12/11/06

I know it is 60’s engineering but if we can agree, for arguments sake, that “automotively” most everything designed today is a re-working or refinement of what has already been designed, then you may understand my desire to fabricate a full monocoque.

In the last several weeks I have been anticipating my next build as the final touches of the McBearen are coming to an end. The physical activities associated with that forward look on my part has resulted in many drawings and a scale model capitalizing on the knowledge and enlightenment gained from the experience, as well as, from the many individuals who have made comments and suggestions here and elsewhere throughout the McBearen build.

I’m not going to disclose the body style of the future project just eyt but I wanted to share with you what I’ve arrived at for the tub. Except for the three primary bulkheads I am planning to use a variety of 3/16 and 1/4” aluminum sheet for the tub and plan to introduce some basic static ground effect channels where possible. Nothing too extreme but I’ve always been interested in air movement primarily as it is related to in/under and around the bottom of a vehicle. I hope to fabricate this aspect of the build somewhat independent of the tub and body to allow adjustments in the design as the information is gathered.

You can obviously deduct from the model that it will be a mid-engine affair with the engine oriented longitudinally. Not so obvious is the fact that the round shape in the nose is a spare tire rather than my grandmother’s discarded hat box. <grin>

So, short of turning this into a discussion of why you like or dislike, approve or condemn a monocoque project, I’m interested in your constructive criticism, suggestions or alerts you may have.

Cheers,

Dick Bear
Rescued attachment IMG_0877.jpg

www.teklam.com

build it like a mosler and you wont go far wrong.

i wish with hindsight i went all out with a project like this rather than a seven type , its much easier to engineer a monocoque with a mid engine vehicle .

I like the idea thoguh obviously can't see any detail. But generally what you must get right is the feeding of the point loads into the monocoque structure. You may find that strategic use of steel is beneficial - corrosion problems will need to be addressed though.

Regarding your model I think I'd try and tie in the windscreen surround and roll bar structure together and into the monocoque better as this will greatly help stiffness. This may be difficult depending on your chosen body style of course.

Chris

[Edited on 11/12/06 by chriscook]

I'd be interested in how you're going to pass the loads from suspension, engine, roll bar into the monocoque. This always seems to be an issue.

Shape looks a little ultima-ish, which i suppose is obvious if youre going for a mid engined car with a roof.

Oh, if the front wheel is going where you've got it, where is the radiator going?

[edited - damn, someone types faster than me!]

[Edited on 11/12/06 by MikeR]

3/16" and 1/4" ally........................................I assume longevity rather than light weight is the aim?

My eyes tend to skip over imperial measurements and it wasn't until NS Dev highlighted it that I noticed. 3/16" and 1/4" ?? That's 6 & 3 gauge which are (roughly) 5mm & 6mm. I'd almost start referring to ally as plate rather than sheet at those thicknesses!

Staniforth's "Race & Rally Car Sourcebook" has some details of the Monopin - an ally monocoque version of the tube frame Terrapin. Now admittedly it was: a race car; a single seater; powered by a bike engine (albeit a supercharged 750). The monocoque was all 18g (that's 3/64" or 1.2mm) - 4 to 5 times lighter material!

I've scribbled a few monocoque versions of my frame. I agree with Volvosport - with a transverse mid-engine, a monocoque works very well. After searching around on the net, everything I could find suggested that 1.6 to 2mm aluminium was sufficient - that's 16g,14g or 1/16",5/64".

The main trick seems to be feeding point loads like suspension etc into the 'coque. Have a look at some of the older formula cars on At Speed Images for some nice photos of bracketry etc. Here's a good example.

Hope this helps and look forward to seeing the build diary for this one.

Dominic

Your choice of alloy is far too thick.

Use thinner section and support long sections, eg side sponsons of tub, with bulkheads of sheet ally with a huge hole in the middle to stop any lozenging.

Just make sure this 'McBearan' replica has 3 seats and I'll be happy!

...oh, and will buy a set of body panels off you....

Cheers,
James

Thanks for the replies.

Judging from Mike’s and Chris’ responses the primary concern seems to be that of accommodating load transfer points for the engine and suspension and neither of these critical issues were apparent in a quick view of a slightly out-of-focus photo of a model. Better then, that I illustrate further what I have in mind so that we can all learn from this exercise.

Once again, let’s assume here that the sheet material(s) used to form the varying plains of the monocoque structure will provide both the torsion and structural strength equal to that of a space frame composed of welded rods and tubes. Unlike a space frame which due to its composition of like materials (steel) makes it relatively easy to integrate the roll cage system and suspension system into the series of parallel and triangular connections of the frame, the monocoque requires that these two systems (roll cage and suspension) be introduced as independent components to the otherwise separate monocoque. This is due primarily because of the dissimilar metals used for each. If we were to construct the monocoque of steel sheets there would be no issue…. We’d simply weld the cage and pin the suspension where needed using steel tabs. This would work here but using steel we’d end up with a mobile anchor defeating our primary goal of strength vs. weight.

Simply stated, when using a monocoque the issues associated with the roll cage and suspension becomes that of attachment and disbursement of forces throughout the aluminum tub.

Here is a simplified illustration of what I’m planning at this point:
- The three primary bulkheads are indicated as green rectangles,
- Each of the tub connections will penetrate into and extend to the bottom of the tub being attached at two or more locations to the bulkheads,
- The roll bar diagonals will have their own secondary bulkheads within the rear portion of the monocoque and
- The roll bar to transom bars will function as both a compression and extension members adding support to the rear suspension connections.

Separating the roll bar system from the other elements in figure #1 illustrates how the this system functions like a truss connecting all principle points of the vehicle from front to rear adding further strength and rigidity to the independently stable tub.

For the front suspension connections I plan to use a series of square tubes that will accept the suspension members at appropriate locations for each. These transverse tubes will be integrated (welded) into the tub and one of the uppers and one lower tubes will also be attached to the front primary bulkhead. The steering rack will also be located in its own transverse tube (welded in place) bringing the total number of these cross members to five.

At the rear, two of the connections will be made at the transom bulkhead with the remaining two connections (one top and one bottom) accomplished using the same tube configuration as described and illustrated for the front using abbreviated tub lengths since they cannot pass through the engine compartment.

Mike asked about the radiator and its’ location. I’m working on that! May be associated with the ground effects mentioned earlier or it may be that the spare tire has to move. I’m not sure at this point but I’m sure there will be one somewhere. J

I hope you can make-out what I’ve got planned in spite of my crude illustrations.

NOTE: although I thought I had placed this new topic in the right category, but after looking more closely I’m not sure but this should be moved to “mid-engine”. If ChrisW agrees, please feel free to move it. Sorry if I butted in where I shouldn’t have!

Dick Bear

PS.... I just saw the surprises recarding 3/16-1/4" sheet (plate). That is why I asked for suggestions! 16-14 sounds better to me and its LOcost too! Thanks.
Rescued attachment roll cage illustration.jpg

Your model looks very simliar to this, having seen the McBearen, i can't wait to see this project.

Keep up the good work Dick.
Rescued attachment monolf03.jpg

and another
Rescued attachment m3008.jpg

Build a scale model out of balsa. It will quickly show how torsionally rigid the proposed chassis is.

Also, there is a lot of debate about how long a stressed aluminum monocoque will last on the street. The problem is metal fatigue, which no one here knows how to calculate. The chassis in the picture above is a real race car, and as such, it will be replaced in only a few seasons. Its lifetime, before fatigue becomes an issue, is measured in hours, not years.

Using really thick aluminum to "buy time" will work, but the chassis will end up weighing more than a steel chassis.

[Edited on 12/12/06 by kb58]

well , if you followed that link to teklam - you could easily have a chassis in couple of days , you just need a router and jigsaw , just make sure you cut it accurately .

then slot peices together and bond it up , hey presto GRP/composite/honeycomb chassis .

loads fed into the chassis with bobbins bonded in - it really is simple , your material cost could be high tho - saying that i was qouted $800 for the materials to make one chassis , so if i get a chance i know what im doing next .

quote:

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Originally posted by kb58
The problem is metal fatigue, which no one here knows how to calculate.
[Edited on 12/12/06 by kb58]

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How many members do we have on here, 1000 perhaps? Okay, fair enough, but 99.9% still don't know how!

