Chassis on top of the floor?

[GD485]

I was thinking about the way caravans need to go in the future.
Lighter, more robust, dry, more aerodynamic, better handling and cheaper (unlikely).
True monocoque construction maybe a step to far for the manufacturers as tooling and design cost could be extortionate.
Being an engineer my train of thought asked; Why is the caravan chassis bolted to the underside of the floor?
Would it not be possible to reshape the chassis so the members are located inside the front bed lockers and on top of the floor.
All the side lockers would be lower and improve the stability.
Can you fellow caravanners suggest something revolutionary for the future of caravans?

 

[DrZhivago]

Lighter, more robust, dry, more aerodynamic, better handling and cheaper (unlikely).

Why?

Why is the caravan chassis bolted to the underside of the floor? ... Would it not be possible to reshape the chassis so the members are located inside the front bed lockers and on top of the floor.

That would be possible along the bed lockers and cooker etc, but you would need to step over the chassis member where you entered by a side door, and anywhere else where the walking area went outboard of the chassis. That is unless the chassis were shaped to swing under the door area - that is done in London tube trains BTW, and makes a weakness that must be compensated by extra material (and weight).

Another point is that the weight of the body would hang from the chassis members by a number of bolts rather than resting on the members. This would impose a series of high "point" loads on the floor rather than the load being spread over an area. The floor would therefore need re-inforcing around, and for some distance from, those bolt points (eg by steel backing plates to prevent bolt pull-out) which would add more weight and complexity.

I think that the bottom line of what you are suggesting is to make caravans significantly lower to the road than they are by tradition. You imply this in the advantages suggested in your opening, and is perhaps the answer to my "Why" further up. But that could be achieved with the chassis below the floor anyway, with no radical change involved. It could cause problems on sloping sites though - I have had one end of the caravan almost touching the ground before now.

 

[Icaru5]

On reflection, post deleted ... B)

 

[GD485]

Hi Dr Z

My OP was a bit of provocation to get some ideas on what we all consider a step toward in caravan design
With tow cars getting lighter and greener then something has to happen to maintain stability.
Particularly if electric cars are the future.
One thing I would like is air suspension, just think how easy to get the levelling sorted.

 

[Damian]

Quote " My OP was a bit of provocation to get some ideas on what we all consider a step toward in caravan design "

Before trying to reinvent the wheel, they should all be making caravans that do not leak and in which everything works properly from the start !!

 

[GD485]

In recent years we had a bit of improvement in construction but caravan quality still isn't great.
Maybe the industry needs a good hard kick in the software to reboot the whole concept of caravan build methods.
The basic box is still made out of lots of panels all fixed together with varying degrees of success.
With composites becoming commonplace in a lot of industries isn't it about time caravans chucked the chassis and build a true one piece body?

 

[chrisn7]

Hi Dr Z

My OP was a bit of provocation to get some ideas on what we all consider a step toward in caravan design
With tow cars getting lighter and greener then something has to happen to maintain stability.
Particularly if electric cars are the future.
One thing I would like is air suspension, just think how easy to get the levelling sorted.

Having replaced air suspension units on an X5, I would say that the weight is probably quite similar to a conventional spring, except that a small compressor is required to achieve (self) levelling, thus increasing weight. So air units do fail, as do compressors, plus the added complexity, whereas simple springs and proven damper technology give reliability even if low tech. Its a bit like the discussion on caravan brakes and whether these should be more modern / complex.

 

[ProfJohnL]

Its good to challenge the accepetd norm, and well done for starting this. Chassis on the inside, Hmmm, its definitely different, and there would have to be some thinking about the doorway as has already been mentioned.

Someone has mentioned monocoque systems, well to some extent the caravan body already uses some of these principles, as the structure requires some of the internal furniture to provide wall stability.

I do wonder if the floor of the caravan could be redesigned to become a fully load bearing element using stressed skin techniques, and thus the chassis of the caravan. The aircraft and marine industry use such techniques.

But as Damain has suggested there are many aspects of current caravan quality that needs to be addressed, before they start using real hi-tech solutions.

The biggest issues with the the UK caravan manufacturers is their consistency of manufacture. We will most frequently hear about products that fail (that's one of the down sides of the internet) but there are some who will have a genuinely good product, so that proves their designs are not without some merit, but the problem is they can't do it consistently, and they don't deem to be doing anything about it.

There are two things they should be doing, the first is to revisit the design, and try to make it impossible to assemble incorrectly, and secondly to incentivise their work force to make quality of work as important if not more so than quantity.

 

[GD485]

Hi Prof

A complete re-think might be what's needed to address the fallibility of current designs when it comes to assembly errors.
A true monocoque maybe possible if sub-frames are created for the drawbar and axle.
Surely one of the caravan manufacturers has the resources to at least prototype the idea?
Colin Chapman managed to build Lotus cars before the days of Finite Element Analsys and CAD software.
Front and rear panels could still be glued on so face lift updates can be done to satisfy the marketing department.

