data =
was</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>excessively
extrapolated.=A0 Like they made a couple of measurements and =
then</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>just filled out the rest
of the chart.=A0 In the case you bring up the =
offset</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>in manifold pressure
readings is only 0.24 inches.=A0 Sounds more like =
someone</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>was extrapolating to
zero rather than giving actual data, as I don't see =
how</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>the friction horsepower
could be so low as to account for only .24 inches =
of</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>manifold pressure.=A0 I
previously guessed 4, which is probably on the =
high</x-tad-bigger></fontfamily>

<fontfamily><param>Arial</param><x-tad-bigger>side.=A0 2 or 3 might be
more reasonable.</x-tad-bigger></fontfamily>


<fontfamily><param>Arial</param><x-tad-bigger>Gary =
Casey</x-tad-bigger></fontfamily>

=
<fontfamily><param>Arial</param><x-tad-bigger>Gary,</x-tad-bigger></fontfa=
mily>

=
<fontfamily><param>Arial</param><x-tad-bigger>=A0</x-tad-bigger></fontfami=
ly>

<fontfamily><param>Arial</param><x-tad-bigger>There certainly is a
fair amount of interpolation/extrapolation in these performance curves
and I confess that I added additional extrapolation to get down to the
0 power condition. Further, I agree that the frictional power loss at
full power is substantially greater than 0.24 inches. In fact it is
probably in the neighborhood of=A06 or 7=A0inches. But, the majority of
the frictional loss varies with the engine speed and load. For
instance, the bearings and the ring/cylinder interface are
hydrodynamic and their power consumption will vary with the cube of
engine speed. Their power consumption=A0will also vary directly with the
cylinder pressure and hence, this portion should be a constant
fraction of the MAP. I was only trying to get an idea of the fraction
of power that is independent of engine load.</x-tad-bigger></fontfamily>

=
<fontfamily><param>Arial</param><x-tad-bigger>=A0</x-tad-bigger></fontfami=
ly>

<fontfamily><param>Arial</param><x-tad-bigger>I found it at least a
little curious that all of the rpm traces from the chart=A0seemed 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".</x-tad-bigger></fontfamily>

=
<fontfamily><param>Arial</param><x-tad-bigger>=A0</x-tad-bigger></fontfami=
ly>

<fontfamily><param>Arial</param><x-tad-bigger>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.</x-tad-bigger></fontfamily>


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