Trailer Axel / Physics Puzzler
 

So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary

Trailer Axel / Physics Puzzler
 

QLW wrote:
I've never built a trailer using torsion axels but I like the concept. I
wonder how to design a 2 axle system to achieve equalization? I'm thinking
a rotating sub-frame would be required. I have built several single axle
trailers with trailing arms and coil over springs that worked well but were
a lot of work to build.
IMHO, the balance point will be over the CL of the wheels.

"Gary Warner" wrote in message
...

So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary





Yes you are correct, the wheels are the pivot point, not the rubberised
section & cross beam (it's sorta like the spring hanger, if you had
them:-)) It wouldn't matter if the torsion fittings attached just behind
the coupling or just ahead of the extreme rear, the trailer & it's load
still pivot around the wheels.

K

Trailer Axel / Physics Puzzler
 

I've never built a trailer using torsion axels but I like the concept. I
wonder how to design a 2 axle system to achieve equalization? I'm thinking
a rotating sub-frame would be required. I have built several single axle
trailers with trailing arms and coil over springs that worked well but were
a lot of work to build.
IMHO, the balance point will be over the CL of the wheels.

"Gary Warner" wrote in message
...

So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary

Trailer Axel / Physics Puzzler
 

QLW wrote:
I've never built a trailer using torsion axels but I like the concept. I
wonder how to design a 2 axle system to achieve equalization? I'm thinking
a rotating sub-frame would be required. I have built several single axle
trailers with trailing arms and coil over springs that worked well but were
a lot of work to build.
IMHO, the balance point will be over the CL of the wheels.

"Gary Warner" wrote in message
...

So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary

Out of curiosity, how does one place the axle? Is it at the centerpoint?
I think you'd want it a bit forward of the centerline. I built a box
trailer some years ago, and was advised to have the axle forward of
center under the box. I knew why at the time, but I've since forgotten.



--
Email sent to is never read.

Trailer Axel / Physics Puzzler
 

On Mon, 26 Jan 2004 01:23:21 -0500, "Gary Warner"
wrote:


So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Looking at the specs and not knowing the exact weights involved
(boat/motor and trailer frame), my opinion would be a tad forward of
the wheel's centerline, but with reservations. I have a suspicion
that if you did some basic experimenting, you would find the weight
transfer somewhere between the wheel and axel - more likely towards
the axel than the wheel, but again, not knowing the weights, I can't
say for sure.

Later,

Tom
S. Woodstock, CT
----------
The years will bring their Anodyne,
But I shall never quite forget,
The fish that I had counted mine
And lost before they reached the net.

Colin Ellis, "The Devot Angler" quoted
in A. R. Macdougall, Jr's "The Trout
Fisherman's Bedside Book" (1963)

Trailer Axel / Physics Puzzler
 

"QLW" wrote in message ...
I've never built a trailer using torsion axels but I like the concept. I
wonder how to design a 2 axle system to achieve equalization? I'm thinking
a rotating sub-frame would be required. I have built several single axle
trailers with trailing arms and coil over springs that worked well but were
a lot of work to build.
IMHO, the balance point will be over the CL of the wheels.

"Gary Warner" wrote in message
...

So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary


Your current thinking is correct, if all things equal, AND if you
didn't consider the torsion of the spring. Again, if you put the wheel
at the center of gravity of the boat, it will be balanced. Trouble is,
when this is done, will the boat's C.G. be at the C.G. of the trailer?
See, you could load the boat on the trailer, and the CG of the boat
could be far enough behind that the tongue has a negative load.

Trailer Axel / Physics Puzzler
 

"Gary Warner" wrote in message ...
So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary

Seems to be a pretty good explanition and info on page two of the PDF
you link to unless I am reading the thing wrong. Otherwise, I think
the best bet would be to call them and ask them to clarify for you.
Scotty

Trailer Axel / Physics Puzzler
 

Harry Krause wrote in message ...
QLW wrote:
I've never built a trailer using torsion axels but I like the concept. I
wonder how to design a 2 axle system to achieve equalization? I'm thinking
a rotating sub-frame would be required. I have built several single axle
trailers with trailing arms and coil over springs that worked well but were
a lot of work to build.
IMHO, the balance point will be over the CL of the wheels.

