Lotus Elan

LOTUS chassis vs Spyder someone pls help!

PostPost by: Craven » Thu Dec 28, 2017 12:41 pm

Fatigue cracks are caused in the main by stress causing flexing of the material, if cracking of this type is stopped, in the chassis case by gussets, then it follows flexing has been reduced. If flexing has been reduced then stiffness must have increased, front and rear towers must surely be more stable when modified in this way.
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PostPost by: el-saturn » Thu Dec 28, 2017 1:04 pm

.there's probably an underdimensioned area where the Cage is finished and doesn't add any additional stiffness: and where the Y starts and the engine starts stiffening, we have "a stiffness jump" and cracks could start: but the Body may also add a bit in that area ?? a colored finite element drawing would help! sandy
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PostPost by: Craven » Thu Dec 28, 2017 2:35 pm

Not much stiffening from engine on rubber mounts!!
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PostPost by: el-saturn » Thu Dec 28, 2017 3:27 pm

the torque i'm thinking about originates from the area where there's the open Y before you get to the rubber Mounts near the clutch. because i'd say the engine, (even) with the rubber Mounts closes the open Y and makes that part of the chassis stiffer?? sandy - PS if i'm wrong i'll hear from ya!
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PostPost by: Davidb » Thu Dec 28, 2017 6:39 pm

Sandy: I think the 'bridge' structure over the top of the 'Y' coupled with the crossmember under the engine brace that area. In my experience the engine mounts will tear out of the chassis in racing use!
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PostPost by: greg40green » Thu Dec 28, 2017 9:41 pm

'Distorted by galvanising' ?
In 1999 I arrived at a Lotus dealers in the North West to collect my brand new un-galvanised lotus chassis .
I got out of my car to see 'a' Lotus Elan chassis being knocked around the car park with a hide mallet.
It was eventually put up against the curb stones in the car park where one of the two mechanics measured from front to back , from corner to corner , the second mechanic then stood on the backbone of the chassis before the first set about hitting the rear upright at one corner of the chassis before repeatedly measuring it again and again.

After watching this process for sometime I went into the show room to state that I had arrived to collect my new Lotus chassis then added that I hoped that the chassis being physically abused in the car park was not mine.
An embarrassed sales assistant assured me that it wasn't mine, then followed a flurry of activity and a chassis without scratches to both paint and metal work was delivered to my waiting transport.
I'm very much aware that the galvanising process can cause 'some' distortion but after witnessing the chassis being beaten into submission and other owners Lotus chassis's both galvanised and un-galvanised arriving very much distorted I would suggest that back in 1999 to around 2005 ish whoever was manufacturing the chassis's was using either a worn jig / tooling and / or the jig wasn't correctly set up in the first place.

One person I know received a new Lotus chassis so badly distorted he returned it to the supplier then promptly ordered a new Spyder item. Not my personal choice but when finished his Elan drove and handled fantastically and continues to do so.

How many different manufacturers are producing the Lotus chassis's now, from the different examples I have seen this last 12 month's it's definitely more than one ?
What I'm suggesting is that the galvanising process was/is still being used to excuse some of the bad manufacturing techniques previously used.
I speak as a qualified and experienced welder , fabricator of many years.

Spyder V's Lotus chassis?
Comes down to driver ability ,personal preference and the person with the biggest balls to drive an Elan on it's limit, In my humble opinion of course.

Spyder fan wrote:Sandy,
It?s pretty impossible to answer your question properly. Most competition formula insist on original equipment as available before a certain cut off date, so in most cases that precludes the use of a Spyder Space frame chassis. Therefore it?s unlikely that you will ever find two GTS 26R clones that are identical apart from the chassis used.

Supposedly the Spyder Spaceframe is stiffer than the standard folded metal item, but it?s not clear to me if this is necessarily a good thing. The modifications over a standard folded chassis carried out to the 26R style chassis most likely address the stiffness difference.

The history of the Spyder Spaceframe stems from a threatened lawsuit when Lotus finally woke up to the fact that they were losing valuable sales for spares that they previously couldn?t be bothered with until they saw how many Spyder were making for an eager public wanting to keep their Elans on the road. The result was a redesign that allowed Spyder to continue producing replacement chassis which they marketed as an improvement over the original pattern which perhaps was an important fact back in the days before ?the cult of originality? gained momentum.

The lawsuit is long gone as is the patent for the folded chassis. Spyder will make a folded chassis for you if you want one with the benefit that you can order it 2k low baked to your colour choice, and it will be guaranteed to be straight and not distorted by galvanising.

