Sway. Before, during and after.

[Collyn]

Re" .I’ve been watching YouTube sway-crash dash-cam video clips — over a dozen so far. Elapsed time between onset and jackknife ranged between 3 and 12 seconds, most around 8 seconds. Each side to side swing took about half a second.

Those dash-cam videos make me doubt whether most competent drivers can successfully regain control after the first 3 or 4 side-to-side swings, assuming lack of electronic anti-sway technology such as asymmetric brake controllers or equivalent.

I’m not familiar with any engineering studies on the subject of how to reliably regain control (without electronic assist) after a trailer has seriously started swinging side to side. I’ve read many opinions, none based on successful personal experience or controlled studies.'



Much of the above post is spot on.
A swaying rig situation is in effect a double pendulum. The trailer trailer is effect a pendulum suspended by an upper pendulum (the trailer).

As Googling 'double pendulums' will show, swinging beyond about 4 or so degrees, causes continue ongoing movement that is virtually random. The build-up and action is not unlike a cyclone.

Any trailer towed via an overhung hitch is thus fundamentally unstable. The swinging is not possible to driver-correct - as the driver has no way of knowing what the rig will do next.

Re: I’m not familiar with any engineering studies on the subject of how to reliably regain control. Nor was I able to do so during my years with Vauxhall-Bedford Research.

There are many engineering papers in this area - from the 1980s onward. I fear however that very few people know much about it. I and a (less technical but accurate) writer in the UK are about the only two (outside academia) who publish on forums in this field.

Forum regs preclude my posting details - but people do seem to find
me.

Collyn

[Vitaver]

How is an ‘asymmetrical’ sway control hitch different than the Blue Ox or Pro Pride? The advantages?

[Vitaver]

Placed this on another thread yet is very consisten to this conversation. Any thoughts on this, in addition to truck sway control, sway hitch (one or both)?

Electronic sway control system helps correct sway in trailers with or without weight distribution. Monitors trailer movement and calculates most effective braking action to correct sway. Activates left or right trailer brakes to counteract sway.

Features:
Electronic sway control system limits side-to-side movement of trailer during towing
Unit corrects sway by activating your trailer's electric brakes
More effective than friction sway control systems by getting ahead of sway event
Continuously monitors trailer angle, movement, speed, and other parameters for real-time braking calculations
Proprietary algorithm signals most effective braking response within milliseconds of detecting trailer sway
Independently applies left or right trailer brakes to counteract movement and quickly correct trailer sway
Automatically disables over rough terrain to prevent unnecessary braking
Unit Remains disabled until rig is back on smooth ground
System enters sleep mode after 30 minutes of inactivity to conserve trailer battery
Exits sleep mode after power returns to brake controller
LED light provides system status for easy troubleshooting
Indicates normal operation, rough terrain or sleep mode, system power issues and more
10' Cord included for mounting light in easy-to-see location on front of trailer
Won't interfere with your brake controller, weight distribution system, or mechanical sway control
Fully sealed, water-resistant construction protects against road spray
One-time, maintenance-free installation
Module mounts 5' to 10' behind hitch ball, along trailer centerline
Splitting electric trailer brake circuit into 2 separate circuits required for corrective braking on one side of trailer at a time
14-Gauge wiring (sold separately) splices into trailer's brakes and connects to trailer's 12-volt battery, breakaway switch, and trailer plug

[ROBERT CROSS]

SNIP>>>>

Originally Posted by Collyn

I’m not familiar with any engineering studies on the subject of how to reliably regain control (without electronic assist) after a trailer has seriously started swinging side to side. I’ve read many opinions, none based on successful personal experience or controlled studies.'
Collyn

Does the slide rule group consider the trailer brakes an electronic assist?
With our single axle Safari...I gently accelerated and applied the trailer brakes during any perceived 'sway' incident.👍

Bob
🇺🇸

[OTRA15]

Originally Posted by ROBERT CROSS

. . .
. . . I gently accelerated and applied the trailer brakes during any perceived 'sway' incident.��

Bob
����

Echoing Post #14:

Originally Posted by OTRA15

. . .
Most sway events can be anticipated if one is "situation-aware," which includes being wide awake, and paying very careful attention to all possible risks. These include wind gusts, semi trailer bow waves, and so forth.
. . .
A careful driver usually sees the risks building ahead of time!

Especially with a semi trailer bow wave [either coming at you on a two-lane road -- or parallel to you on a divided highway], you must already have one hand on the manual brake controller, ready to apply the trailer brakes first. If this is done correctly, there should be no need to step on the gas also IMO.
. . .

Travel safe . . . and . . .

