Lotus Elan

Lightweight Safety Improvements?

PostPost by: mrdoow » Tue Nov 10, 2015 11:16 pm

Lining the floor pan inside and outside worked nicely for my Elan Sprint. I also fabricated carbon/Kevlar side impact beams. It was a lot of work yet the stiffness the carbon brings to the body and doors appears to add a significant degree of safety. I used vacuum bagging and sand bagging techniques to accomplish the carbon lining process.

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PostPost by: Own Little World » Wed Nov 11, 2015 8:59 am

I love it. I have to admit that I have absolutely no idea about the skills, processes, tools etc. required to fabricate Kevlar reinforcements. Did you make up those pressed panels yourself? how do you form them?

(Edit - I just re-read. Vacuum/sand bagging. Time for more research)

I like the idea of doing the whole floorpan especially.

In the meantime though I have done a quick internet search and seen a few people selling Kevlar tubing, which could send me in a completely new direction.

Prior to that I had also been thinking of fiberglass over (don' laugh) bamboo. My dad used to make split cane fishing rods that were works of art and incredibly strong.

Would you guys have shown me the door if I drove around in an electric bamboo +2?
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PostPost by: Own Little World » Wed Nov 11, 2015 11:09 am

I am thinking along the current lines now; kevlar/carbon tubing made into frames by joining the ends of the tubing with cylindrical "L" and "T" shaped aluminium plugs. The frame can be laid in place (say, around the perimeter of each footwell side) and then Kevlar sheet laid over the top and cemented in.

That should be considerably better than nothing shouldn't it?
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PostPost by: vxah » Wed Nov 11, 2015 1:19 pm

Hmmm, bamboo spears for crash protection? Sorry just thinking out loud...
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PostPost by: wotsisname » Wed Nov 11, 2015 1:30 pm

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vxah wrote:Hmmm, bamboo spears for crash protection? Sorry just thinking out loud...


sorry, couldn't resist.
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PostPost by: Own Little World » Wed Nov 11, 2015 2:33 pm

The Kevlar is for wearing, in that example.
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PostPost by: Matt Elan » Wed Nov 11, 2015 8:57 pm

I'm really uncomfortable about how this thread is going. If you are really concerned about the safety of the Plus 2's shell then you should have a properly engineered, properly stressed re-design of the body shell using a proper structural engineer or get a reputable party to design and install a properly designed roll cage. Local mods to various parts of a shell may well not work, or transfer stresses from the point of impact to somewhere else in the car with potentially fatal results, which is why any design should be properly integrated.
Quite frankly, if I was going to improve a Plus 2's crash survivability I would not start with a Plus 2 body shell. If two tons of modern 4x4 decides to take you out in a Plus 2 I doubt there is much you could have done which would help you survive. Even if the body shell doesn't crumple, then the acceleration/deceleration shocks will not do you much good.

On an aside, the Elite/Eclat/Excel was designed with safety in mind and had a designed in passenger cage, with what Lotus called a 'Ring of Steel' around the passenger cabin. This was a tubular steel roll bar, which carried the to the door lock plates on the B post and was fixed to the sills. The sills were foam filled glass fibre boxes, integrated into he overall structure, and each end of the sills met with transverse more foam filled box sections in GRP, to form a complete box around the passenger compartment. (note that the foam was there to form the box sections using the VARI process) Side impact / intrusion from errant vehicles was catered for with steel box sections in the doors, which connected to the door plates and hinge plate. The point is that it was a proper integrated design, properly stressed and tested.

The major problem that I see with improving the Plus 2 shell is its size - its small and that gives very little room to fit any useful energy absorbing structures or re-engineer the existing structure; the current overinflated size of modern cars is mainly due to their structure being engineered to meet current safety standards. Maybe rather than use a Plus 2 an Elite/Eclat would be a better basis for what sounds like an interesting project? Your Plus 2 even without an engine is probably worth 3-4 times the price of an Elite/Eclat/Excel.

HTHs

Matt
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PostPost by: Own Little World » Wed Nov 11, 2015 9:47 pm

Hi Matt,

Yes that does help - thanks.

Firstly, please do not take any light hearted talk of bamboo cars too seriously, although I'm sure you realised that anyway.

I take on board your comment about a halfway job having possible adverse effects in terms of transmitting loads unpredictably and possibly even making things worse. I assure you that the plan is not to cover the car in bandaids and the idea of discussing it here is not to try and perform a critical design review (or even phase A study), merely to throw around ideas for an approach.

To be honest I am fairly optimistic that using modern materials such as kevlar and carbon fibre could actually result in something that is better than what was available in 1967. I'm under no illusion that it would be perfect or even take a good left hook from a 4x4 but then nor would a Smart. The brief is simply something that is appreciably better than stock and not prohibitively massive. (I love +2s and I'm sticking with this one ;) ).

