Lotus Elan

"Monocoque"

PostPost by: garyeanderson » Thu Nov 17, 2011 9:50 am

Thank you Bill for those detailed explanations. I think you understand the problem as well as any of us. If you have a later Elan (36 or 45) you may not know what the stiffness of the roadsters were. There is a great deal more fiberglass in many (like the whole body) locations. Would an S1 or S2 body take all of the loads the way they were built, probably not, but as I said before they are probably not that far off. The top skin mold for the body would not have changed a great deal, the under tray mold was probably a lot easier to modify to accept the full length steel back bone frame. I believe that this monocoque would have come off as planned except for the cost (time and lost time for generating income) that Lotus could not afford. They had the talent to do it, just not the paying public that would wait for it. Lotus needed it now in 1962.

I have kind of been taken by this topic, first good topic in a long while that has never been BEATEN to death. I hacked out some other drawings and while very incomplete they give me an idea of what may have been. I didn't spend much time on the back subframe, about 12 lines drawn. I am not sure how this would have developed in respect to the decision to incorporate an independent rear suspension. I guess I mean when was the rear strut type suspension decision made in relation to the monocoque time line . The front pickup points seem to be something that was well along in the design process when the folded steel backbone decision was made and the monocoque concept scrapped. As usual have a look and then a laugh :)

The front is missing the engine bay cross brace, I have seen them in racing Elans and there seems to be room for it. that makes 4 different sub assemblies just for the front and that seems excessive. Then again I am not a qualified anything, so this is just an idea on paper to see what it looks like.
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PostPost by: bcmc33 » Thu Nov 17, 2011 11:29 am

GrUmPyBoDgEr wrote:I know a guy in the midlands who has spent years collecting all of the right Elan bits (including a stretched frame) to fit into an unused Elite body.
As far as I know he's not started properly on the project but enjoys talking about it :roll:

His name wouldn't be Martin, would it, John? :roll:
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PostPost by: GrUmPyBoDgEr » Thu Nov 17, 2011 2:04 pm

bcmc33 wrote:
GrUmPyBoDgEr wrote:I know a guy in the midlands who has spent years collecting all of the right Elan bits (including a stretched frame) to fit into an unused Elite body.
As far as I know he's not started properly on the project but enjoys talking about it :roll:

His name wouldn't be Martin, would it, John? :roll:


Sorry Brian,

I've checked & can't find his name or Tel. N° in my (not impeccable) records & me with names; well just forget it.
Anyway considering the project, he must be pretty unique here in the UK.
The man is always at the Donington do & regularly attends the Midlands Club Lotus/LDC meetings. He lives in a suburb of Birmingham.

So why do you ask?
Anything more detailed should go to PM, I think.

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PostPost by: bcmc33 » Thu Nov 17, 2011 4:23 pm

GrUmPyBoDgEr wrote:
bcmc33 wrote:
GrUmPyBoDgEr wrote:I know a guy in the midlands who has spent years collecting all of the right Elan bits (including a stretched frame) to fit into an unused Elite body.
As far as I know he's not started properly on the project but enjoys talking about it :roll:

His name wouldn't be Martin, would it, John? :roll:


Sorry Brian,

I've checked & can't find his name or Tel. N° in my (not impeccable) records & me with names; well just forget it.
Anyway considering the project, he must be pretty unique here in the UK.
The man is always at the Donington do & regularly attends the Midlands Club Lotus/LDC meetings. He lives in a suburb of Birmingham.

So why do you ask?
Anything more detailed should go to PM, I think.

Cheers
John

That's the guy. He's a member of our local club. He's been building it for at least three years to my knowledge.
He says the stretched frame is complete, and he's in the process of building the Twink.
At last month's meeting he brought an Elite boot & bonnet in an attempt to show this 'doubting-Thomas' that the project really does exist.
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PostPost by: dodo_z » Thu Nov 17, 2011 9:23 pm

I'm curious no one mentioned some kind of sandwich structure for creating stiffness. This possibillity was well-known in the early sixties.

I had some thoughts about changing the Elan to a monocoque design. First of all, I would have closed the sills with honeycomb or foam filled sandwich laminate. Second I'd use another sandwich plate to stiff the area behind the dashboard, or even replace the dashboard with a grp laminate. Third I massively reinforce the tunnel and floorpan with some kind of sandwich, including the bulkheads. This would add a lot of stiffness to the overall design, and act just like a Elise chassis. Of course all the material will add some weight, but on the other hand the body will be somewhat saver.

