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  #11  
Old 04-13-2017, 01:59 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by David-aviator View Post
It is true.

CAFE FOUNDATION established some years ago with extensive flight testing, EI offers little advantage over magnetos until above about 8500.

Go to cafe.foundation and dig it up, the report is still there somewhere.
This report establishes some of the fundamental advantages of EI - namely that the lean mixtures at altitude are hard to light and slow to burn, but we need to remember that the features of variable timing offered in some of the latest ignitions were not explored back then. The ability to retard timing from data plate numbers is a huge benefit from those of us who are concerned about detonation at takeoff power. So yes, when fat and low it does not take much to start the ignition event - but being able to control the slope of that curve is a big deal. Magnetos offer no ability to shift timing, most EI's have a limited ability to alter timing, but a scarce few have the capability to build a complete curve. That's where we in aviation are just beginning to draw back the curtain.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #12  
Old 04-13-2017, 02:29 PM
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Quote:
Originally Posted by KatanaPilot View Post
Dan, can you provide a link and/or data that shows this information? It's a little hard to understand that a mag with fixed timing would somehow be better than EI with MP based variable timing. Thanks.
http://www.vansairforce.com/communit...d.php?t=148100

Get an online subscription to Kitplanes. You can read everything in current issues plus all the back issues.

Here on VAF, the quick version:

http://www.vansairforce.com/communit...6&postcount=15

Quote:
Originally Posted by N941WR View Post
I'm not sure that is a correct statement.
Bill, are you listening to yourself? You and your partner created a device to modify the supplied p-mag advance values.

The result is still not anywhere as good as a dual map system, but that's not your fault.
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Last edited by DanH : 04-13-2017 at 02:38 PM.
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  #13  
Old 04-13-2017, 02:43 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by DanH View Post
...

Bill, are you listening to yourself? You and your partner created a device to modify the supplied p-mag advance values.

The result is still not anywhere as good as a dual map system, but that's not your fault.
Dan, I am listening to myself, and I would say the timing of the P-mags is overly conservative, if anything, not overly aggressive.
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  #14  
Old 04-13-2017, 03:21 PM
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f14av8r f14av8r is offline
 
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Default P-Mag Advantage

I can't contribute to the timing discussion but I will say I'm quite happy to be rid of my Bendix magneto. Faced with a choice of overhauling the antiquated Bendix or replacing it with something different, I chose the E-Mag P-Mag. It went in easy, is a piece of cake to time, and works great. Auto plugs and harness is an added advantage. Frankly, I'm surprised any experimental owner is still running a magneto, and I'd be even more surprise that any experimental owner actually paid for a 500 hour IRAN or overhaul on a magneto. The P-Mag is just SO MUCH BETTER.
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  #15  
Old 04-13-2017, 04:23 PM
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Quote:
Originally Posted by N941WR View Post
Dan, I am listening to myself, and I would say the timing of the P-mags is overly conservative, if anything, not overly aggressive.
In God we trust. Everybody else has to bring numbers.

Quote:
With my 8.5:1 O-360, which is spec'ed at 25 degrees before TDC, the P-mags do not start advancing until you are going through 4,000 to 6,000' at climb power.
That's the point Bill.

The published data, from a professional test pilot, says there is no good reason for significant advance while running best power mixture at any reasonable altitude. Yet he measured 36 degrees for the P-mag before 22". Optimum was found to be 28 degrees when less than 23"MP.

It's not anomalous. Here are two examples. On the Sky Dynamics dyno, even a full-boogie motor at 3000+RPM was losing power when advance was pushed past 30 degrees. Best torque was at 25 degrees.

Deg HP-RPM Torque-RPM
20 217-3050 411-2424
25 228-3082 430-2456
30 232-3082 422-2461
33 223-3004 413-2434

I run the 390 at a base timing of 23 degrees. Given best power mixture, there is no detectable speed or power difference at 27 degrees, at any altitude I've checked. All it does is run up CHT.

The above is ROP. LOP is different. One might argue that the P-mag is "conservative" because 36 degrees is less than the 40 degree maximum in Nigel's series, at MP's less than 20". Works for me. Don't think anyone has a complaint with P-mag timing when running high and lean of peak. Trouble is, you gotta get up there in the first place, while we retarded folk have already climbed away into the next county.
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Last edited by DanH : 04-13-2017 at 09:46 PM.
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  #16  
Old 04-13-2017, 05:34 PM
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Ironflight Ironflight is offline
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You guys are living in the wrong part of the country - out here, we are HIGH and LEAN when we start our take-off roll.....
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  #17  
Old 04-13-2017, 09:42 PM
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Quote:
Originally Posted by Ironflight View Post
You guys are living in the wrong part of the country - out here, we are HIGH and LEAN when we start our take-off roll.....
If you're a reader out there on the learning curve, please understand that Paul is kidding.

At higher elevations a pilot may choose to lean before takeoff, in the same manner as the flatland pilot who uses the "target EGT" method of leaning in the climb. The idea is to adjust a mixture that gradually goes rich with increased elevation, returning it to best power or slightly rich of best power. Exact isn't necessary, as the power vs mixture curve is quite flat in this region.

How flat? Paul's home field is at 4400 MSL. As compared to a sea level observation, a Bendix RSA-5 (or Precision EX-5, or Airflow Performance FM150) will enrich enough to reduce EGT by approximately 50F. All a pilot needs to do in order to restore maximum available power for that altitude is lean 50 degrees. If he did nothing and just left the mixture knob in the full rich position, the power loss would be a little more than 1%.

Note that Western pilots lean on the runway and in climb to restore maximum power. Unless in the habit of deliberately reducing power by pulling mixture to the lean side of peak, the situation is exactly the same as detailed in Nigel's work. The optimum timing for rich of peak, best power operation is less than 30 degrees BTDC, for all altitudes tested.

If anything, the P-mag's advance schedule is even more wrong for a mountain pilot than it is for a flatlander. At least the flatlanders get to climb a little before the advance starts rising.
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Last edited by DanH : 04-13-2017 at 09:50 PM.
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  #18  
Old 04-14-2017, 05:55 AM
David-aviator David-aviator is offline
 
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Another thing guys tend to forget is with old Lycoming technology engine, fuel, in addition to creating power, is also a median for cylinder head cooling.

Get the internal temperatures too hot for too long, the exhaust valves will fail.

That and very poor inlet airflow distribution convinces me to be cautious about this stuff. This engine is not a modern auto engine designed to do what some are trying here.
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  #19  
Old 04-14-2017, 06:08 AM
6 Gun 6 Gun is offline
 
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Smile cyl temp

That's a very good point David with an air cooled engine .
Bob
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  #20  
Old 04-14-2017, 06:12 AM
Tomcat RV4 Tomcat RV4 is offline
 
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Come on guys & girls ,it's about time aviation moved into this century, in 1995 I would not trust electronic ignition, but today ,no reason not to use it along with NORMAL spark plugs !
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