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Not The Typical Leaning Question


Well-Known Member
Jul 15, 2010
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This question is more about the Cherokee versus Lycoming manuals. I have read all the other forum discussions on leaning, seen the on-line seminars, etc., not trying to recreate that discussion. I have a '64 180 B model. The leaning instructions are covered in the uncontrolled (no FAA revisions, supplements, etc.) "Owners Manual", not the AFM. The B manual basically says absolutely nothing about leaning other than "lean" in cruise as needed to save fuel. I then went and read the Cherokee 180 C manual and it said something interesting. The manual said that for best power, lean to peak EGT then enrichen 25 degrees F less of peak (ROP). For best economy, lean to peak EGT and continue to lean further until 25 degrees F less of peak (LOP). I was surprised that a mid-1960's manual recommended LOP operations for carbureted engines. I also wondered if this recommendation applies to my B model since the engines are TC'd the same (maybe a different carb). All the 180's seem to come with EGT's, so EGT leaning is what is only described in all the manual. The Lyc manual for this engine says (from my memory) 75 degrees ROP for best power and 25 degrees ROP for best economy. Since the B manual is totally useless, I officially have no procedures for leaning. And while the C manual may be the closest official procedure to my airplane, the 25 degrees ROP/LOP recommendations are frowned upon by the current "experts" because that is near the highest (theoretical/charted) CHT points - so while ROP/LOP is usually recommended, just not at those temp settings. Confusing to say the least. By the way, everything I am saying is for high altitude (i.e. less than 75% power) cruise. Not a problem for me as my home airport's pavement starts at 5000 MSL.

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