"Gary Warner" wrote in message
...

So the axels that we have are torsion axels (no springs). They will just
attach
directly to the underside of our trailer. The thing is, it's not just a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.

Gary

Out of curiosity, how does one place the axle? Is it at the centerpoint?
I think you'd want it a bit forward of the centerline. I built a box
trailer some years ago, and was advised to have the axle forward of
center under the box. I knew why at the time, but I've since forgotten.

If a standard type of axle, and if placed at the c.g. of the trailer,
it would be in equalibrium, ie: balanced. If placed aft of the
centerline, it would have tongue weight, if forward, when you unhooked
the tongue, it would rise. Now, if using the torsion springed axle,
where there is a lever arm all of this goes out the window, because
the spring torsion, depending on which direction the wheel arm is
pointing, will either try to raise the tongue, or lower the tongue.

Trailer Axel / Physics Puzzler
 

Thanks all for the replys.

I will call the company and ask them too, but I always like
the comments and thought processes I get here.

Trailer Axel / Physics Puzzler
 

"Harry Krause" wrote:

Out of curiosity, how does one place the axle? Is it at the centerpoint?
I think you'd want it a bit forward of the centerline. I built a box
trailer some years ago, and was advised to have the axle forward of
center under the box. I knew why at the time, but I've since forgotten.


I'm not an expert (obviously) but our thinking is: We experimented
with the trailer WITH the boat on it to find a point that is just BACK
of the true center of gravity. A single axel placed right AT the center
of gravity would give essentiall no tongue weight. Moving the single
axel back just a little gives some tongue weight.

In our case we are putting tandem axels. So one axel will go forward
of the point we found and the other back of that point by the same
distance.

Trailer Axel / Physics Puzzler
 

"Gary Warner" wrote in message
...


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .


Over the wheels.

To be precise, over the point at which the wheel contacts the ground, which
had better be directly under the axel.


A thought just crossed my mind: You should also check the tongue weight
when the trailer is empty. From your description it sounds like you won't
have a problem, but I have seen trailers built for a center engine boat that
had negative tongue weight when the boat was NOT on the trailer.

Rod

Trailer Axel / Physics Puzzler
 

A clarification on my previous answer:


"Gary Warner" wrote in message
...


The thing is, it's not just a straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In other
words,
the tires are off-set 6" behind where the axel is.

By definition, an axle (vs axel, which is a figure skating jump) is the
shaft on which the wheels rotate about. In other words, axle = spindle.
The tube that goes across the trailer that contains the torsion bar would be
called something else.

So, the pivot point is at the wheel, where the spindle/axle is.

Sorry for the confusion.

Rod

Trailer Axel / Physics Puzzler
 

"Gary Warner" wrote in message
...

Thanks all for the replys.

I will call the company and ask them too, but I always like
the comments and thought processes I get here.



Since the axle is fixed to the frame, it is part of the frame. The spindles
go where the axle would go if it were straight across. Consider the vector
through the center of mass of the boat and trailer. It should be just
forward of the center of the spindles which is where the upward vector from
the ground passes up. The remainder of the torque is supplied by the force
upwards on the tongue. Just remember that the sum of the torques about any
point must be zero. So pick a convenient point and draw the force vectors.

del cecchi

Trailer Axel / Physics Puzzler
 

"basskisser" wrote in message
om...

Your current thinking is correct, if all things equal, AND if you
didn't consider the torsion of the spring.

What?????

The torsional forces can not have any effect on the trailer balace as long
as the wheels are round or allowed to rotate.

Again, if you put the wheel
at the center of gravity of the boat, it will be balanced.

No, it would need to be at the center of gravity of the boat + trailer.

Trouble is,
when this is done, will the boat's C.G. be at the C.G. of the trailer?

