Noseweight advice

Are you changing your mind now a bit ? you did mention a nose up being the cause of possible accidents: I dealt with many accidents caused by instability - almost certainly caused by bad loading, causing a nose high attitude. and when leaving is it hitching up level?

Now you're saying nose up or down? 

Personally a nose down attitude is better, probably not going to make that much difference but under severe conditions or braking it all helps, as I described before.

Why, with correct nose weight, can a nose up attitude cause instability? When the caravan's brakes are applied, the front end will always tend to dip, the same as the car when its brakes are applied, and that is so regardless of whether the caravan's nose was already down in the first place or nose up.

Surely you are not suggesting that it is more important to get the outfit even than to get the noseweight right? What is so special about an even outfit other than it 'looks right'?

suggest you direct your questions at that website that I took the quote from(did you look at it?) https://caravanchronicles.com/guides/understanding-the-dynamics-of-towing/

It seemed convincing to me and I agree with it's findings.  But perhaps you could go into the forces and moments and prove your statement to contradict their findings?  as maybe  it's not that obvious? 

also are you contradicting one of your previous posts? that nose weight is less when you have a nose up attitude?.

"https://caravanchronicles.com/guides/understanding-the-dynamics-of-towing/

It seemed convincing to me and I agree with it's findings." 

The "chronicler" seems to have forgotten halfway through the van is not an unbraked trailer but has its own brakes. So unless its braking is ill set up the forces it transfers will be low in magnitude.

Plus they are simply assuming the van's centre of mass is located vertically inline with the axle; that the nose weight varies much when lifting and lowering the hitch of particular vans indicates that there that is not the case. Realistically it must be higher than the axle as all but everything is physically above the axle.

I do have my suspicions that the nose up attitude would bring in "ground effect" wedging of what air is getting trapped under the van? This coupled to the tipping from the drag forces on the front of the van both contribute to lowering the dynamic nose force. Not the best of news re stability.

Posted on 11/11/2017 09:51 by Cornersteady

also are you contradicting one of your previous posts? that nose weight is less when you have a nose up attitude?.

I see no contradition. A nose up attitude will result in a slightly lower nosweweight, but this will increase again under braking, just as it would nose down. Besides, the difference in static noseweight between nose up and nose down is minimal compared with the dynamic forces that occur under braking and disappear into insigificance in the resultant net effect.

The 'caravanchronicals' article has a number of shortcomings that don't stand up to scrutiny.

The thing is Lutz, and don't get offended by this, but it's a pattern that you state things like the website has shortcomings that don't stand up to scrutiny  or that nose up will reduce nose weight and you expect us all to accept your statements as if they are true? For example it is so easy to say that about the website but you don't say how/where these shorting comings are or how they do not stand up to scrutiny. Equally you never give any real maths/physics behind your statements, just assuming we accept your profound knowledge as gospel.

Yes my reasoning and the underlying maths is pedantic, I gladly admit it, I was 'educated' not to make mistakes which are easy to do in mechanics, where things look to be explained but aren't, hence how Newton really showed what was happening rather than the errors in Aristotle's physics (heavy bodies fall faster than light ones is a classic case which seems true but isn't) which everyone accepted for a few thousand years because they appeared to work.

But while pedantic no one has pointed out any errors in my maths/physics (while plenty in my use of English)  and I can show things to be true.

So how does nose weight decrease when nose up and increase when nose down. It's a clockwise moment whether (or is that weather) above or below the horizontal? Over to you.

"So how does nose weight decrease when nose up and increase when nose down".

Is this seriously in question?

Relative to what it is if horizontal and moving within realistic amounts.

Because the van's C of G is located higher than and forward of the wheel axle shafts.

So lowering the nose moves the C of G forwards away further from the vertical through the axles and the hitch lever length reduces. Lifting the hitch also shortens the lever arm but the C of G moves backwards more towards the axle overcompensating this.

Thanks but it was aimed at Lutz, who I hoped would have provided a  explanation rather than one if his statements.

I think ocsid explained quite well. I would have said about the same, but using other words. Tipping the nose of the caravan up shortens the horizontal distance between the centre of mass and the axle, hence reduces the moment about the pivot point (the axle). As, at the same time, the horizontal distance between the hitch and the axle remains virtually unaltered because hitch and axle are roughly at the same height, the force at the hitch will also reduce.

In the case of my small trailer one can tip the nose end up so far that the centre of mass moves behind the axle, so the noseweight crosses zero and turns negative so that the trailer stays like that on its own until physically pushed down again.

To go into details of where the 'caravanchronicals' article doesn't stand up to scrutiny would be beyond the scope of a forum thread like this. In order not to bore other readers it would have to be discussed separately elsewhere.