Thursday, 26 March 2020

Folllowing on from Our Host's Post...

How about this.  If you are going to design a simple minimalist sports car, using readily available mechanical parts, you always seem to end up here - and this is just a short selection



Lotus 7 1963


Dutton B Type


Locost - see the Haynes book
 Westfield 7 pre - litigation



14 comments:

DCBain said...

I don't doubt that they're a ton of fun to drive but watching them race is more boring than Formula One - and from my perspective that's saying something!

Mark Wadsworth said...

Exactly, the inevitability of design convergence if you have a few basic rules.

Lola said...

DCBain..only the Lotus 7 was designed as a racer. And i disagree about boring. Because they have no aero you can have 4 to 6 going into a corner together. I actually race a coupe version and it's a hoot.

Mark Wadsworth said...

... like a great white shark and a killer whale. Made by 'different manufacturers' out of 'different parts', but look and function much the same.

Tim Worstall said...

Not so much really. They're all trying to copy the Lotus 7.

There are other species of kit car. Those trying to copy the Morgan for example (Marlin etc).

This result is from mimicking, not technological determinism.

Mark Wadsworth said...

TW, yes, there is an element of that. But only because Lotus got there first (the race to the lightest, cheapest, most basic).

Most lorries or buses look the same. Are they copying each other, or is that just the best design for the job?

Lola said...

TW. I disagree. As MW says Lotus was there first with the 7 (actually its predecessor the Lotus 6 - or MKVI https://en.wikipedia.org/wiki/Lotus_Mark_VI was the firts commercial version). And if you want to be pedantic Derek Bennett's first Chevron looked very similar, as did pretty well all 750 formula cars. And they all used stock parts - Triumph Herald front uprights or split beam axle swing arm, ford or BMC live axle, Ford or BMC engine/gearbox and a home designed space frame. Chapman happened upon an iconic design at just the right time.

Lola said...

TW - to expand. The pre war establishment of the 750 MC really set the template for what followed and lead up to the 7.

Andrew S. Mooney said...

Lola - In short, no. What this shape represents is actually the result of a set of requirements at the production stage that meant this type of design was good in the sixties. However, if challenged to design a low-cost small sportscar today, the fabrication and design technologies we have are different, and so it would look very, very different. (TLDR - It looks like the Ariel Atom.)

The Lotus 7, certainly, the Westfield clone, and the Locost design as well, all feature what is known as a backbone chassis. They have the characteristic high "tunnel" between the passenger seats and it isn't just for positioning the driveshaft and gearbox - It is actually the main structural member of the car, all the body panels, which in a mass production car would be spot welded and load-bearing, are simply cosmetic - As in shaped sheet metal to keep the wind out and nothing more.

The backbone chassis design is very stiff for it's weight - and because it is smaller than a pressed steel body of any kind, is not cosmetic and so does not need to look good, can be welded together in a shed, as Lotus did back in the day and presumably homebuilders still do now. This is vital because pressed steel bodies require millions to tool up for and the production numbers would just not justify it.

But this was partly also due to the technology they did not have, in that composite parts and large, injection moulded plastic components simply didn't really exist. (Think the size of a wheelie bin or a plastic rainwater barrel.) They require tools and dies to make them just like a car body does. Fibreglass panels did exist in the sixties, but they were flat and required moulds and tools to manufacture, and yet to get the flared wheel arches in metal, all you needed was a brummie, a shed and an English Wheel.

To make a small sportscar today, a car like the Ariel Atom exploits modern ideas like a Spaceframe - Not that radical but way easier to design now using computers - It also uses composite materials such as carbon fibre (Which cost silly money in the sixties and was not a way Chapman could "Simplify and add Lightness," if you were not in the military.) It can use moulded plastic to create a passenger compartment and the CNC machining to create the injection moulding to create the part is very cheap.

Finally, there is the existence of cheap crate engines like the Honda Type R powerplant, that can pep up any design simply by dialiing up the turbocharger - A device which didn't meaningfully exist until the 80's.

