Snaking!!!

[Philspadders]

Relative to the caravan itself it does not move, relative to the centreline of the towcar of course it does when the caravan goes into a snake.

Lutz, the Centre of Mass cannot change ( unless you have founded a new branch of physics ) unless the contents of the van move position, it is fixed . It can not move. Tbe cnetre of mass is not a dynamic entity.

The snake . please , try to understand the actual mechanics of a snake .

How does the ATC work ?. ok . in snake the caravan starts an uncontrolled snake , which is actually a yaw. This develops into a harmonised yaw that becomes an oscillation. This applies a load to the rear of the towing vehicle and as we all knoNewtons 3rd law - dont we- the towing vehicle has to react in the opposite deitection.
Due to the nose of the towin gvehicle now moving away for the front of the caravan the driver tries to correct, but this movement will start to increase the amplitude and frequency of the oscillation because the driver can not correct fast enough.
Viewed from above the towed vehicles wheels actually describe a series of arcs , and it is this motion that needs to be controlled. The outside wheel of the arc has to accelerate , it cant do anything else, ( thats physics again then the van rolls back and past the centre of swing , which means this wheel now starts to decelerate and the other slower wheel starts to accelerate and the same starts to occure to the rear of the towing vehicle.

The braking system on the van sarts to apply the brake to the accelerating wheel there by slowing it and in doing so reduces the size of the described arc made by the wheel. Then as the swings back to centre then the brake is released and the opposite brake is applied,. This action satrt to dampen the yaw.

On towing vehicles the same system works , call it ESP , TCP , whatever you want, but thats how it works.

Also , a large , high 4 x 4 is the worst vehicle to be in when a large uncontolled yaw starts, simply becuse arge 4 x 4 have a very high c of m, soft anti roll bars , large sidewalls on the tyres and a long suspension travel. Its 4 x 4's that usually flip. Thats a fact as well.

A little knowledge eh ?
Now then , where is the ignore button?

 

[ValA.]

Soozeeg - what sort of pear cider do you recommend to prevent 'snaking' on the way home from the pub?

 

[Philspadders]

Lutz, where did you dig up Aerodynamic Centre , are you sure you did not mean Centre of Pressure ?

Ps i like mine with a Bite, 1/2 cider , 1/2 lager, Snake Bite, great falling over water.

 

[Soozeeg]

Soozeeg - what sort of pear cider do you recommend to prevent 'snaking' on the way home from the pub?

Preferably a strong one to distract me ******* (MOD Note: Part of Post removed,)! Actually, I've got a raspberry cider tonight, and very nice it is too.

Nice one, Val

 

[Lutz]

Ray, you have failed to understand me. Of course high sided vehicles are more susceptible to the effects of cross wind, but your question was specifically related to length, not height. A low but long trailer will behave totally differently in cross wind to a high short one with the same cross sectional area.
Phil, did I say that the centre of mass of the caravan changed? No, I emphatically did not. But as the caravan swings from side to side during the snake so does its centre of mass move with it. I would have thought that that is obvious. I said no more, no less.
Furthermore, an unstable caravan can and will go into a snake even if the driver does not try to correct, as you suggest.
Also ATC, or any other electronic stabiliser for caravans, when it deploys, does not apply the brake only on the outboard wheel but uniformly on both sides of the caravan. ATC does not monitor the relative speed of the inboard and outboard wheels, but only lateral acceleration of the whole caravan. I would also ask you to appreciate the distinction between ESP and TCP (or TSP, as some manufacturers call it) before replying to the thread. TCP requires ESP, but it perfectly possible to have ESP without TCP.
Call the aerodynamic centre, centre of pressure if you wish. I have no issue with that.

 

[joeby]

I cant believe there still at it , its off again , please some one give in

 

[Damian]

Whilst this topic seems to be unending, no one is forced to read it, and as no forum rules have been infringed by the main posters, I see no reason to stop it.

