Leaning in Cruise

[gvgoff99]

I have always had some difficulty finding the sweet spot for leaning in Cruise even with four cylinders monitored and an EIS that has a leaning feature.
In reading Mike Busch's advice about inflight Mag checks and information he and others have published about leaning I started to think "what about combining the two?"
I like simple, so I now do the inflight Mag check but when checking the second Mag instead of flicking it back on immediately I started to lean on one Mag. When things get lean it runs rough (no surprise but it goes from smooth to rough in a tight window and it is very noticeable) but instead of immediately enriching the mixture I flick the second Mag back on. Voila! smooth engine and I don't touch the mixture.
The CHT's and the EGTs all line up well. The CHT's all run in the 360 to 380 range depending on the OAT.
I am puting this out for food for thought and also wondering if anyone else has tried it.
I do have dual P-Mags so the electronic ignition may have an effect.

[ScottSchmidt]

Tell me more about this in-flight mag check as well as the thoughts behind leaning on one mag. What if we have one mag and one electronic ignition? Which would you lean on?

[gvgoff99]

Mike Busch http://www.savvyaviator.com/ has a lot of ideas that make sense and he has researched the technical stuff, like leaning. He also recommends an in-flight mag check. This is quite simple to do. You are flying along at cruise and turn one off then the other. The effect should be the same as it is during run up when you perform the same operation. The engine should get a bit of a RPM drop but nothing dramatic. The purpose is to see if those guys are doing the same job at altitude and under load as they do on the ground. At altitude there is a higher probability of an arcing of the spark internal to the mag because the dielectric component of air is less up there than it is a SL. So if there is a problem it is apt to show up at altitude more than at SL. It?s easy to check and a good idea to warn your passengers so they won?t look for their chutes when there is a sudden change in the engine RPM.
In the October 1999 Cessna Pilots Association magazine he wrote an article that had the title "Leaning Without Fear." Using a lot of the GAMI research he concluded that the hottest CHT were achieved at 50 degrees rich of peak. This is right where most of us were taught to run the engine. What we were taught was based on intuition and not on research. So his conclusion was that the GAMI research demonstrated that running lean of peak was cooler and more economical. I know this is a controversial subject and I do not want to get into a rich vs. lean or peak EGT temp discussion about which is best. Everyone can do what they want. I elect to run as lean as possible and have had no problem to date. CHT's and EGTs are even and stable, compression is excellent.

So to answer your question about which to use to lean, Mag or EI: I don't know. I would probably use the mag because the engine would probably run rough sooner than the EI would. A little in-flight evaluation would be OK. Try one way then try the other.

I figure that my car runs on one set of plugs so my plane can too for the short time it takes to check the mags and lean the engine.

[osxuser]

Yep, at high power settings running between 50 LOP and 100 ROP should be avoided from what GAMI's research shows. I run 100ROP in the Cardinal with carb at high power settings, and as lean as I can with <65% (Which usually ends up about peak or a touch LOP.)

I don't know if I agree with your method of leaning or not. As I understand it, and this is based on the assumption you are running ROP, you lean as lean as you can, until the engine bumbles. If that is still somewhere in the ROP area, when you go to the other ignition, the mixture will get effectively leaner (Faster, more complete ignition) and you'd be right in the middle of the 50LOP to 100ROP range somewhere. If you at low power settings, this is no big deal.

If leaning this far gets you past peak onto the lean side of things, then bringing the other ignition back online still makes it leaner, but in this case it isn't a bad thing since it is getting farther from the middle danger zone.

Of course, this only applies to high power settings. I'm firmly convinced that the red knob can go just about anywhere without damaging the engine at low power settings.

And of course, this is just my understanding, reality could be something completely different.

[gvgoff99]

Stephen, You got it. I am leaning in the 70% or less range so a little less conservative than you are but probably no big deal of difference. I think the same as you in that the worst place to be is 50 degrees rich of peak (where a lot of engines have been run) and I also believe that in the lower power settings it is probably infinately unlikely that damage will be done at almost any smooth setting.

I found that with my engine I could find that "most lean" mixture pretty fast when I leaned running on one mag. I then flick on both and things smooth out without any further messing with the mixture. I agree with all that you say especially:

Originally Posted by osxuser

I'm firmly convinced that the red knob can go just about anywhere without damaging the engine at low power settings.

I am just currious if others had tried this. If so did they find the same result? Thanks, George