Hi italia458,
As stated numerous times, if the flight velocity is zero, there is zero THP - that is what the equation says, not me.
That's odd because the relationship "THP = SHP * p.e." is from NAVAVSCOLSCOM-SG-111 page 4 and the equation tells me that I am developing THP if I am converting SHP using a propeller which has an efficiency >0. There is no mention of aircraft speed.
Your formula involving aircraft speed is good for explaining climb performance etc. but is not exclusive to explaining THP.
So, standing on the earth we consider that to be an inertial reference frame.
I disagree - standing on earth is not an inertial frame of reference. Your observation of the "free fall" flight of a golf ball shows you that you are in an accelerating frame of reference.
A "balanced turn" can simply be measured using a spirit level. The bubble has to be in an accelerating reference frame (that's gravity to those of us who haven't studied general relativity) else it wouldn't "float" to the top.