What you say about the Elite/Excel/?clat is very interesting indeed so thanks for that too. In honesty everything you mention had already been considered except I think I had suggested aluminium rather than steel for the hoop. Similarly the box around the passenger compartment you describe is similar to what I was attempting to describe (maybe badly, I admit) except in Kevlar tubing rather than glass fibre tubing. Again the tethering of the frame to the door locks and hinges had been discussed.

I agree with you that the actual design and implementation would need more than just a forum thread to hammer out. Thanks again for you thoughts.

Alec
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PostPost by: stevebroad » Wed Nov 11, 2015 10:12 pm

What Matt says.

Alumimium roll cages/hoops were banned from competition some years ago, for obvious reasons :-)

As far as I am concerned, the only way to make the Elan as safe as is possible whilst retaining the car's exisiting shell and chassis is a full roll cage, period.

Do you want light or safe? Your choice. Faffing about with carbon fibre/kevlar, no matter how much you put in, will not be as safe as a properly designed and fabricated cage. An added advantage of a cage is that the seats can be mounted to it rather than the fibreglass floor.

A well designed cage can be bult so that it is close to the shell and allows the 'rear seats' to still be used.

Kevlar nose/boot skins are probably a good idea.
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PostPost by: vxah » Thu Nov 12, 2015 9:12 am

Have to say, when rebuilding my own +2, I looked at the body shell and thought I probably would not want to be in a crash in this and, what can I do to make it safer? I too thought about adding things to make it stronger but without crash testing you simply don't know how your "improvements" will react nor what small things could make a big difference, good or bad? As has been said it's not all about strength but about energy absorption? You could have a bit of a side impact, smack your head on that new steel roll cage and thats it? Remember the Chrysler Voyager that had air bags fitted? In crash testing the top of the column sheared off and the whole thing went out of the side window! Thats not me or you in our shed "improving" things!
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PostPost by: Robbie693 » Thu Nov 12, 2015 10:25 am

Back in the day when the Plus 2 was being designed/produced it was put through crash testing, presumably to to attain a type approval. Would any deviation from that design negate this? Does the type approval only apply to cars sold in the first instance, i.e. new from the manufacturer and not to someone modifying a 48 year old design? Who would be responsible for enforcing this anyway? Surely not the MOT test...

I would have thought though the insurers would need to be notified of any modification at least.

Just some thoughts, without any specific knowledge or experience :D

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PostPost by: stevebroad » Thu Nov 12, 2015 10:39 am

vxah wrote: As has been said it's not all about strength but about energy absorption? You could have a bit of a side impact, smack your head on that new steel roll cage and thats it?


That's why it has to be designed properly and tubes close to your head suitably covered which, If fitted close to the roof, won't cause an issue.

Any 'improvement' or 'safety device' has inherent pros and cons which you have to consider. Nothing is perfect.

As previously stated, the Elan isn't exactly a modern design so you aren't going to get modern day safety no matter what you do to it. Your kids won't be as safe as they are in your daily driver so you have to deicide whether the increased risk of injury (however small) is worth the fun they will have in it. Bear in mind that they grow up very quickly and will not fit in the rear, but will want to borrow it :-)
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PostPost by: Own Little World » Thu Nov 12, 2015 10:57 am

Thanks once again for your replies. The answer to the question, ?light or safe?, in the context of the original post would probably be ?light and safer?. The wisdom of that can naturally be debated and I am glad to see all the responses. Clearly, ?as safe as possible? means a steel cage, as does competition spec (but how many road cars would attain that?).

Steel side impact member and roll hoop (connected together) appear to be bare minimum for either goal. However, it is still interesting that Lotus themselves (at least at some point in history) considered a steel hoop and composite side impact protection sufficient. Does anyone know of empirical evidence relating to how the Eclats etc fared out there on the streets? If the fibreglass boxing in the compartment actually worked then is there any reason why a suitably designed kevlar/carbon one wouldn?t?

It also looks as if nose and boot skins are a no brainer, whatever the goal. If I were take an incremental approach to this, from nothing all the way up to full roll cage then this might be one place to start. Thanks for that recommendation.

Thank you everyone for your inputs. I am enjoying the debate.
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PostPost by: Own Little World » Thu Nov 12, 2015 11:01 am

Hi again Steve,

The daily driver is a Landrover, so yes, the Elan would be a rare treat for the kids (if at all, thinking about it).
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PostPost by: rgh0 » Thu Nov 12, 2015 11:07 am

stevebroad wrote:What Matt says.

Alumimium roll cages/hoops were banned from competition some years ago, for obvious reasons :-)

.


Yes I know they were banned but the reasons are far from obvious. I was told at the time it was due to abrasion concerns that the aluminium could be worn through if the car was skidding along the road upside down :roll:

If the reasons are obvious I would love to understand them.

cheers
Rohan

PS In Australia at least we were allowed to keep our aluminium roll bars in historic racing if we had them installed and a log book issued already before the time of the ban which I had done.
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