Probably not. Which is why you would want to use the C.G. of boat + trailer
for any calculations.


See, you could load the boat on the trailer, and the CG of the boat
could be far enough behind that the tongue has a negative load.

A universally true statement. Take any boat and trailer, load the boat far
enough back and the tongue weight will go negative.

What's your point?

Rod

Trailer Axel / Physics Puzzler
 

Gary,
When using tandem axles some method of equalizing the weight must be used to
keep one set of axles from being over loaded. The trailer will rarely be
setting perfectly level and without an equalizer the tires will be unequally
loaded as well. In the case of leaf springs, it's done using a common,
rotating equalizer. In your case, I'm not sure. I'd ask the manufacturer
of the axles. This catalog shows the normal axle setup and may show your's
as well.
http://www.championtrailers.com/catalog_pdf.htm


"Gary Warner" wrote in message
...

"Harry Krause" wrote:

Out of curiosity, how does one place the axle? Is it at the centerpoint?
I think you'd want it a bit forward of the centerline. I built a box
trailer some years ago, and was advised to have the axle forward of
center under the box. I knew why at the time, but I've since forgotten.


I'm not an expert (obviously) but our thinking is: We experimented
with the trailer WITH the boat on it to find a point that is just BACK
of the true center of gravity. A single axel placed right AT the center
of gravity would give essentiall no tongue weight. Moving the single
axel back just a little gives some tongue weight.

In our case we are putting tandem axels. So one axel will go forward
of the point we found and the other back of that point by the same
distance.

Trailer Axel / Physics Puzzler
 

"Rod McInnis" wrote in message
...

A thought just crossed my mind: You should also check the tongue weight
when the trailer is empty. From your description it sounds like you won't
have a problem, but I have seen trailers built for a center engine boat
that
had negative tongue weight when the boat was NOT on the trailer.


That's a great point and one I hadn't thought of. Will do it.


Rod

Trailer Axel / Physics Puzzler
 

"Rod McInnis" wrote in message
...
A clarification on my previous answer:


By definition, an axle (vs axel, which is a figure skating jump) is the
shaft on which the wheels rotate about. In other words, axle = spindle.
The tube that goes across the trailer that contains the torsion bar would
be
called something else.


Makes sense and well said. Thanks.

Trailer Axel / Physics Puzzler
 

"QLW" wrote:


Gary,
When using tandem axles some method of equalizing the weight must be used
to
keep one set of axles from being over loaded. The trailer will rarely be
setting perfectly level and without an equalizer the tires will be
unequally
loaded as well. In the case of leaf springs, it's done using a common,
rotating equalizer. In your case, I'm not sure. I'd ask the
manufacturer
of the axles. This catalog shows the normal axle setup and may show
your's
as well.
http://www.championtrailers.com/catalog_pdf.htm


Question: On this axle each wheel has independent suspension. Would this
take care of the situation you mentioned?

Seems to me it might. For example, say the trailer was on totall level
gound
except for one wheel which was on a rock sticking up 3" above level.

Hmmm, maybe not. I just don't know.

Trailer Axel / Physics Puzzler
 

On Mon, 26 Jan 2004 13:33:17 +0000, Gary Warner wrote:


Thanks all for the replys.

I will call the company and ask them too, but I always like the comments and
thought processes I get here.

...then you are one sick and twisted individual! :)

Lloyd

Trailer Axel / Physics Puzzler
 

Lloyd Sumpter wrote:

On Mon, 26 Jan 2004 13:33:17 +0000, Gary Warner wrote:


Thanks all for the replys.

I will call the company and ask them too, but I always like the comments and
thought processes I get here.

...then you are one sick and twisted individual! :)

Lloyd


This from a man who used to have a relationship with a woman known as
Vinyl Valerie.

--
Email sent to is never read.

Trailer Axel / Physics Puzzler
 

"Lloyd Sumpter" wrote in message
...

I will call the company and ask them too, but I always like the comments
and
thought processes I get here.

