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Old 03-13-2012, 08:17 PM   #1
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Rivet Collyn Rivers on towing dynamics

I found an interesting set of discussions from Down Under on towing dynamics and stability. Let's start with Collyn Rivers on Caravan Dynamics

The clarity is outstanding. As are the references. These links (and this thread) are for those who find the technical aspects of trailering of interest.

This link goes into a bit of depth: Caravan World Article and Sway

And a calculator as a help to both links above: Kilograms to Pounds (kg to lbs) Conversion

Another good page discussing stability on the Australian caravanersforum.com. Very interesting posts by Collyn Rivers there from Nov 16 through Nov 18, 2011. With a nod to the value of 2airishuman's great input on such subjects, I originally had a lengthy quote from Collyn Rivers in my original post re: independent suspension from this last link on that forum. A bit much per copyright concerns. But let's summarize that...

As with aerodynamics, the science of suspensions goes back to the beginnings, sometimes to the very beginning (1903 in this case) and much was accomplished by the 1920's (IFS FA with leaf sprung RA on a TV for instance) and the quote ended with the idea that the interactions between the axles on a TV (in this instance) are already complicated enough before one adds the TT. The difficulty of prediction.

A quite interesting aside about engineer Maurice Olley and his influence to this day. From the post on Nov 18:
Quote:
Originally Posted by Collyn Rivers on CaravanersForum
He suggests roll axis position is better measured than calculated (and, having tried, feel he is not wrong!). He fortunately even shows how to build a rig do so - and commercial rigs are available today that follow his concept (that he did in fact build).
. . .
. . .

Apologies to most readers - but this issue is only rarely discussed - and will be of probable interest to some and is really best described in engineering terminology. It further illustrates the extraordinary complexity and interaction of vehicle handling issues - even before one tows another one!
.
.
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Old 03-13-2012, 08:51 PM   #2
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I miss 2 air. Not long after we joined he disappeared. I hope it wasn't something we said. I search old threads and there he is. I hope he's doing well.

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Old 03-13-2012, 09:00 PM   #3
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Trailer Dynamics References

Also (in the event the thread links above are lost):

University of Bath .pdf
The Dynamics of Towed Vehicles

Bailey of Bristol:
Towing Safety: Trailer Loading Stability Game

.
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Old 03-13-2012, 09:09 PM   #4
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Originally Posted by Disneysue925 View Post
I miss 2 air. Not long after we joined he disappeared. I hope it wasn't something we said. I search old threads and there he is. I hope he's doing well.

Sue
Yes, I lit a candle on March 5th myself. Think of 2Air as one of the blazing comets. Generates heat, light, dissension. No time to waste on niceties as time is limited . . . would it be that we are around for the next appearance.

Maybe, as apparition, but even more fun as Il Commendatore (from Don Giovanni[Samuel Ramey])


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Old 03-13-2012, 10:12 PM   #5
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Must Read

Good thread and thanks for posting.

For those more experienced transport drivers this information is not new but its always good to review the facts.

Anyone without that experience that is going to tow a trailer should read and try to understand this concept of weight and mass.

This information will help you make decisions that might keep out of trouble.

Dave

Quote:
Originally Posted by REDNAX View Post
He'd have already linked this great .pdf from Down Under. Probably the day after it went online:

Collyn Rivers on Caravan Dynamics

The clarity is outstanding. As are the references. These links (and this thread) are for those who find the technical aspects of trailering of interest.

This link goes into a bit of depth:

Caravan World Article and Sway

And a calculator as a help to both links above:

Kilograms to Pounds (kg to lbs) Conversion

A quote from a related forum post re Independent Suspension (TV):
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Old 03-15-2012, 12:01 PM   #6
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Hello readers. Thank you for your patience as we worked out a copyright issue. That has led me to more in-depth reading of REDNAX' research. Most excellent!

And I would readily refer anyone to the full range of articles at the Collyn Rivers index page from which REDNAX got his first link - http://caravanandmotorhomebooks.com/articles/index.htm

Happy reading...
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Old 03-15-2012, 02:02 PM   #7
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REDNAX and others: Thank you so much for the posts and references to the Collyn articles and other material. The information on vehicle dynamics is outstanding, and I will need to re read it again to digest it all. It is very interesting to me at the moment, especially with my new towing setup problems with the Jeep Quadra Lift air suspension on my TV. His references to WD hitches is most interesting, as well as his take on how sway control systems are involved. His take on placement of the mass in the trailer is giving me some additional thoughts on how my own rigs are set up.

