@"dennis@home"
Now do that without the chemical energy
being used by your muscles!

That's absolutely correct Dennis - and why I stated:

"To put it back in the skateboard example, the energy to power my arms
has to
come from somewhere ..."

Rubbish.
snip
Any attempt to move air by the propeller
must use energy by definition.

You are again correct -- by definition, a propeller *does work on the
air*(but only relative to itself) and it must be provided an input
torque on it's shaft to do to so. But it's not rubbish in any way to
assert that a propeller can be used to slow the wind down relative to
the ground even when it's traveling at the speed of the wind -- and
that's what the paragraph that you 'Rubbished" said.

Nice set of brakes there.

And again, correct -- to extract any energy from the rotation of the
wheels, there will of course be a resultant braking force. This
braking force can be calculated as can the thrust of the propeller.
Only if the thrust is equal to or greater than the braking force can
any given speed be maintained or accelerated from.

Go on then.

I will do so, but give me a bit to put a post together. I'm off to
lunch at the moment.