Nose weight too high
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I agree that one needs to be cautious when taking technical advice on a forum unless you know who is giving it. Despite my qualifications in electrical engineering and participating on the IEE Wiring Regs committee (as was) I am conscious of the fact that (a) I am not up to date with the very latest Regs. (b) I occasionally get things wrong when answering in haste. It is still frustrating though when you get contradicted by people who have very little technical knowledge and who offer advice which can be unsafe.
As for hitch weights, the applied maths on moments is extremely elementary but it must be very obvious that mass placed generally forward of the axle will increase the nose weight - the nearer the hitch the greater the effect. We had to add weight in the rear bathroom of our Bailey to get down to 100kg hitch weight. Not recommended practice but no other option. It doesn’t help that gas bottles are usually in the front locker so as the gas gets used the nose weight decreases significantly. Perhaps that’s why Bailey switched to putting gas bottles (and battery) close to the axle.
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well take it from me, it is forward of the centre of mass not the axle. It simply has to be, you cannot change the laws of physics as the song goes. Like I said the CoM is the balance point of the caravan. also putting more weight on the axle will compress the springs and the hitch will move pulling the attached van up? If you put enough weight on the axle then eventfully the centre of mass moves nearer and will actually be on the axle, and all the wight will be there and no nose weight? Do airline pilots when there are small numbers of passengers make you sit in the seats near the CoM or over the wheels? Same thing.
saying things like it is obvious in mechanics has caused so many problems for students
Unlike IEE regulations which change and evolve, mechanics has not changed since Newton's day, (ok unless you are moving near the speed of light then Newtonian mechanics breaks down) but for a static caravan they hold perfectly.
the diagram below shows a simplified diagram of a van facing right. It is in equilibrium, all the forces balance, and there is no resultant moment so about A F1d1 = F2d2.
If you took moments about P1 (the axle) then F2(d1+d2) + (F1+F2)d1 = 0 it has to equal zero as the van is in equilibrium so therefore
(F1+F2)d2 = -F1(d1+d2)
what this means is that while you thought the the weight of the caravan through the C0M is trying to turning the van clockwise, in reality it is trying to turn the van anticlockwise. This is Jenny's error.
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That was good MM you can’t deny the logic👍🏻😊, very clever Corners👏🏻👏🏻
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I think you are winding my legs as well as pulling them here? But please I'm not always right so point out the error in my maths? Might be harder to do of course than just posting things have changed?
A reversion course for you:
The principle of moments.
” When an object is in equilibrium the sum of the anticlockwise moments about a turning point must be equal to the sum of the clockwise moments.”sum of anticlockwise moments = sum clockwise moments. Things only turn when there is a resultant turning effect, aka moments
Now as a caravan has two points on contact, the wheels and the hitch. So as it is in equilibrium (it is not moving or turning) there must be equal anticlockwise and clockwise moments. If the van is facing left, taking moments about the axle point of contact must mean that if the turning effect on the hitch is anti clockwise, then the turning effect on the centre of mass must be clockwise according to the above. Is that simple enough? They cannot both be anti clockwise as that means there is a resultant turning effect and the caravan starts to turn.
Bythe way you should have been taught this at school
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DD, no need to apologise but thank you. Perhaps I thought you were winding me up and went to that conclusion too quickly, which is apt for me don't you think ?
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Yes me too, jolly irate I was too. Now I see the logic, thanks Corners I can confirm you are correct👍🏻🤣🤣🤣
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I don’t believe that anybody is disputing the “two boys on a see-saw” type calculation. Even young kids seem to work out that the larger kid has to sit nearer the middle but I can only take your word that some find it difficult. My point was simply that as the C of G (to use the old fashioned term) is less than 20cm forward of the axle then in layman’s terms putting weight forward of the axle increases the nose weight. True though that if you were to put a 100kg load 10cm forward of the axle by mistake then the nose weight would go down slightly. About 2kg I believe.
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it doesn't matter if there are two forces or 200, the same principle applies, if it is not turning then the sum of the clockwise moments equals the anticlockwise about any point.
Of course you could do the same thing vertically to find out how those lockers full of things affect the vertical height of the GoM. Every new vans now appears to come with a microwave which are quite heavy?
The difference between centre of mass and gravity for a caravan would be the same and like you it was gravity in my schooldays
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I often wonder why caravans have two wheels and not four? There must be some advantage to just two? Cost?
Actually just on a pitch that slopes so much that it would be impossible for a MH to use it, my caravan rear is less than 6 inches off the ground while the front has the steadies almost fully extended and they and the jockey wheel on concete blocks that were on the back of the pitch.
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A single axle trailer will turn 180° in its own length so is very manoeuvrable. Whilst a twin axle trailer will distribute the load more evenly and reduce the tyre and axle loading, it will also be more difficult to manoeuvre than a single axle as it will always pivot on the leading axle and drag the following axle sideways. Just watch an artic trailer doing a tight turn.
A wheel on each corner turns the trailer into a “drag” and needs a front steering axle. It also needs a highly skilled driver to safely tow it.0 -
as always thanks. I'll just stick to the tried and tested design then
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I think that you don’t mean,”put a 100kg load”, rather you mean move a 100kg load. If adding new weight in front of the axle but behind the CofG reduced nose weight then all that would be needed to release the hitch skyward would be a pile of lead placed carefully between the CofG and the fulcrum. It’s a vision that won’t ever happen. A more pragmatic soul might add a little lead to the rear of the axle. That’s why the boys mother balances the load by adding weight to the thin boys side of the seesaw. Not 10cm on the fat boys side. Mind you she never excelled at maths, but majored in common sense.
