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Old 09-13-2012, 07:48 PM   #29
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I can't get the link to work. It just gives a link to a pdf converter not the paper.

Perry

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If anyone is interested in the SAE paper aforementioned, it can be read here for no charge: download/delphi__com pdf techpapers 2008 01 1228.pdf download article pdf. There may be other sites too, but this is the one I found.
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Old 09-13-2012, 08:11 PM   #30
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Yep the driver is usually the destabilizing force. When the conditions are such that the driver is perturbing a poorly damped system then bad things happen. Sway control is what keeps the system from becoming unstable when the driver and other forces perturb the system. When the trailer is swaying a lot slow down. I have found rutted highways are the most troublesome because the trailer is wider than the two vehicles and it wants to be in a different part of the rut than the tow vehicle.

Sway can happen even without a trailer. I lost control of my truck in the rain. The road was very slick with an oil film, there was nothing in the back of my truck, and one rear tire was overinflated since it had just been patched and I had not let some air out of it. I changed lanes and the truck started fish tailing to the point there it was yawing 180 degrees and my front bumper caved in the door of the truck next to me. I finally locked up the brakes and stopped the oscillations and almost ran off the mountain in the process. If the truck had a hand brake to pull the truck straight I could have gotten out of it. Steering into the skid made it worse because I was out of phase and was making it worse.

Perry

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A damped oscillation in response to transient road effects is completely normal, and is NOT a cause for concern. The thing we're concerned about is uncontrolled growing oscillations. Most times, the driver is an important part of causing those oscillations, and if he would stop trying to "correct" things would die down again. However, the stability equations for trailers DO indication some conditions when uncontrollable sway can occur, and the following factors most exacerbate this:

1) insufficient tongue weight
2) grossly excessive speed
3) trailers loaded with high polar moment of inertia.

There are others, as others have commented.

- Bart
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Old 09-13-2012, 08:56 PM   #31
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The best articles I have seen on trailer towing dynamics and sway are the ones by Colin Rivers pointed out in this thread by Rednax.

http://www.airforums.com/forums/f238...ics-88681.html
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Old 09-13-2012, 10:46 PM   #32
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I definately agree with that statement, and I'll stick my neck out and say any travel trailer will sway, if it's towed fast enough.

Additionally, I'll state that not all travel trailers tow the same, and what's more, not all Airstreams tow the same.

As an example, we had a 23' Airstream that we towed a lot, and NEVER had a swaying event. But, later had a 25' that was a bear to tow, wanted to sway all the time, and only stopped after I switched to a ProPride hitch. Interesting also this same trailer wore tires very rapidly, so I suspect that axle alignment contributed to the tendency to sway.

These statements are from my expereince towing trailers, not from an engineering viewpoint as I am not a mechanical engineer.
So is this something with all the longer Airstreams? I've seen a number of pictures on the net with 23' & small being towed by a 1/2 ton pickup and parked in the ditch next to the road because of what the drivers reported as sway. I had thought that the 25' and longer were perhaps more stable when being towed. The wife and I are considering a 25' or 27' to be towed by a 3/4 ton pickup and I am just curious about what I can expect.

Cheers,
Rion
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Old 09-13-2012, 11:10 PM   #33
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So is this something with all the longer Airstreams? I've seen a number of pictures on the net with 23' & small being towed by a 1/2 ton pickup and parked in the ditch next to the road because of what the drivers reported as sway. I had thought that the 25' and longer were perhaps more stable when being towed. The wife and I are considering a 25' or 27' to be towed by a 3/4 ton pickup and I am just curious about what I can expect.

Cheers,
Rion
Hi, you can expect to have many-a-great-time with your trailer. The list is too long, but with driver ability, the truck and trailer combination that you mentioned, both vehicles maintained and loaded properly, and a proper hitch set-up you should be fine.