Of course, you can save a lot of weight using up to date glass oder even carbon fabric impregnated with epoxyd resin. It should be possible reducing weight while increasing overall stiffness.

Just some thoughts about state of the art usage of GRP and CFRP.

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PostPost by: GrUmPyBoDgEr » Thu Nov 17, 2011 11:01 pm

dodo_z wrote:I'm curious no one mentioned some kind of sandwich structure for creating stiffness. This possibillity was well-known in the early sixties.

I had some thoughts about changing the Elan to a monocoque design. First of all, I would have closed the sills with honeycomb or foam filled sandwich laminate. Second I'd use another sandwich plate to stiff the area behind the dashboard, or even replace the dashboard with a grp laminate. Third I massively reinforce the tunnel and floorpan with some kind of sandwich, including the bulkheads. This would add a lot of stiffness to the overall design, and act just like a Elise chassis. Of course all the material will add some weight, but on the other hand the body will be somewhat saver.

Of course, you can save a lot of weight using up to date glass oder even carbon fabric impregnated with epoxyd resin. It should be possible reducing weight while increasing overall stiffness.

Just some thoughts about state of the art usage of GRP and CFRP.

dietmar


Hallo Dietmar,

The use & application of glass fibre in the early 60's was very much in its infancy & even the aero-industry were just in the experimental stage with it.
In fact the Bristol Aeroplane Company (BAC) were chosen to produce Elite bodies after Maximar failed to attain the necessary quality standards.
Amazingly the experience at BAC at that time was only the manufacture of fibreglass pipes for "civil engineering" applications & some experimental lamp posts; not very high tech' at all.
And they were the company that eventually built the Concorde!

I agree that if a number of the solutions you suggest had been implemented a monocoque solution may have been achievable but Lotus had made major losses on sales of the Mk14 Elite & the lesson learned from that was that the manufacture of its successor had to be cheap enough to provide a good profit.

Übrigens, dein Schreibfehler "oder" anstatt "or" hat mir sehr gefallen.
Auf am. englisch (glass) oder = (glass) Geruch! Passt irgendwie weil das Zeug stinkt wirklich oder? :D

Viele Grüße
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PostPost by: dodo_z » Fri Nov 18, 2011 6:26 am

GrUmPyBoDgEr wrote:Übrigens, dein Schreibfehler "oder" anstatt "or" hat mir sehr gefallen.
Auf am. englisch (glass) oder = (glass) Geruch! Passt irgendwie weil das Zeug stinkt wirklich oder? :D


Hallo John,

das passiert, wenn die Frau deutsches Fernsehen schaut und man versucht nebenher die eigenen Gedanken in verständliche Sätze zu formen.

Polyester resin is really offensive smelling, Epoxyd resin is more or less neutral.

About the time and the possibillities: http://en.wikipedia.org/wiki/Akaflieg_Stuttgart_FS-24 The knowledge about fiber reinforced plastics was given at that time.
Those of you understanding german, should also read about the "Hütter H30".

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PostPost by: garyeanderson » Fri Nov 18, 2011 10:30 am

Debating the feasibility of the Monocoque is bit old hat, I believe Frank Costin solved those problems a bit later on. To make the Elan what it was intended to be was not a technical problem in my opinion. It was a financial/survival issue. Some of the band aids on the 26r chassis seem like more rules chasing and not all that effective compared to putting the strength into the outer sills like the do with Steel unibody shells that are converted to roadsters and that is to double the sills with second inner box. If the Elan was doubled, the weight would be minimal in the amount of extra fiberglass. There are some issues with this in that it encroaches into the throttle pedal area of the RHD type 26 but could be molded such that the pedal would function, not much of an issue in the LHD.
P6150005.JPG and

A fiberglass panel could easily be added during manufacturing or after the Elan was molded to the existing steel lattice to form a double box. to be more precise, a double triangle with a shared side being the steel lattice.
sill doubler 1.JPG and


a better view in the daylight on the let hand side
sill doubler 2.JPG and
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PostPost by: bill308 » Sat Nov 19, 2011 2:18 pm

Composites

The original composites were GRP. In Chapman and Hick's days, carbon fiber and Kevlar were not available.

I am not an expert in composits but I do know the the vast majority of the strength is in the fiber content. The resin merely holds everything together and adds little to the final strength and stiffness.
Epoxy's hold everything together better than polyesters, but are much more expensive and sensitive to catalyst ratios. Epoxy's also suffer much less degradation when exposed to moisture.

