Chicken !!!!!?????
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Towing Issue - pulling and pushing
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Engineering, wether, aircraft, ships , cars , childrens toys, are all intregated by, designers, engineers and fitters, , who are then supplied by chefs, cooks and servers, cleaners and re cylers. And we all do a wonderfull job.
Remember we can all learn from the last person in the circular team.
Hutch
Remember we can all learn from the last person in the circular team.
Hutch
ProfJohnL said:
The speedometer comparison is not really a good one, since these are not allowed to under-read, and therefore tend to over read, giving the driver a margin.Therefore he doesn't have to worry about the inaccuracy of the instrument as long as he keeps within the indicated maximum speed. Noseweight gauges are another matter though, as the literature does not quote accuracy within a given range, so I agree with you there. However you may be pleased to hear that the Reich Weight Control device does state an accuracy within 3% (which I assume is either side of the indicated weight)
Hello Chris,
On the contrary, the speed limit example is a very apt one. It clearly demonstrates that where there is a need for a criteria to be measured to enable the user to comply with a legal limit, the manufacturers of the users equipment need to ensure the equipment is reliable at achieving the desired aim. Motor manufactures are under an obligation to ensure their speedometers do not under read the real road speed. The reason for this is that the speed limits are absolute, with no tolerance built into the legislation. So it falls to the driver to ensure they do not exceed the limit., And the same applies to ALL legal limits including weights and loads.
This means the users should only use measuring equipment where the degree of error is known or managed in such a way that the user will not be taken outside of the limit if they follow the instruments readings.
On the contrary, the speed limit example is a very apt one. It clearly demonstrates that where there is a need for a criteria to be measured to enable the user to comply with a legal limit, the manufacturers of the users equipment need to ensure the equipment is reliable at achieving the desired aim. Motor manufactures are under an obligation to ensure their speedometers do not under read the real road speed. The reason for this is that the speed limits are absolute, with no tolerance built into the legislation. So it falls to the driver to ensure they do not exceed the limit., And the same applies to ALL legal limits including weights and loads.
This means the users should only use measuring equipment where the degree of error is known or managed in such a way that the user will not be taken outside of the limit if they follow the instruments readings.
EH52ARH said:
Hello Hutch,
At last, someone else who has taken the time to really look at the forces involved. Yes it is precisely the position of the COG and it's relation to the effective pivot of the road wheels that gives rise to this very real effect. The complication is the fact that as soon as you change the position of any of the items in the caravan it affects the three dimensional location of the COG, and if the trailer has change in attitude, then the arc through which the COG moves affects it's horizontal displacement to the turning point.
In terms of nose load we can effectively ignore any lateral displacement and are only concerned with longitudinal and elevation.
As you suggest the height of the COG is a significant factor that affects the degree of nose load variation, and that is an aspect that cannot easily be seen or measured by a caravanner. There is no simple way of measuring the height, but through a wide experience of towing, and observed effects, coupled to the disposition of components found in caravans, I guess the COG will usually reside somewhere between about 1 to 1.5M above ground. Crucially above the caravan's axle. This of course changes when payload is added. In a normally set up caravan there will be a nose load that pushes the nose down. This is the result of the COG being trimmed to just forward (and higher) of the axle.
The effect changing the height of the hitch is to cause the caravan to rotate about its axle, this also rotates the COG and it's loci will described an arc about the axle. Relatively speaking nothing changes, but in reference to gravity, the COG moves horizontally relative to the axle the closer the COG moves to the axle the smaller nose load it will produce. If the cog moves to be directly above the axle, the nose load becomes zero, and if the COG moves behind the axle the nose load becomes a lifting force. It's reasonably easy to see how this affects a Single Axle (SA) trailer, but the effect on a TA is far more complex and dramatic.
Whilst the processes involved are not necessarily easy to comprehend (especially the TA) fortunately in the real world we only really need to know the result which is the nose load, and that is a practical feature for us to assess. All we need to do is to measure it. But if we are to assess it properly, it needs to be measured correctly and height is therefore a variable which must be controlled.
One of the characteristics of a tow vehicle is the height of the hitch will change when a load ( such as a caravan ) So the true nose load can only be assessed with the hitch at its towing height, and that is how the authorities would have to measure it as that is the way the relevant regulations describe it.
The issue is even more important for TAs because depending on the geometry of the caravan, the COG may reside between the axle's, and that changes the whole dynamic of the load change with hitch height. The rate of change is much faster and bigger, and it is possible the for the load to go negative within the normal range of high heights. So TA nose load is more critical to get right.
Just as you explained it to me Parksy!
Parksy
Moderator
Gabsgrandad said:
I'm sure that the OP is so glad that he asked such a simple question and it's good to know that every other newbie who browses this stuff will sleep easier at night now that it's all been so briefly summarised for them. :dry: .....Me you say? I wonder to what degree my lightweight front towing cover affects such a safety critical and vitally important parameter? I'll make sure that no damp leaves settle on my A frame before towing and then I'll continue to do exactly what I've always done and fearfully await the dreaded dawn raid. 🙁
, Its time for a siesta. 
I've read the whole thread with a lot of interest. But wasn't there a caravan produced by Bailey (Olympus, or Pegasus) that owners had real difficulty with as its ex works noseweight was quite high. Around 80-90kg from memory and this from a company that works with Bath University to research caravan stability. As the caravans' ex works noseweight were around the figure specified for many cars towballs I guess that loading may have required quite a degree of ingenuity!
Yes my U1 has a 88kg ex works weight so i have to load behind the axle to keep it down to my towbar limit of 88kg.
Its not easy at first as you don't feel back loading is ideal, but in practice its never been a problem regarding stability.
Later versions relocated the gas locker to the axle, removed the front cupboards, and located the battery more central to help with left right weight distribution.
Its not easy at first as you don't feel back loading is ideal, but in practice its never been a problem regarding stability.
Later versions relocated the gas locker to the axle, removed the front cupboards, and located the battery more central to help with left right weight distribution.
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