9061 as of a couple of minutes ago..

But, yes your point is valid.......Chris is one of a small group (I would have included myself a few years ago...but I'm a bit rusty...)

The point, I think, is like FEA, pre-preg CF, etc. monocoques don't fall readily into home building. Not impossible, obviously, but not easy or generally recommended.

Just IMO of course.

Alan

Hi, i've found this thed very intresting as i was thinking along these line for my own build, but ruled it out due to cost and to the fact of my limeted experience with ally tubs. But this has got me thinking again...........

I'm sure your familiar with the Robin Hood Lightwaight a 7 type car, it,s been about a while now, and i was assured it was heavly tested on the road before it was released, this has a 12gage sheet constusion, with box tube riveted in, i took a close look at a show, and while i was not impresed by the finnish, i think it's a very possible home build, if you got the design right.

I would also compair this to the Lotus Elise/Exige chassis, I work (loosly) at a Lotus spicalist, so i've climbed all over these cars, ally tub, extruded tube everywhere, gavanized steel rear subframe, the only thing i dont think could be replicated is the baked bonding (which i no nothing about) which I'm told is a very expencive material and prosess. I'll try and get some pic's of the Lotus chassis up, I also hve some experience with the Morgan Areo8, which has a simular chassis construction.

I think with time and a bit of thought it's very possible, IMHO.
Rescued attachment Picture 021.jpg

Meant to add one of these >>>>

Doing the fatigue analysis on that chassis would be challenging to say the least. Even if you could get hold of decent material properties, realistic loads, create suitable dynamic and FE models. Even then the best result could be within a factor of 2 for life.

To say doing a full fatigue analysis is beyond the home build is absolutely correct - it's beyond many car manufacturers! (And I'm certainly not saying I could do it all either)

[Edited on 12/12/06 by chriscook]

I hear you guys.... but from a practical standpoint how many of us know or are able calculate the fatigue factor associated with anything we build. It's really a non-issue when with several hundred welded connections in a space frame (none having been tested) are created by an equal number of individuals each posessing different welding skills are driven on the street, raced and enjoyed everyday successfully.

One can only assume that the basic technology resulting in aircraft flying overhead today, tho' built 30, 40 and even 50 years ago, is technology suitable for building an experimental auto monocoque suitable for a few hours of driving enjoyment each year.

In reality none of the projects we build can be quaranteed against failures of one sort or another. The best we can do is attempt to anticipate adjust to what we percieve as a weak point or problem by reinforcing those areas.

To do nothing because we're unable to move the slide rule expertly enough to figure conclusively every bit of information we might want to know about a structure is not our mission nor should it be an excuse not to explore new areas for having fun!

Some may feel that because they heard something, somewhere about metal fatique we should all limit ourselves to producing our dreams with only hollow tubes of steel and that that is where our safe zone should terminate.

Come on ... You guys are building competition type vehicles for goodness sakes. Everytime you strap on your helmet and head into a corner you take more risk than someone does builging a monocoque tub while following generally recognized precautionary design proceedures.

METAL FATIGUE, yes metal does fatigue. In fact it also rusts, bends and cracks and snaps under certain conditions. So what? Isn't that's the intrique of what we are doing.

Attempting to build a reliable monocoque is just an another avenue of interest that I can't ignore simply because I'm unable to calculate everything relating to doing so, mathmatically. I admire math-whizzes but if I had always limited myself to addressing only those things that I could "mathimatize" I'd have never done anything in my life.

So.... what else can you enlighten us all with conserning the design and building of a monocoque?

Dick Bear

[Edited on 13/12/06 by Dick Bear]

quote:

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Originally posted by Dick Bear
METAL FATIGUE, yes metal does fatigue. In fact it also rusts, bends and cracks and snaps under certain conditions. So what? Isn't that's the intrique of what we are doing.

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This whole materials thing needs to be put into perspective.

Some of my 'bread and butter' comes from designing and building monocoques, in various forms and materials.

The racecars that are still built in ali are certainly lifed, but usually come to grief well short of that. Lotus saw fit to do their modern cars with ali mono's, so for specialist applications, it's ok.

We'll rule out carbon, because without the proper gear (autoclaves, car size ovens and such), and the tooling costs, it is not worthwhile for home/garage builds. And not done properly (this means NO wet layups!!!!), can fail catastrophically.

I've seen no mention of steel sheet mono's here yet. Why not? After all, your car is a steel mono. A home build steel mono can end up much better than a spaceframe, and lighter when you factor in the panelling of the spaceframe. After all, the sheet mono is only the panelled spaceframe, without the tubes!

I did a prototype project for a local company a good few years ago. When all the numbers were crunched, and 'street cred' and sales value were factored in, the decision to go with a 1.2mm stainless sheet mono was easy.

Not the lightest, but easily built with a mig welder and the basic cutting and bending gear that was to hand.

The stainless sheet will last forever, is not too difficult to work with, and relatively easily patched without special welding or any other tools.

If I were Dick Bear, I'd be having a serious look at a thin sheet ss mono. ~1mm plus stiffeners strategically placed.

Cheers,
Syd.

Edit: I just reread some of the above posts. For the ali bonding adhesive, Bondmaster do a 'filled epoxy' one part that is cured at 120c. All the glue companies do a similar product. You'll tear the ali before the glue lets go........... that's if you've prepped the ali properly in the first place. Not expensive at all, just the oven costs a bit.

[Edited on 13/12/06 by Syd Bridge]

I would deffinately take a look at the lotus elise chassis. There are plenty of pics online. The part of the chassis that may interest you most is the extruded beams that form the mainstay of the chassis.

I am interested in building a carbon/kevlar monocoque chassis. and I thank Dick for his comments which amount to 'GO FOR IT!' However Syds comments about 'No wet layup' for a cf mono make me worried.

I have experiance with CF rowing boats. These hold eight people and weigh very little. The weight of the men rowing such boats is 800kg ish. And the force exerted by the crew to move the boat is around 1000kg of force, much of which is exerted on the hull of the boat.
My point being, that these boats are made with a wet layup, which is vacuum bagged with the only addition of heat from infra red heat lamps.

My intention is to use the same technique as the boat builder to build a cf monocoque for a car.

Nuts, Syd Bridge beat me to it. I was thinking that myself, why not a steel monocoque? It has a lot of appeal and I'd consider that, just not aluminum!

SSteel? Thanks Syd that has a geat appeal! All the benefits of aluminum and steel rolled into one. Great suggestion!

I will explore that idea further.....

Dick Bear

Dick,
You can work well with metal sheet, obviously. So, the ss monocoque tub with the ali skin should be a very worthwhile proposition. I wouldn't mind it myself!

If you need any design tips, give me a yell.

Hammerhead,

A rowing boat is supported on its entire surface, and the only point loads and local highs are near the oars. The seats are supported over a good length. So, no high local loadings. A car tub is a very different animal. The wet layup will have excess resin and the possibility of resin rich areas, where the laminates are not homogeneous. Sources of the catastrophes! I've seen far too many failures in racing yachts built just as you describe, to not even contemplate a car tub. Do it with prepreg and an autoclave, or not at all!!!!!!Well, if you want to live a long life, anyway.

Cheers,
Syd.

Edit: I'll add, re carbon mono's-----The layup needs to have a good percentage of unidirectional content, and this is extremely difficult to wet out without being prepregged.

[Edited on 13/12/06 by Syd Bridge]

are you suggesting we make robin hoods now syd ?

what about these ?
www.darrian.co.uk - 2 motoring news championships and the British GT championship - cant be doing much wrong .

ive seen the aftermath of big accidents , and i think , if i make one , ill live !!!

My advise:
KISS

keep it simple and stupid

Is stainless a bit messy to cut (I say this teasing a ss splinter out of my hand between typing) and at 1.2mm thick you would need quite a large gilateen, to large for my budget.

