Hi Sutts,
I agree with you but would state it slightly differently:
Although manifold pressure ("boost") and rpm are linked in a physical sense, the Merlin boost controller manipulates the throttle valve to maintain a boost pressure setpoint. It will compensate for rpm and height changes within it's mechanical limits, and thus keep boost pressure constant.
IvanK:
Very interesting report. It does make sense that the airscrew efficiency curve could cause a reduction in thrust with increasing rpm. But I think you are right that this is an unusual finding in a specific case that requires investigation. There is not much point giving 3000 rpm availability on the CSP control generally (as was ubiquitous on Hurris and Spits) if this represents a thrust reduction due going past an optimum on a prop efficiency curve.
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