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From: Walter Atkinson <walter@advancedpilot.com>
Subject: Re: [LML] Where has all the power gone?
X-Original-Date: Fri, 30 Dec 2005 10:26:22 -0600
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Bill:

Your supposition is correct.  But, the change in effective timing=20
between 2500 and 2200 rpms is very small.  In most cases, the prop is=20
more efficient at 2200 rpms.

Walter


On Dec 29, 2005, at 9:01 PM, Bill&Sue wrote:

Dumb question for you smart guys.
=A0
I've been reading all of the spark timing information with great=20
interest. We have a while before we have to settle on an ignition=20
system for our non TC 550 and, of course, would like to make the most=20
informed decision. Soooo, George, Scott, Hamid, Paul, Rick, et al, how=20=

about this:
=A0
Seems to me that rpm changes effectively=A0adjust ignition timing. For=20=

example, if you're running at 2500 rpm and the spark occurs at 25 btc,=20=

the flame propagates at a rate that produces max pressure at some point=20=

after tdc, lets just say 15 degrees. If you reduced the rpm to 2200 and=20=

the spark occurred at 25 btc the flame would propagate at the same rate=20=

as before but the piston is moving slower. Seems to me that the max=20
pressure would occur at somewhere less than 15 after tdc, effectively=20
advancing the ignition.
=A0
Most agree that the majority of the advantage of adjusting spark=20
timing=A0happens at lower power settings. To me, it looks like the=20
advantage is better fuel economy as opposed to more power. Couldn't one=20=

simply pull the prop control back to gain this same advantage?
=A0
Probably lots of flaws in my thinking, but I'm not smart enough to see=20=

'em. Help me out.
=A0
Bill Harrelson
5zq@cox.net
N5ZQ 320 1,100+ hrs
N6ZQ=A0 IV=A0 4.239%
=A0
=A0
=A0=

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Bill:


Your supposition is correct.  But, the change in effective timing
between 2500 and 2200 rpms is very small.  In most cases, the prop is
more efficient at 2200 rpms.


Walter



On Dec 29, 2005, at 9:01 PM, Bill&Sue wrote:


<fontfamily><param>Arial</param><smaller>Dumb question for you smart
guys.</smaller></fontfamily>

=A0

<fontfamily><param>Arial</param><smaller>I've been reading all of the
spark timing information with great interest. We have a while before
we have to settle on an ignition system for our non TC 550 and, of
course, would like to make the most informed decision. Soooo, George,
Scott, Hamid, Paul, Rick, et al, how about this:</smaller></fontfamily>

=A0

<fontfamily><param>Arial</param><smaller>Seems to me that rpm changes
effectively=A0adjust ignition timing. For example, if you're running at
2500 rpm and the spark occurs at 25 btc, the flame propagates at a
rate that produces max pressure at some point after tdc, lets just say
15 degrees. If you reduced the rpm to 2200 and the spark occurred at
25 btc the flame would propagate at the same rate as before but the
piston is moving slower. Seems to me that the max pressure would occur
at somewhere less than 15 after tdc, effectively advancing the
ignition.</smaller></fontfamily>

=A0

<fontfamily><param>Arial</param><smaller>Most agree that the majority
of the advantage of adjusting spark timing=A0happens at lower power
settings. To me, it looks like the advantage is better fuel economy as
opposed to more power. Couldn't one simply pull the prop control back
to gain this same advantage?</smaller></fontfamily>

=A0

<fontfamily><param>Arial</param><smaller>Probably lots of flaws in my
thinking, but I'm not smart enough to see 'em. Help me =
out.</smaller></fontfamily>

=A0

<fontfamily><param>Arial</param><smaller>Bill =
Harrelson</smaller></fontfamily>

=
<fontfamily><param>Arial</param><color><param>0000,0000,FFFF</param><small=
er>5zq@cox.net</smaller></color></fontfamily>

<fontfamily><param>Arial</param><smaller>N5ZQ 320 1,100+ =
hrs</smaller></fontfamily>

<fontfamily><param>Arial</param><smaller>N6ZQ=A0 IV=A0 =
4.239%</smaller></fontfamily>

=A0

=A0

=A0=

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