[RTOS_LLC]

Hmmmm. Watching the last dialogs I probably need to provide some insight into how asymmetric (Tuson) sway controller works, and how it electronically "dampens" sway using brake/tire friction. First, it contains a 3 axis gyroscope which means I know rotation around the x, y and z axis. I also know the sway velocity (change in angle over time) and acceleration (change in velocity over time). If I see "vertical movement" exceed some threshold I know a pothole hit or off road and thus can disable some sway control functionality. I am not going to disclose various "algorithms" but if trailer sways right and exceeds various thresholds the right brake will be applied, the faster the sway the greater the braking pulses. If it sways left the left brake is applied in a similar manner. When going from left to right, right to left there are points in time when some left and some right brakes are applied. If you start apply brakes (blue wire pulses) during a sway event the sway pulses widths are added to the blue pulse widths so you still get sway control even tough some braking is occurring. If you watch the video links I provided you will see the phenomena often referred to as the "tail wagging the dog" where sway left will push the rear of the tow vehicle right and vice versa. So think about the hitch being the "pivot point", where when trailer sways left and the left brake activates it will pull the hitch left trying to straighten the angle with brake/tire friction. Too much brake, not good, too little brake not good. I also do some "stuff" that if I don't see sway reduction during sways I increase some "gain stuff" to apply more braking or if I see too much reduction in sway I reduce some "gain stuff" to not brake as hard. Remember different trailers require different levels of braking based on lengths, weight and so on. Of course if your brakes are NOT working, the sway controller can't "electronically dampen" the sway. Thus there are various diagnostics provided to affiliate identifying some forms of brake faults. I would "love to provide" some screens on say a direclink brake controller's command module where you could even do some "gain adjustments" to increase sensitivity of activation under some scenarios while using blue wire as a network to talk to the sway controller, similar to how it talks to a hydaulic brake actuator. When EABS is available, even more diagnostics can be provided and when combined with sway functionality the diagnostics are "kind of extreme" and likely communications to tow vehicle will become an option. So does this stuff work? Watch the linked videos I provided on the web page previously referenced and watch the end user testimonials. If the automotive manufacturers would provide me with the steering angle request and response messages for their various vehicles accessible from the OBDII connector I could even do a better job, similar to retrieving vehicle data that is used by DirecLink brake controller to perform braking. Trust me, there is a LOT of code that is used to NOT activate sway control under numerous driving scenarios and steering angle would "really help". The dampening available at a hitch is great for low amounts of sway, but wind gusts and evasive maneuvers are beyond their capabilities but having brakes a long distance for the "pivot point" is what enables sufficient dampening to significantly dampen the sway. I hope this helps.

[Iowa]

I worked at an Airstream dealership for two years and talked to several people that had rolled their trucks and trailers. They both bought a Hensley after that and said there is no comparison when towing. We installed several Hensleys for people and they all called back and told us to pass the word on that they make a world of difference.

I purchased one for my first Airstream, a 20 foot and transfered it to my 28 foot. There is no sway. If I am traveling on the interstate with a 30 mph cross wind and semi trucks go by it may move me over 6 or 8 inches but the whole rig moves together and there is no sway. With a Hensley the trailer can not make the truck sway due to the way it is designed.

When sway happens the natural tendency is to correct with the steering wheel which only makes it worse. Don't do that, hold the steering wheel steady and slow down and if thinking and practiced as mentioned above apply the trailer brake slightly. Or purchase a non sway Hensley or Propride etc. They are a lot of money but far less than a roll over.

[Vitaver]

The thread shows good arguments for all the components, correct loading, right hitch, virtues of hitch, automatic sway control by TV and even the sway control acting on the TT tires. Question is, how well they play together: the hitch, the TV auto sway control and the TT auto sway control? Will you use them combined, 2, 3 of them? Just one? Anyone with insight on this? Thank you!

[Collyn]

While not dismissing the suggested 'solutions' by far the best is to have a towing vehicle that is at least as heavy as the (correctly) laden trailer and minimise trailer length. (If short, its weight is less of an issue).

If that trailer has much of its weight centralised it's weight is less of an issue.

Better by far to get these (Newtonian) basics right as you will have far less of an issue to contend with.

If you do not understand (Newtonian) basics - consult any science-minded teenager - he/she will explain.

Collyn

[Andrew T]

Hi Collyn

I wonder if part of the equation is where the weight is located in the tow vehicle. A diesel 3/4 ton for example has a large mass forward and high off the road (actually getting heavier and higher all the time).

My personal tow vehicle for the last 14 years have been a 2004 followed by a 2012 Jaguar XJ. The suspension in these is tuned like a sports car, not like a luxury sedan. What I like about them is they drive like a sports car but don't look like one. The car is well balanced with huge sticky performance tires of course independent suspension and a low center of gravity. However it is made of aluminum so it only weighs 4000 pounds which is pretty light for a 4 door 120" wheelbase sedan.

In our slalom and lane change tests with a 7000 pound Airstream the Jag is much quicker and easier to handle than a 7500 pound pickup towing the same trailer. In fact it is about as quick towing as the truck is solo. However the handling degrades more from what the car is capable of solo than what the truck does. It just starts from so much higher a level it still winds up better. It would be interesting to test a 7500 pound low profile well balanced tow vehicle for comparison but nothing exists to test.

