modifying an old VW splitscreen van, side impact risk

[dubin]

Hello,

First post. I would like some input from knowledgeable vehicle body structural engineers around a debate that is raging in the Splitscreen van community (whilst most of the people involved have been working with the vehicles for 20+ years none in my opinion have your level of knowledge).

Setting aside that a split screen van built in the 50's has little safety anyway as you are basically sat inched away from a head on collision with no protection, we are debating the safety of a side impact at the b-post area behind the front wheel!

why?

Well VW produce several different type of vans and a member wishes to convert their bulkhead panel van to a swivel seat van by removing the bulkhead and wonders what, if any, additional strengthening should be added.

To start the debate these where the models produced by VW and the bulkhead/strengthening used.

1. Panel van, bulk head side to side from B-pillars, raised rolled floor side to side under seats.

2. Walkthrough, 2 tubs around the rear of the front seats, raised floor cut in the middle and lower section added to from a walk-through area.

3. Swivel seat, same as above with the tubs cut right back to just form triangular support at the b-post.

4. Flip-seat, same as above with the triangular upright supports removed.

Below is a bulkhead model with the bulkhead cut out

At the B-post area is a metal hoop running up the b-post, across the roof and under the floor is one of the main chassis section cross members.

So if the bulk head of a Panel was cut out you would be left with 4(a flip-seat) model, how much weaker is this and did the original bulkhead offer any protection from a side impact or is it just stopping goods in the back of the van flying forward and hitting the driver?

What additional support should/could be added to provide greater protection?

I realise we have no data for any real calcs, but what engineering principles come into play here that could be used to guide a decision?

 

[evelrod]

I have a friend that is nuts about VW vans. He is a competent builder and has done several over the years. After a minor front end crash he went about "strengthening" the thing.---(That's in quotes for good reason.)---Steel roll cage type construction around the front and side footwell areas along with a very nicely concealed rollover bar in the B pillar area. I'm not sure that it might not be the van in your photos...I don't participate in that forum.

Now, my opinion is that all the work may be worth the effort in a minor crash incident...Anything over walking speed, the driver/passenger still being 'soft tissue', is much akin to playing Russian Roulette by choosing a .22 over a .357"!

Rod

 

[MikeHalloran]

To get anywhere near a formal evaluation, you'd have to look at the transverse section of the various B-pillars. (I.e., the section image when cut in a horizontal plane)

Any B-pillar whose transverse section forms a closed tube is going to be much stronger than a B-pillar whose transverse section is similar, but not completely closed, or channel-like, or angle-like.

It's probably easier to just insert a NASCAR style tube hoop.
... and a connected half-hoop in the front, protecting knees and hips.
... sort of.



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

Roll cages in street cars are problematic due to heads hitting tubes.

Cheers

Greg Locock


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[patprimmer]

I was a real VW fan way back when they actually made a peoples car, but I never really got into vans.

To be frank the VW vans really frightened me for several reasons, not the least of which was the fact that the internal energy absorption media for the front crumple zone was the driver and passenger.

Crash bars only make the structure hard, they don't prevent injury, they simply transfer the injury from external body parts to internal organs.

Regards
Pat
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[GregLocock]

Having said that a /good/ structure further back and a 4 point harness would be a step forward. Your thigh bones will still end up in your kidneys, and the steering wheel will pierce your heart, but at least your neck won't be broken.

Cheers

Greg Locock


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[MikeHalloran]

Honest, I _was_ going to mention that the rollcage has to be far enough back that you can't possibly bump your head on it, _and_ covered with frangible foam for when you find out that's not far enough.

... and that the half-hoop going forward to protect thighs and feet probably needs to lie completely outside of the doors and front bumper in order to actually afford any protection.

... but I got distracted by something and didn't flesh out the message.


I was also not quite talking about boxing the B-pillars if they are not already closed, and it occurred that such boxing would work even better if the pillars were first tightly packed with fitted hardwood.




Mike Halloran
Pembroke Pines, FL, USA

 

[dubin]

Lots of replies already, thanks.
I understand the van is a huge risk anyway, but what is the best way to try to reduce that risk (obviously not including selling it and driving a modern vehicle!).

The van is quite high, by rally car standards, so I don’t think there is a huge risk of hitting your head on a cage if fitted, but also it would need to be done aesthetically, no one is going to want to climb over a huge diagonal cross section over the front door! Is it viable to try to think about crumple zone! If the front seat area was protected would the force of an impact then be transferred into the rear or is the sub frame just too strong for that?

Here is a schematic of the van frame

 

[dubin]

OOOpps, got my tag wrong.

 

[dubin]

There is obviously a trade off between what I would be willing to add to the van for strength and usability, for example, I am unlikely to consider cross bracing the doors something I can live with! It is also unlikely I am going to roll the van so maybe a full rollcage is not really adding full value.
I am primarily interested in adding some more protection against a head on crash, a side impact into the wheel well (increasing this side to side strength now the bulkhead is removed) and putting back any rigidity lost from the removal of the bulk head.

If I was to add a cage like this would it add much additional protection or is it a waste of time. Organs crushing inside your body aside, would I be more likely to still have legs left with this sort of additional protection?

 

[thruthefence]

How about adding some airbag seat belts like we are seeing in small general aviation aircraft these days?

http://www.amsafe.com/

Seems to me the old vedub vans were underpowered already, what will be the weight penalty for your "beefing up"?

 

[patprimmer]

I don't see a lot of advantage of the internal front cage.

