Brian, you just described a prop pushing a water stream over a rudder. pull is
different.


An experimental rig for visualizing fluid flow over
rudders etc., is easy to make and provably representative of 2-D flow.

It consists of an inclined board with side rails to stop the water
film dripping off. A reservoir at the top, into which water from a
hose pipe flows, and a sump at the other end to lead the waste water
to a drain.

At the top of the incline, permanganate crystals trail stream lines
down the incline.

The model (a rudder cross section, for instance) is placed in the
stream. The stream lines tilt sidewards ahead of the rudder, when it
is inclined at a modest angle to the flow, and tilt sidewards the
other way after the model trailing edge.

This is an easy way to show the "molecules give lift by hitting the
proximal surface" enthusiasts how fluid dynamics really works.
(about two thirds of the side force from the distal surface, and one
third from the proximal surface.) You can work it out from the
streamline spacing over both surfaces.

Brian Whatcott Altus OK