LocostUSA.com

Hello Everyone,

I have read plenty of posts with many interesting idea's so my disclaimer is I have no plans for 3 turbo's, carbon fibre etc. I have also answered the 7 questions and know I am up for the challenge. I am located in Ontario, Canada.

I have been reading through the boards the last little while and have taken the McSorley 442 chassis prints and have come up with a mid-engine version of this platform (I know I am not original - just my vision for this hobby car). I am 6' 2" and have read enough to understand the original chassis would be too narrow and short for my general comfort. The attached images show the actual passenger area to continue with the original design. The front of the car is shortened, the rear 'cradle' lengthened and the roll bar supports carrying over a similar structure to the original. The windscreen, front suspension are stock Miata and in the back is an ecotec - This is all for reference i.e. no pickup or motor mount locations setup in the file.

First, I am looking for general comments regarding the structure and where to improve it? i.e. where to increase/decrease tube size or where to add additional triangulation. From there I will begin to work the suspension pickup points.

The McSorley plans for the most part use 1" square tube with 16 gauge walls. Has anyone decided to continue with the same wall thickness and go up to 1.25" tubes?

I have read the 'second car' build post and noted some people recommended more attention to roll cage or using tubing instead of square? My general use for the car would be hobby and the odd track day. Would I really need much beyond a roll bar for this type of activity?

Thanks,

First of all,I'd like to welcome you to the 'Funny Farm'! Anything I say needs to be taken with a grain of salt, as I'm still in the dreaming and drawing stage myself. Hopefully my building will start soon. I like the looks of your plans thus far, but it looks a little short coupled IMHO. I ask because on cars as light as these are, moving the drivers compartment too far forward can also adversely affect your weight distribution. What wheelbase are you working toward?

Again, welcome!

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Mike - Read my story at http://twinlakesseven.blogspot.com/

With a longitudinal rear engined car moving the driver forward can only help weight distribution. I'd also suggest a gas tank between the seats, actually more like alongside your legs, like the MR2 to help balance your weight distribution.

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mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

You should consider building Midlana. For the price of a book you get a well fleshed out car design. There are other builders and a completed car being thrashed in the real world. The 442 is not a good place to start for a mid-engine car.

Designing your first frame is an educational experience. That should give you pause for thought. Education can be expensive, there is no guarantee your first frame would work at all!

There is a major flaw there but I'm going to give you time to think about it or look for it. Or someone else can chime in. If you find it yourself you'll learn more, I think.

Good luck and keep at it!

The Midlana designer posts here and also has a forum for the car.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Two things at first glance:

1. Triangles only, open rectangular bays are no good
2. The front left suspension, the lower rear mount is right in your foot well, that'll cause all sorts of issues.

As was suggested, you might want to get my book to get some additional insight before deciding which way to go.

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

I built a mid-engine Mini and the gas tank was placed where a traditional transmission normally goes, on centerline next to the pedals. It helped give the car a 45F/55R weight distribution.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Thanks guys for the input, I think this will be a great board for input.

I will try to answer a few of the questions plus ask a few more:
1. The wheel base on this car is 92" the way it is drawn. I could move to 98 - 100" if I push the front suspension to clear a stock miata front control arm.
2. The lower control arm on the front suspension does sit in the passenger bay, I was assuming I would have to keep the same pickups in cross-car, but the fore/aft position would drive a redesigned lower arm that did not enter the passenger area.
3. I do have the Kimini book, perhaps the MidLana is next and using that design sounds to be a better start point. I can always pull that design into CAD and then get some input on thoughts on design changes.
4. Aside from many open area's lacking triangulation - My fault, I wanted to get a design to talk about and can quickly edit for improved strength and the lower control arm location. I am unsure of the fundamental flaw - Since I am learning, I would love to have it pointed out?

If I'm not mistaken Car 9 also has a rear engined version which would be good to look at too. And it's free.

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

There has been work on a longitudinal midship version of Car9 but no one has really pursued it yet. Kurt has done a plenty good enough design for the transverse setup that I don't see any reason to try and do that. With a built car, a book, a forum and other builders I think that base is well covered and there is a lot to be said for having existing examples of a design being used in the real world. Can't emphasize that last point enough.

Sorry if I seemed catty by not saying which important tube was missing. If you look at the side view the upper rail meets a diagonal by the drivers elbow. So the whole weight of the car is trying to bend that tube at it's middle. That node needs a tube going down to the bottom of the bulkhead behind the driver. Than you have triangles meeting triangles. I'm sure you would have figured that. It's pretty crucial though and once you are used to looking at these frames it will stick out and bother you when you see it.

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

There is also a longitudinal lower rail on the side of the engine compartment that connects to an unsupported section of the lower crossmember of the seatback frame, but could be that the floor will be structural?

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Mike - Read my story at http://twinlakesseven.blogspot.com/

Pat yourself on the back, your point has been well emphasized. I am ordering the Midlana book tonight. I have a couple of thoughts that I will poke Kurt about, but I will get to that at a later date.

Not 'catty' at all. I actually had that node triangulated in a 3D sketch, but had not added the tube in the frame structure yet. For now, I will hold off on this frame (Places file on shelf) and focus on the Kurt's mid-engine car.

Cheers,

Someone should tell me what that rectangular sectioned structure between the seats is about ? I have never seen one of those in an actual racing car.

Also, I wonder what would be wrong with substituting a riveted and bonded panel for some of those diagonals ? Not enough weight ? Too easy to build ?

Many race cars are single seater or have a midship engine and in those cases you are much less likely to see a large driveshaft tunnel or center structure, you do see it in the Lotus Europa though. The reason it works is because you can make it complete, it isn't missing diagonals. A steel tube just a few inches in diameter is as stiff as an entire car because it doesn't have the flaws required for where drivers and other components fit.

I think a big plus for a midship car is you gain the room where the flywheel and transmission of a front engine roadster go.

There's nothing wrong with using stressed skins, they're just harder to build than putting in a diagonal tube. It isn't really that hard to build a stiff steel tube frame.

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

In my brother's LS-powered Locost he had a lot of trouble with the headers cooking the master cylinders, but also frying the foot wells.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

I hesitate insisting about the between seat structure as Mr. C Chapman is generally seen as god like on this site. BUT, one only needs to recall the last Lotuses that used such a structure, the 30 and 40. They were a total bust. One 30 even broke in half in use. Jim Clark couldn't drive one. Len Terry refused to draft the proposal. In fairness to ol' ACBC the 30 was the first non-tubular, V8 powered sports car he did. Why he repeated the idea in the 40 I can't imagine.

So leave the structure out there where it might help in a T bone.