After lunch discussions of engine management with George and Tim, George took me up for a miniseminar on engine management as we checked the final adjustments.
As usual, fly your plane per your POH and ignore the nuts on the internet. But Deakin’s articles on the subject bear regular rereading.
Georges results show that so long as you are 50-100F or more LOP, you may regulate your engine power by the mixture control from 55% to 85%, with the CHT’s telling you if you are asking too much. His redline is 380F, based on metalurgy. The only place he noted caution is VERY low, say 500ft MSL on a cool day, where you want to be 100F LOP not 50F to prevent excessive cylinder pressures.
The cruise technique is known as Wide Open Throttle Lean of Peak Standard Operating Procedure (WOTLOPSOP) and relies on the Big Pull. Climbs are conducted full power, ROP per the POH. To enter cruise, you reduce to 2500rpm at full power, level off, let airspeed build, then pull the mixture back in one motion on a 5 second count until you just feel the plane deaccelerate slightly. That will put you 75-100F LOP, and as George puts it, ‘parks’ the engine in a safe place. It doesn’t require you to watch any gauges since it is all done by feel and works well in a busy ATC environment. For me that ends up around 14gph. To verify you are LOP, you can push the mixture slightly forward and observe the EGT’s rise, then go move it back. You can do power reductions with the mixture; we were able go 12.5gph at 27" with no roughness whatsoever. To climb, advance the mixture to rich, for descents lean for reduced power if desired. Basicly we never touched the power lever until entering the traffic pattern for landing. Who needs FADEC?
While running WOTLOP is the best time to check your mags. It is the most demanding on the spark, and will detect marginal plugs much earlier than a ground runup. George has a very specific technique–turn the key to MAG2 and then pull your fingers off the key as if it is hot! You should observe the EGT’s rise on all cylinders. Then go back to both and repeat for MAG1 – pop your fingers off the key! Again EGT’s rise.
The reason for the hot-key release is if you have a bad mag. With a bad mag the engine will die. What he doesn’t want you to do is instinctively turn the key back to BOTH. That will produce a potentially damaging backfire. If the engine dies, then you should pull the throttle&mixture back to idle before turning the key to BOTH, then smoothly add back the power mixture then throttle. By yanking your hand off the key as you turn it, you prevent your instinct from taking over.
I use ROP for climbs, since climbs make the engine get richer, and LOP for descents since descents make the engine get leaner, WOTLOPSOP for cruise below 10,000MSL, and standard ROP at 2700rpm for high altitude cruise. The LOP operations produce noticeably cooler CHT’s and should prolong engine life.
Now if we could just turbonormalize this engine and turn the plane into the 200kt cruiser it should be! But that’s the subject of another trip report…