The most common form of glass fiber used in boats and automobile bodies is matt of various weights. Matt is great for forming the complex curves often found in automobile construction. For high stress applications, unidirectional fiber orientation is desireable. This technique can align the fibers in the direction of the expected loads. Consider an I-beam supported between simple supports at either end and a central verticle load. The beam will sag in the middle. The lower flange will be in tension, the upper flange will be in compression, and the web will be in shear. To minimize sag (maximum strength and stiffness), the upper and lower flanges should be made of unidirectional fibers running length wise. The web should be made of fibers running 45 degrees to horizontal in 2-directions to resist shear. Great care in the layup can yield significant increases in strength and stiffness for a given weight. Substituting carbon fiber or Kevlar fibers can add increased stiffness, strength, and toughness.

Matt is great for modest omnidirectional loads, but for a first class structual application, directional orientation must be exploited.

Gary, you posted a picture of a cardboard panel to replace the sill latice. The idea you propose here is to strengthen the sill area and a good one it is. In the existing Elan, the sills are intended to support the occupant/seat on the outboard side. All suspension loads are currently taken out by the steel subframe. If one were to develope your idea a little further, to make this structure replace the backbone chassis, one would want to extend this pannel to the front wheel well and to the rear wheel well, and vertically on either end, to the body under surface. In addition, the sill would want to be taller in the door area to take advantage of the h term suggested by the (bh^3)/12 moment of inertia equation. The upper horizontal surface, immediately below the bottom of the door, would benefit from front to back unidirectional fiber orientation as would a layer or two of unidirectional fiber running front to back on the floor surface immediately below the sill. The trade off for the occupant is increased difficulty in getting in and out of the car due to the higher and perhaps wider resulting sill.

Honycomb structures

The GT-40 is reported to have used a honycomb central section for the cockpit. I don't know the details of this but I sat in an ERA replicar and know the sills were high and wide. The honycomb structure would have used metal skins where a top and bottom skin were joined by the honycomb. For maximum rigidity, all core pieces would have had to be securely bonded to the upper and lower skins. I do not know how they ensured this consistant bonding but it must have been a nightmare. A foam core would have been easier to do but the stiffness properties would not have been as good IMHO.

Chassis stiffness

My Elan is an S2 and I do not know what the torsional stiffness of the chass/body is. Maybe some day I'll measure it. This would require the careful fixing of 2 or 3 of the 4 suspension pickups and loading the forth to determine torsion.

My understanding is that the minimum value for a world class structure is in the 8000 ft-lb per degree range. The stiffer the better. One wants the suspension to do the work, not the chassis.

Almost any torsional stiffness will do. Early Morgans and MG's flex a lot compared to modern offerings. At one time it was thought acceptable and even necessary for a frame/chassis to flex. Over time it was found that chassis flexure was not a good thing especially when the opening of doors was affected by where one parked. In the modern world, body flex is a bad thing. What is acceptable is up to the buyer.

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PostPost by: CBUEB1771 » Sat Nov 19, 2011 2:26 pm

bill308 wrote:I am not an expert in composits but I do know the the vast majority of the strength is in the fiber content. The resin merely holds everything together and adds little to the final strength and stiffness........This technique can align the fibers in the direction of the expected loads.


Bill,
That is what modern composite design and manufacturing as all about. The carbon or kevlar fibers in the tape are aligned such that as much load as possible becomes tension in the fibers. Computer controlled tape laying machines get the fiber orientation correct. The resin does little more than keep the fibers in proper alignment.
Last edited by CBUEB1771 on Tue Nov 22, 2011 6:39 pm, edited 1 time in total.
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PostPost by: garyeanderson » Sat Nov 19, 2011 3:02 pm

bill308 wrote:Composites



Gary, you posted a picture of a cardboard panel to replace the sill latice. The idea you propose here is to strengthen the sill area and a good one it is. In the existing Elan, the sills are intended to support the occupant/seat on the outboard side. All suspension loads are currently taken out by the steel subframe. If one were to develope your idea a little further, to make this structure replace the backbone chassis, one would want to extend this pannel to the front wheel well and to the rear wheel well, and vertically on either end, to the body under surface. In addition, the sill would want to be taller in the door area to take advantage of the h term suggested by the (bh^3)/12 moment of inertia equation. The upper horizontal surface, immediately below the bottom of the door, would benefit from front to back unidirectional fiber orientation as would a layer or two of unidirectional fiber running front to back on the floor surface immediately below the sill. The trade off for the occupant is increased difficulty in getting in and out of the car due to the higher and perhaps wider resulting sill.


