Slowrotor
That is the answer.
I finally understand, I think, what you've been getting it. The high speed outboard sections on the rotor have the highest profile drag. Now, you stated that at high speed the induced drag is less, that is the crux of the problem. The induced drag is that component of the lift in the horizontal. In autorotations, it is the same component that provides the driving force for the rotor. As you say, it is less at higher speeds, so, as you move outboard along the rotor, the profile drag increases while the horizontal component of lift reduces. I think my explanation, with the lift vector tilting backwards can be ignored. This may very well never happen. More important is the fact that at some point along the blade span, the profile drag will exceed the driving force. From this you can also see that the blade mid-sections driving force is bigger than the profile drag there. This 'surplus' is used to overcome the drag near the root and that at the tip.
Dave
I'd completely forgot about Gordon Leishman's book! Thanks for reminding me. Yeah, phi is always the inflow angle.