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-   -   Test procedure/schematic for single Pmag (https://vansairforce.net/community/showthread.php?t=100553)

Lycosaurus 06-07-2013 01:35 PM

http://blog.savvymx.com/2010/03/mag-check.html

"The usual pre-flight mag check is a relatively non-demanding test, and will only detect gross defects in the ignition system. To make sure your engine's ignition is in tip-top shape, we recommend performing an in-flight mag check at cruise power and a lean mixture (preferably a lean-of-peak mixture). Because a lean mixture is much harder to ignite than a rich one, an in-flight LOP mag check is the most demanding and discriminating way to test your ignition system. It's a good idea to perform one every flight or two.

The in-flight mag check is performed at normal cruise power and normal lean mixture (preferably LOP). Run the engine on each individual mag for at least 15 or 20 seconds. Ensure that all EGTs rise, that they are stable, and that the engine runs smoothly on each mag. If you see a falling or unstable EGT, write down which cylinder and which mag, so your mechanic or SAMM account manager will know which plug is the culprit."

Toobuilder 06-07-2013 01:44 PM

Quote:

Originally Posted by Beer30? (Post 777542)
...I'm not familiar with the cruise power LOP mag check. Can you elaborate...

Sure,

The end of runway mag check is not much of a test - anything but a gross ignition failure is going to show up as "good". OTOH, high altitude, LOP operations are challenging for ignitions. Just getting the fire lit at all is tough for some magnetos. The fact that EI's do this job better than magnetos does not mean they aren't getting a workout. So to see if they are both actually healthy, simply do a conventional "mag check" when established in your normal cruise power setting. For me, that's ~ 8,000 feet, 50 LOP. On the ground, my "mag check" produces zero RPM change between ignitions, so I have to look for the EGT rise to verify that one ignition is in fact shut down. If my ignitions are healthy, the cruise LOP method delivers the same result. I started doing this after a plug change once and discovered a weak coil. Worked fine on the ground, worked fine on ROP climb, but once I went LOP, the one side just couldn't hack it. Now, this is my normal cruise checklist item.

EDIT: someone beat me to the punch....

Toobuilder 06-07-2013 01:57 PM

On those same lines...

If you're cruising along LOP (let's say 50 degrees) and notice that suddenly you're some significant value warmer - say 10 LOP or even slightly ROP, don't adjust the mixture right away.... There's a good chance that you have lost an ignition. Do a mag check first, but expect the engine to fall on its face or quit when you shut down the "good" side. If the ignition checks out, then you might think about chasing the mixture back to where it needs to be.

PMags (like most EI's, I suspect), work so well that the engine runs quite happily, even at altitude, on just one. That's why having one drop out on you often produces only the slightest clues. The first time it happened to me I just assumed I bumped the mixture a little rich. There was no obvious indication the ignition checked out.


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