Lotus Elan

Lightweight Safety Improvements?

PostPost by: Own Little World » Mon Nov 09, 2015 8:59 pm

I have been thinking lately about trying to improve the safety of the +2 shell in a lightweight way due to the fact that (a) my project will hopefully be electric powered and (b) I would like to be able to take my two girls in the back.

The three main areas of attention are (a) side impact, (b) head-on collision and (c) roll-over.

a) From the perspective of side impact, and given the shape of the backbone chassis I don't see much alternative to a thick steel bar, like the Spyder product to protect against side-on collisions and the wheel in the foot well scenario. However, I am wondering whether you could safely reduce the mass with extruded aluminium (like an Elise). Would this be enough, in conjunction with the steel sill inserts? Also, if you were to weld or bolt struts from the suspension castles to the back of the door lock on the B post and the hinge on the A post, would a door bar (from hinge to catch) offer any protection?

b) I am considering an aluminium belly pan in the front bay to improve aerodynamics (the engine will be replaced mostly with battery cells) and I hope that this would create a more effective crumple zome between the front bumper and the chassis. I have seen the head-on pictures on this forum that look as if the nose has vapourised on impact and then the car has decelerated VERY quickly as soon as the chassis joined the fray.

I am also wondering whether you can buy purpose built "crumple bar" or similar? Or Would several aluminium struts between the bumper fixings and the chassis work?

c) I am not really interested in full rollover crash cages as this is far too heavy. All I am thinking about is something that would give the fiberglass shell a similar strength to any ordinary small steel-roofed car. I am wondering whether formed and anodized aluminium extrusion could be successfully bonded to the inside of the shell and then fibreglassed over and re-trimmed? The lines of the roof pillars etc. seem to suggest some logical positioning. Has anyone done this? Would it be effective?

Thanks for any thoughts.

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PostPost by: gherlt » Mon Nov 09, 2015 10:29 pm

Regarding c) The Lotus Exclat/Excel had a roll-bar integrated into its roof, maybe you should take a look...
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PostPost by: jimj » Mon Nov 09, 2015 11:16 pm

I really can`t imagine the steel cill strengtheners providing much, if any, side impact protection. They`re too low and though fibre glass is surprisingly effective at energy absorption I imagine any significant accident will not end well. The backbone chassis will protect you more from a frontal collision, preventing the engine from being pushed back, but I do think you have to accept that any classic car without a full roll CAGE will not supply the passive safety that`s taken for granted in more modern cars.
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PostPost by: stevebroad » Mon Nov 09, 2015 11:48 pm

If you want protection for your kids then a full roll cage is the ONLY way in an Elan. Modern cars are carefully designed to withstand a roll and you can't replictate that by adding a little aluminium to a fibreglass roof! :-)

I fitted this to my Elan. It is made from T45 seemless tube, which is much stronger than traditional roll cage tube, so a thinner walled tube can be used. There are two bars giving side impact protection. This whole cage weighs in at 32Kg, not much for peace of mind. You could forgo the front roll bar and the tubes into the engine bay.

However, a full roll cage has the added advantage of stiffening the chassis quite considerably (they are like soft licorace when a lot of torque is applied) so the front roll bar (to which the A pillars are glued) and the engine bar tubes make quite a difference.

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PostPost by: mbell » Tue Nov 10, 2015 12:56 am

For energy absorption I'd be looking at glassing in some alu honey comb in the noise and boot area.

I had thought about fitting a loop up the b pillar, along the roof and down the other b pillar, joined to the chassis both sides. Never going to stop full intrusion but might be enough to be useful. Never got more than thinking about it when I couldn't get to sleep.

Had the bumper off my daily drive the other week and that just a big alu beam. Was pretty sturdy and not too heavy.
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PostPost by: Sea Ranch » Tue Nov 10, 2015 2:44 am

Steve, do you have a thread on that Elan you've pictured above?

If so, please direct us to it. Looks like quite an amazing project . . .

And now, back to regular programming (thread topic) . . . :mrgreen:

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PostPost by: wotsisname » Tue Nov 10, 2015 9:35 am

I don't have any answers, just a few thoughts

From the front: can you do something with the sill closure plates to prevent wheel intrusion, alternatively you are looking at the roll cage type structure as mentioned. I would see the other significant danger being the steering column being pushed back (particularly if you have a solid steering shaft)

Side impact. As has been mentioned the beam is pretty low. most modern cars would likely come over the top of that, especially a 4x4. Also. If that takes a significant impact there is only the bodyshell to prevent it moving. I seem to remember people talking about the seat frame taking the impact (probably on a Elan rather than +2).
can you build door beams in (no idea how you would get it to fit) and a corresponding structure in the rear wheel arch to brace... I think the Elise is an example of this.