Users who do not wish to contribute, in a constructive way , would be best advised to just not read it, and certainly not post sarcastic or rude or offensive replies.

It is simple really, if you dont want to participate, no one is going to force you to, as no one is going to force you to read it either.

 

[Philspadders]

lutz,if only there was a shaking head smiley.

 

[Lutz]

Perhaps there's no shaking head smiley because smiley's found nothing content-related to shake his head about.

 

[Gafferbill]

I have had a post removed from this topic..... presumablly because the moderator thought wrongly that I was making sexist comments about our bored female contributors.
I merely asked in a colourful way why they were reading it!

I will take his advice and not contribute further.

 

[Damian]

Gafferbill,yes that post was removed, but not for the reason you have decided it was.

 

[Dustydog]

Philspadders said:-
Also , a large , high 4 x 4 is the worst vehicle to be in when a large uncontolled yaw starts, simply becuse arge 4 x 4 have a very high c of m, soft anti roll bars , large sidewalls on the tyres and a long suspension travel. Its 4 x 4's that usually flip. Thats a fact as well.

Now into my second week's break it is amazing that near on 50% of the tow cars at this site are 4x4, mostly Sorento's.

Phil
If so many of us have got it wrong please tell me what we can tow our Senators and Conquerors with please?

As for the rest of the technical tuitions I'm amazed the likes of Bath University haven't had an input. There's enough on here to last me a lifetime and I must say some of it is most interesting.
I still say it's the Bypass Modulator valve causing the problem?????????????

 

[DerektheSecond]

Does anybody remember steve56616 ?????

 

[seth1]

Yeah, i dont think he'll ever ask a question on here again.Its dragged on that long he'll have to replace the tyres on the van now.............................................

 

[Philspadders]

"If so many of us have got it wrong please tell me what we can tow our Senators and Conquerors with please?"
and where exactly did i point out that 4 x 4 owners had got it wrong? I made an observation about large 4 x 4 vehicles that most people do not take into consideration when buying one.

Dusty, the sorento is a heavy and powerful towing vehicle, but like all long wheel base , large flexible side walls on tyres,soft anti roll bars narrow, high centre of mass vehicles it is prone to overturning even at lopw speed and especially when making violent manouvres as can happen in an uncontrolled yaw situation.
Most large 4x 4's are exactly the same.

I have one. And its something i take in to consideration when towing.

The beauty of the large 4 x 4 is its weight ... but thats all when driving normally. It may help to reduce the possiblity of an uncontrolled yaw starting but when it does .... watch out.

if you dont believe me then pull down your sun visor in the car and read what it says on the information panel.

There are large saloon cars that will hapily tow a conqueror, but we avoid these and choose 4 x 4 instead.

(Ps , i have seen 3 caravans overturned on the motorway in the last 2 years, and they were all towed behind Sorentos , and the Sorentos were on their roofs.... One poster on this site has had an overtuen , with a Sorento, that overturned.)

 

[Lutz]

Just one more good reason to have an ATC, iDC or LEAS stabiliser fitted to the caravan and/or a towcar with TSP (or TCP or whatever it's called). No matter how prone your 4x4 (or any other car for that matter) is to overturning you won't get into trouble with a snake if you have one of them fitted, even if you're way over 100% weight ratio.

 

[Philspadders]

prove it.

 

[xtrailman]

Does anybody remember steve56616 ?????

Never heard of him?

 

[Lutz]

Prove what, Phil? If you've got an electronic stabiliser you can prove it for yourself by deliberately provoking a snake. You'll find that the outfit just won't allow itself to get into an uncontrollable condition. Alternatively, ask anyone who has an electronic stabiliser how it has reacted when a snake was imminent.

 

[Philspadders]

prove that your statement is 100% correct. supply the data that backs up your statement.

 

[John_374564913]

I already posted the below article but obviously nobody read it what I can tell you though is I do not make stories up this was an actual event and as the saying goes proof of the pudding is in the eating.

