Riva Destiny Towing Stability

Perhaps some wealthy person who can afford the top of the range dandy with posh inside toilet could buy one and take it to the next dandy meet.

 

Perhaps when the posh Dandy is actually paid for he might have some spare cash to fund it.

It would be good fun at a meet though rolling a dozen Dandys back and forward over it and finding all that stashed booze infringing the suspension limits  

I bet if I have a couple of glasses myself later I'll end up ordering one  

I took our Dimension to the weighbridge when we first bought it. It weighs 750Kg unladen which is as expected. You'd think the Destiny would be more than 30KG heavier though wouldn't you?

The weight spec for the Dimension might be correct but ours is quite a bit longer than the Riva spec sheet!

Our previous 1995 Designer weighed approx. 420Kg unladen at the public weighbridge. That includes winterised sidewalls and under-floor heater.

Steve

If any of you have got to the point of thinking about ATC or ETS as opposed to stabilisers I was surprised at the price for a retrofit £530.00. Not cheap but comparable with stabilisers. [You must be registered and logged in to see this link.]

See this Which Caravan article about towing with an AL-KO ATC system. [You must be registered and logged in to see this link.]

A Dandy doesn't have an AL-KO chassis though so can they fit it?

 What about Knott's ETS system then? Well from the instructions it looks like it can be self fitted.  http://www.ets02-pferd.knott.de/media/repository/default/Content/Projekte%20Kunden/Knott/ETS02/Betriebsanleitung/PDF%20Fremdsprachen/Knott_ETS2_Anleitung_EN.theme/en.original.pdf
Page 13 gives the model numbers of Knott brakes that are suitable.
Going to Knott's online shop I couldn't work out the difference in the two products for sale [You must be registered and logged in to see this link.]  Lost some interest when i saw the price for the unit without fitting £2,000.93 Wonder if I've read something wrongly, it doesn't seem to be in direct competition with the AL-KO system.

navver wrote:I calculated them from the weights and dimensions of the dandies. The meaningful figure is the ratio between destiny & designer of 5:1.

Yaw inertia is mass x distance squared.
Constraint is distance from wheels to hitch.

For constrained yaw inertia I divided the yaw inertia by the constraint.

The yaw inertia is the flywheel effect trying to turn the dandy and imposes a sideways force on the back of the car. The distance from wheels to hitch is a simple lever opposing it.

I seem to have been a bit asleep on this topic.

navver from your past posts I've little doubt of you but can you talk me through this?

A yaw inertia of 1,125  with a Destiny = mass X distance² If I start off with a loaded mass of 500Kg I'm looking at a distance square value of 2.25 so a distance of 1.5  If the later quoted unladen mass of 390Kg (as against the earlier quoted unladen mass of 300Kg) then  a distance squared value of 2.885 or so then a distance of 1.7 or so. Then I noticed a wheel to hitch distance of 6 so looks like we are looking at feet being the distance measurement. Then wondered if the mass values are Imperial, then had desperate brain fade after trying to think of the concept of mass in Imperial units?
Could you explain where the values come from.
Take it as a compliment as it shows I was at least reading your post with some attention. (eventually)

Also now realise that Owd Lad's comment was our only one about an older Highside Destiny.

Units do not matter as everything is a ratio when comparing a designer to a destiny.
Yaw inertia = mass x distance squared.
Mass = 500kg
Distance = 1.5. This is the distance to the mid point of the mass in feet. A circle of 3 feet diameter spinning about the centre of the mass.
1.5x1.5x500 = 1125. This is the flywheel effect.

Constraint for a designer is the distance from the wheels to the hitch in the same units as the yaw inertia i.e. feet.

Divide the yaw inertia by the constraint distance gives a measure of the control exerted by a longer tow bar.

The meaningful figure is that the toilet destiny is 5 times more likely to snake than a designer. That is a ratio of two numbers so all units cancel out. As long as all units are the same that is valid.

navver wrote:Units do not matter as everything is a ratio when comparing a designer to a destiny.
Yaw inertia = mass x distance squared.
Mass = 500kg
Distance = 1.5. This is the distance to the mid point of the mass in feet. A circle of 3 feet diameter spinning about the centre of the mass.
1.5x1.5x500 = 1125. This is the flywheel effect.

Constraint for a designer is the distance from the wheels to the hitch in the same units as the yaw inertia i.e. feet.

Divide the yaw inertia by the constraint distance gives a measure of the control exerted by a longer tow bar.

The meaningful figure is that the toilet destiny is 5 times more likely to snake than a designer. That is a ratio of two numbers so all units cancel out. As long as all units are the same that is valid.

As I said I do have little doubt in you.

I can comprehend that if we are looking at a ratio then units are unimportant.

Glad I'd read through it well enough to at least appreciate the figure for distance was 1.5. Perhaps I asked a lazy question though. I'd said "Can you tell me where the values come from" after focussing on numbers.
It should have perhaps been can you talk me through the concept.

