While I certainly understand the concept, can anyone interpret what they see on the user guide, pages 174-175, figures 207 and 208.Specifically, please interpret what these two figures are saying! I believe fig 207 shows #1 peaked the first #4 peaked second while 2&3 haven't peaked yet. I don't get what the 1-10 and the -06 mean. my wild guess would be that #1 is now 10 degrees lean of peak and #4 is 6 degrees lean of peak. Fig 208 looks like #1 is 19 degrees lean of peak and is the first to peak and there is 0.1 of a gallon difference between the first and last cylinder to reach peak. I'm just not sure!
What I really need to know is which cylinder peaked the first and set the mixture accordingly.
You are mostly correct. However you want to know the last one to peak from the rich side (or first to peak from the lean side), and then lean from there. Lest do a virtual flight in a NA airplane.
Take off, full rich WOT/Max RPM.
Climb at Vy x 1.32 or Vz
Target EGT should typically be 1300dF EGT, every now and then lean to this target in the climb.
Level out, let the plane accelerate, then do a BMP (Big Mixture pull) That is a swift and progressive sweep, not like shutting down to ICO, but a quick and progressive sweep. As soon as it decelerates or changes tone, stop!!! You are now nicely LOP.
Let things cool off.
If you want to squeeze the optimum out of the engine, find peak from the lean side, using the first one to peak, then lean to the appropriate amount LOP. This is NOT 50dF LOP, not unless you are up around 75+% power.
Stay LOP for the cruise and the descent. Go full rich on final if you want to, but hey, most RV's have too much mumbo so a LOP go around is perfect. If you land rich, re-lean again on the ground for taxi.
What is appropriate LOP?
Simple, Best BSFC. Where is that then?
80% Power or more: 60-80dF LOP
75% power: Approx 40dF LOP
70% power: Approx 25dF LOP
65% power: Approx 10-15dF LOP.
Remember this though, if you look at a Lycoming power setting table or graph, this is rich mixture powers. So a MAP/RPM that gives you say 78% power will actually be 10% less when you are appropriately LOP. In other words if you start at 78% power and lean to the lean side of peak EGT, you will end up appropriately LOP around 71% power. So how much LOP should that be? Around 25dF of course! Serendipitously the BMP works at all MAP/RPM and the references above just always work.
The Dynon system is one of the few that actually guess the LOP/ROP state pretty well. It can get confused slightly when at high altitudes, and it might think you are around peak, when in fact you are LOP, but dont worry, these things are never perfect.
Once you know your critical cylinder (richest) just sue raw data on that one, forget using the lean find. Lean find is a great educational tool but the hysteresis and the algorithm will never be as good as you and the raw data. Lean find usually gets you slightly leaner than optimal and a few knots slower. Not harmful, just not optimised.
Last of all, 500 feet, ripping up the beach, WOT/2450 and 60-70dF LOP, breaks the rules of old wives tales. Grossly over square and well above 65% or 70% power.............and the engines LOVE IT. There is no such limit or anything on LOP or for that matter over square which DOES NOT EXIST. They are both old wives tales not matter what you have read, where you read it or what your mates think. Science rules supreme, and the data has no opinion.
Hope that helps. And thanks to the crowd for the kind words. My colleague and good friend John Deakin would be proud of y'all.