I would specifically like to comment and agree with what Lutz has written I wouldn't normally as I am no expert on the subject being discussed.
However I can comment on what I have experienced

whilst driving through Slovenia this year we crossed a viaduct on the motorway which had considerable cross winds which must have caught the caravan whilst driving at around 60mph.
At that point the ATC engaged as the Mercedes car I have has TSP (trailer stability Programme) The cars brakes actuated the dashboard lit up red and the vehicle power was cut at a rate which allowed the vehicle to be pulled over on to the hard shoulder where the engine ticked over.
At this point what was required was to switch of the ignition and then restart which reset both the ATC and the TSP and we continued on our journey as if nothing had happened.
The only reason I mention this is it substantiates exactly what Lutz had quoted above

Regards

John

 

[Lutz]

I have the LEAS stabiliser which works on the same principle as the ATC. After fitting it, I took the outfit out to an open and empty car park, set the noseweight down to zero to make it as unstable as possible and then, while doing about 30mph (due to the size of the car park I was unable to go any faster), induced a snake by heavy see-sawing motions of the steering wheel. As soon as the system monitored the snake, (the LEAS unit also has a warning buzzer in the towcar to let you know that it has deployed) the caravan's brakes were applied and the caravan was steadied without further input from me. The same result is to be expected from the ATC and BPW's iDC. However, the LEAS system resets itself within about 16 seconds so you can continue driving and don't have to turn the ignition off, as John has described.
I have a video, given to me by the manufacturer, showing how the same outfit handles when taking avoiding action at a higher speed than what I tried, once with the electronic stabiliser switched on and then going down the same stretch of road with it off. In the latter case, the caravan was swaying so much that the inside wheel lifted off the ground completely. An accident was prevented only because the driver was an absolute expert, close to being a stunt driver.

 

[runnerphil]

My drive is on a slight slope so when I measure the nose weight I level the van using the jockey wheel then use a nose weight gauge (in the hitch) on a breeze block. The van is level at the time of establishing the correct nose weight even if the drive isn’t. Dose any one else do this or do you wait till you get to a level bit of road or filling station then check?

 

[ProfJohnL]

Hello Baldylocks,

At the risk of upsetting a number of contributors by simply answering, I have to state that you have not understood the the necessary criteria for establishing the actual nose weight. for your outfit.

For reasons that have been explained exhaustively elsewhere, the actual load the hitch produces depends on how high it is above the horizontal plane of the axle. This sounds complicated, and it is if the caravan is on any sort of incline, but it all becomes so much simpler if it is measured on level (Horizontal) ground. measuring on a slope will affect the nose load reading.

Please note it is the ground that needs to be horizontal, not the caravan. In fact the attitude of the caravan is determined by the tow vehicle and its tow bar system, and it is perfectly possible for a caravan to nose down or up or on rare occasions actually level.

The correct way of establishing the real nose load is:

Using level (horizontal) ground. Load the car and caravan with all passengers and luggage just as if it is ready to roll.

Set Measure and record or remember the height of the hitch above the ground.
Set the nose gauge to exactly the same height as your measurement,
Chock the wheels and Unhitch the caravan, and hitch the caravan to the gauge. re check the height of the hitch and adjust if necessary. ( the gauge will compress and become shorter as the load is applied)
The result is the true nose load.

Hopefully you can see that the height of the hitch will change if you change the load of either the car or caravan, so its something that should be checked before each journey.

The height of the hitch is very important and also note that the attitude of the caravan may be anywhere between nose down to nose up. the attitude is determined by the height of the tow ball, and for all modern private cars, the loaded height of the tow ball must fall between 350 and 420 mm ground to centre of the ball. If yours is outside those limits either the load is wrong, or the cars suspension is faulty or broken.

 

[Lutz]

The subject of measuring noseweight on an incline was covered recently under the following topic: Noseweight checking. Someone by the name of Rubix raised the same issue. To avoid repeating everything again I suggest that you look at that thread.