One other thought related to what you mentioned is the old 34' Airstreams handle amazing considering their size and relatively light hitch weight, you can really make one sing and dance. I always attributed that to the tri axle and I am sure that is part of it but the lack of polar inertia is also likely a big factor.

Thanks

Andy

[Collyn]

It is vital that the tow vehicle does not oversteer whilst towing. If it does, jacknifing is likely.

Towing 7000 lbs by a 4000 lb tow vehicle is akin to having a 10 year old child walk an 150 lb Great Dane. Its just fine as long as that dog behaves - but ..........

Collyn

[Andrew T]

The rear tires are 285/35 x 20 high performance summers so breaking them loose takes serious work. It is very difficult to achieve oversteer.

The 2012 has enough power that I should turn off the traction control and do a video of a 4 wheel drift while towing. See if it looks as cool as it feels.

[JonDNC]

Originally Posted by Andrew T

The rear tires are 285/35 x 20 high performance summers so breaking them loose takes serious work. It is very difficult to achieve oversteer.

Give me <5 minutes bet I can. In a parking lot for safety. The equivalent of a skid pad.

[Collyn]

Originally Posted by JonDNC

Give me <5 minutes bet I can. In a parking lot for safety. The equivalent of a skid pad.

From personal experience of doing this under controlled conditions (with outriggers) I advise against it. The chances of a roll-over are quite high.

(The above was at the UK motor industry proving ground many years ago).

Collyn

[JonDNC]

Originally Posted by Collyn

From personal experience of doing this under controlled conditions (with outriggers) I advise against it. The chances of a roll-over are quite high.



(The above was at the UK motor industry proving ground many years ago).



Collyn

Been there, as part of some advanced / high performance driver training. It’s amazing what you can do with proper throttle control at the limit. Especially when there’s reduced traction .. wet skid pad training g was interesting to say the least.

My point was not hard to make happen.

[RTOS_LLC]

Originally Posted by Vitaver

How is an ‘asymmetrical’ sway control hitch different than the Blue Ox or Pro Pride? The advantages?

Sorry for the delay in this response, but your question prompted me the create a new document describing the difference between symmetric and asymmetric electronic sway controllers since I couldn't find any related documents, and that took a while. One was created as a simple explanation will not "fit" this message format. The referenced document doesn't explain how the sway hitches work, where I will leave that up to those "skilled in the art" to provide an answer. The sway control document will provide insight into the side forces that must be provided to "counteract sway forces" and thus you can assess the hitches effectiveness. For a direct download of document go the "www.realtimeobjects.net" select the "downloads" tab and select "symmetric versus asymmetric sway control" .pdf file OR go to "sway control" tab and scroll down and select the only .pdf on that page. If anyone has a "simple web explanation" of sway hitch operation I will gladly add the link to the sway hitch page as this topic is not currently covered.

[RTOS_LLC]

Originally Posted by Vitaver

Do you leave the TV anti sway assist on while using the hitch’s similar system, both working combined/in tandem? There is literature suggesting to disable one or the other. Very interested in your experience.

I had to get an approval before providing the following document which is are the test results run by Ford Motor Company with the vehicle's sway control system turned on as well as the asymmetric trailer sway controller to see if the work together and if they meet SAE J2807 tests. The .pdf may be downloaded at "https://www.realtimeobjects.net/downloads". This should provide information relative to whether or not a system would, could or should be disabled.

[Vitaver]

Lift kit not secured. The cause for an unfortunately experience was uncontrollable/uncontrolled sway initiated probably by moderate wind gust, but exacerbated by a lift kit, installed at an AS dealer, with the 8 bolts not torqued: loose in fact. If you have anyone install a LK, please make sure you dive under the coach and check for the bolts being tight, torqued to specs and I suggest loctited as well.

[Collyn]

Originally Posted by RTOS_LLC

I had to get an approval before providing the following document which is are the test results run by Ford Motor Company with the vehicle's sway control system turned on as well as the asymmetric trailer sway controller to see if the work together and if they meet SAE J2807 tests. The .pdf may be downloaded at "https://www.realtimeobjects.net/downloads". This should provide information relative to whether or not a system would, could or should be disabled.

Am surprised permission was needed re the above. It appears to contain nothing that was known and understood at least a decade ago.

Collyn

[RTOS_LLC]

Primarily, I don't work for either of the companies signing the tests. Don't know about others, but having worked for Eaton and Rockwell, if anyone ever published an internal document, whatever it contains, they would likely be toast. So minimally to be ethical approval was needed. Some asked for test results (proof versus hearsay), so I provided some that shouldn't be controversial. There are tests others that show amazing results for hydraulic ABS stopping distances on slick surfaces, but can't publish those yet, and that's not the topic here anyway. Agreed, electric brakes asymmetric trailer sway control works and far better than the sway control feature option on trucks. After all, the trailer brakes have FAR more leverage at the point of sway than any vehicle can provide with its brakes. People wanted to know if since they had it on their vehicle does that solve the problem of trailer sway control. The test indicates not passing SAE test and when trailer electric brake asymmetric sway control added, it passes.