Again, great information and thanks so much for the post.
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Old 03-31-2012, 05:05 PM   #8
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Going back to my phyiscs and aircraft performance classes, he's right on the money about end weight being much more difficult to control once a swaying motion gets going.

But I think he missed a big factor that actually makes it worse, and made me slap my forehead for not seeing it earlier. What is right at the front and rear on many of our airstreams? Water tanks. Particularly that fresh water tank that's right under the rear goucho in mine. Please correct me if I'm wrong, but these tanks are not baffled, correct?

If you get a strong wave motion going inside the fresh water tank, it's going to be a fair amount of energy slopping from side to side at the tail end of the trailer. This is going to work towards maintaining the wave motion, and thus working toward maintaining the swaying motion at the rear of the trailer.

Run an empty tank, and you don't have any water mass to worry about. Run a full tank, and there isn't any empty space for the waves to build on, and thus no space for the mass to shift. Run a 2/3 full tank? Pretty close to the perfect amount to generate the maxiumum wave moment.

-Hans
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Old 03-31-2012, 07:32 PM   #9
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Question

My equalizer hitch that came with my 27 foot Overlander extends out the back of my receiver hitch socket almost 2 feet more than a regular hitch does.. Not only does this extend the down force on the rear of my TV,, but adds to the distance from the rear axle almost 30% more..

Just for fun,, I picked up a normal length receiver hitch and 2 5/16" ball the other day to just set the trailer onto the ball to see how much less rear sag I ended up with without the weight bars.. The TV would sag 6" at the ball without the load bars and with the shorter hitch/ball it only pulled it down about 3"...

I must say with the equalizer hitch all set up proper,, and with strong cross winds I felt I had to be totally be awake to keep it all stable at 60mph.., No where near the safe point I would ask my wife to drive for any distance.

Now my first idea was to just cut off and drill a new pin hole in the old hitch system bar to get the ball more near the step bumper like a normal hitch would be.. But I guess I just need to understand why its so long to start with?

Need some sharp AS experts to help me understand all this..

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Old 03-31-2012, 09:02 PM   #10
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Originally Posted by Sodbust View Post
But I guess I just need to understand why its so long to start with?
Sodbust
Two of the reasons that the "stingers" are available extra long are: a.) to help insure that you can back the trailer in a cramped turn nearly jacknifed and not have the corner of the trailer hit the corner of the tow vehicle (or vice-versa ...), and b.) so that the rear tailgate / doors of the tow vehicle can be fully opened while hitched up without them hitting e.g. the propane tank covers or tongue jack on the trailer. But as you note, there is a price to be paid with this extra lever arm length. All of life is compromise.
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Old 03-31-2012, 10:00 PM   #11
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Originally Posted by HHaase View Post
Going back to my phyiscs and aircraft performance classes, he's right on the money about end weight being much more difficult to control once a swaying motion gets going.

But I think he missed a big factor that actually makes it worse, and made me slap my forehead for not seeing it earlier. What is right at the front and rear on many of our airstreams? Water tanks. Particularly that fresh water tank that's right under the rear goucho in mine. Please correct me if I'm wrong, but these tanks are not baffled, correct?

If you get a strong wave motion going inside the fresh water tank, it's going to be a fair amount of energy slopping from side to side at the tail end of the trailer. This is going to work towards maintaining the wave motion, and thus working toward maintaining the swaying motion at the rear of the trailer.

Run an empty tank, and you don't have any water mass to worry about. Run a full tank, and there isn't any empty space for the waves to build on, and thus no space for the mass to shift. Run a 2/3 full tank? Pretty close to the perfect amount to generate the maxiumum wave moment.

-Hans
I look forward to all these different points. Vehicle spec country to country colors advice and certain assumptions, as well as use (paved versus unpaved roads for example) but Mr. Ross is good reading no matter any potential differences.

As to the water tank I see it as being one of advantage, not disadvantage. Water is the second most important "function" of a travel trailer (after mobility: the ability to travel), and as such is crucial. A full fresh water tank is part of the definition of a travel trailer as I see it. I know that there are those who travel with little to no fresh water trusting that clean potable water will always be available to them en route and at their destination. I disagree, and I believe the designers/engineers who put the overlapping concerns of a TT together did also.

