Jim,

I would define fully unloaded as flight at pitch speed, at the fully unloaded RPM. It is a function of a rising variable, which defines itself.

If an engine tachs at 12K on the ground and unloads in flight to 14K. And at that speed the engine manages to "screw" the prop through the air; the blade's angle of attack is 0, relative to the surrounding medium. I would call this a fully unloaded condition.

Prop blades have drag even at 0 degrees and it is far from zero. With the blade tips exceeding 0.7 Mach, it is very tangible.

A high pitched prop is statically stalled to a higher extent, because more of its blade disk area is at an excessive angle of attack. This is the reason such a prop is quite low on static thrust.

You do need to richen the main needle before flying, as I described in post #6 in the thread, or your own way. After flying the plane and listening, you can fine tune the richness.

Sincerely,