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.