This is the distance to the mid point of the mass in feet. A circle of 3 feet diameter spinning about the centre of the mass.
1.5x1.5x500 = 1125. This is the flywheel effect.

"This is the distance to the mid point of the mass in feet" from where?
"A circle of 3 feet diameter spinning about the centre of the mass." So what is spinning about the centre of mass?

I've asked for some large inputs from you and the last one on electrics I've still not responded to properly. Sorry I will. Having the distinction of failing both my maths and physics A level I accept my abilities might be behind yours. Though I wasn't too shabby on the mechanics side of maths.
What I believe though is if we quote something as a fact or factual concept we should at least try to talk members through it. Far too many lazy sites saying something or worse still linking to something be it on the dynamics of towing or on law or best practice where the idea or concept isn't validated and is actually a crock of shite.
I hasten to add that I don't suspect that of you but we should explain a concept.
I think your next post might not be a short one. I'm not asking for it immediately bet you love me no end for this.

Lazy Links And Justifying What You Said

I swear I hadn't seen this when I posted my last comment.

Please watch this video from the Camping Channel featuring John Wickersham



So the video is made by the Caravan Channel and it features the very well respected John Wickersham what could possibly be lazy about linking this? Well just because a big name made it it doesn't stop it from being wrong.

I am entertained by John Wickersham he authored both the Haynes Caravan Manual and the Haines Motorcaravan Manual he has also written several other caravaning and motorcaravanning books.

It was wonderful to see him talking about the model that simulates towing made by the university of Bath for Bailey Caravans that I have referred to several times but I'd have to say in the videos that he does he tends not to tell the whole story about a subject. I'd say his videos for the Caravan Channel that are more slickly made are worse than his own but both tend to miss out key issues.

The key thing that was wrong was the second feature on what you are licensed to tow. Unfortunately because I wrote it the piece on towing law on this site is long winded and laborious to read but it is at least right. No point being slick and wrong. [You must be registered and logged in to see this link.]

While not strictly relevant to here my point is that posting links to items is just the same as saying something yourself. You should only post something instructional when you can validate what is being said.

I know it's off topic but did anyone spot the key point that is wrong.

Hello,

sorry to butt in and my contribution maybe a bit late but we have a 2005 Destiny high side and it does get unstable over 65 mph this 'feeling' makes me back off to 60 mph.
Out tow vehicle is a 1992 Daimler Jaguar, some say this is unsuitable because of the rear overhang of the car, I find it great; tows well, steers well and I can reverse the unit with aplomb which is good for me!
As for the downward stance at the hitch which is more pronounced with our car; with experience has not improved stability.
When we viewed the Destiny there was a stabilizer fitted but the tight owner removed it so I sort of knew there would be stability problems.
I load the unit as I bought it but did question in my mind why is like this so we now put the heavy items in the unit above the axle and the unused awning goes into the Daimler.
As you need access to the roof poles it does take planning and trials to get it right.
Personally I don't have a problem towing at 60 mph (although the Daimler is more efficient at 75-80) we are on holiday so what does it matter.

Regards Ian

Great video, clearly demonstrates how load effects stability

Ian

"This is the distance to the mid point of the mass in feet" from where?
"A circle of 3 feet diameter spinning about the centre of the mass." So what is spinning about the centre of mass?

The centre of mass is the centre of the flywheel.

A caravan on 2 wheels is a flywheel. It has mass (weight) and will rotate on it's 2 wheels., just like a wheel turning on it's axle. As soon as it starts turning it has rotational inertia which will keep it rotating indefinitely if there is nothing to stop it just like our planet earth etc. This is quantified as a moment of inertia equal to the mass multiplied by the distance of the mass from the centre of rotation or axle squared.

When a caravan snakes it is inertia which keeps it snaking. All I have done is to take a dandy designer which is 6 feet square approx and said it is rotating about the middle of it. I have assumed that the mass is equally distributed meaning each square inch of floor space weighs the same. I know it isn't quite equal but for the sake of keeping the sums easy it is reasonably equal. If it is eqully distributed, the centre of the mass describe a circle of 3 feet diameter if the dandy is rotating. The distance of the mass from the centre must be 1.5 feet.

The mass is the 500kg weight of the dandy when fully loaded.

Now this may not satisfy a professor of dandy stability but it simplifies the sums and for a simple comparison between a destiny and designer produces a result of reasonable accuracy. As an engineer, I love doing basic simplified maths which achieves the desired accuracy often in my head. Yes you can always take 50 extra factors into account but will go mad doing it and make a mistake. Even if you get it right (with your computer), the difference in the result is negligible. You need a 6 inch pipe for that mate, no you don't, you need a 5.578365420967 inch pipe.

The constraint is the length of the dandy from it's centre to the end of the hitch. The longer that is the more force the car can exert on the snaking dandy. A lever in other words with a linear relationship. You've often commented on this effect.

For reference I would refer you to Mr Newton.