|
On the subject of LOP operation, I am going to summarize my current understanding of the subject, as it would apply to operating a P337 in the real-world. I would like to hear from any of you that are knowlegable on the subject if you detect in errors in my thinking.
1. The main argument for running LOP is that you can save around 10% on fuel at the same effective power setting (same BMEP). Secondary arguments are that LOP operations are cleaner, and therefore better for the engine and the environment, and that peak cylinder pressures and temperatures are also lower.
In a P-skymaster flown 100 hours per year, this would translate into approximately 250 gallons saved per year, or around $750 on fuel costs (about $7.50 per hour). There is the potential for further savings resulting from cleaner running and having good engine monitoring (eg: spotting problems early). These savings could be substantial, but are difficult to quantify.
2. The main impediments to running LOP are that (1) the air/fuel distribution to individual cylinders varies too much and, therefore, they peak at different times. So, if you lean enough to get the richest cylinder running LOP, the leanest cylinder will probably be too lean to run properly, resulting in rough operation. This is the problem that GAMI injectors are designed to solve.
3. The secondary impediment to running LOP is that you need good instrumentation to make sure that each individual cylinder is running within appropriate temperature limits even if you have GAMI injectors, because there is still some variability between cylinders. This problem is solved by getting an engine monitor (eg: JPI).
4. While some people do climb LOP, most people restrict LOP operations to the cruise mode of flight. To implement LOP in cruise, the power is set at some known level (eg: 65%) according to the POH settings. The engine is then leaned so that the richest cylinder is operating at around 50 degrees LOP. This leaning should be done fairly quickly (especially at higher power settings) because you don't want to spend much time at settings in the neighborhood of 50 degrees rich of peak (this is where temperatures and pressures are greatest). The manifold pressure is then advanced to restore the lost airspeed (used as a proxy for power). If done correctly, this should result in the engine operating at the same power, but with CHT's approximately 30 degrees cooler than the same power given by the POH at "best power" settings. It will also result in the roughly 10% fuel savings.
5. In any event, one is not likely to cause detonation, or otherwize damage the engine, if indivual CHT's are kept below 400 degrees or so, no matter what you do with the mixture control (or the manifold pressure for that matter).
Comments?
|