Sandy,
Bring your car to the UK and stay with me as my guest, we will do some track days and test your theory about being able to keep up! :mrgreen: 8)
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PostPost by: Mazzini » Thu Dec 28, 2017 10:32 pm

Gartrac make them nowadays and their products are spot on.
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PostPost by: gus » Fri Dec 29, 2017 4:18 am

alan.barker wrote:
Foto%202.JPG

Let the photo do the talking
Alan


No I won't

There is, as far as I can tell , a total of one such photo

There are hundreds, if not thousands, of factory frame failures, most due to rust.

Unless you have more evidence, the photo is meaningless
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PostPost by: el-saturn » Fri Dec 29, 2017 7:22 am

i bought my car in 1981 with a terrible "widened" Body. the car never saw any rain (an architect bought it in 1965 and made a mess of the Body) the Chassis was perfect: nothing bent and NO corrosion whatsoever; so it got bathed in zinc. 1st bath was to burn off the original paint etc.. and 2nd bath for the actual zinc coating: t's been that way ever since. the real good Thing is: i don't know many Lotus owners who still have the original Chassis and i'm glad i don't have to justify a Change. here in switzerland you don't get a Veteran Status (= 6 years MOT) for a car which has a replacement Chassis!! PLUS i'm sure my Chassis is as stiff as some of the best as it has a safety devices roll Cage. sandy :D
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PostPost by: alan.barker » Fri Dec 29, 2017 7:44 am

gus wrote:
alan.barker wrote:
Foto%202.JPG

Let the photo do the talking
Alan


No I won't

There is, as far as I can tell , a total of one such photo

There are hundreds, if not thousands, of factory frame failures, most due to rust.

Unless you have more evidence, the photo is meaningless

Your right i should have explained what i was trying to show.
Excuse me but I fail to agree with you, there are no gussets where the pivot pins are welded. This to me is bad engineering practice.
On a Lotus chassis there are gussets.
Maybe it's best for us to agree to differ.
Alan
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PostPost by: el-saturn » Fri Dec 29, 2017 7:52 am

we DO agree Alan: the original has gussets - the COPY evidently doesn't and e.f. the bottom wishbone bolt which is welded to the crossmember (square profil and not round as spyder) can bend and is easy to bend back BUT doesn't break off like spyders can! sandy
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PostPost by: rgh0 » Fri Dec 29, 2017 7:53 am

Craven wrote:Fatigue cracks are caused in the main by stress causing flexing of the material, if cracking of this type is stopped, in the chassis case by gussets, then it follows flexing has been reduced. If flexing has been reduced then stiffness must have increased, front and rear towers must surely be more stable when modified in this way.



I am afraid the above analysis is incorrect. The total chassis flexing is not reduced, just the local stresses induced by various loads being fed into the chassis

The chassis cracking experienced is caused by local stress concentrations due to fabrication details. The various 26R style mods help to correct some of those local deficiencies with local reinforcement. The do very little to nothing to stiffen the total structure between the front and rear suspension cross members in torsion.

The stiffening done on the front and rear towers reduces local stresses and cracking due to stiffer suspensions, but deflections in these suspension towers locally are already very small. The mods do not do much to reduce the torsional resistance between the front and rear suspension

regards
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PostPost by: el-saturn » Fri Dec 29, 2017 8:42 am

gussets designed for house construction look similiar to the loti ones. a proper gusset like on aircraft solutions is not just triangular, but really designed, which provides for a real load distribution. i agree with you rohan.
whereas composite chassis allow you to add more (usually unidirectional) material where needed and your fiber layout plan can easily be modified if you notice a critical area while you're producing it --- much like cooking, with similiar disadvantages: salt can't be removed (food becomes inedible) NOR can too much resin if hand laminated, so prepregs are better and lighter! sandy PS - i quite composites more than 10 years ag?!
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PostPost by: nmauduit » Fri Dec 29, 2017 10:49 am

el-saturn wrote:much like cooking, with similiar disadvantages: salt can't be removed (food becomes inedible) NOR can too much resin if hand laminated, so prepregs are better and lighter! sandy PS - i quite composites more than 10 years ag?!

if you use nylon tearing fabric, superfluous resin should be very limited, so nothing to remove even when applied manually... it also helps taking bubbles out and conforming to the intended shape : the extra cost is well worth it.
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PostPost by: Craven » Fri Dec 29, 2017 11:40 am

I think this problem was recognised by Spyder fairly early on hence the move to a single continuous pivot pin through the x member supporting a wishbone on either side.

alan.barker wrote:
Foto%202.JPG

Let the photo do the talking
Alan
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