In article ,
"Tim" wrote:

The point was how much do you gain by stopping a fixed pitch prop, as
opposed to letting it wind mill.

A lot.

You can actually do this experiment in a plane with a variable-pitch
prop. Idle the engine, and play with the prop control. I did this
years ago in a 182RG during dead stick landing drills. The difference
in glide performance between the two extreme prop settings was quite
dramatic, almost like having an extra set of very fast acting flaps.

There's also the conservation of energy argument. If the engine is
turning, the energy to overcome friction and compression has to come
from somewhere.

rg