Lotus Elan

Lightweight Safety Improvements?

PostPost by: Matt Elan » Thu Nov 12, 2015 4:01 pm

The Elite/Eclat /Excel certainly did very well in crash testing - I don't know how they do in the real world. But, and its a very big but, the body shell was designed from the start to meet the then current and any known future standards. Hence the body was designed from scratch to incorporate the right structures to give the right level of crash resistance. Secondly, the body was not hand layed up like the Plus 2, but used the VARI system. This meant a much more consistent build quality, and was much less reliant on the skills of an individual in producing the body. In a Plus 2 body there is likely to be air gaps, poorly wetted areas of mat and/or voids due to poor or rushed construction, all of which make the body weaker.

As for a cage - all well and good on the race track but the drivers will be wearing helmets, and have proper race harnesses to keep them in place. And I'll bet (well I'd hope) that the seats in a race car aren't just bolted to the floor through small bobbins.
What I'm saying is that any changes to a Plus 2 would need to be properly designed and really well implemented to offer any significant improvements to the existing safety of the structure which is not easy or cheap.
Matthew Vale - Classic Motoring Author
1968 Plus 2 - Somewhat cosmetically and mechanically modified
1969 Plus 2S - Currently undergoing nut and bolt restoration
Visit me on matthewvale.com
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PostPost by: stevebroad » Thu Nov 12, 2015 5:09 pm

rgh0 wrote:
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.


Same here re old cars/cages, but you can't put a new aluminium cage in an historic car and get it certificated.

As I understand it, it was because they weren't strong enough to meet the regulations. To make a roll cage out of aluminium that was as strong as a steel one, the tubes would have to be larger and thicker (negatiing most of the weight advantage, especially when compared to T45) and post heat treated. Even then, steel has a far better 'springiness' so can absorb more impact forces before failing.
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PostPost by: Lotus 50 » Mon Nov 16, 2015 2:15 am

Aluminum does not have the strength or stiffness of steel, so it would take more aluminum than steel for the same level of protection. But a cage could be done with less weight in aluminum.

I've never worried about rollover in sports cars driven on the street. Statistically front, side, and rear impact in that order.

For a frontal crash, I think an old Elan or Plus 2 would be pretty good for their era, and pathetic by modern standards. Somewhere I saw a picture of a post crash tested Elan. The cockpit remained pretty much intact, which was unusual for the era. As note above, the front is useless for absorbing energy, and the peak G's wre probably pretty high. But for the 60's that was good.

For side impact, pathetic for any era.

I just don't see the project as feasible. Go ahead and add weight and cost to your car if it makes you feel good. But without some crash testing and or a lot of computer simulation it's just guesswork. Or a steel roll cage that you can't get in an out of practically.

I love my Plus 2, but I'd much rather be in a modern car if I had to crash.
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PostPost by: Own Little World » Mon Nov 16, 2015 11:46 am

I saw the same picture of the snub-nosed +2. The whiplash must have been horrendous.

The statistics you mention seem to confirm the idea that front and rear skins will probably be a benefit.

I too have never bothered with a roll-over bar either (in the MGB Roadster). Maybe I have just been lucky for 20 years.

As far as side impact goes, my colleague is a good mech. engineer and I may do a trade with him to get some finite element analysis done, although as Matt mentions earlier the strength of the existing layered shell is the biggest unknown in the equation.

Failing all that, a pair of steel side impact bars shouldn't destroy my mass budget completely. Either way, I think there is a need for something in that area.
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PostPost by: Gray » Mon Nov 16, 2015 12:26 pm

I think general strengthening around the passenger cell, adding side sill bars and a roll cage is a good idea. I've strengthened most panels on my S4, it weighs very little more. The chances of making it worse if you are using common sense is unlikely.

I survived being forced off the road around 40 mph and hitting a telegraph pole in an Elan many years ago, my back has never been the same since, but it shows how well fiberglass can absorb impact. My father hit an air tank on the M4 from an accident on the other side which damaged the front suspension on a Scimitar GTE and ended going down the central barrier for several hundred yards before it stopped. The fiberglass which was thicker than a Lotus was well ground down, but repairable!

My everyday Audi is much safer (and quicker) but not as much fun as an Elan - must get back to working on those 26R arches.
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PostPost by: Lotus 50 » Tue Nov 17, 2015 12:14 am

I thought about this on my long commute today. There's no point to trying to engineer crumple zones without serious computer assist. Behaviour of materials beyond yield wasn't even taught when I went to engineering school (82 grad). I think crumple zones are beyond home design.

But making the passenger cockpit more secure, ie prevention of intrusion, could make sense. The solution is not bamboo, but it could be balsa wood. It's a pity, but the outer layer of glass is chopped strand, which is not as strong as it could be. What it really lacks though is core, and then an inside layer of glass. Fiberglass performance boats are made from a glass/core/glass sandwich. People are using composites now, but for decades the core of choice was end grain balsa wood. Balsa wood weighs almost nothing, so you wouldn't be adding that much weight. The core material is only loaded in compression and doesn't have to be that strong. The strength comes from the outer and inner layers of glass, and the distance between them.

Poorly made fiberglass boats allowed moisture in to rot the balsa core. The idea now with composites is that the composite won't rot. But you could read debates all day about what composite to use. Some very high quality boats are still made with Balsa and that's my preference.

As I said above, I would not worry about the roof. On the weekend I watched a Top Gear DVD where they discussed a Bond film where they had to use pyrotechnics to get an Aston Martin to flip. Low, relatively wide cars don't roll that readily.

One area that has not been discussed is the seat belt anchorages. In any random R16 sled test the load on the anchorages is about 10KN outer, and 20K at the buckle. I don't think these loads were understood in the mid/early 60's when the Plus 2 was designed. I'd add a lot of glass where the retractor bolts to the body and larger metal reinforcements behind the outer anchor (bolts to sill) and inner anchor (bolts to chassis). Use SAE grade 8 bolts or whatever the UK equivalent is.

From SAE J800:

Reinforcing plates shall be of steel and free from burrs and be rounded on the peripheral edges adjacent to the vehicle. The reinforcing plates shall be at least 1.5 mm (0.06 in) in thickness and at least 2580 mm2 (4.0 in2) in area. The distance between any edge of the plate and the edge of the anchorage bolt hole shall be at least 15.2 mm (0.6 in). Corners shall be rounded to a radius of not less than 6.4 mm (0.25 in) or cut so that no corner angle is less than 135 degrees and no side is less than 6.4 mm (0.25 in) in length.

The Plus 2 was one of the very first cars to have 3 point seat belts as standard. There was one Volvo around the same time and nothing else I know of. The Volvo application is said to be the first. 3 point belts = good, but did they fully know what they were doing?
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PostPost by: Own Little World » Tue Nov 17, 2015 11:08 am

Very many thanks for the insights.

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