The rear hoop looks good. If you want to retain walk through, the X bars could be raised where they meet the upright and drop diagonally to the floor on its side near the edge of the walk through. A heavy cross beam could be added below the floor to reinforce the walk through area and the diagonal buttresses could tie to that.

The doors should have side intrusion bars.

The front cage should be external and out front as far as reasonable. It should be relatively soft to absorb energy as it deforms.

Regards
Pat
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[MikeHalloran]

Agree with Pat; you get the most added protection for the least cost by adding side intrusion beams to the doors.

On the external front cage, you could have fun with that and make a set of 'roo bars' with a giant VW logo built in.





Mike Halloran
Pembroke Pines, FL, USA

 

[dubin]

The original 1200 engines these things had are long gone, everyone runs at least a 1600 now and most people a lot more than that, so you are now flying along at 80mph in your metal coffin! Hence the advice being sort to try and make things a bit safer.

Those seatbelt airbags look great, wonder if they have ever fitted them in a vehicle? Any idea on price? With an air bag to protect your soft internal organs then I guess making the van exterior more rigid is a good proposition to protect your limbs and such!

Under the floor where the roll cage sits is one of the two main chassis cross struts in the van, this is where the outriggers and jacking points are located so I think it is pretty strong, but could be re-enforced if people think that is required?

As for the X-cross between the B-posts I am happy this will not get in the way too much when walking from front to back and will allow the seats to swivel into the back and be useful without bars in your face! but if they are offering no additional later support and protection (?) then I would prefer to not have them, smaller triangular struts could be used instead which would also not interfere with swivel seats. (I have added these in red here)

It is possible to brace across the door (again shown in red) without it getting in the way of being able to get in and out of the van easily. Would this add significant strength improvements to the cage? Or is it just to protect against side impacts?

As for the front, this is where we need the most protection; I really want to try to make that as strong as possible. The original bumper location was ideal when the vehicle ran at stock height, however now a days we all lower then bus at least 4” so the impact area, in a head on, would most likely be above the line of the main chassis where the bumper attached.

The idea I had with the front was several vertical bars, more than the 2 I have shown in red, to try to stop the front of the van folding around your legs. Then the diagonal red bars braced up from the chassis to assist in keeping the whole thing vertical and the horizontals coming off the two main up and over side bars.

Obviously I am not a automotive structural engineer so just working with designs I have seen of how a roll cage fits together and trying to work that into the space we have available in a van. It is not ideal, but will it offer additional protection, or is it a waste of time and money?

An external front cage is not an option, aesthetically no one would go for this, so we are left with working with the inside as best as possible.

 

[patprimmer]

You will always be compromising space and convenience for safety. That is just how it is. Maximum safety is gained by large crumple zones with soft structures and a hard structure that is a close fit to the occupants.

Being held in place with a device that allows controlled deceleration with the load spread evenly over the body.

Retrofit airbags are a problem from what I can see. Full harness seat belts are good bur a reasonable inconvenience and mostly illegal due to not being automatic adjusting.

Regards
Pat
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[dicer]

Well all the talk about crumple zones etc, has me thinking about the average nascar roll cage, and how many folks walk away just fine from 150 plus mph crashes. As well as the drag racing, crashes. Personally I say make the structure as solid and resistive to deformation as possible. Problem is then weight plays an important part. If you had the proper restraints and you were in an army tank, you could do a head on crash with most anything and survive just fine with no injurys. Just curious what the crumple zone would be of 4 to 10 inches of reinforced armor plate?

 

[MikeHalloran]

The crumple zone is entirely in the _other_ vehicle.

... except maybe for the paint.



Mike Halloran
Pembroke Pines, FL, USA

 

[dubin]

My thoughts exactly, although didn't want to say I was planning on using the other vehicle, which is bound to be modern, as the crumple zone!

Weight wise it depends on the material used. A typical full cage used in motorsport is made with CDS and weighs around 45kg, obviously in the van I would not be going this crazy so expect the weight to be around 30kg.

As for material to build the cage from, all these cages you see use round tube, either T45 or CDS, both of which are expensive and bulky; T45 is the lightest and strongest but suspect out of my budget.

Mike you said
"Any B-pillar whose transverse section forms a closed tube is going to be much stronger than a B-pillar whose transverse section is similar, but not completely closed, or channel-like, or angle-like."

What are the benefits of using a true circular tube over a closed curved box tube? I used some curved edge box tube, the same as they use for making kit car chassis, for an inner hidden bumper on my split. Why? It was the strongest material I could fit in between the panels. This stuff is relatively cheap and you can form it yourself around curves easier than circular tube which is a lot more prone to kinking. If I made my sudo cage in this material it would be easier to get it butted up to the van and thus easier to hide. Here is a photo of the inner front bumper I had made and a sample of the material can be seen on the bench:

Can you also give a bit more detail to your comment:
“and it occurred that such boxing would work even better if the pillars were first tightly packed with fitted hardwood”

 

[patprimmer]

When was the last time a NASCAR or Drag car had a head on crash while racing.

In my observation, they all travel in the same direction and reasonably parallel or tangent to the walls. They also wear very well designed harnesses and helmets and often wear neck protection restraints and sit in very well designed seats.

They also do have softer sections at the ends of the structure.

Regards
Pat
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[MikeHalloran]

For any closed tube, some improvement in buckling resistance is possible by stuffing the tube with hardwood to support its walls, just as a mandrel in a bender helps a tube resist buckling.

So, stuffing a stock pillar should add some intrusion resistance.

Sistering a stock pillar is likely easier and more effective, but harder to hide.



Mike Halloran
Pembroke Pines, FL, USA