 

[ProfJohnL]

I fully appreciate the ground breaking advances that Colin made to the automotive world, but I fear it may asking too much to expect the caravan manufacturers to have people of that calibre working for them. Realistically the skill sets are quite different anyway.

I feel a rant coming on. :evil:

Cars have many thousands of bits, often with close tolerances, where as caravans have far fewer bits and tolerances you could drive an elephant through, That why they need so much mastic, and flexible filler.! hmy:

But whilst Lotus did make its mark in the concept stakes, B) very much like our current the caravan industry Lotus's of the day were notoriously unreliable. and many leaked. I know becasue my brother's mate had one. That sounds strangely familiar. I suppose I'm saying the UK caravan manufacturing is still working to 1960's methods and non existent quality standards. inch: They should be so embarrassed by their poor quality

What really appals me most, is that from the earliest caravans I can recall (Circa 1950's) water ingress has been a constant issue for caravan owners right up to today's products. The industry has had decades to work out how to join panels together in reliable and water tight way, and they did nothing about it until about 5 years ago. And despite their much too late efforts they still produce leaky caravans!. :blink:

Just in case they hadn't noticed we have sent men to the moon in leak proof vehicles, The vast majority of motor cars keep rain and spray out very effectively. - Why cant caravans???? :woohoo:

The manufacturers can giveany excuse they like but none of them should be considered valid. They should have had it totally sorted by now.

 

[GD485]

Lotus was given a cruel but true acronym based on its name: Lot Of Trouble Usually Serious!

I feel the Prof and I are singing from the same hymn sheet.

Why has the caravan industry suddenly woken up and made a half hearted effort to improve the construction methods? Are they feeling guilty about all the customer complaints or is the cost of repairs starting to effect the bottom line.

 

[emmerson]

It is perfectly possible to build a caravan shell out of only two GRP pieces, one top and one bottom, and glued together around the waist. Hence a leak-proof structure, with added sub-frames for the oily bits.
It worked for Holivan, and, and , I think Freedom.
My ancient Royale has GRP front, rear and roof, but I cannot understand why they then used wood and aluminium for the sides!

 

[GD485]

Hi Emmerson
I knew those two makes used GRP clam shell body mouldings but are you sure they didn't have a chassis?
One thing for certain they proved the concept works.
So what's holding back progress with all the other manufacturers?
As it is they all share components suppliers why couldn't they share body mouldings?

 

[Hutch]

I love this Thread, the leaky caravan, a car with a whisleling window, take it back to the manufacturer, I used to work on $28,000,000. YES 28 MILLION , And these things still leaked. Sikorsky S92. When the windscreen leaked, we told the pilots it was to keep them awake. , When it leaked on a passenger because the manufacturer used a plastic hose that cracked under heat, and dropped water on them.. !!! Bad manufacturing, The manufactures, then asked the operaters, US, where the problems were , and Then , how to fix it. .
Hutch

 

[ProfJohnL]

Hi Emmerson
I knew those two makes used GRP clam shell body mouldings but are you sure they didn't have a chassis?
One thing for certain they proved the concept works.
So what's holding back progress with all the other manufacturers?
As it is they all share components suppliers why couldn't they share body mouldings?

That would remove the capacity to be different. There is plenty of debate about new designs when they are mentioned on the forum, and I suspect, that shows there is need for diversity to satisfy those non communist party members hmy: .

 

[GD485]

Most of the individualism in caravans boils down to cosmetic changes to the front and rear mouldings including the hardware stuck to it.
The styling inside and layout is the main difference between models.
The need for furniture to be a structured component would be removed so complete freedom of design would be possible.
As it is there are lots of uk brands but few manufacturers as in the Swift group and Elddis.
Demands from us and the environment to produce a better product needs a new approach.

 

[JTQ]

Why is the caravan chassis bolted to the underside of the floor? ... Would it not be possible to reshape the chassis so the members are located inside the front bed lockers and on top of the floor.

That would be possible along the bed lockers and cooker etc, but you would need to step over the chassis member where you entered by a side door, and anywhere else where the walking area went outboard of the chassis. That is unless the chassis were shaped to swing under the door area - that is done in London tube trains BTW, and makes a weakness that must be compensated by extra material (and weight).

.[/quote]

The chassis could of course loop up over the doorway.

Puny chassis are IMO half the later life leak problem with 'vans; their flexing tries to work the fragile bodies and in particular the side to roof and sides to end joints all of which are hopelessly inadequate structurally to take on the task, so the bonding/jointing fails and damp and destruction soon follow.

 

[GD485]

Hi JTQ

The lightweight chassis fitted to modern caravans has minimal torsional stiffness but does handle the bend loads as a result of loading and braking quite well.
The torsional bracing of the chassis, I feel, is assisted by the body strength. So your theory regarding leaks and body movement maybe a part of the problem that needs addressing.
The caravan construction method has been tweaked over the last 40-50 years but the problem with leaks has been a constant problem.
It's time for a major rethink.