push vs pull vis a vis rudders
 

On Thu, 01 Apr 2004 13:01:41 GMT, (Steven Shelikoff)
wrote:

On 01 Apr 2004 03:15:26 GMT, (JAXAshby) wrote:

yeah, sure. rudder right, tranny forward, throttle forward and what
happens
....???

Most times you go right. Sometimes you go left. If you've never gone
left when doing the above, you need some more experience.

sherr tells us the more experience he has the more he don't know which way
his
boat is gonna go thusly:

Joxie, say it ain't so! With all your claimed sea experience you've
never had the boat turn in a different direction than where you had the
rudder pointed? Oh, that's right. You're just a hired hand with no
helm experience. If you had any time at the helm in poor conditions
you'd know just how foolish you're looking right about now.

schlackoff, when the wind and/or current was pushing me one way or the other I
knew it long before I put the boat in forward or reverse.

Of course. Just like you *should* know about prop walk but apparently
don't if you don't know which way you boat will turn when you throw it
in reverse.

And in those conditions, just like prop walk in reverse, you won't know
which way an unfamiliar boat will turn when you put the rudder one way
or another. In all cases, that doesn't mean the rudder has no effect.
It only means it can't overcome other effects

Steve

push vs pull vis a vis rudders
 

On Thu, 1 Apr 2004 11:45:50 +0100, "JimB"
wrote:


Steven Shelikoff wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"

So I hung the spatula just behind the fan. Lo and behold, the
same
thing happens but just a little less. When I rotate the
spatula to the
left, there is a noticable *left* motion to the blade... i.e.,
it's not
only drawn forward into the blade but it also moved to the left
from
where it was when the spatula blade was perpendicular to the
fan. When
I turn it to the right, the spatula swings to the right.

Steve, that was the experiment I first did. Then I realised that,
to yaw the boat, I had to look solely at lateral force. To do
this I had to constrain the card so that it could only hinge
laterally (no fore and aft motion permitted). This is where the
bits of wire came in. The card had a bit of wire attached rigidy
to the top, sticking at 45 deg horizontal angle to the card. The
card end of the wire bent down to stop the card swinging around
the wrong end of the wire. I hung the card (your spatula I
guess!) through two loops (hinges) first mounted parallel to the
centre line of the fan, then at right angles.

This gave a different result, very little lateral swing, lots of
fore and aft swing. Of course (a weakness in the experiment) it

Your experiment seems to be flawed if you're trying to look solely at
lateral force with no fore and aft motion permitted and yet you get a
lot of for and aft swing.

To prove to myself again that there is a lateral force even with no fore
and aft movement, I put a string around the bottom end of the spatula
which would allow it to swing laterally but hold it from being moved
toward the fan. So, we have a plastic spatula hung by the little
hanging hole at the top from a hook which allows it to swing in all
directions like a pendulum but I can firmly control the angle of the
blade by turning the hook. And there is a string looped around the
handle just above the blade which I can hold to prevent the blade from
moving towards the fan so there's no fore and aft motion.

Result: same thing. When it's behind the fan and you turn the blade so
that it's not perpendicular to the fan, the spatula swings *only*
laterally since there's a string keeping it from moving toward the fan.

My initial conclusion has only been reinforced.

Steve

push vs pull vis a vis rudders
 

On Thu, 1 Apr 2004 11:45:50 +0100, "JimB"
wrote:


Steven Shelikoff wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"

So I hung the spatula just behind the fan. Lo and behold, the
same
thing happens but just a little less. When I rotate the
spatula to the
left, there is a noticable *left* motion to the blade... i.e.,
it's not
only drawn forward into the blade but it also moved to the left
from
where it was when the spatula blade was perpendicular to the
fan. When
I turn it to the right, the spatula swings to the right.