...then you are one sick and twisted individual! :)

Lloyd


You know, you aren't the first person to make that observation ;)

Trailer Axel / Physics Puzzler
 

"Rod McInnis" wrote in message ...
"basskisser" wrote in message
om...

Your current thinking is correct, if all things equal, AND if you
didn't consider the torsion of the spring.

What?????

The torsional forces can not have any effect on the trailer balace as long
as the wheels are round or allowed to rotate.

Bull****. Are you telling me that if you have a moment arm, and apply
a torsional spring constant to it, that it won't try to rotate about
the axis of the axle???????? If that is true, then a torsion spring,
and it's ensuing torsional constant, aren't doing any work.

Again, if you put the wheel
at the center of gravity of the boat, it will be balanced.

No, it would need to be at the center of gravity of the boat + trailer.




Trouble is,
when this is done, will the boat's C.G. be at the C.G. of the trailer?

Probably not. Which is why you would want to use the C.G. of boat + trailer
for any calculations.

Duh.....that's why I asked...geez... AND, how do you know WHERE that
center of MASS will be?


See, you could load the boat on the trailer, and the CG of the boat
could be far enough behind that the tongue has a negative load.

A universally true statement. Take any boat and trailer, load the boat far
enough back and the tongue weight will go negative.

So, now you want to talk about center of mass as opposed to center of
gravity?

What's your point?

My point is, he didn't mention the relationship between the center of
mass of the boat, and the center of mass of the trailer.
What is YOUR point? I notice you've not interjected one thing to help.

Trailer Axel / Physics Puzzler
 

"basskisser" wrote in message
om...

The torsional forces can not have any effect on the trailer balace as
long
as the wheels are round or allowed to rotate.

Bull****. Are you telling me that if you have a moment arm, and apply
a torsional spring constant to it, that it won't try to rotate about
the axis of the axle????????

Nope. If the wheel is free to rotate (which it will be unless the brakes
are applied AND the wheel is somehow contrained from rotating) then there
will be no moment about the axel.

There will be a moment about the torsion bar, which is NOT the axle .

If that is true, then a torsion spring,
and it's ensuing torsional constant, aren't doing any work.

Correct! Any engineer would be able to tell you that the forces exerted by
a spring (including a torsion bar) do no work when they are at a steady
state condition. A spring will store "potential" energy. While it is
holding that engery it does no work. Work requires a force applied over a
distance. Just an applied force does no work.


Duh.....that's why I asked...geez... AND, how do you know WHERE that
center of MASS will be?

Well, geeze, he said very clearly that he put the boat on the trailer
(actually, he said he put the trailer under the boat) such that the boat was
sitting on the trailer as it was expected to be. Thus, any measurements he
takes will be for the boat + trailer. What each one individually is doesn't
matter for the purpose of this discussion.

So, now you want to talk about center of mass as opposed to center of
gravity?

Nope. On level ground and constant velocity it doesn't matter. To expand
the discussion to include an "accelerated frame of reference" is a lot more
work.

My point is, he didn't mention the relationship between the center of
mass of the boat, and the center of mass of the trailer.

Which is totally irrellavent. He only needs to be concerned about the two
together, which he has taken care of by putting the two together when he
made his measurments.

What is YOUR point? I notice you've not interjected one thing to help.

My point is that some of your comments are false and do nothing but confuse
the issue.

Rod

Trailer Axel / Physics Puzzler
 

"Gary Warner" wrote in message
...


"QLW" wrote:
When using tandem axles some method of equalizing the weight must be
used


Question: On this axle each wheel has independent suspension. Would this
take care of the situation you mentioned?


I thought you were building a single axle trailer. If you are building
tandem axle, then the approach for finding tongue weight is likely to be
wrong, and frankly, I am not sure what the right approach would be.

If you are building a single axle trailer, then "independent suspension" is
not really a factor.

Rod

Trailer Axel / Physics Puzzler
 

On Mon, 2 Feb 2004 11:22:01 -0800, "Rod McInnis"
wrote:


"basskisser" wrote in message
. com...