Lola said...

Andrew S Mooney, er, not quite. The Lotus 7 did not originally have a central tube tunnel, the Caterham 7 might have. The Locost does. The Dutton does not. The Westfield pre litigation - I don't know. The original 7 used stressed skin aluminium side panels (rather like the 18). In my opinion none of these frames are true space frames (as neither is the Ariel Atom - which actually is remarkably similar to a Terrapin) they are really multi-tube chassis. By the way a 'space frame is not at all a 'modern idea'. It's been current in engineering for donkeys years. Often in roof construction - Stansted terminal buildings are a good example (I think).

If you want to build a cheap front mid engine two seater from proprietary parts the Lotus 6 / 7 (and the 750 formula type) then you end up like the 7. Today you might use an independent rear end; some used the Sierra rear axle. But again this is not new. The 1960's car I race is as close as the designer could get to a space frame (i've discussed it with him at length, but he still considers it a multi tube) and that has IRS with fabricated arms and unique uprights with an A Series diff in a custom made carrier.

Also you could in the mid to late 60's as an amateur make a monocoque, using either aluminium sandwich panels as used in aircraft. Again I know of at least one Terrapin made like that.

Even today, if you want low cost then the multi-tube is still competitive. Or (I have a friend) who makes kit cars using a quasi monocoque out of laser cut stainless steel. The car still ends up looking vaguely 7 ish.

Going back to the cars I have raced, including a Lotus Elite - which is a fibreglass monocoque made and designed in the late 1950's you could make excellent moulds to produce complex body shapes.

Of course computers permit quicker and better stress calculations for all chassis, finite element analysis requires thousands of calculations, and you'd be silly not to use one. OTOH a slide rule ans mathematical tools got many 60's designers much more efficient chassis than pre and immediately post war sports / race car makers. The bloke that designed the car I race was an aeronautical structural engineer with De Havilland.

Otherwise some of your points are obviously true - life moves on, we lean more every day.

And is you want to see a real backbone chassis look under a Lotus Elan, Europe, 30 or 40.

Lola said...

All
Lotus 7 restoration - no 'backbone' there:-
http://lotusdriversclubonline.org.uk/topic/27-1962-lotus-seven-restoration/

Lola said...

Further comments on 'back bone chassis'. Chapman happened upon this idea when Len Terry was working for Lotus. I can't remember all the facts, but from memory Terry was quite critical of the idea. Chapman then applied it to the Lotus 30 (to exploit the big money available in the CanAm series. The thing was not at all stiff. I have a friend who rebuilt one and has confirmed that. Of course the backbone worked well in the production Elan which did not need to endure the demands of racing. The 26R being the racing Elan version. Today, people fabricate and weld / bolt in a roll cage which largely acts as a stiffener or the weak backbone Elan chassis. I should also say I helped build an Elan kit in 1968. Black badge and all.

I think I'd better shut up now...

Andrew S. Mooney said...

"The Lotus 7 did not originally have a central tube tunnel, the Caterham 7 might have. The Locost does. The Dutton does not. The Westfield pre litigation - I don't know."

Yes, it turns out I'm thinking of the Elan.

The central tube on the Caterham and the Locost is doing something but it's a bit of an extra, in that I knew they had one and the purpose is to stiffen the car, but it is not the be all and end all in terms of how the car is strengthened, like I thought.

Spaceframes are quite a "modern" idea, in that just about every design is different and they cost a lot to optimise and get right. Porsche, in designing the 917, gave up upon optimising the design (Different diameter tubes, different material grades, etc.) and just took to slightly underbuilding the tubing, filling the sealed tubes with compressed air, and if the air leaked in testing/commpetition, a gauge alerted the driver to pull over, and for the team to inspect the chassis and look for where the frame had cracked. The alternative was to spend a fortune to analyse the problem mathematically. It is possible to then see why an inexpensive, non-cosmetic internal part like a stiffened backbone is then attractive.