From the rear there is a lot of boot before the chassis / tank area.... would this be where you would site the batteries ?
Is there a big risk with batteries & electric motors causing fire / electrocution ?
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PostPost by: stevebroad » Tue Nov 10, 2015 9:40 am

Sea Ranch wrote:Steve, do you have a thread on that Elan you've pictured above?

If so, please direct us to it. Looks like quite an amazing project . . .

And now, back to regular programming (thread topic) . . . :mrgreen:

Randy


I have PM'd you, Randy, so as not to hijack this thread.
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PostPost by: stevebroad » Tue Nov 10, 2015 9:55 am

Just thinking out loud here......

There is a lot of fibreglass stcking out of each end of the chassis which does very little in the event of a collision other than shatter.

2 options to improve existing structure:

Line with carbon fibre. This would add a lot of structural rigidity but also reduce 'give'. IE it will handle greater impacts than fibreglass but when it fails it fails spectacularly.

Line with aramid fibre (Kevlar). Not quite as strong as carbon but much more forgiving - ie doesn't shatter so will give greater protection, IMO. Surprisingly, it is cheaper than carbon fibre.

However, if your major concern is the safety of your kids then you have two options:

Don't let them in the car.

Convert a safer car.

In a big shunt with a modern car anyone in an Elan, no matter how much protection has been added, is in for a bad day.
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PostPost by: Own Little World » Tue Nov 10, 2015 11:51 am

Wow. Thanks for the replies everyone. It is clearly a subject that gets a lot of thought from Lotus owners.

Steve, that is a great cage you have built and I am stunned that it comes in at 32kg. The problem with the cages and rollover bars I have seen is that they preclude the option of people sitting the back, especially the ones that have the diagonal bracing (yep, I know it's there for good reason). Don't worry about hijacking - please hijack away!

My main thinking with the roof reinforcement is not necessarily that the cage should do all the work, rather that a (nonetheless rigid) lightweight metal structure could be bonded along its entire length to the fiberglass structure. In other words become an integral part of the shell. In the same way that increasing the cross section of a member exponentially increases it strength, a frame bonded to the shell would surely be greater than the sum of the parts.

Ghertt, it is interesting to learn about the Excel/?clat. I will do some reading on that. It may turn out to be exactly along the lines I was thinking.

Kevlar/carbon/honeycomb all sound like good options for the boot and nose. Probably better than the crumple frame I was imagining.

Thanks for all the suggestions.

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PostPost by: tvr78 » Tue Nov 10, 2015 12:22 pm

Health and safety madness! Take a driverscourse if you're afraid.avoid the accident . Ren?
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PostPost by: Own Little World » Tue Nov 10, 2015 1:05 pm

I did a search but couldn't find any passengers' courses. ;)
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PostPost by: stevebroad » Tue Nov 10, 2015 2:20 pm

What kind of lightweight metal structure are you considering to bond to the roof?

As for the roll hoop diagonal, that can be placed as per mine, away from the seating area.
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PostPost by: Mick6186 » Tue Nov 10, 2015 5:39 pm

Hi,
As far as roll over protection is concerned the original Clan Crusader competition body shells were interesting. The shell needed MSA approval for use in stage rallying. I used one of these cars in the 1980's and was intrigued by the FIBREGLASS roll cage. I contacted the RAC gent who tested the strength and he said it was tested by placing a full size rubbish skip on top of a bare shell and filling it water! He said the shell bowed out a bit but then returned to normal when the skip was emptied and removed, with no apparent ill effects.
The roll cage appeared to consist of a square section approximately 6 inches by four inches in section that went up the inside just behind the seats then across the roof. There was a thinner section that went across the centre of the roof to the screen to bond with another square section that went across the roof by the screen and down the screen pillars. Apparently the 'cage' weighed no more than 10lbs!! It made for a very rigid fibreglass monocoque, with no chassis.
The rally scrutinisers were always intrigued until they were shown the type approval certificate.
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PostPost by: Own Little World » Tue Nov 10, 2015 9:58 pm

A skip full of water? Fibreglass only? Holy shizzle!

Given that I don't have the cash for R&D or (possibly desctructive) testing I won't be able to take the fibreglass only route.

Steve, I the kind of frame I was imagining of would start with:

1) Side impact bars similar to, say, the Spyder product, made from fairly thick gauge, possibly rectangular aluminium tubing and bonded/fibreglassed over the part that is parallel with the sill.
2) A hoop from the above bar, over the top and down again, bonded all the way over and fibreglassed over.
3) tubes from the chassis along the rear roofline up to meet the hoop, either bonded (or brazed?) to the hoop and fibreglassed over.
4) A few added bits that I am yet to dream up. It is difficult to visualise without all of the above yet in place.The front of the roof is clearly missing reinforcement.

I am really needing the advice of a mechanical engineer to advise on the required guage/shape of tubing.

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