Operation with the engine at maximum boost should be limited to
- prop at fine to prevent overstressing the engine.
- prop at coarse to prevent overstressing the engine.
- prop at windmill to prevent overstressing the engine.
Explanation from PART66Online
Maximum boost is take-off power, and it is used with the propeller in fine pitch so the engine turns at its maximum governed speed. What overstresses a piston engine is the opposite arrangement, high manifold pressure held against a low rpm: the over-square condition raises mean and peak cylinder pressure and gives the charge the time and temperature it needs to detonate. Hence the handling order, rpm up before boost is applied and boost off before the propeller is coarsened, which is why the propeller lever is the first control forward and the last one back. A fine setting does not invite an overspeed on a constant-speed installation, because the governor holds the selected speed and the fine pitch stop is set at certification so that full power against it cannot take the engine far beyond its maximum permitted speed.
Storklubba asked · 17 Mar 2024
While the question and answer is not wrong, the wording seems ambigious. "Maximum boost" is not a very technical term, and a simple (overspeed) clarification behind overstressing would be good. When i read this question i think that maximum boost means maximum power, and with the propeller at coarse you would be extracting more power from the engine therefore possibly "overstressing" it. I offcourse understand the answer they are looking for is coursing off the blade to not overspeed the engine and prop at high power. Am i missing something?
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