I've found that in general, splinters are only a REAL problem when using a die-grinder.

If you use one of those cutters that has the scissor-type cutting head, that works well. It's the diabolically sharp edges that cut like a knife, you have to watch out for.

Thanks once again,Syd!

I'll U2U with some specific question I have on the mono configuration.

Regarding cutting of Ssteel. I've always had good luck getting a clean edge on Ssteel with my plasma cutter. Doesn't cause any edge distortion or out-of-straights associated with sissor-types and is ready for body panel tac-'n-stich welding technique.

Some plannishing of the seams will be necessary but other than that being a bit more difficult in Ssteel than it is in aluminum it should be pretty straight forward, eh?

Dick Bear

I regularly cut stainless steel with the 4 1/2"grinder witrh the 1mm cutoff disc. Knife through butter! No mess and splinters. Just clean up the sharp edges (which you get with any metal cut, not just ss), with a flap disc on the second grinder.

For a guillotine, the 1.2 ss is no more difficult than ms. Maybe I'm lucky having a few places local who have the huge hydraulic things that cut 12mm plate with ease.

I took som pic's of an Elise chassie today at work, it had some temp stickers left on it from where the bonding was baked, temp went up to 175degC, if that sheds any light.

My point about cutting SS is that, unless you have some expencive kit, it's messy to cut, far more messy than ally (that's not that i dont like mess)

More pics of the elise chassis on my profile, if you intrested!

[Edited on 14/12/06 by NDC790]
Rescued attachment Picture 043.jpg

quote:

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Originally posted by NDC790 My point about cutting SS is that, unless you have some expencive kit, it's messy to cut, far more messy than ally

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Messy to me means it's hard to handle without taking extra care.

If a die-grinder is used, it produces 1000s of stainless splinters which are so small you can't even see them to remove from your hands. They even go through leather gloves. Cutting the material with shears leaves a very sharp edge, much sharper than steel or aluminum.

I know this because I have a stainless floorpan.

quote:

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Originally posted by NDC790 unless you have some expencive kit

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quote:

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Originally posted by Dick Bear In my build there will not be a kit involved as the project will be scratch built based on my own design.

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Thanks gt58 for sharing your definition of messy with us.

Your mini floor pan must have been a real 'bear', (pardon the pun) to be even partially responsible for formulating a definition for the word 'messy'. :-)

I agree that extra care is required when handling sheet material!

I wonder what was meant?.... 'messy' is such a generic
word.

Dick Bear

Dominic,

You snuck one in on me while my typing expertise was showing its' lack of expertise!

Thanks for the clearification... It always interesting to read the different British words on the site. Most times they don't throw me but there are times when I know a word I've not ever heard before means something very specific to everyone else and I haven't a clue.

Ironically I'm currently trying to find out what is 'messy' when working with Ssteel. I really want to know... been thinking about it all day. :-)

Thanks again.

Dick Bear

SS is no more 'messy' to me than ordinary mild steel. Go near any metal with a die grinder, and depending on the cutter used, you'll get those splinters. NOT JUST WITH STAINLESS!!!

As I put, I cut it with the 1mm wheel on the 4 1/2" grinder with no probs. The sharp burr you get with a guillotine, again, is something that is on all metals guillotined.

When you work with metals often(as I do, and obviously Mr.Bear does), you learn to deburr everything as soon as it's cut. And gloves become the normal everyday workwear.

You lot take fright at the slightest thing. Bunch of pansies!

Some common sense would go a long way. But then again, common sense seems to be a rare commodity these days, from the top of the country's leaders to the lowest labourer.

Cheers,
Syd.

Oh, and I would hope that the Elise chassis are not cooked at 175c, that's getting into dangerous territory for aluminium, of any sort. Most, if not all, of the epoxy adhesives used in the auto stuff is below 140c.

[Edited on 15/12/06 by Syd Bridge]

Having worked as a fettler on cast iron, in steel foundries casting stainless and a boiler factory I think I've had my share of metal. Someone once remarked that everything you do to metal either makes it sharp so it cuts you or hot so it burns. In the boiler factory we had guillotines that would cut and presses that would punch holes in metal 10mm thick and the thicker you get the less sharp edges you get.

Sorry Dick, please forgive me.

By kit I ment - equipment/tools.

& by messy I ment - dust, fileings, sharp edges, time to cut Ect.

As you may have guessed, i'm better with a spanner & welder than I am on com-po-ter!!

And sorry again NDC is me, Nicholas David Carr...........but Nick is fine!

It's very dificalt on here to judge other peoples experience, abilities and facilities, if thay have any, for me, I have some of the first two, but none of the last. So knowing what I want to do and being able to achive it, are two differant things. I've been spoiled at work in the past, being able to use any tool or machine when ever needed. As my Dad call's me, Mechanical Tart.

[Edited on 15/12/06 by NDC790]

Sorry, had to drop an idea into the pool since this thread got me thinking last night. What about a steel/balsa construction. I did a test piece last night, a simple 12x12'', 22ga carbon steel and 1/4 balsa core and it is incredibly stiff. and comes in at 3lb/ft^2. I'm doing more test pieces of 24 and 26ga skins this weekend and the weight should drop roughly 17% between ga. I'll do some puncture and modes of failure testing next week, as well as machinability. I'm curious about how well routing would work. But these samples are done very grass roots style. Glass beaded the skins to get rid of rust and contamination, generic 2 part "tuffy" grade epoxy and a couple of weights for pressure. I did do a 100C post cure, but a lower temp post cure can be done in a standard garage environment with a little imagination. Naturally the core thickness can be increased for stiffness but I'm keeping them all the same for consistency in testing right now. Anyway, just a thought for consideration. Cheers!

Thanks Nick,

That is basicly what gt58 and others thought you had meant but I just didn't want to miss some really messy situation with Ssteel that had been experienced by you.

Although I don't have everything I might want, I do have most everything in the way of "kit stuff" (did I use that word correctly) needed for metal fabrication and having what I do I haven't experienced stainless to be any more "messy" than other metal materials. As Pete said.... it all cuts and burns regardless of its' make-up. It is however great fun to work with!

Thanks again for clearing the mystery!

Dick Bear

No problem Dick.

I guess it's a personal thing, myself I like using ally, posibly the motorsport backgrownd, SS too heavy!

But before everyone starts, JUST MHO!

For what it's worth.

Nick.


Dick, like the lugfast!


[Edited on 16/12/06 by NDC790]

Hey Nick,

Thanks for your thought on LugFasts.

You must have been checking out my MarketPoint Productions web site. It was on a very hot and humid day at Bristol, TN while I was helping one of my charges set-up the Winston Cup Scoreboard and communications sytem for the night race that I watched from the press box all the teams, but especially the Jack Roush team, sweeting out the process of attaching five lug nuts to what seemed to be an acre of wheels. Seeing the 4-men involved over several hours of time I thought there must be a better way to do this than what they were doing.

That began my experimenting with alternatives until I arrived at the LugFasts solution. I patented it around '95 and now they have become a mainstay on pit roads across the US and Canada. When the Rolex series began to require green flag pit stops a couple years ago LugFasts were quickly expanded into that racing environment as well.

If your racing efforts involve pit stops I'd be happy to send you a few gratis tubes to try out.

Cheers,

Dick bear

Hi Dick,

How do you intend to get the ground effects to work?
My understanding is that a vehicle needs to be very close to the ground to get a ground effect and preferably sealed at the sides (Going back to the F1 ground effect era).

I had a conversation once with an ex-automotive aerodynamicist who gave me the impression that he felt very little could be done under a road car to help with aerodynamic grip.

On the folded and riveted structures I originally wanted to go this way. Having spent a couple of years working in aircraft design it appealed to me from a manufacturing point of view, though the complexity of the math problem was not one I wanted take on for my first project.

An alternative might be the type of hybrid structure I and Fred W B are doing where the main loads are carried in steel members with alloy structures being used improve the stiffness of the whole frame. I guess the difference being if the alloy fails in this situation you get a slightly wobbly car and not a disaster.