"Also you could in the mid to late 60's as an amateur make a monocoque, using either aluminium sandwich panels as used in aircraft. Again I know of at least one Terrapin made like that."

I would be a bit concerned about what might be under the car's skin when NDT'd (Did they even have the technology back then?) If that is all that you've got holding the car together you'd have to very careful about voids, delamination, pockets of glue etc. I'm sure that the quality control back then was not what it is today, especially if you are cutting it up to create panels that have got be chamfered, which is probably why many people never even considered it.

"Going back to the cars I have raced, including a Lotus Elite - which is a fibreglass monocoque made and designed in the late 1950's you could make excellent moulds to produce complex body shapes."

I'll bet they cost a fortune in terms of labour, however. In my day job, epoxy tooling block for that purpose is still considered expensive, so you don't waste it, but it's advantage is it can be CNC machined with minimal supervision, whereas I'd bet that whatever the moulds were made of back then, they were prepared by hand.

Lola said...

Andrew S Mooney:

"The Lotus 7 did not originally have a central tube tunnel, the Caterham 7 might have. The Locost does. The Dutton does not. The Westfield pre litigation - I don't know."

Yes, it turns out I'm thinking of the Elan.

The central tube on the Caterham and the Locost is doing something but it's a bit of an extra, in that I knew they had one and the purpose is to stiffen the car, but it is not the be all and end all in terms of how the car is strengthened, like I thought.


Answer: There is no ‘central tube’ in the structural sense in a Lotus 7. I haven’t seen a drawing of a Caterham chassis so I can’t comment. The Locost does have a structure between the middle bulkhead and the rear bulkhead and it can have a stressed skin.

Spaceframes are quite a "modern" idea, in that just about every design is different and they cost a lot to optimise and get right. Porsche, in designing the 917, gave up upon optimising the design (Different diameter tubes, different material grades, etc.) and just took to slightly underbuilding the tubing, filling the sealed tubes with compressed air, and if the air leaked in testing/commpetition, a gauge alerted the driver to pull over, and for the team to inspect the chassis and look for where the frame had cracked. The alternative was to spend a fortune to analyse the problem mathematically. It is possible to then see why an inexpensive, non-cosmetic internal part like a stiffened backbone is then attractive.

Answer. Not really. Spaceframes, or more accurately multi-tube designs, are relatively easy to stress. I have a1950’s book that sets out how to do it for a sports car frame. I think it was the 908 that first had that. It was an aluminium tube space frame and pressurised with nitrogen (from memory), And Porsche did an awful lot of sums stressing their spaceframes.

"Also you could in the mid to late 60's as an amateur make a monocoque, using either aluminium sandwich panels as used in aircraft. Again I know of at least one Terrapin made like that."

I would be a bit concerned about what might be under the car's skin when NDT'd (Did they even have the technology back then?) If that is all that you've got holding the car together you'd have to very careful about voids, delamination, pockets of glue etc. I'm sure that the quality control back then was not what it is today, especially if you are cutting it up to create panels that have got be chamfered, which is probably why many people never even considered it.


Answer. Again, I have the book, the drawings, the design parameters, construction techniques and photographs of the car (s) to evidence that this was easily possible and carried out.

"Going back to the cars I have raced, including a Lotus Elite - which is a fibreglass monocoque made and designed in the late 1950's you could make excellent moulds to produce complex body shapes."

I'll bet they cost a fortune in terms of labour, however. In my day job, epoxy tooling block for that purpose is still considered expensive, so you don't waste it, but it's advantage is it can be CNC machined with minimal supervision, whereas I'd bet that whatever the moulds were made of back then, they were prepared by hand.


Answer. The Elite was ground breaking. There were two main mouldings that were bonded together. It was quite feasible and Lotus subcontracted the work to (I think) the Bristol Aeroplane Company. The car was a premium product but even so Lotus lost money on every one. Since then various kit cars have used a fibreglass monocoques.. The Mini Jem and Mini Marcos spring to mind.