Mixture Leaning

October 18th, 2014

Just doing some final editing for our Cessna 172 ibook release, and found this article again. I’d read it some time back, I think it sums up the concepts nicely.

http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning198162-1.html

If you haven’t got time to read it all, essentially what is says, is lean as much as you can, while maintaining both smooth running, and acceptable engine temperatures. Lycoming and continental both recommend never operating with the CHT over 400 degrees for sustained periods, he adds a margin to this and sets himself a limit of 375, which is what I also do when I can, I never lean if the temps are above this. (We operate in very high ambient temps, and some engines run hotter than others, one of our aircraft usually runs slightly over 400 in the climb if the OAT is over 40 degrees Celsius – full rich.)

The only part I disagree is with lean of peak, since Lycoming and Continental both prohibit it in their bulletins on leaning issued in the 1990s. Sure it’s cleaner and cooler, but it’s also it’s on the steep side of the power curve, where leaning further causes a sharp drop off in power.

I usually operate either at peak power, at peak EGT or slightly rich of these if I need the cooling in hot temperature, and again, I have to run it full rich, or level off (for climbs) if my CHTs climb above 375.

Cessna Training Manuals

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