On Sun, 28 Mar 2004 00:35:03 GMT, "Derek Rowell"
wrote:

.....
That's not how we do business in science and engineering. We calmly look
at a situation, make hypotheses and conjectures and then think of a set of
experiments to disprove or prove our ideas. We invite others to disprove
our theories, and rejoice when they do, because we learn something.


From: "Derek Rowell"




Derek,
In hopes you didn't give up on this list altogether, here's a little
puzzle you might enjoy. There is a demonstration of the Feynman
sprinkler puzzle somewhere at MIT.

What simple modification could you easily introduce to the nozzle in
order to demonstrate a force due to suction as well as that due to
pressure? Perhaps I could hint that it would augment the force? :-)

Brian W

to demonstrate a force due to suction

there is no force in nature called "suction". none.

There is a demonstration of the Feynman
sprinkler puzzle somewhere at MIT.

the link was posted last night. the guy who hijacked the professor's email
addy should have taken greater care in whose address he grabbed, for it would
seem the real professor at MIT would have long ago known of the demo that any
student -- or his mother or even little sisten in grade school -- could walk up
to and push the button to see for himself.

On 27 Mar 2004 23:50:22 GMT, (JAXAshby) wrote (with
possible editing):

derek, your fricken fraud. I just now noticed your fiticious email address of
mit.edu. NObody from MIT would write what you wrote.

geesh, dude. get a life.

From: "Derek Rowell"


oops! He's a professor there!
--

Larry
Email to rapp at lmr dot com

maybe *some* derek rowel is a professor at MIT, but the clown posting as he
here most definitely is not. NO professor at MIT would write the tripe he
wrote.

hell, you know the poster is a fraud. he both claims to be a Mechanical
Engineer and an expert in fluid flow.

the poster claiming to be derek rowell is probably the janitor. the guy who
learned his "fluid flow" knowledge cleaning toilets.

derek, your fricken fraud. I just now noticed your fiticious email address
of
mit.edu. NObody from MIT would write what you wrote.

geesh, dude. get a life.

From: "Derek Rowell"


oops! He's a professor there!
--

Larry
Email to rapp at lmr dot com

On Sun, 28 Mar 2004 13:47:47 GMT, L. M. Rappaport
wrote:

From: "Derek Rowell"


oops! He's a professor there!


Not surprising that he's offering an opinion on fluid dynamics.
While supersonic flow is studied more by aero engineers these
days, slow speed fluid flow is the province of mechanical engineers.

Take a look at "Fluid Mechanics" Fogiel/Cimbala
for an example.
Cimbala is Prof of Mech Eng at Penn State.

Brian W

brian, you have been suckered. that was not derek rowell professor of stress
analysis in Mech Eng, but rather someone pretending to be him. NO professor at
MIT would write what that clown wrote. None. He would be laughed at the rest
of the staff, and some disgruntled student would report him to the president
for disciplinary action. Who would pay money to "learn" something that is
known so wrong by the entire staff?

L. M. Rappaport
wrote:

From: "Derek Rowell"


oops! He's a professor there!


Not surprising that he's offering an opinion on fluid dynamics.
While supersonic flow is studied more by aero engineers these
days, slow speed fluid flow is the province of mechanical engineers.

Take a look at "Fluid Mechanics" Fogiel/Cimbala
for an example.
Cimbala is Prof of Mech Eng at Penn State.

Brian W

supersonic flow

supersonic flow was mentioned by no one in this context, and is not important
to note in this context.

Derek Rowell wrote:
Would you all agree that in areas of dispute the truth may be revealed by an
experiment?

Yes, if the experiment is setup properly, and the data is
*accurately* analyzed and interpreted.

Please try the following:
Take a fan, say a large house cooling fan (that's your propellor). Take a
flat surface, for example a stiff lightweight book (thats the rudder).
Turn the fan on and hold the rudder at an angle on the outflow side
(transmission in forward). Does the flow exert a torque (turning effect) on
the rudder? Let go one corner and see. Is there a sideways thrust that
you have to oppose to keep the rudder in position?

Clearly. f=ma, i.e. force is the product of Mass times
acceleration. In this case the mass of accelerated air will apply
disproportionate force to the 'book' as a function of aspect
ratio. Basically, the book will "weathervane" until the force
applied to each side equalizes.

Repeat the experiment with the "rudder" on the inlet side of the fan
(transmission in reverse). Is there a turning effect (torque) or not? Is
there a sideways thrust on the "rudder"?
You tell me - I just did it. The answers to all four questions is yes.

And...irrelevant! YES there is force on the 'vane', just as there
was on the downstream side. Less due to the the wider flow pattern
on the suction side, but still significant.