One thing I think you should do if you go down the all alloy route is treat the car like an aircraft in terms of inspection for fatigue wear through the life of the vehicle.

For certified aircraft it’s my understanding that there’s always an example of the type somewhere in a wiffle tree being fatigued to braking point, hopefully a long time before any flying examples have the same failure.

On the car side of things all the volume manufacturers physically fatigue test all of their vehicles to the design life of the vehicle (~90,000 miles in most cases these days). And parts still fail during these tests even with all of the engineering, design and computing power available to them. Obviously no real production car today is riveted together out of ally so fatigue is not confined to that type of structure.

The link has some good pictures of wiffle trees:

http://www.dsto.defence.gov.au/publications/4219/DSTO-TR-1773.pdf

Doug,

At the risk of being blind sided again by a message from one participant on this forum who is obviously less than enamored with my efforts and felt it necessary to accuse me of being stubborn, ignorant, unaware, a liar, careless, having a death wish, an endangerment to others, an opportunist, arrogant, and dangerous within the context of a single private email, I will continue my thoughts along the lines of making a true monocoque. Perhaps throughout a lifetime I’ve been guilty of most of these but surely I can’t have all those character flaws at once this moment so I’ve pretty much dismissed his rudely written opinion. Fact is, my wife and kids think I’m kind and, for the most part, responsible so I’m not sure where he is coming from.

Thanks for the information and link to the Australian structure fatigue test program. Very interesting reading… Wouldn’t it be great to have such a facility available to us to test each of our designs? Unfortunately we don’t and therefore, as with most state-of-the-art information until the relevant findings trickle down from the top, we who occupy the lower echelon are forced to advance our knowledge and augment our design and construction techniques using products and methods after they are developed by individuals and manufacturers occupying positions in the information chain above us.

There is nothing new about this situation. It has always been that way in art and science. Philosophically I believe we should shun any thoughts and pressure by others to limit exploration or to accept our ‘last to know’ position as an excuse not to attempt new methods. Using the skills and knowledge we should press onward. Hopefully, our successes will out number our failures!

You have accepted this challenge as you methodically use your ability in 3D CAD (a skill I wish I possessed) to draw and design what you envision to be the best solution possible in your build. Capitalizing on each of your abilities while anticipating and creating situations that need to be solved you will, I’m confident, arrive at solutions that others would not even attempted. Most, if not all, of your solutions will be positive and those that are found lacking in the final analysis can be addressed further, once more information is gathered. Individuals who limit themselves to or feel bound by formulas, charts and opinions of those who came before simply disciples. They are forever relegated to achieving only that which has already been achieved. Rather than originals, they are copiers regardless of attempts to disguise themselves as something more.

GROUND EFFECTS: I agree with you and your aerospace associates that achieving any advantage from ground effects on a road car might be minimal. Certainly it is impossible to attain the same level achieved by teams at the height of its use in F-1. The fact is no one should want to attain that level of achievement even if they could for all the same reason that those design practices were ruled illegal by F-1. However, I feel that somewhere short of the extremes practiced by F-1 teams there is a level at which ground effects can be beneficial and achieved safely resulting in better handling and cornering of a road car.

I submit that somewhere between dangerous and void, there is an acceptable level of achievement. Helping to hold the nose of a car down and increase stability simply by attaching a vertically fastened front air dam beneath the nose has been proven effective and is accepted as safe so much so that that feature is present on nearly every road car manufactured today. The fact that a full seal of air cannot be achieved on a road car is a good thing because it eliminates the possibility of carrying any design to a dangerous level.

We should, I feel, explore ways in which we can create specific areas of negative pressure beneath the car to enhance stability and increase the vehicles’ cornering ability. We will have taken a huge step forward once we’re able to increase both stability simply by the effectively using the constant (usually disruptive) dynamics of air rushing between the car and the roadway.

Doug, your suggestion that I plan for regular inspection on the monocoque if I go down that avenue, is well taken. Because we are all tinkerers at heart we should include in our tinkering the inspections of all components in the vehicles we design and build. You are right.

Well, this ended up being a longer post than I had envisioned when I started so I will stop for now.

PS. Has anyone heard the results from the metal clad balsa wood experiments? I’d like to see what was discovered.

Dick Bear

Hi Dick,

A very thoughtful post.

Because a thing has not been done before is to me very good reason to go and do it, at the very least you’ll find out why nobody else did it!

For my own design I am very focused on getting as stiff a frame as I can come up with and suspension that hopefully will give me good mechanical grip, weight or lack of it is not a top priority for me.

I’m sure some people on this forum won’t like what I’ve come up with it as it’ll be thought of as too heavy and too complex.

But those are my personal goals, so what they think is up to them.

On the CAD side I don’t think it’s hard to learn and looking at your post you’ve obviously got technical drawing skills and can think in terms of 3D so I doubt it’d be too much of a problem for you to understand. Thankfully for me when I started learning Solid Edge this year my initial design was horrible so it wasn’t too much heart ache to start again when I realized I’d done it all wrong from a CAD point of view.

I’m nearly at the point to start fabricating the main frame, my aim to date has been to address the major structural issues in the model before I make a mistake for real, I’m taking this approach as I’ve stuffed up other projects in the past for lack of planning.

There may be some confusion with 'ground effects' and 'undercar aerodynamics'. Two completely different things.

Ground effects relies on a low pressure area being set up under the car, by stopping air getting under and thus creating a partial vacuum.

Undercar aero concedes that it is impossible to seal the underside, so sets out to create a big inverted aero section underneath, to act as a foil to produce 'lift' downwards. This needs all sorts of splitters, gates, and dams to guide airflow and keep the flow organised.

Cheers,
Syd.

quote:

---

Originally posted by Doug68
Because a thing has not been done before is to me very good reason to go and do it, at the very least you’ll find out why nobody else did it!

---

Very interesting but of questionable value:

"However, this thread involves creating an aluminum monocoque, which has been done before."

…And I might add… done very successfully starting with the Can-Am’s and hundreds of racers and production vehicles since then.


"The limitations are very well known, specifically metal fatigue. There's no shame in reading and learning what happened to those who did try something new."

....If you believe that the Comet’s airframe construction was something new you have a lot of research to do. The something new that is associated with the Comet program was the fact that it was the first jet passenger plane. Certainly not that it was the first monocoque type airframe.

"The British airliner, the Comet, killed many people because of metal fatigue, which wasn't well understood at the time. It is now, so why ignore the lessons?"

...My reading of the Comet disaster (early 1950’s) is somewhat different than yours. I conclude from my reading that metal fatigue was the issue but rather than draw the generalized conclusion that all such construction is doomed to failure, I find that it was fatigue of a specific area of the plane (the square corners the engineers designed for the plane’s windows). If you read further about the planes extended life, rounding the corners corrected the problem. That’s the lesson to be learned from the Comet rather than what you conclude and inappropriately assign to all monocoque design. I suggest that you re-read the articles regarding the Comet!


"While building a car isn't the same as a plane,"

....Well you get one point right but lose everything with your next questionable conclusions.

"the metal fatigue issue certainly is, even more so, due to the increased vibration and pounding it takes."

....I take it you’ve never witnessed or viewed video of a naval aircraft landing on aircraft carrier. The violent and nearly instant transfer of weight from the wings in flight to the landing gear is far greater than the relatively slow weight transfers taking place in a vehicle frame.

"Having a suspension mount become unstuck is as life threatening to the driver as to those around him."

....No one is talking about ‘sticking’ something to anything? I prefer the phrase, ‘securely attach’ with universally accepted methods such as welds and bolts.

"I'm impressed at those here who can calculate the stresses, and therefore the life, in an aluminum monocoque."

....Calculating the stresses doesn’t necessarily result in the ability to predict the life of anything. I would assume the engineers had calculated the stresses factors on the Comet but their error in window design resulted in a shortened lifespan for at least two of their planes.

"I have no idea how it's done, but if I set out to build one, I'd certainly do my research. But building one, with no research, thinking, "It'll be fine", is far worse than what happened with the Comet. Those engineers didn't know what would happen - we do. We have the advantage of hindsight - why pretend it doesn't exist?"

