912i Why full rich only beyond 92% throttle?

[FlyingForFun]

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[CharlieTango]

92% throttle, much like your 912ULS approach WOT and you are full rich.

OK, so that means you should pitch your prop to very fine to get optimum performance at altitude. That way, you can approach 5500 RPM with less than 92% throttle, so you'll still get good leaning. Correct?

Sure, that would meet the objective to achieve best climb and best cruise speeds with some detuning in order to remain in a leaned condition. Look at it this way, there are 2 methods to achieve economy, 1 is coarse prop and low power settings but this does not accomodate good climb and high speed cruise, the other method is to rely on leaning instead of coarse pitch and this method can take advantage of high speeds due to flat pitch.

My mission is better suited if I focus on best speed and climb and not compromise to be in a leaned condition so I get a bit more performance but more often I am full rich.

There is another factor, you can only move so much air through an engine at high altitude so the burn is reduced and I can plan on 5gal / hour instead of 6 even though I am full rich.

[CharlieTango]

You guys lost me, but if the engine is too rich running WOT at altitude, it needs less fuel or more air. So if turning the engine at higher rpm would move more air, and it would, that seems logical. It would have more air, a more proper fuel/air mixture, make more power, and waste less raw fuel. I think. Then the limiter might be how fast can/should you turn the engine for an extended period of flight. I'm sure prop efficiency and stuff such as that factors in somewhere.

Or get a turbo charger.

RPM decrease with altitude, I can turn 5,500 at 11,000' but it falls way off at 14,000' so the idea that a faster turning prop can give you a more proper mixture is backwards.

I have always flown at high altitudes and the limitation isn't how fast we should turn the motor altitude limits that, instead the limitation is available power. Rotax's design forces us to fly rich when at altitude if we want to realize all available power which is limited.

[FlyingForFun]

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[CharlieTango]

the 914 offers an unbelievable performance increase but has a real need for an adjustable prop and isn't being widely offered. The 912i not.