However, in the context of the boat model, this force is virtually
irrelevant. In the first case, water is forced over the rudder at
an angle to the boat centerline. It's a simple vector equation.
Water moves to starboard, reaction force is thus to port, the boat
turns starboard.

In REVERSE, the water flow, *irrespective of rudder position* is
along the centerline of the boat, thus the reaction force is
parallel to the keel line, and the boat moves straight back
(ignoring the precessional forces that result in 'prop walk' that
is). It's only when the boat moves through the water that the
rudder can have an effect - another simple vector equation. There
must be additional non-parallel force applied in order to produce
a turn, and that is caused by *additional* water flow past the
rudder caused by boat movement.

Aero/hydrodynamic lift/drag is determined by the flow patterns over surfaces
(Bernoulli effects, etc), not by the simple minded pseudo-science that is
being thrown around here.

Lift and drag are irrelevant. Consider, what is the effect of lift
on the rudder? Heeling action, not turning action. You appear to
be confusing hdyrodynamics with simple force/vector equations.

It's a VERY complex situation.

Not at all. Oh the precessional effects are definitely complex,
all the more so when hydrodynamic effects are added in the
equation, but precession, while important to why your stern always
drifts one way in reverse (i.e. force applied to a spinning object
- the propeller - will be translated 90° in the direction of
rotation, creating a turning force), is not a factor in why the
rudder is ineffective in reverse.

We all agree
that in practice the effect is much, much weaker in reverse but it is still
present. (The reason that it is weaker is that only a small fraction of
the in-flow to the propellor actually passes over the rudder in reverse.)

Sorry, but that's just not accurate.

Keith Hughes

nice, accurate response, Keith.

From: Keith Hughes
Date: 3/27/2004 7:07 PM Eastern Standard Time
Message-id:

Derek Rowell wrote:
Would you all agree that in areas of dispute the truth may be revealed by
an
experiment?

Yes, if the experiment is setup properly, and the data is
*accurately* analyzed and interpreted.

Please try the following:
Take a fan, say a large house cooling fan (that's your propellor). Take a
flat surface, for example a stiff lightweight book (thats the rudder).
Turn the fan on and hold the rudder at an angle on the outflow side
(transmission in forward). Does the flow exert a torque (turning effect)
on
the rudder? Let go one corner and see. Is there a sideways thrust that
you have to oppose to keep the rudder in position?

Clearly. f=ma, i.e. force is the product of Mass times
acceleration. In this case the mass of accelerated air will apply
disproportionate force to the 'book' as a function of aspect
ratio. Basically, the book will "weathervane" until the force
applied to each side equalizes.

Repeat the experiment with the "rudder" on the inlet side of the fan
(transmission in reverse). Is there a turning effect (torque) or not?
Is
there a sideways thrust on the "rudder"?
You tell me - I just did it. The answers to all four questions is yes.

And...irrelevant! YES there is force on the 'vane', just as there
was on the downstream side. Less due to the the wider flow pattern
on the suction side, but still significant.

However, in the context of the boat model, this force is virtually
irrelevant. In the first case, water is forced over the rudder at
an angle to the boat centerline. It's a simple vector equation.
Water moves to starboard, reaction force is thus to port, the boat
turns starboard.

In REVERSE, the water flow, *irrespective of rudder position* is
along the centerline of the boat, thus the reaction force is
parallel to the keel line, and the boat moves straight back
(ignoring the precessional forces that result in 'prop walk' that
is). It's only when the boat moves through the water that the
rudder can have an effect - another simple vector equation. There
must be additional non-parallel force applied in order to produce
a turn, and that is caused by *additional* water flow past the
rudder caused by boat movement.

Aero/hydrodynamic lift/drag is determined by the flow patterns over
surfaces
(Bernoulli effects, etc), not by the simple minded pseudo-science that is
being thrown around here.

Lift and drag are irrelevant. Consider, what is the effect of lift
on the rudder? Heeling action, not turning action. You appear to
be confusing hdyrodynamics with simple force/vector equations.

It's a VERY complex situation.

Not at all. Oh the precessional effects are definitely complex,
all the more so when hydrodynamic effects are added in the
equation, but precession, while important to why your stern always
drifts one way in reverse (i.e. force applied to a spinning object
- the propeller - will be translated 90° in the direction of
rotation, creating a turning force), is not a factor in why the
rudder is ineffective in reverse.

We all agree
that in practice the effect is much, much weaker in reverse but it is still
present. (The reason that it is weaker is that only a small fraction of
the in-flow to the propellor actually passes over the rudder in reverse.)

Sorry, but that's just not accurate.

Keith Hughes