A full fresh water tank is -- in itself -- heavy, but where it is located is the only real concern. Atop, between or near the axles is enough to take care of the adverse weight problem. Additionally, a full fresh water tank helps keep COG [center of gravity] closer to ground level which is a distinct advantage. The shape and capacity of these tanks isn't going to support much of a wave side-to-side. Proper hitch rigging and tire pressure is far more important . . this concern is quite a bit lower in the scheme.

One would be advised that loading the trailer ends, either, is of concern, especially behind the axles. Thus the discussions elsewhere over two things: proper tongue weight, and individual wheel/tire weights where both are sorted if necessary after checking on a certified scale. Tire load reserve (not just load rating) pretty well covers this given a stock configured trailer so far as I'm concerned.

I would no more pull out of a location with an empty fresh water tank than I would without a pre-trip inspection. It is -- water -- central to the most basic function of a travel trailer, and the trailer is designed to take that into account. Full propane is third. These -- mobility, water, propane -- constitute a trifecta of what is most important to a TT.

The adjusted "empty" weight of a trailer includes full propane tanks and full fresh water tanks plus permanent trailer supply & equipment as an important first step in determing individual wheel loads, TW and axle weights. I have not -- yet -- found where a full or empty water tank shows on an individual axle much less a wheel position from derived scale weights (yes, I have stood around the truckstop near the CAT Scale and drained the water tank to determine if there will be a difference) unlike the difference between empty and full propane tanks on TW (still not worthy of worry).

Now there may be trailers out there with compromises (my least favorite is rear or front kitchens) where changing the several hundred pounds of water/propane can make a difference. Maybe when near to GVWR or potentially quite heavy TW. I would hope it is not on an A/S or AVION, SILVER STREAK or STREAMLINE. Maybe a front slide TT would be more prone to changes. It certainly would be an engineers challenge given the propensity some owners might have for their food & supplies loading to go overboard without a scale check.

There have been some frame-off, ground-up rebuilds with, in my mind, questionable changes to water tank locations, but it is well-understood, I think, to keep them low and central. Two tanks might actually be more common that one big tank for this reason (and not just due to location constraints), but there aren't many TT's with twin fresh water tanks to my knowledge.

.
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Old 03-31-2012, 10:40 PM   #12
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I ignored the quote I took above, in that I am sorry to hear of any other locations (etc.), but caught myself too late to edit the above.
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Old 03-31-2012, 11:17 PM   #13
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Excellent comments folks.

B/c of the "wave motion effect" on stability of the AS, ( and the weight ) we travel with our fresh water tank,( and the other two as well,) as empty as possible, especially at highway speeds, which for us is about 62mph. The higher the speeds, the more dramatic the wave motion dangers.

We plan fresh water fill closer to our intended destination if we believe we it necessary. We usually stay at a CG close to our intended boon dock destination to fill tanks,etc.

Great discussions. Thank you....Zigi
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Old 04-01-2012, 09:16 AM   #14
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Brain food,, MORE please!

Lots of good info here.. I would think that from what I see is the AS holding tanks are very shallow.. Not large square top heave boxes like some of the SOB have. This should help cut back the wave action of the fluids as long as the tanks are near full or near empty..

All I know first hand was our SOB had a rear kitchen... It towed well until my wife loaded up her 34 pot and pans,, and several large cast iron skillets, and a month's worth of canned food.. Then the tail wanted to wag bad..

As for my equalizer hitch being 2 foot longer than what I would call normal ,, from the one post that addressed this for me says that I should think about cutting it back as much as I feel I can get away with before the trailer wants to rub paint with my TV..

A great uncle,,, and early AS lover had an older equalizer hitch that also stuck out 2 feet longer than it should.. He went to move his AS one day and the metal in the hitch had fatigued over the years and broke off right at the hitch receiver.. Since the trailer had sat for years with no land line the battery was dead so the trailer brakes did not kick in.. The trailer coasted down a hill and crashed into some parked cars taking out the whole front end of his 1958 AS.. A sad day for sure..

What made matters worst was he was a handy man with no limits,, and took it upon himself to fix it with some roofing flashing and sheet metal screws and it looked like crap when done..

Sodbust
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