On 29 Mar 2004 23:27:42 GMT, (JAXAshby) wrote:

schlackoff, you are using a constrained airflow? know what that means? know
how it is different from unconstrained.

Interesting that you think it makes a difference. Ok, try it again but
this time with a theoretical infinitely sized wind tunnel, or a physical
one large enough that the difference between constrained flow and
unconstrained flow is negligable, like a 1 mile diameter wind tunnel and
a 1" rudder. In one case the air in an infinite wind tunnel is being
pushed at 1mph past the rudder and in the other case it's being drawn
past the rudder at 1mph. In both cases, air is flowing past the rudder
at 1mph and the rudder is at a 45 degree angle. Does the rudder
generate a lateral force in both cases?

Steve

wtf are you talking about?

Bzzzt!!! Wrong answer jox. Try again. It's clear you don't understand
the sprinkler problem. While you're cogitating on why you're wrong in
applying feynman's sprinkler problem to this arena, here's another,
simpler question for you:

Say you have a wind tunnel with a rudder mounted at the test point.
First case is a blower at one end forcing air though the tunnel and past
the rudder at 1mph. You turn the rudder at a 45 degree angle to the
airflow. Is there a lateral force generated by the rudder?

Second case is a blower at the other end of the tunnel but now it's
sucking air through the tunnel past the rudder at 1mph. You turn the
rudder at a 45 degree angle to the airflow. Is there a lateral force
generated by the rudder?


Intuitively, most people sense that water "pulled" over a rudder will
cause
a
rudder to change direction of a boat in much the same way as water
"pushed"
over a rudder does. However, intuition misses some things along the way.
[...]
end) to port. However, the water drawn over the rudder's port side hits
that
side and is deflected towards port. Then the rudder would push the boat
(after end) to starboard. And equal and opposite reaction. Net, net, the
boat
does not turn. The pressure on each side of the rudder is equal. Nada.


Jox, since you're such an "expert" on Feynman inverse sprinkler problem
and how to misapply it to any situation, maybe you can answer a question
about it. While it's true that the sprinkler won't turn when water is
being sucked in, it's not true that no net force is generated by sucking
the water in. In fact, there is a net force generated. It's just not
in a direction that will turn the sprinkler.

In relation to your discussion about about equal and opposite, net net,
no net force, etc., how do you reconcile that with the fact that it's
not true for the inverse sprinkler problem?

Steve

steve, consider just where the air on the "supply side" of the fan blades come
from and consider how that differs from the air on the "demand side". the
demand side is more or less a stream that expands. the supply side is more
like a hemi-sphere of air (actually, air from the demand side passes back to
the supply side as each blade of the fan passes, i.e. tip vortices).

Consider, also, that *if* fluid drawn over a rudder by a prop have any effect
on the rudder, mariners would all know which direction the stern moved with
which rudder position. Even the guys who insist pulled water affects a rudder
don't have a clew which way the boat turns. indeed, the "good professor" was
reduced to claiming that friction in the rudder bearin made the difference.

schlackoff, you are using a constrained airflow? know what that means?
know
how it is different from unconstrained.

Interesting that you think it makes a difference. Ok, try it again but
this time with a theoretical infinitely sized wind tunnel, or a physical
one large enough that the difference between constrained flow and
unconstrained flow is negligable, like a 1 mile diameter wind tunnel and
a 1" rudder. In one case the air in an infinite wind tunnel is being
pushed at 1mph past the rudder and in the other case it's being drawn
past the rudder at 1mph. In both cases, air is flowing past the rudder
at 1mph and the rudder is at a 45 degree angle. Does the rudder
generate a lateral force in both cases?

Steve

wtf are you talking about?

Bzzzt!!! Wrong answer jox. Try again. It's clear you don't understand
the sprinkler problem. While you're cogitating on why you're wrong in
applying feynman's sprinkler problem to this arena, here's another,
simpler question for you:

Say you have a wind tunnel with a rudder mounted at the test point.
First case is a blower at one end forcing air though the tunnel and past
the rudder at 1mph. You turn the rudder at a 45 degree angle to the
airflow. Is there a lateral force generated by the rudder?

Second case is a blower at the other end of the tunnel but now it's
sucking air through the tunnel past the rudder at 1mph. You turn the
rudder at a 45 degree angle to the airflow. Is there a lateral force
generated by the rudder?


Intuitively, most people sense that water "pulled" over a rudder will
cause
a
rudder to change direction of a boat in much the same way as water
"pushed"
over a rudder does. However, intuition misses some things along the
way.
[...]
end) to port. However, the water drawn over the rudder's port side hits
that
side and is deflected towards port. Then the rudder would push the
boat
(after end) to starboard. And equal and opposite reaction. Net, net,
the
boat
does not turn. The pressure on each side of the rudder is equal. Nada.


Jox, since you're such an "expert" on Feynman inverse sprinkler problem
and how to misapply it to any situation, maybe you can answer a question
about it. While it's true that the sprinkler won't turn when water is
being sucked in, it's not true that no net force is generated by sucking
the water in. In fact, there is a net force generated. It's just not
in a direction that will turn the sprinkler.

In relation to your discussion about about equal and opposite, net net,
no net force, etc., how do you reconcile that with the fact that it's
not true for the inverse sprinkler problem?