Bill


Hi Bill

Not much detail on my part but the idea of the cardboard panel is "in addition to" not "replace". There is much that was left out, you know how prepared you are at 4 am? Same here. The rant had no detail on the execution, just a good place to start. The longest piece of cardboard I could find was the one you saw in the photos. The idea would continue up in the sides. I don't want to change the height of the door opening this is just a question of what 10 lbs of glass and resin could do if implemented in right way.

Gary
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PostPost by: ardee_selby » Sat Nov 19, 2011 3:11 pm

CBUEB1771 wrote:
bill308 wrote:I am not an expert in composits but I do know the the vast majority of the strength is in the fiber content. The resin merely holds everything together and adds little to the final strength and stiffness........This technique can align the fibers in the direction of the expected loads.


Bill,
That is what modern composite design and manufacturing as all about. The carbon or kevlar fibers in the tape are aligned such that as much load as possible becomes tension in the fibers. Computer controlled tape laying machines get the fiber orientation correct. The resin does little more than keep the fibers on proper alignment.


Can't, immediately, lay my hands on my old lecture material...but I always understood that strength was also derived from the energy needed to break the grip between fibres & resin i.e. fibre pull-out from the matrix material which, apart from fibre lengths, was also a function of the resin composition.

Cheers - Richard

STOP PRESS: Just found this...

http://www.doitpoms.ac.uk/tlplib/fibre_ ... ghness.php
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PostPost by: Elan45 » Tue Nov 22, 2011 4:24 am

I've been off list for a couple of weeks, escaping Ohio winters for Florida sunshine. Next trailer load heading south will have to have an Elan inside and all necessary to finish putting it back together.

Let me state that I was the person who asked Mr Hickman at LOG 14 why the type 26 had the little flat lid and that it wasn't until the type 36 that the boot lid reverted back to the style of the type 14.

I remember Ron saying that even the boot lid on the 26 was a compromise with Chapman who wanted the boot accessibility to have been from inside the cockpit, ala Bugeyed Sprite. This all was in consideration of the attempt to keep the monocoque structure.

All of my library is back in Ohio, so I can't say which book it is in, but somewhere there is a photo of the Falcon bodied Elan test bed. Its not a good photo at all. I have been wanting to find more on this test mule since I have the other unique Falcon bodied car. See http://sebringsprite.com/falconsprite.html The body on my car is much more likely to be of the same type used on he Elan mule than the Carribean, shown earlier in this thread. My Sprite special was built in late 1959 and I believe the Carrribean was the last of production from Falcon, maybe 1963. Another item that needs consideration is that the Berkley sportscar of maybe as early as 1956 is a monocoque constructed car. It is also a roadster. Part of the strength of the Berkley is due to aluminum sheet metal panels inside the tub and there are very lightweight subframes to mount the motorcycle derived powertrain.

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PostPost by: elj221c » Tue Nov 22, 2011 12:51 pm

I have read and reread this thread and I can't find any reference to the Robinshaw and Ross book wherein, in my edition at least, there is a drawing showing clearly how the Elan might have been without the backbone frame.
It is on page 127 under the heading; The Two-Seater Elan. Some further notes. (Written by Ron H)
I assume that Gary has not seen this as his idea is based around a Spyder type frame. I suspect a few other contributors to this thread haven't seen it either. Interestingly the diagram has question marks pertaining to the suspension mounting reinforcing frame at the rear and what looks like some kind of outrigger to the battery box mouldings both sides and being attached to a tunnel reinforcing frame. Or maybe the thought was that the whole tunnel reinforcing fabrication might be superfluous? There are nine seperate sections but the dashboard is bolted to the front bulkhead of the tunnel.
1 & 2. The sill reinforcing latice.
3. Front turrets and cross member.
4. Rear turrets and diff cross member
5. Tunnel member formed of a bottom and three bulkheads.
6. Cross brace under the engine.
7. Cross brace to presumably hold the headlight actuators.
*. This number is not used although the S1 style dash is highlighted as one of the components so I assume it is number 8.
9?.Rear suspension mounts. Not sure why the question mark as I would have thought that this bit would be required.
I would like to have scanned the drawing but it is copyright to Motor Racing Publications Ltd. Essentially all the components look similar the those that we recognise except the are now all joined by more sheet steel, the tunnel reinforcement being the exception as we know that the other three sides have been added. I'm not sure about 7 as I do not have pop up lights. Is there a cross brace at that point on 'proper' Elans?
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PostPost by: GrUmPyBoDgEr » Tue Nov 22, 2011 1:07 pm

Whale oil beef ------ if I can find that in my copy of the book, published 1989.
But I think I've seen something similar elsewhere in the dim & distant past.

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