"My trailer is eight years old. It has been in 13 Western States and in three Provinces. Towed in all kinds of weather, in heat, cold, wind, rain, snow, and even ice. My Alaska trip alone was over 10,000 miles. And with all of this, my trailer has only swayed, violently out of control once; It was parked in my driveway during a 5.0 Earth Quake."
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Old 09-14-2012, 06:03 AM   #34
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Mr UKToad - what kind of gas mileage are you getting with the Sienna?
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Old 09-14-2012, 08:12 AM   #35
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Originally Posted by GinMame View Post
So is this something with all the longer Airstreams? I've seen a number of pictures on the net with 23' & small being towed by a 1/2 ton pickup and parked in the ditch next to the road because of what the drivers reported as sway. I had thought that the 25' and longer were perhaps more stable when being towed. The wife and I are considering a 25' or 27' to be towed by a 3/4 ton pickup and I am just curious about what I can expect.

Cheers,
Rion
Rion, Sway is not a normal happening with an Airstream if everything is setup right. Since I had those troubles with the 25', I've owned two other trailers, a 28', and now a 31', and neither have had any sway issues.

And, as far as length goes, I once towed a friend's 34' when his truck broke down, and the 34 was far more stable than any other trailer I've ever towed. I suspect that is because of the three axles.

As ROBERTSUNRUS said, you won't have any troubles. Just get an expereinced Airstreamer to help you set up the hitch, and no most dealers are NOT good at setting up a hitch. They just want you out the door after they have collected the money.
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Old 09-14-2012, 08:47 AM   #36
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Rion, Sway is not a normal happening with an Airstream if everything is setup right. Since I had those troubles with the 25', I've owned two other trailers, a 28', and now a 31', and neither have had any sway issues.

And, as far as length goes, I once towed a friend's 34' when his truck broke down, and the 34 was far more stable than any other trailer I've ever towed. I suspect that is because of the three axles.

As ROBERTSUNRUS said, you won't have any troubles. Just get an expereinced Airstreamer to help you set up the hitch, and no most dealers are NOT good at setting up a hitch. They just want you out the door after they have collected the money.
Sway can happen with any size Airtstream.

I settled a claim for the trailer, with a family that lost their mother and father
in a loss of control accident caused by a sway, that resulted in a roll over.

The tow vehicle was a 1/2 ton truck.

The trailer?

A 17 foot Caravel.

No load equalizing hitch, or sway control was in use.

Andy
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Old 09-14-2012, 09:00 AM   #37
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Sway

Sway can very easily be caused by a mother nature gust of wind, and/or by a large passing or oncoming vehicle.

Wind speed tests were made in 1970, and filmed.

Andy
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Old 09-14-2012, 11:15 AM   #38
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Here is a link to a sway simulator that can be a useful tool in understanding sway. Sway can be initiated by anything, wind, the driver, a bump in the road etc. If you run the game/simulation you will see that as your speed increases the sway gets worse and takes longer to go away. At a certain speed anything can cause you to lose control. The higher the speed the closer you get the natural frequency of the system. You can slow down, change the way the trailer is loaded, or add damping or some combination of the three. Running at high speeds with no sway control and an improperly loaded trailer is trouble waiting to happen. Your trailer and tow vehicle are a mass spring system and there are certain combinations that are unstable. By unstable, I mean that you disturb the system and the oscillations get worse and you wreck. A stable system is one where the oscillations get smaller and damp out. You can tell when the system is on the edge. Just a little steering input will cause the trailer to sway. This means SLOW DOWN. Act like a sheep die like a sheep. Pay attention to how your trailer is behaving and you won't have problems. Learn to hitch properly and use sway control.

http://www.towingstabilitystudies.co...udies-game.php

Perry
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Old 09-15-2012, 05:15 PM   #39
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That's a nice simulation Perry. Thanks for that link.
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Old 09-15-2012, 07:38 PM   #40
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I stole the link from another post but I thought it was a useful tool.
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Old 09-15-2012, 08:11 PM   #41
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Hi, this was very interesting and I have about four points of interest.

(1.) Note the axle location on the caravan; Near center.

(2.) Note the 7% tongue weight on a Caravan.

(3.) Note the difference caused by speed.

(4.) Note that on my trailer, my fresh watertank is located between my axles, and therefore is OK to travel with a full tank.
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Old 09-15-2012, 08:15 PM   #42
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Also notice in the video when the model swayed out of control, they had the trailer tail heavy. I thought everyone knew that was the worst situation.
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