Steve

On 30 Mar 2004 00:17:24 GMT, (JAXAshby) wrote:

steve, consider just where the air on the "supply side" of the fan blades come
from and consider how that differs from the air on the "demand side". the
demand side is more or less a stream that expands. the supply side is more
like a hemi-sphere of air (actually, air from the demand side passes back to
the supply side as each blade of the fan passes, i.e. tip vortices).

Consider that it doesn't really matter as long as there is flow of fluid
media over the rudder.

Consider, also, that *if* fluid drawn over a rudder by a prop have any effect
on the rudder, mariners would all know which direction the stern moved with
which rudder position. Even the guys who insist pulled water affects a rudder
don't have a clew which way the boat turns. indeed, the "good professor" was
reduced to claiming that friction in the rudder bearin made the difference.

Consider the fact that fluid drawn over a rudder by a prop may have an
effect on how the stern moves, but one that is much less then prop walk.

Steve

Consider that it doesn't really matter as long as there is flow of fluid
media over the rudder.

but it does, because the rudder and prop are hooked together. If the prop were
fixed as to direction, the rudder would turn into it until the movement
stopped.

Consider the fact that fluid drawn over a rudder by a prop may have an
effect on how the stern moves, but one that is much less then prop walk.


the "good professor" argued that without friction in the rudder bearings rudder
would move. I say it doesn't.

plainly, a shot of forward throttle with the rudder turned turns the stern, and
all (most?) mariners know in which direction the boat will turn from
experience. nobody can remember which direction a boat will turn with a shot
of reverse throttle because nobody has seen it.

On 30 Mar 2004 01:37:32 GMT, (JAXAshby) wrote:

Consider that it doesn't really matter as long as there is flow of fluid
media over the rudder.

but it does, because the rudder and prop are hooked together. If the prop were
fixed as to direction, the rudder would turn into it until the movement
stopped.

no it doesn't. It doesn't matter that they are attached. The rudder
will have an effect if there is water flowing over it. Whether that
effect is just to lessen or greaten the larger effect of prop walk, it's
still an effect.

Consider the fact that fluid drawn over a rudder by a prop may have an
effect on how the stern moves, but one that is much less then prop walk.

plainly, a shot of forward throttle with the rudder turned turns the stern, and
all (most?) mariners know in which direction the boat will turn from
experience. nobody can remember which direction a boat will turn with a shot
of reverse throttle because nobody has seen it.

Of course that doesn't mean the rudder has no effect at all, which is
what you claimed.

Steve

think it through, steve. think it through.

no it doesn't. It doesn't matter that they are attached. The rudder
will have an effect if there is water flowing over it.

so, which way does the stern move if the rudder is to port?

On 30 Mar 2004 19:53:18 GMT, (JAXAshby) wrote:

think it through, steve. think it through.

no it doesn't. It doesn't matter that they are attached. The rudder
will have an effect if there is water flowing over it.

so, which way does the stern move if the rudder is to port?

forward or reverse? rh prop or lh prop? how much prop walk?

Steve

Of course that doesn't mean the rudder has no effect at all, which is
what you claimed.

you can't see it, you can't measure it, you can't detect that it is there at
all, but it still exists? How is that?

And which way does the stern move with the rudder one way or the other?


Steve

On 30 Mar 2004 19:54:48 GMT, (JAXAshby) wrote:

Of course that doesn't mean the rudder has no effect at all, which is
what you claimed.

you can't see it, you can't measure it, you can't detect that it is there at
all, but it still exists? How is that?

You can measure it. You can detect if it's there or not. All you need
are stress sensors on the rudder post to measure what the rudder is
doing.

And which way does the stern move with the rudder one way or the other?

That's a big "it depends". Of course that doesn't mean the rudder has
no effect. The same thing can be said for the engine in forward. I.e.,
you can't predict which way the boat will turn when you turn the rudder
one way or another if other factors, like the wind, have a greater
effect than the rudder.

Steve

Steven Shelikoff wrote:

Consider that it doesn't really matter as long as there is flow of fluid
media over the rudder.

Again, here you're assuming laminar (or at least unidirectional)
flow. When inserted into a laminar flow stream, and angled surface,
such as a rudder, will certainly be subjected to a force related to
the mass of the fluid deflected. Fluid flow on the 'suction' side is
nowhere near laminar, and will in fact be totally non-uniform around
the rudder. All fluid will be redirected immediately upon clearing
the rudder, and the resulting reaction force is parallel to the
boats centerline.


Consider, also, that *if* fluid drawn over a rudder by a prop have any effect
on the rudder, mariners would all know which direction the stern moved with
which rudder position. Even the guys who insist pulled water affects a rudder
don't have a clew which way the boat turns. indeed, the "good professor" was
reduced to claiming that friction in the rudder bearin made the difference.


Consider the fact that fluid drawn over a rudder by a prop may have an
effect on how the stern moves,

It *may* for a brief instant until an equilibrium is reached and the
pressure equalizes on both rudder surfaces (remember, water is *not*
elastic in the way air is, so you can't create a vacuum in water
like you do in air - if you do, you cavitate and dissolve gases come
out of solution until the partial pressures equalize and/or until
water 'fills in the void' and the gases redissolve).

but one that is much less then prop walk.

Many orders of magnitude less IME and IMO.

Keith Hughes