Today's Message Index:
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1. 05:19 PM - Ignition timing with the auto advance mags. (Walter Lannon)
2. 11:41 PM - yak-list: ignition timing (Frank Stelwagon)
Message 1
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| Subject: | Ignition timing with the auto advance mags. |
A question for everyone:
All of the engine manuals I have seen to date give a mag setting angle
relative to the propellor and corresponding to the individual magneto
advance angle.
That makes good sense since the prop shaft is the only accessible
reference.
The Polish manual for the AI14R engine is the only one to also include
the corresponding crankshaft angles, probably for educational purposes.
All manuals of course give the desired ignition advance angle for the
model engine. Theoretically, knowing that information, one can then
determine the setting angle for the particular magneto with simple math.
For example the Huosai 6A ignition angle is 31 +/- 1 deg. BTDC (from the
Maint. manual - the Specs. manual is different - another question) and,
lets say we are installing a 25 deg auto advance mag.
31 - 25 = 6. The setting angle is 6 degs BTDC with reference to the
Crankshaft. To determine the prop angle simply multiply by the gear
ratio:-
6 X 0.787 = 4.7 Deg.
Now check the table in the manual and for a 25 deg mag you will find a
setting angle of 6.9 deg.
This applies to all engine models using the auto advance mags. The
"fudge factor" varies slightly but always within 2 - 3 deg. and toward
retard.
The question is " WHY is there a fudge factor". I have one theory but
the fact is I do not know.
Does anyone else???
Message 2
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| Subject: | yak-list: ignition timing |
I don't think that one needs to worry about the fudge factor. The
engines will run better with 2-3 degrees more timing than the book calls
for. Remember the Chinese certified the engines for 70 octane fuel, so
with 100 octane you have a huge detonation margin.
Frank CJ6-A
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