The torsional forces can not have any effect on the trailer balace as
long
as the wheels are round or allowed to rotate.

Bull****. Are you telling me that if you have a moment arm, and apply
a torsional spring constant to it, that it won't try to rotate about
the axis of the axle????????

Nope. If the wheel is free to rotate (which it will be unless the brakes
are applied AND the wheel is somehow contrained from rotating) then there
will be no moment about the axel.

There will be a moment about the torsion bar, which is NOT the axle .

If that is true, then a torsion spring,
and it's ensuing torsional constant, aren't doing any work.

Correct! Any engineer would be able to tell you that the forces exerted by
a spring (including a torsion bar) do no work when they are at a steady
state condition. A spring will store "potential" energy. While it is
holding that engery it does no work. Work requires a force applied over a
distance. Just an applied force does no work.


Duh.....that's why I asked...geez... AND, how do you know WHERE that
center of MASS will be?

Well, geeze, he said very clearly that he put the boat on the trailer
(actually, he said he put the trailer under the boat) such that the boat was
sitting on the trailer as it was expected to be. Thus, any measurements he
takes will be for the boat + trailer. What each one individually is doesn't
matter for the purpose of this discussion.

So, now you want to talk about center of mass as opposed to center of
gravity?

Nope. On level ground and constant velocity it doesn't matter. To expand
the discussion to include an "accelerated frame of reference" is a lot more
work.

My point is, he didn't mention the relationship between the center of
mass of the boat, and the center of mass of the trailer.

Which is totally irrellavent. He only needs to be concerned about the two
together, which he has taken care of by putting the two together when he
made his measurments.

What is YOUR point? I notice you've not interjected one thing to help.

My point is that some of your comments are false and do nothing but confuse
the issue.

Now, do you actually believe this guy basskisser's claim to be a
structural engineer, and have a PE license?

Steve

Trailer Axel / Physics Puzzler
 

"Rod McInnis" wrote in message ...
"basskisser" wrote in message
om...

The torsional forces can not have any effect on the trailer balace as
long
as the wheels are round or allowed to rotate.

Bull****. Are you telling me that if you have a moment arm, and apply
a torsional spring constant to it, that it won't try to rotate about
the axis of the axle????????

Nope. If the wheel is free to rotate (which it will be unless the brakes
are applied AND the wheel is somehow contrained from rotating) then there
will be no moment about the axel.

Really? Have you thought about the fact that the wheel is NOT "free to
rotate"? There is drag from the bearings, and the tire is not round,
the contact patch is virtually flat, affecting the outcome even more.

There will be a moment about the torsion bar, which is NOT the axle .

If that is true, then a torsion spring,
and it's ensuing torsional constant, aren't doing any work.

Correct! Any engineer would be able to tell you that the forces exerted by
a spring (including a torsion bar) do no work when they are at a steady
state condition. A spring will store "potential" energy. While it is
holding that engery it does no work. Work requires a force applied over a
distance. Just an applied force does no work.

so you are trying to say that all will be fine with your analysis up
to the point where a load is applied, and or the trailer is moved,
correct? I think I want to measure MY trailer's performance under
actual conditions. I could care less about it's performance when
parked, except for it's abiltity to resist the forces of the boat, and
wind, snow, etc. loads.


Duh.....that's why I asked...geez... AND, how do you know WHERE that
center of MASS will be?

Well, geeze, he said very clearly that he put the boat on the trailer
(actually, he said he put the trailer under the boat) such that the boat was
sitting on the trailer as it was expected to be.

Very clearly said that? That's odd, here is the original post:
So the axels that we have are torsion axels (no springs). They will
just
attach
directly to the underside of our trailer. The thing is, it's not just
a
straight
across axel. Well, the axel goes straight across, but coming from the
center of the axel is a 6" arm that goes back to the spindle. In
other
words,
the tires are off-set 6" behind where the axel is.

For a picture go to this web sire (really an Adobe PDF document)
and see page 5 (the 2,300 lb to 3,500 lb Torflex axel).
http://www.redneck-trailer.com/pdf/A/810torflex.pdf


PUZZLER: Does the axel "balance" the weight over the
axel or over the wheels? .