....I don’t think anyone is contemplating building a monocoque without research. Certainly not without thought and no one here seems to take the attitude that “it’ll be fine”. And once again, the only hindsight advantage anyone can legitimately draw from the Comet tragedy you present is the understanding that sharp, square corners of cutouts are not appropriate.

Quite frankly gt58, your prediction of certain doom is based upon a less-than-careful reading of two plane crashes that happened nearly 50-years ago. You seem bent on comparing apples to oranges and are guilty of making broad generalized statements that are neither substantiated nor defamed by your one case study. You are ignoring the fact that monocoque design has been successfully for years both in the air and on the ground.

And finally, your less then professional assumption that anyone contemplating such a project universally lacks the ability to conduct research, is unable to think, is ignorant of history or is guilty of ignoring facts speaks more to the delusions of grandeur you have for yourself than it does to any weaknesses that may exist in those you are attempting to convince or impress.

Cheers,

Dick Bear

Wow.

SMURK

Wasn't the post "Open to suggestions"?
Not lets have a spat, slanging match or stand off?

You are absolutly right Uphill Racer.

Hopefully the dust has settled and we ALL can get down to offering ideas ans suggestions without condemnation.

I'm certainly ready to get back to a level playing field.

Cheers,

Dick Bear

The monocoque has been around and in successful use for decades, if not more.

Most LeMans cars of the 60's-90's were ali mono's. And not sandwich, either. Just folded sheets. Some still are.

The carbon mono's in use are just ali designs, with the material changed. I know, I make them!! The cfrp monos could be much more considerate of the material, but the 'people that be' are used to seeing ali, so that's the shape they think things 'should' be.

Lotus use an ali mono, and if you inspect one closely, it's not 'rocket science'. It's not very much science at all!! The glue is generic off-the-shelf. The curing process dates back generations, as does the metal forming process.

Some may be overwhelmed by something they see as different. But, when you deal with these things as often as I do, they become fairly pedestrian.

Mr. Bear is to be commended for venturing to do what he is attempting. None of the technologies are new, just some of them to him, and obviously to a lot of you who are reading this.

Open your minds, and be prepared to learn 'HOW' to do something, and not tell someone how they can't.

Cheers,
Syd.

When I was at Uni doing mech. eng. (nearly 4 years ago now ) we touched on most of the subjects covered so far, but I'm not going to go into 'steel vs alloy' or fatuge as such (I really hated fatuge at Uni - and now I do structural steelwork, its much easier when things don't move )

Other than the Comet (which was stress consetrations from the lage sqare windows) there was another earlier high profile case (or several) that propmted some of the first proper studies into fatuge - the Liberty ships

If you don't know already, they were an old ~1900 style ship re-designed to be build quickly in the US for WWII (I think the record was less tha 5 days) they were some of the worlds first fully welded ships - they had square hatch holes (to make them easier to build) and made form the cheepest steel avalible - being welded nothing to stop a crack growing once it started - in the most extreme cases the ships literaly snaped in two and most had problems in cold water/ weather (there is still 1 modded one left in SF I think)

Anyway 3 things came from this:

1 - stress consetrating features that I'm sure most people know about - as it was put to us 'square corners = bad'

2 - limiting crack grow - if a crack forms it will grow till it reaches the edge of the plate or component
if your car has a fully welded chassis then it could in theory snap in two - if your panels are rivited or bolted on it should stop and the only way it can spread futher is to form a new crack in the next panel (of course bolts and rivets can also be stress consentrators them self )

3 - Material Grades some materials are better than others, not just in ultimate strength but also in fatuge resistance (as well as corossion, workability.... and so on) - high strength or cheep alloys of alloy and steel will tend to be more britle (especialy at low temps.)

Dick, I'm sure that you are already aware of most of this (especially how different materials & grades behave) but I didn't see it mentioned already

As for how to design your car,
its general accepted engineering practice to design as far as you can (sensably) on paper (or computer) then build models/ prototypes to see if your right

-Robert

ps - You might guess spelling isn't my strong point

[Edited on 21/12/06 by mcerd1]

Hey guys,

This is great. Just what is needed. Information based on education and years of experience.

Thanks! It's all going into the storehouse for referencing as I begin the monocoque design and build process.

Good stuff!

Just got told the amount that will be required to paint the McBearen (ouch!). Perhaps I should have put some of my effort into learning to paint!

Dick Bear

I'm interested in the bonding side of the ally tubs, is this something that could be done in a home build i.e. in a garage? What are the materials, where do you get them, how do you cure them, cost? that kind of stuff.

Also, is there any point in bonding ally pannels to a powder coated steel frame, I would assume the frame would be less substantial as normal space frame?

Anyone done or know of anything like this?

I think some of the vhb tapes may be usable in things like this, but Syd will know more about that than me. Bonding to a powder coated anything seems a waste of time, as it will only be bonded to the coating, not to the metal, as you may well require. I doubt that the powder would be enough to ensure a good connection.

quote:

---

Originally posted by Dick Bear
... one participant on this forum who is obviously less than enamored with my efforts and felt it necessary to accuse me of being stubborn, ignorant, unaware, a liar, careless, having a death wish, an endangerment to others, an opportunist, arrogant, and dangerous ...
Dick Bear

---

Dick,

Have you seen here for ideas?

http://www.chaparralcars.com/2e.php

Gives some good pictures.
Rescued attachment carbuild3.jpg

To add to this, without meaning to make enemies here, I don't think that the "just give it a go'' attitude is entirely unjust or unsafe. This whole forum originates from a car build where such an attitude is the whole idea. From how I see it, it is no different with new ideas such as the monocoque. If people didn't try different things there wouldn't be such a fantastic variety of machinery around today. A lot of the time, basic common sense with a decent understanding, you can't go too wrong!

Anyway… the point of my post. If I could point you in the direction of my posts on this thread:

http://www.locostbuilders.co.uk/viewthread.php?tid=58053&page=2

To add: The ally is 18gauge (I can't tell you what grade, it is important) and the steelwork is zinc plated to avoid any accelerated corrosion issues

[Edited on 12/1/07 by andylancaster3000]

quote:

---

Originally posted by andylancaster3000
To add to this, without meaning to make enemies here, I don't think that the "just give it a go'' attitude is entirely unjust or unsafe. This whole forum originates from a car build where such an attitude is the whole idea. From how I see it, it is no different with new ideas such as the monocoque. If people didn't try different things there wouldn't be such a fantastic variety of machinery around today. A lot of the time, basic common sense with a decent understanding, you can't go too wrong!

[Edited on 12/1/07 by andylancaster3000]

---

You've gotta wonder what the chassis designers at Lotus would be thinking, if they read this thread???????????????

All those Elises and Exiges with those ali mono chassis??????? Must be time to scrap the lot of them!

Cheers,
Syd.

They're only held together with Airfix glue, how can they be safe

Designed by knowledgable engineers and with no rivets.

Thanks J Roberts for the link.

After looking closely at the series of photos and being fully aware of my friend kb58's cautions conserning tub construction I have to admit that that C2 tub looks very skimpy. Rivets (and I assume adhesive of some sort but I didn't see any evidence) fastening what appears to be 1/8" aluminum panels with just a few cross members with the suspension connection points not showing any appearent bulking of materials .... I am amazed!

Since my decision to explore further the making of a Monocoque I have collected a large photo collection of Monocoques from evry web site I can find. These are monocoques that are being built today and I must say, the Chaparral version is by far the lightest weight found to date. No one can ignore the fact that Jim Hall was a great driver and a pioneering engineer with vision and although his DNF record left something to be desired in Can-Am no one serious about competition vehicles can poo-poo his design talent. Add to that the fact that he is still around to offer this "Continuation" program and one would have to admit that his equipment (tubs) performed safely under the most cruling situations imaginable.

Engineers like Jim Hall and a host of intuitive designers like him have forgotten more about chassis, suspensions and materials than most of us will ever know. Learning from their advances in design technology is one aspect of what we are all about.

