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Frank
Joined: 10 Jan 2006
Posts: 69
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 Posted: Tue Feb 07, 2006 5:53 pm Post subject: OPTIMIZED TIMIMG SETTING |
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Yakkers
Anyone want to take a stab at why 16.5 Deg advance was chosen by the Russian engineers as the optimum timing advance to use through the RPM range of the M-14? I'm specifically interested as to what RPM setting this timing advance was chosen to optimize........... ie was it chosen for best power at takeoff or optimized for cruise?
Any thoughts are welcome.
Thanks
Frank
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wlannon(at)cablerocket.co
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| Posted: Tue Feb 07, 2006 7:19 pm Post subject: OPTIMIZED TIMIMG SETTING |
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Frank;
Where did you find the figure of 16.5 degs advance?
I do not have the M14P manual in front of me but as I recall the setting for the M9F (fixed spark) magneto is 23 +/- 1 deg BTDC. That by the way refers to the crankshaft angle NOT the propellor shaft angle. IMHO that is the only correct way to refer to engine timing angles. It is true that this angle cannot be directly measured in a geared engine but to refer to it in any other way only leads to confusion.
To set the spark advance angle you must use the corresponding angle of the prop shaft which, for the M14P, is marked on the propellor mounting flange. That angle is the firing angle X the gear ratio.
In this case it is approx.14.5 to 15.8 degs ( or 15.15 +/- 0.65 degs) at the prop. flange. Still not 16.5.
Walt
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Frank
Joined: 10 Jan 2006
Posts: 69
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| Posted: Tue Feb 07, 2006 7:48 pm Post subject: OPTIMIZED TIMIMG SETTING |
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Walt
Interesting...... I thought 16.5 was the static setting on an M-14 without regard to the gear reduction (I'm not near my manuals so going by memory). Now that I think about it, I'm not sure what the factory static setting is supposed to be set to. Can anyone straighten me out? What I'm looking for is crankshaft degrees.....I don't want to have to factor out the gear reduction unit. I thought 16.5 was the crankshaft static setting.........Dennis, you bugger, I know you know this... 
Most naturally aspirated engines take something on the order of 20-25 degrees crankshaft advance but supercharged engines like the M-14 have to be retarded to (what I thought) is 16.5 deg BTDC because the supercharged mixture burns faster. That's what made me wonder what the factory static setting was optimized for on the M-14.
I'm wondering why the factory chose the static setting it did, what that static setting is and what flight regime it's optimized for.
Regards
Frank
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