"Doug" wrote in message
ps.com...
Actually, on a moving river, water speed matters and frequently speed
(well, distance really) relative to the ground matters.
....local obstructions dictate
you concern yourself with distance of run relative to the land....

Sure. That's why I said that *if* the river is arbitrarily long, and if you
don't care where you land, *then* you just ignore the land and care only
about the speed of the air relative to the water. (Those stipulations make
the situation analogous to the hypothetical conveyor belt scenario.)

The ideal setup
is to have a headwind while pointing downstream. That way you have
slowest waterspeed and shortest run.

The plane's speed relative to the water (the plane's waterspeed) depends
only on the plane's airspeed and the speed of the air relative to the water.
It doesn't depend in any way on the speed of the water relative to the land;
hence, it doesn't depend on whether you're going upstream or downstream.
Rather, it just depends on whether you're going upwind (relative to the
water) or downwind.

As for making the shortest run (relative to the land), wouldn't you want to
be going upwind (relative to the water) and upstream, rather than upwind and
downstream?

--Gary