Put another way: Say we had a rectangular frame 20 feel long and
it was perfectly balanced at the 10 point. (No boat or anything on
it yet.) So a straight across axel put at the 10' point, it'd
basically
balance. But with our axels, where the wheels are off-set 6"....do
we put the AXEL at that 10' point or do we have the
WHEELS at that 10' point.

Our current thinking is that it's the wheels. It's pretty hard to
test
because of the weights involved and we have to weld the axels on
(not bolt 'em) so we'ld like to get it right the first time.


Thus, any measurements he
takes will be for the boat + trailer. What each one individually is doesn't
matter for the purpose of this discussion.

So, now you want to talk about center of mass as opposed to center of
gravity?

Nope. On level ground and constant velocity it doesn't matter. To expand
the discussion to include an "accelerated frame of reference" is a lot more
work.

My point is, he didn't mention the relationship between the center of
mass of the boat, and the center of mass of the trailer.

Which is totally irrellavent. He only needs to be concerned about the two
together, which he has taken care of by putting the two together when he
made his measurments.

Wrong, again, please read the above ORIGINAL post.

What is YOUR point? I notice you've not interjected one thing to help.

My point is that some of your comments are false and do nothing but confuse
the issue.

Nah, that's YOU!

Trailer Axel / Physics Puzzler
 

"basskisser" wrote in message
om...

Really? Have you thought about the fact that the wheel is NOT "free to
rotate"? There is drag from the bearings, and the tire is not round,
the contact patch is virtually flat, affecting the outcome even more.

Well, up to now the discussion had been limited to the trailer sitting still
in the driveway, so rolling resistance wouldn't be a factor. Even so, the
drag from the bearings is so small that it can safely be ignored. The drag
of the brakes might be measurable, but the rolling resistance of the tire
(essentially the flexing of the sidewalls) will dwarf everything else. Even
so, I have never even heard of anyone even attempting to calculate or
measure what the rolling tongue weight would be in comparison to the
stationary tongue weight.


so you are trying to say that all will be fine with your analysis up
to the point where a load is applied, and or the trailer is moved,
correct?

I don't know how you made this leap. All the discussion has been with the
boat (the load) applied.

I think I want to measure MY trailer's performance under
actual conditions.

Loading the boat on the trailer and measuring the resulting tongue weight,
which is what Gary did, is about as close as you can come to measuring under
actual conditions, unless you want to go to the trouble of constructing a
strain gauge on your hitch to measure the forces as you travel down the
road.

I could care less about it's performance when
parked, except for it's ability to resist the forces of the boat, and
wind, snow, etc. loads.

So far, I have only commented on the tongue weight, and have made no
predictions about the "performance" of the trailer. Tongue weight is
generally considered to be a "static" problem. As I have said several
times, to analyze the trailer in an accelerated frame of reference is far
beyond anything that we have discussed. This would require knowledge of the
material strength of the trailer, the exact construction, and how boat and
trailer contact each other.

I have no idea if this trailer is going to sway or fishtail. This is a
dynamic problem. I can tell you what the tongue weight will be (except for
wind effects) while it is at a constant velocity. That is a statics
problem.


Very clearly said that? That's odd, here is the original post:

Yes, he very clearly said that the boat was sitting on the trailer. Why did
you quote his description of the axle? It has nothing to do with the
discussion of how the boat was sitting on the trailer when he measured the
tongue weight.

Perhaps you didn't follow the entire thread. Go back and read it from the
beginning. Look at the pictures that he provided. Read how he placed the
trailer under the boat, supported the entire rig on blocks and measured the
tongue weight. Examine the table he created where he moved the axles and
extended the tongue. Once you understand what the discussion is about, then
maybe you can offer an explanation as to why the tongue weight didn't change
much when he extended the length of the tongue. Or maybe you can't,
considering you making false claims back when we discussed this in theory a
couple of months ago.