Quote:
Originally Posted by RV10inOz
DA is what effects the engine. And while Superior print what they print, that is so dummies do not do dumb things at high power, but I can assure you there is no scientific reason not to run LOP at 1000' but "do not lean the mixture" really means do not lean it on the rich side of the curve at high power settings.
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David is right, in that the manufacturers instructions really don't have anything to do with altitude. Let's look at specific examples.
Subject is an IO-360 angle valve at 20 degrees timing, running with the pro-detonation thermal conditions (very high CHT, oil temp, and intake air temp) required by certification.
Mixture sweep at 2700 RPM and full throttle, i.e. 28.5 MP. Note that as the mixture is leaned (right to left on the chart) it gets into light detonation from about 50 ROP to 50 LOP.
2700 RPM and 26.8 MP. It doesn't matter if the 1.7" MP reduction is due to altitude gain or throttling. The result is the same; no mixture position results in detonation. At this undersquare RPM/MP, you can do anything with the mixture knob, despite being at about 81% power.
2400 RPM and full throttle (28.6"), an oversquare setting hard against the "Maximum Manifold Pressure For Continuous Operation" line on the left side of a Lycoming power chart. At fuel flows higher that 70 lbs per hour there is no detonation, but you most surely
would not want to lean below 70...not even a big pull to somewhere LOP. Under these conditions you would need to be more than 100 LOP to stay out of detonation. Point here is that merely being LOP is no blanket guarantee of safe operation; there are other factors in play.
Linear Mode
