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Topic: Caravan stability ( Topic Closed)
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03/11/2016 at 8:53pm
Location: Outfit:
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Quote: Originally posted by JTQU on 03/11/2016
Quote: Originally posted by JohnMW on 03/11/2016
Hi
1. loads on any vehicle should be placed evenly along the chassis with a bias on the front whether it be an Artic or a Caravan - I fulfill this with bikes on the back of the van by ensuring that there is the maximum allowed on the ball all within the max weight of the axles.
I don't buy your very first premise.
If the load can be carried undistributed then instead of spreading it, you can place it just far enough in front of the van's centre of yaw, typically the axle, to achieve the requisite noseweight.
With a centralised load, its monent of inertia is as low as that load can be, therefore the natural frequency to yawing is as high as it can be. Definitely higher, probably enough to be out of harms way, than if that mass was evenly distributed as you assert.
Load is definitly not best evenly distributed, its best from stability consideration located at the point it could swing about. Hence the often stated requirement to place heavy items as near the axle as possible and as low down as possible.
You do have a good point , however, if you take the dynamic load as you say you have an imbalanced beam so if you take the high wire artist analogy if he had one end heavier than the other he would lose control - this is the best analogy I can serve you with. When a force hits the side of the van it could be the front or the rear of the axle. If it was the front then the momentum would build and affect the tow car in such a way that it would require more effort to regain control - it would have no assisted balance from the rear. It would tend to drag the caravan as if the pendulum had been reversed - that is why it should be balanced evenly - of coarse if the force was exactly in the middle then it would make no difference either way. The tires would resist until the slip angles forced it out of line which is when the oscillations would commence. Were it a true pendulum without an interruption from an axle at mid point then putting the weight at varying points along the length from the fulcrum would certainly make your point valid. I think I got it - I'll check with my observation notes.
Just prior to sway the whole beam swings about the axle , this is the start of the sway if the beam is out of balance then the dynamics build to affect the tow car, if the tow car is not loaded correctly the frontal loaded van swings about the axle and can destabilize the tow car. if it is balanced the ends cancel out the side force which resists further oscillations. If the oscillations gain momentum the resistance from the tires either breaks down and they skip or slip, it then turns into an uncontrolled sway from the tow ball - all hell breaks lose. The answer is don't let it start by using a balanced beam and a control system.
Post last edited on 03/11/2016 21:26:51
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04/11/2016 at 10:19am
Location: Hampshire Outfit: Hymer Nova S
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Assuming that the technology works, and there is yet no evidence available to us it does or does not, the benefit it brings over the established trailer stability systems is that it facilitates towing otherwise very poorly loaded caravans. An example of this being as in the OP's case hanging heavy electric bikes right on the rear end.
Now I would not dream of doing this as I know how destabilising it is, in the OP's case things are “safe” without intervention up to 52 mph, but even at that an disturbance is all that is needed to provoke a natural frequency driven oscillation. I simply can't do this, tow an inherently unstable unit, depending on some device to constrain it.
I accept all towed units can be inherently unstable but I want that point of instability way outside whatever speed or forced provocation I could realistically encounter; but on top of having a tame unit, I still want the likes of an ATC should everything stack against me.
Envisage a double bike rack dropping right off an overtaking vehicle as it swings back in front of you; that is one I know all about! The involuntary, or unthought out “Elk” manoeuvrer that is needed to be made would destabilise anything towed.
Now I can see that hanging two electric bikes on the rear is exceedingly expedient so is attractive, as there are little other options available. Mine would simply go in the Disco as they do now but many have not that option. So I could see the OP's product appealing to that niche and growing market, for takers who can come to terms with an add-on controlling what is otherwise a very dangerous animal. It is though a finite market and any retailer would have to think very carefully indeed about the litigation that could come should a unit doing that vital task “fail” to do so.
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