However, I still find it hard to believe that the tub shown in J Roberts link and being built according to original engineering specs of the C2 is as light weight as it seems to be from the photos. Especially when you consider that the engines that drove these rockets were not the light weight aluminum blocks of today and each generated horsepower that few, if any of us, will have the honor of piloting no matter what kind of chassis we dream about.

Simply amazing.....!

Dick Bear

[Edited on 14/1/07 by Dick Bear]

quote:

---

Originally posted by kb58
Designed by knowledgable engineers and with no rivets.

---

OK, the Chapperel may be a bit on the "light" side, but that shouldn't rule out this type of chassis construction. That chassis was designed in an era when the car wasn't expected to do more than a season (if lucky).

In Staniforths book the single seater monocoque was made from 16 gauge sheet, and the builder noted that after a trip to Pilbeam or somewhere, that he may have over built it.

As long as the suspension loads are directed into the corner of boxes, or into bulkheads, as pictured below, you will be amazed at how thin the material used can actually be. Just take a look at any modern bicycle frame for instance, tube butting has been used for years to reduce weight without saraficing strength, some steel frames are as thin as 0.9mm in the centre!

Go for it Dick, take up Syd on his offer!
Rescued attachment Image11.gif

elise chassis has rivets here and there, which enable better contact while curing the glue + prevent joint peeling off in a case of an accident..

I had a word with a guy that is building lemans type prototypes (spice I believe) and they are using an typical alloy monocoque method with a special glue and rivets.... I would suggest you look into special glues for this application...

If you look at the bottom plate it is quite thick. I would imagine the design puts most of the lode to this plate. I worked for an electric motor manufacturer a while back that was looking into automotive/aircraft adhesives, the engineer said that the metal would tear before the adhesive would delaminate.

My guess would be there's nothing thicker than 16 gauge on the chassis.

Well make no mistake, I’m going to do it and the really strange fact is that my doing so is not unusual in any way. There are numerous large and small shops creating fantastic products using monocoque design technologies. That is what has surprised my the most over the last several weeks…. Seeing the discouragement of some in an almost defeatist attitude seemingly to ignore the reality of 50-60 year of monocoque design from airplanes to racing, ships to deep divers. Quite frankly, none of the extremes experienced in either of these environments will be experienced by the sport/handling vehicle I’m planning to design and build. I truly appreciate all the honest concern and I value the input but I’m convinced that they are wrong as, it seems, many other quite capable designers do.

Rivets, no rivets. Adhesive, no adhesive. My Lord, the space shuttles and space station use rivets and adhesives in addition to “ fatal design system” known as monocoque. Goodness sakes, very airplane in the world today uses that technology. Ships, submarines and deepwater diving vehicles are based on that lightweight, strong and proven design. Without it, none of the accomplishments made in flight, space or on the sea and under it by these vehicles in the last 60-years could have been accomplished. What’s the big deal? I just don’t get it. Sure there have been failures. Sh@t happens even to those who are qualified to place a PE after their name but should those failures prevent us from moving forward? I think not!

Syd and I have had conversations about my using his expertise and once the program gets going I’ll surely take him up on his generous offer to assist and guide me through the sticky spots.

This is so bazaar. Rather than having a discussion on what would result in the best solution, the discussion has been centered on weather or not a monocoque system is safe, feasible and responsible. I’d truly be a fool if I entered this process committed to being irresponsible or having a desire to create an unsafe product. Trust me, I have not fallen off the log enough times [yet] to be foolish enough to willfully destroy myself or anyone else in the process. I’ve made mistakes, like we all have in our building efforts. My feeling about that is, “No harm, No penalty” and it’s time to move on.

Thanks to all of you have entered into this with links and ideas for development. I hope you will continue to share your knowledge and discoveries with everyone on the site.

Dick Bear

in that picture above, the bottom actually looks thick due to the lip folded into the front. As said, its probably no thicker than the rest.

GRP moncoque with integral roll cage - you have to guess the body style going over it .

and those special rivets are self piercing rivets - the new jaguar uses them aswell .

its £3.5k for the basic tooling - if i was to be building moncoques for a while id definitely be having one .

Now, not to flirt with controversy, but.........

A GRP monocoque CAN be a dangerous thing. If not properly carried out, with meticulous choice of materials and orientation, explosive catastrophic failure is in the realms of reality. (This means NO csm, NO woven roving or cloth,NO poly resin. Heck, you may as well use metal. )

Ali is a lot safer, and can be quicker and cheaper to build. I'm amazed at what some people see as progress, thinking that nobody has done what they are attempting before.

Drawn it, built it, seen it fail...now know better than to try it again.

Cheers,
Syd.

that chassis design has been about for oh - 40 years , not bad eh ? ive seen them in accidents and they stand up very well indeed - oh did i mention its big brother won the motoring news tarmac rally championship 'twice' oh and er the British GT series .

so what would you think of the bonded honeycomb grp/kevlar thats used in aeroplanes for the mosler chassis ? thats won the british GT series aswell , not a dig , but i think you knock it too much .

While a car/boat/airplane can be made from many differnent materials, the difference between a good and a bad design is how the material is used. How thick, what grade, what heat-treat, which composite material,what weave orientation, how many layers, which epoxy, cure temperature, etc.

The true design work is in the details, and there's a big difference between fabricating something and designing it. It's what separates amateur builders from the pros.

[Edited on 1/16/07 by kb58]

Kurt, I agree with you on that. I'm encouraged that you seem to be opening a crack in your previously expressed position of zero tolerance of a monocoques.

Dick Bear

I didn't think Kurt ever said he was anti-monocoque. I think his concern (which I share) is amateur designed/built monocoques, which is a whole other thing.

If there was a "Build Your Own Alloy Monocoque Sports Car for $2000" then there may be a baseline to work from. But in the absence of that or anything similar it has to said that building your own monocoque is a very different proposition to building your own spaceframe. I'm not saying it's impossible or not to attempt it. Where I agree with Kurt (although not as stridently ) is that such an endeavour must be entered into with eyes very wide open. I suspect that a monocoque will not respond to a "looks right, is right" design philosophy. The other alternative to actual design theory is to just overbuild it (ie 1/4" plate etc) which kinds defeats the purpose.

Again, I'm not saying it shouldn't be tried. I've often considered a monocoque version of my chassis but I know that I don't have the engineering knowledge (yet) to be sure it's safe. Or more so, convince an engineer and the registration authorities that it's safe so I can drive it on the road. If you can build one then publish a book on how - I'm sure the Locost community will all make a beaten path to your door to buy a copy each.

Good luck and looking forward to progress,


Dominic

quote:

---

Originally posted by Volvorsport
that chassis design has been about for oh - 40 years , not bad eh ? ive seen them in accidents and they stand up very well indeed - oh did i mention its big brother won the motoring news tarmac rally championship 'twice' oh and er the British GT series .

so what would you think of the bonded honeycomb grp/kevlar thats used in aeroplanes for the mosler chassis ? thats won the british GT series aswell , not a dig , but i think you knock it too much .

---

This whole thing has got VERY off track, so here's a repeat of what I wrote on the first page.

Now, everyone let poor Mr. Bear go and build his car!!!

quote:

---

Originally posted by Syd Bridge
This whole materials thing needs to be put into perspective.

Some of my 'bread and butter' comes from designing and building monocoques, in various forms and materials.

The racecars that are still built in ali are certainly lifed, but usually come to grief well short of that. Lotus saw fit to do their modern cars with ali mono's, so for specialist applications, it's ok.

We'll rule out carbon, because without the proper gear (autoclaves, car size ovens and such), and the tooling costs, it is not worthwhile for home/garage builds. And not done properly (this means NO wet layups!!!!), can fail catastrophically.

I've seen no mention of steel sheet mono's here yet. Why not? After all, your car is a steel mono. A home build steel mono can end up much better than a spaceframe, and lighter when you factor in the panelling of the spaceframe. After all, the sheet mono is only the panelled spaceframe, without the tubes!