Steve, that was the experiment I first did. Then I realised that,
to yaw the boat, I had to look solely at lateral force. To do
this I had to constrain the card so that it could only hinge
laterally (no fore and aft motion permitted). This is where the
bits of wire came in. The card had a bit of wire attached rigidy
to the top, sticking at 45 deg horizontal angle to the card. The
card end of the wire bent down to stop the card swinging around
the wrong end of the wire. I hung the card (your spatula I
guess!) through two loops (hinges) first mounted parallel to the
centre line of the fan, then at right angles.

This gave a different result, very little lateral swing, lots of
fore and aft swing. Of course (a weakness in the experiment) it

Your experiment seems to be flawed if you're trying to look solely at
lateral force with no fore and aft motion permitted and yet you get a
lot of for and aft swing.

To prove to myself again that there is a lateral force even with no fore
and aft movement, I put a string around the bottom end of the spatula
which would allow it to swing laterally but hold it from being moved
toward the fan. So, we have a plastic spatula hung by the little
hanging hole at the top from a hook which allows it to swing in all
directions like a pendulum but I can firmly control the angle of the
blade by turning the hook. And there is a string looped around the
handle just above the blade which I can hold to prevent the blade from
moving towards the fan so there's no fore and aft motion.

Result: same thing. When it's behind the fan and you turn the blade so
that it's not perpendicular to the fan, the spatula swings *only*
laterally since there's a string keeping it from moving toward the fan.

My initial conclusion has only been reinforced.

Steve

push vs pull vis a vis rudders
 

schlackoff wrote:

push vs pull vis a vis rudders
 

schlackoff wrote:

push vs pull vis a vis rudders
 

On Thu, 1 Apr 2004 12:24:46 +0100, "JimB"
wrote:


Limitations of the experiment:
It didn't check for associated force changes at the fan
The scale of 'rudder' against fan size is way out
The wire had a little flexibility
Fag ends produced smoke which rose too fast
Reynolds numbers were wrong.

And, just in case you mis-understood, my hinges were pendulum
hinges which did not allow the 'rudder' to rotate around its
vertical axis (except in the 'rudder kick' experiment). They only
allowed pendulum movement laterally, or when re-oriented, fore
and aft (subject to wire flexibility).
.....
JimB


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

push vs pull vis a vis rudders
 

On Thu, 1 Apr 2004 12:24:46 +0100, "JimB"
wrote:


Limitations of the experiment:
It didn't check for associated force changes at the fan
The scale of 'rudder' against fan size is way out
The wire had a little flexibility
Fag ends produced smoke which rose too fast
Reynolds numbers were wrong.

And, just in case you mis-understood, my hinges were pendulum
hinges which did not allow the 'rudder' to rotate around its
vertical axis (except in the 'rudder kick' experiment). They only
allowed pendulum movement laterally, or when re-oriented, fore
and aft (subject to wire flexibility).
.....
JimB


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

push vs pull vis a vis rudders
 

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

push vs pull vis a vis rudders
 

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

push vs pull vis a vis rudders
 

On Fri, 02 Apr 2004 01:59:44 GMT, Brian Whatcott
wrote:

On Thu, 1 Apr 2004 12:24:46 +0100, "JimB"
wrote:


Limitations of the experiment:
It didn't check for associated force changes at the fan
The scale of 'rudder' against fan size is way out
The wire had a little flexibility
Fag ends produced smoke which rose too fast
Reynolds numbers were wrong.

And, just in case you mis-understood, my hinges were pendulum
hinges which did not allow the 'rudder' to rotate around its
vertical axis (except in the 'rudder kick' experiment). They only
allowed pendulum movement laterally, or when re-oriented, fore
and aft (subject to wire flexibility).
....
JimB


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.

A refinement of this setup is the Heale-Shaw device, in which the flow
is enclosed between two parallel transparent plates. The models are
the same thickness as the spacers that close the sides.

This keeps the flow truly 2D without any surface waves to distub it.



Rodney Myrvaagnes NYC J36 Gjo/a


"Curse thee, thou quadrant. No longer will I guide my earthly way by thee." Capt. Ahab