| Please do NOT lean a turbocharged aircraft in the climb below critical altitude (or even then, in most cases.). A turbo always thinks it's at sea level. While being full rich does aid in CHT control it is NOT because the extra fuel cools the cylinders. It is due to the burn rate of the richer mixture altering the thetaPP--not the heat of vaporization of any additional fuel.
Leaning to a Target EGT for a high altitude takeoff or in the climb is for normally aspirated engines ONLY.
The reason we keep a full rich mixture to to maintain the detonation margin during the high power operation. Some year ago, a turbo-charged aircraft was leaned during take and climb, resulting in four deaths from the engine failure due to detonation, which destroyed a plug ceramic and resulted in pre-ignition.
Please don't lean a turbo-charged engine at full power--unless you fully understand the issues and decide to do a LOP climb. Those work, but are more pilot workload and as a result, we don not recommend LOP climbs fro any but the fully knowledgeable of the issues. On Oct 18, 2013, at 8:55 AM, Robert R Pastusek wrote: Keith wrote: Question about climbing "full rich". Would it not make sense to maintain sea-level EGT's through the climb, rather than truly full rich all the way up to 17K? As you climb higher, 'full rich' is a whole lot richer than the mixture you had during takeoff. This is something I learned through John Deakin's Pelican Perch articles a few years back when I first got the Lancair. I usually 're-lean' every 1000ft or so during my climbs to maintain around 1320 EGT. LNC2 N360JH Keith, Leaning to maintain a power setting as you climb will work as you note. The result is that the engine continues to produce as much heat at altitude as it does at sea level, while the air thins and doesn’t carry the heat away as well. This usually results in higher CHTs and oil temps. The reason for using “full rich” during climbs…or any high power operation for that matter…is to deliver extra fuel…for cooling…to the cylinders. Not the most efficient use of expensive fuel, but it has other advantages, principally that of keeping the engine temps within limits at lower airspeeds while still delivering sufficient power to climb. The throttle control on our Continental and Lycoming engines (and probably others?) is designed to also deliver extra fuel at wide open throttle (WOT)--to aid cooling. So climbing at WOT and full rich “wastes” fuel, but really helps the engine deliver its rated service life. As many have said in these pages, it’s all about keeping the engine temps within specified limits. As long as you can monitor and control CHTs and oil temps on our air-cooled engines, you should be OK to lean during climb, but if the temps start approaching the specified limits, you need to change things. This can include increasing airspeed/cooling air flow, reducing power, or adding more fuel--via the throttle and/or the mixture control.
Hope this helps…
Bob
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