I did a prototype project for a local company a good few years ago. When all the numbers were crunched, and 'street cred' and sales value were factored in, the decision to go with a 1.2mm stainless sheet mono was easy.

Not the lightest, but easily built with a mig welder and the basic cutting and bending gear that was to hand.

The stainless sheet will last forever, is not too difficult to work with, and relatively easily patched without special welding or any other tools.

If I were Dick Bear, I'd be having a serious look at a thin sheet ss mono. ~1mm plus stiffeners strategically placed.

Cheers,
Syd.

Edit: I just reread some of the above posts. For the ali bonding adhesive, Bondmaster do a 'filled epoxy' one part that is cured at 120c. All the glue companies do a similar product. You'll tear the ali before the glue lets go........... that's if you've prepped the ali properly in the first place. Not expensive at all, just the oven costs a bit.

[Edited on 13/12/06 by Syd Bridge]

---

i know what you do syd !! i have spoken to you before .

but i still think a home taught laminator could produce it as long as they were good at it .

if you design for strength , the stiffness is there .

the darrian chassis uses polyester resin and csm/woven roving/kevlar and carbon in all guises .

yes it would be better in epoxy but it can be done .

so , im just pointing out it can be done at home for the specialist builder .

quote:

---

Originally posted by Volvorsport
............the darrian chassis uses polyester resin and csm/woven roving/kevlar and carbon in all guises .

---

Sorry to carry it on Syd, but you know as well as anybody else, and this is very often the case with competition cars, that the Darrian works, and works extremely well.

As tarmac rally cars they are both very safe (proven in a number of big accidents) and extremely quick, and, relative to most rally cars, very light.

As circuit cars, just look back a few years to the success of the Swansea institute cars, running millington 4 cyl engines against the big boys in GT racing and doing very nicely.

I know nowt about composites, thus won't be using them, (at least for the foreseable) but poor or good or indifferent as it may be, the darrian is a well proven and highly successful competition car.

(hell they even won loads with the horrid imp suspension still used when they were still Davrians!)

[They've got away with that for as long as they have because of excess material. Way, way too much excess, and the weight that goes with it.]

Your 'lightweight' is my 'battleship'.

Please read what I posted fully, and without the influence of alcohol!

Questions will be asked after the tutorial.

Cheers,
Syd.

Guys,
We all seem to agree on so many things here but we also disagree on the same things and are slagging off each other either directly or implied.
IMO a semi-monocoque structure that is implemented correctly, is the strongest and most suitable structure for our type of use full stop!. What material that this structure is made of is down to cost and the skill of the individual. These days people are willing to pay considerable amounts of money for over-engineered parts just because they look good (carbon dashboards etc)
Looking through this forum, there are many topics where an individual has made thier own chassis - with an admission that it was the first time that they had done any metalwork and/or welding, which I think is both foolish and dangerous but the responses are generally polite and encouraging. Mr Bear here has emmense skill with sheet metal but because he followed the monocoque route and didn't unwrap his welder and learn to weld on his front suspension he is continually flamed. Look how many posts there were last year about the front wishbone mounting points for the shocks and the catastrophic failures that ensued, not to mention the numerous admissions of twisted chassis - give the man a break - he asked for advice!

I have an interest in both sides of the chassis arguement - I love sevens and their simplicity but equally I am a structural engineer and know the benefits of the monocoque. I am a time served apprentice in structural engineering (1000 hours with hammer in hand and then another 6 weeks of advanced stuff a number of years later) where my skills lie in the use of mainly Ali, be it bonded/bolted/riveted or whatever.
Anybody that has worked with sheet metal in it's various forms of heat treatment, will know how difficult it is to form to a specific size/shape/flatness etc. We are talking to tolerances of thousandths of an inch not halfan inch and pull in the gap.

Many posts have had replies saying "make a model from whatever material and see how it acts/reacts". This is basically sound un-technical advice, but please know the basics behind the point of this exercise. Here are a couple of links that will help explain the forces that our structures need to withstand and how you may engineer for them:

http://instruct1.cit.cornell.edu/Courses/ansys/shell/index.htm
(Youngs modulus will show you how a structure will behave under a given load in a given direction. It will allow you to see the point at which a structure will fail under a given load)
another:

http://www.nps.navy.mil/avsafety/gouge/stress.htm

Syd and Mr Bear here are gods in their field (IMO again) use them as references for their skills - don't flame them for being RIGHT but learn from their knowledge of structures and techniques.

regards

Steve

There is only one God, and I am not He !!

Cheers,
Syd.

a note on primary structural metal bonding.

much like the process syd uses to build composite structures, primary structural metal bonding REQUIRES an equivalent level of knowledge, skill, and equipment. not to mention extremely expensive materials.

unless you know EXACTLY what you are doing, do not soley rely on bonding metal with an off the shelf adhesive/resin sytem. and i do have to agree that polyester resins are inferior and should be limited to secondary structures, fairings, mouldings etc.

this does not mean that it cannot be done by someone outside of the motorsports/aerospace industry. preparation is critical for a sucessful metal to metal bond.the process'shat i know apllies to 2024-t3 this alloy, so there are no guarentees for other alloys.

Phosporic acid anodization(PAA developed by boeing, deposits a layer of pourous oxide film on to the metal, leaving a suitable bonding surface, this requires tanks of dionized water, 12% phosporic acid solution, anodizing euipment etc. and then you need the bonding primer, very expensive with a limited shelf life. Boeings spec must be follwed to the T to guarantee performance, i have yet to obtain this document, so i cannot give specifics. once prepped your ready to bond. if your serious about metal bonding, hysol/henkel/loctite, offer adhesives in film form that can be bonded at room or elevated temperatures. EA9309.x, EA9309, EA934, Magnolia 6398 are all suitable metal bonding adhesives and offer excellent performance ONLY if you follow the directions, i cannot stress this enough. the joint much like a aluminum or composite monocoque, must be engineered to take advantage of advanced resin systems.

another method commonly used now in the field is the PAsa jel method, which is a jel applied to the substrait, and converts the surface into a suitable bonding surface. this eliminate the tanks and anodizing equipment, but bond primer is still required, and once primed the part has a shelf life. the shelf life can be extended by an elevated temperature post cure and stored for later use. one avenue i may prusue and i can say is by far doable at home is prebond metal. i have used this in the helicopter industry in its 7075-t6 variant, it is backed with a scrim cloth that can be pelled away to expose a already prepped metal, one downside is that its pink. its really pricey too, unless you have a guy on the inside at the place you used to work. there do exists other methods but im not gonna type all night.FLP,panta,sol-jel...

and i stress again that the process i just talked about are certified for repair on various aircraft, NOT manufacturing, you will never get that out of boeing, airbus, BHT,eurocopter, their process are different at the manufacturing level, are proprietary. the field metal bonding methods are design for small repair doublers, core replacements, etc, not so you can manufacture your own wing plank/skin.

it was mentioned earlier in this post that a single component adhesive was used on various aluminum parts and the aluminum "ripped apart" during destructive testing, could the authour elaborate on the alloy type and thickness if know. these results are impressive to hear, but really theres more to it.

also i understand that various automotive aluminum parts are bonded during assembly, with room tempurature cures with minimal preparation. dont let this confuse, as there is no wonder glue out there thats gonna get squeezed out of a tube and hold one of the worlds finnest sports cars together, the elise. was the chassis anodized somewhere during the pre assembly stage. was there a protective cover over the bonded areas. all things that we dont know and lotus isnt going to tell us.

.... on ther hand metal bonding for non primary structural reasons is totally doable for the motavated individual. i have excellenty results by simply abbrading with a maroon scrotchbrite pad, rinsing with water, alumiprep acid wash, rinse, chromic acid conversion, rinse, air dry, dont touch it BTW, and bond with a decent epoxy paste adhesive.

i hope this was informative, and i personally know enough to know that primary structural metal bonding CANNOT be done safely, economically, realiably at anything other that the proffesional/industrial level.

question for Dick..
are you building an aluminum moncoque to extrapolate maximum performance out of aluminum and the monocoque design?

or just for the novelty?

