Originally Posted by
Kasserine06
I know this is going to start a lot of controversy, but leaning properly is better for the engine then just leaving the mixtures forward. Every type of engine is different, so it is impossible to make a blanket procedure. It also helps to have cylinder head temps for each head. To simplify it, when you pull the mixture back, it is true that you have less fuel to absorb heat so the temperatures rise, but then pull it back some more and then there is less fuel to make the fire burn hot. The reason so many people don’t like this is because the engine will start to run rough and shake off its mountings. If that happens, you have a poor fuel system. If you have a good fuel injector system, this should not happen.
If you don’t believe me, hunt around the internet for lean of peak operations. I believe John Deakin had a big series on it on AVweb.
For the average pilot, there is "properly leaned". This is typically about 50 degrees F rich of peak (ROP). This provides several benefits:
- Near-peak performance, which means good power and fuel economy.
- Cooler-then-peak temps, which reduces engine wear and possibly avoids catastrophic failure.
- Allows some "slop", or margin-of-error for cylinders which are not all getting EXACTLY the same fuel-air-mixture.
For the high-end operator, there is Lean-of-peak. LOP has these advantages:
- Very near-peak performance, for max power.
- Cooler-than-peak temps.
- Significant fuel savings due to being on the lean side of peak.
The big downside to LOP: It requires a high degree of precision because you have to operate closer to peak than when using ROP. This means that there is NO allowance for slop between mismatched cyclinder or you might have one running at peak which could destroy it in flight. You need some technology:
- Fuel Injection for precise fuel metering. Also the injectors should be matched.
- Individual EGT monitors so you can catch it if one cylinder is dangerously mismatched. A single EGT in the exhaust stream sees only an average of all cylinders, you might not notice if one was out of whack.
Basically, peak mixture provides stoichiometric, or chemically matched combustion. This produces max power and temperatures. ROP operates on the rich side of the peak bell curve, and uses extra fuel to cool the cylinders (somewhat wasteful) . LOP operates on the lean side, but very close to peak. Close enough to get near max power, but just far enough lean to reduce temps to a safe level and save gas. If you get too lean, the engine (or one cylinder) runs like crap.
See your POH for proper procedures, and don't try LOP without the right training and equipment.