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Constant Pitch Propeller increasing RPM keeping TAS constant

Assume I am flying straight and level with power setting 21 inches of MAP and 2300 RPM with TAS=100 kts, now I change my Prop lever only (MAP = no change & TAS = no change) from 2300 to 2500, since now with same power output from engine and demand for propeller to spin faster, the governor will fine-tune the pitch, now keeping the TAS same and propeller RPM increase thereby leading to fining the pitch, the blade AOA will reduce, or doesn't it?

The image given is for constant pitch propeller, is there a similar diagram for constant speed propeller?

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When you adjust a constant speed propeller to a higher rpm, this will be done by making the propeller blade AoA smaller.

Contrary to your question though, manifold pressure and power output will not remain constant unless you adjust the throttle. Neither will your airspeed, not surprisingly.

Exact effect will depend on the engine, but basically power is torque x rpm, so for a constant throttle position, increase in rpm will increase power output unless we are near max rpm.

See What is the relation between manifold pressure, RPM, and power, in a constant speed prop? for reference.

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There's a one word answer for this, yet the site discourages brief answers. But the answer is yes, your reasoning is correct. I'm not sure what kind of diagram would help clarify that fact.

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