Andrew

Thanks Andrew, I've been waiting for a post like this.

I've been looking into bonding for the past month or so, been to all sorts of web sites ie Loc-tight, cotronics etr. Also have investigated The Lotus and Morgan chassies and have found many bond types and spec's, but like you mensioned, no prosses of bonding.

I have done some repair work on both the Mogan and the Lotus, and it seamed to go quite well, which is why I'm keen to explore the possibility of building a one off chassie of my own.

Do you think this is possible, and what would be the hurdles as you see them for this type of project?

Many thanks,

Nick.

possible.. yes... will you safely , reliably be able to get the best performance from the materials alone by just bonding... i still don think so. lotus still supplements the bond line with mechanical fasteners. if you were to do this, i would consider the chassis to be a disposeable item as bonds do degrade over time just like some metals fatigue, and aluminum can easily corrode in a bond line.

an excellant example is the aloha 737 that had a lap joint failure and had its roof torn open in hawaii. the point im trying to illustrate is that lap joint in the 737 is bonded and riveted. just the rivets alone are sufficient for the structure, but the addition of an adhesive sealant between the two sheets, reduces the load taken by the fasteners and therefore prolongs the life of the joint. those machines were high cycles in a humid, and corrosive environment. the bond between the laps eventually failed due to corrosion of the metal and required the fasteners to take 100% of the load in a localized area. due to the frequent and repetative cycles of the aircraft the joint was unable to sustain the strains and cracks propogated from the rivet holes.

if a disbond(not to be confused with a delamination) were to occur the fastener would still provided some joint strenght, but at a much lower amount. its a safety margin and in addition, its a clamp most likely required during the bonding process, and they just left it there.

however, i will be taking advantages of panel bonding in my vehicle which will use a steel/aluminum hybrid semi monocoque. the lightweight steel bulkheads,longerons and diagonal bracing, will carry the suspension loads into the aluminum skin which will be bonded AND riveted into place. i dont have the capabilities to just bond them on. the aluminum will be .063 2024-t3 sheet, which is standard structural aircraft alumnum. i will use the process i described earlier to prep the aluminum and use a room temperature cure 2 component rubber toughend epoxy resin for added peel resistance. the rivets are 5/32 monel cherryax rivets that are 100% mandrel rentention rivet with equal shear strengh to their aluminum solid cousins of the same size. i will use an 426 AD solid rivets where their is sufficient acess to both sides for the tooling(gun and bar).

my design relies upon the steel structure to be adequately rigid for safety reasons, so if there was no aluminum panels, the car, in my opinion would still be safe to drive, but would not be rigid enough to make the most of the suspension system, i plan on using a spring rate equal to the corner weight , and the wheel ratio is 1:1.

the aluminum panels are there to increase the rigidity of the chassis for the least weight penalty and to provide some intrusion protection for the occupant. basically instead of adding additional tubes for rigidity and then panelling the car, im asking the panneling to take more of a structural load.

The composite guys might be interested in Dennis's latest chassis ideas

here

Cheers

Fred W B

My 2ps worth:

Having done some recent research (chassis design project for university ) I wonder if you've seen the lotus elise chassis? Its a bonded aluminium monocoque just like what you are designing and might be worth a look For suspension a good solution would be to build a separate cage/partial frame which is then separately attached to the monocoque, this is a growing trend in monocoque design.

Another way to simplify things is to use the engine as a stressed member - as seen in some F1 and high end ferrari applications where the suspension bolts onto the block - mainly to save space; I couldn't say whether this could be a good idea or not though...

Seems like a long thread - How is the design progress going?

Chris

Thanks Andrew, my idea was to build a aluminium monocoque, from extrusion and sheet, whick would be bonded and riveted (or simular mechanical attachments). This would all be under a steel roll cage which would also link the front and rear subframes, also steel construction. The front subframe would mount the front suspension, steering rack and pedal box, while the rear subframe would mount the rear suspension and cradle most of the engine waight.

What do people think? Be nice please



Andrew, I would be interested to hear about you chassie design, as it sound very simular to my plan "B".
How are you going to coat your steel frame, powder coated? Would you mind explaining you bonding method again, in a way a mear mechanic would understand.

Many thanks

Nick.

quote:

---

Andrew, I would be interested to hear about you chassie design, as it sound very simular to my plan "B".

---

Thanks,
I presume most of the bonding companies will be able to to advice me/supply me with the materials to prep in my aplication?

How long do you expect you chassie to last? And (hopefully this will never happen) after any damage, is it possible to make repairs to your chassie without having to rebuild it?

Sorry for all the questions, I seemed to have developed an unheathy intrest in this subject now!


[Edited on 24/1/07 by NDC790]

quote:

---

Originally posted by NDC790
Thanks,
I presume most of the bonding companies will be able to to advice me/supply me with the materials to prep in my aplication?

How long do you expect you chassie to last? And (hopefully this will never happen) after any damage, is it possible to make repairs to your chassie without having to rebuild it?

Sorry for all the questions, I seemed to have developed an unheathy intrest in this subject now!


[Edited on 24/1/07 by NDC790]

---

Again, many thanks.

I now think I'm a few steps closer to my final design. I will take on bord your coments about the correct materials and preporation when doing the bonding on my frame, I also think I will keep the bonding to a minimum, you know the bonding will be to level of my knowledge, i.e. LIMITED! The main part, the more complicated, will be fabricated in steel, and welded, where I have alot more knowledge and experience. It's where the two materials meet which was my bigest concern. In these areas I think I rely mainly on mechanical means, backed up by bonding to cut down any movment and posibly to absorb some shock transfer. What do you think?
Effectivly reducing the aluminium in the fame to four, maybe five main peaces, the floor, two sides (extruded RHS), front scuttle/bulkhead and possibly the tunnel/backbone. It's simple, and simple is normaly best? for me anyway!

I now have to transfer these IDEAS into drawings, with the dreded soilid works, so I can post them on here and then be shot down in flames and sent back to the drawing bord!

Anyway, good luck with yours.

Well, we seem to have the issue of adapting a monocoque to a street vehicle resolved to one degree or another. Thank you all for your comments, recommendations and views per my request for suggestions. Each opinion (pro and con) has been noted and will be considered once the project is begun.

While mulling over the different suggestions I have been designing what I would like to have the exterior of the vehicle look like. Understanding that likes and dislikes of a car’s appearance is a personal thing (remember several at GM thought the Aztec was cool enough to go to full production) and knowing I will probably receive the full gambit of critique for the design, I’m throwing caution to the wind by presenting it here on Locost first. You may flame it, accept it and/or offer suggestions.

Obviously I think it’s cool and hope that my body shaping skills are up to the task of creating the real item based on my attached PhotoShop rendering. The Swarm M8 will be a monocoque frame with a longitudinal V8/transaxle drive train the specifics of which I am still exploring. As I’ve noted before, I’m not an engine expert of any sorts and come to this love for cars as a designer/fabricator not a mechanic. Therefore, I welcome any suggestions for what could be married most effectively in the area of power plants. If you know of and would like to suggest specific engine and transaxle combinations I’d welcome that from you.

Now I’ll run for cover and peek up just long enough each day to see what comments have been posted!

Dick Bear
Rescued attachment Swarm M8.jpg

Now living in Salem surely it has to be a small block Chev with 4 barrel Hollie on top?

For the trans I'm going for a Porsche Boxster unit.
The best would be to get a Porsche G50 but they more money for a good one compared to the Boxster unit.
However as yet I've not actually seen anyone use a Boxster unit I may have bought an expensive ornament for the garage, and mating plates etc will be custom as a result.
The Audi, Renault units referred to often here are more or less non existent in the states.
I'm also lead lead to believe the trans in Fieros were all rubbish except the very last generation of them.

mosler have the porsche G50 mated to the ls6 . its a bolt up bellhousing - so maybe you could give them a call .

if youre intending to sell lots of them ,perhaps pick someting more mainstream .

Use a 914 for suspension and trans, infact a 914 donor should provide most of the pieces needed. Adapters http://www.kennedyeng.com/index.htm