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Yup, can’t beat it.
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I meant exactly what I said. The point was to illustrate that putting extra weight close to the axle has very little effect. It is impossible to create zero nose weight by putting extra weight forward of the axle or, indeed, over the axle when the centre of mass to start with is 20cm forward of the axle.
We used to put large bottles of mineral water in the rear shower to keep the nose weight down, contrary to all loading advice. Not good having 120kg nose weight.
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OK thanks for the clarification - we’ve loaded similarly ourselves. On this van we carry our water barrels in the rear bathroom with the wastemaster and other paraphernalia under our fixed bed. Which is also behind the axle but less effective for counterbalancing than bathroom loads because of its proximity to the axle. We’ve had other vans which need a nose weight top up, so all water containers have been in the front. In all cases, once the van has the required 75kg noseweight, loads are placed centrally ie within a few cm of the axle, and as low as possible.
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If adding new weight in front of the axle but behind the CofG reduced nose weight then all that would be needed to release the hitch skyward would be a pile of lead placed carefully between the CofG and the fulcrum
wow Jenny you don't give up even when you have been proved wrong, placing a new weight in front of the alxe but behind the CoM will reduce nose weight. At time I've (all 75Kg) gone in to van by the door behind the axle and gone forward to set the fridge, the hitch has not gone skyward.
I'll try again with even simpler words:
Take which rotation point you want, you like the axle, as the van is not rotating about it, then the clockwise turning forces equals the anti clockwise turning forces.
clockwise turning effect = anti clockwise turning effect
If you add 100 Kg you are applying a new turning force, so on one side of that equals you have added an extra turning effect but the van still does not rotate. So the the equal sign still holds, if the equals sign still holds then whatever you have added to one side must be subtracted from the other. Some turning effect must go down to compensate.
As I've shown that if you take the turning effect on the hitch as a anti anticlockwise effect then by the principle of moments the turning effect on the CoM must be anti clockwise, so the nose weight reduces. Clear? Well it doesn't matter if you don't agree as my explanation and maths is correct.
You bit about the seesaw (and this I think is where your misconceptions comes from I would say) is just strange. First parents and children don't want the seesaw to be balanced, much more fun if it isn't. Then the mother carries a number of weights with her to balance it? And finally a common sense approach is to move the heavier child nearer to the centre?
Luckily for us those that design caravans and cars... use maths rather than common sense.
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The reason that a caravan doesn’t rotate when the CogG is moved forward isn’t because it’s in or out of equilibrium, it’s because it’s firmly prevented from doing so by the ground it’s resting on which produces an equal and opposite opposing force. There being two points of support for a caravan, the axle and the noseheel/ hitch All of its mass is distributed between those two points and while that mass acts through the centre of gravity, it’s distribution across the two point of Support will vary in line with any horizontal shift on the c of g. Remove Support from either point and the van will rotate around the remaining support until the c of g lies directly under that support. Note it doesn’t rotate around the centre of gravity unless both supports are removed. On object falling in free space is at liberty to rotate around its c of g. An object firmly resting on the ground rests on its support points and isn’t free to rotate around its c of g,
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Good idea to put the rear steady down when carrying out these scientific experiments because, I guarantee, it is perfectly possible to rotate the van if you walk to the back!
Anyway, it seems to me that everybody who has contributed to this discussion fully understands the elementary maths related to moments; it’s just the words that seem to get in the way.
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I am with Jenny, cobblers to the rest,ex teachers make me itch.😎
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I'm wondering Jenny if you're just saying this nonsense just to wind me up (I hope so) or you really think all this stuff to be true? I mean you are not totally wrong in this case but miss out the important stuff. You appear to have studied physics and mechanics before but you are now in state of being completely mixed up remembering some bits and misapplying others. You once incorrectly stated that if weights were added in front of the axle the nose weight would go up, rather than in front of the centre of mass, which I had to disprove and now you show an appalling knowledge of what equilibrium means or is or how it is applied.
The forces you talk about create equilibrium, they can be used to prove or disprove equilibrium. But equilibrium means no resultant force and no resultant moment or turning.
It's circular argument, if a caravan is stationary (no motion or rotation) it is in equilibrium. If it is in equilibrium there can be no rotation but of course there can be motion. So yes being in equilibrium means it cannot rotate, that's all a physicist needs to know, what causes it to be in that state is just used to get the proof.
Btw I never talked about why it was in equilibrium only that as it was, and used it to show your 'weight in front of axle theory' was totally wrong.
You seem to take an Aristotle type of physics, where you use observations to make statements that appear correct but are just plain wrong. I expect you think heavier caravans will fall faster than lighter ones? or no motion is possible without force acting on the moving object?
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I’d love to hear your erudite take on it Hooker😂😂😂
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No Corners, I’m not winding you up. I enjoyed a very enjoyable and increasingly wel paid career in applied engineering for many years. I’m sorry to say that on that journey I encountered many who could quote the maths but couldn’t apply it to real life situations. Fortunately for me I can apply the maths, it runs in the family. My father, sister, daughter, all of whome have enjoyed successful careers well beyond a teacher’s expectations. You’ve read more than a few posts here, which refute your understanding, while being serially insulting to me. I’m sorry too that you feel it necessary to do so in support of your beliefs.
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Hey, Jenny, you liked your own post. 😀
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