What is it about the GT40 monocoque chassis?

[Bill D]

What is it that makes us drool so much when we see an original style chassis? No other car chassis garners so much attention as a mono.

[Steve26]

I agree Bill, it's functional engineering art and I never get tired of looking at it. I have almost worn out my GT40 books from looking at them so often. I have been telling Fran that his Mono chassis is fantastic and that I wish I had thought of it! Great job Fran you big stallion.

Steve

[Dalton]

Hey, steady on. Fran does build great chassis' but if you praise them too much he'll hike the price up.
Just kidding, Fran.

Back to the thread. Some other chassis type cars are very well made and strong (eg. DRB here in Oz), and perfectly capable, but there is certainly beauty in the original type monocoque.

Dalton

[I LOVE GT40- Paolo]

for me is a sort of feticism.
Dont think monocoque cars are SO better than tubolar ones (for many point of view they can be worst and much more expensive to repair).
Think the monocoque cars are the only ones ok for the FIA appendix K,ready to race in historical fia events...but no so sure of this.

Sure...also just to see the mono is a pleasure for eyes.

[Doc Watson]

It is a piece of automotive art.... over 300 pieces of thin metal sheet fashoned into a lightweight functional racing icon.

Roll on the summer I might actually have one then..... I had to sell my soul to the devil to get it though.......

[Fran Hall RCR]

Paolo.
I dont think that the FIA is going to allow replicas...no matter how accurate, to race in Europe.
I heard a whisper that even the new Lola T70 continuation from Lola is having issues being accepted to race.....

[Big-Foot]

This will be an interesting thread!

While the aviation industry is known as the root of monocoque design - the true birthplace of it is in boats.
Canoes actually.
But it's the Aviation & Aerospace industry that has taken the basic premise of monocoque design to the levels of strength seen today.

Be that as it may, it's my observation that the automotive industry (racing at the forefront) that followed the aviation industry's lead in embracing monocoque principles to decrease weight and increase strength.

I think monocoque is the logical connection of Aviation to Aerospace to Race Cars to Street and Exotic Automobiles.

To my line of thinking - this association brings along with it an air of quality - not to mention a connection to the roots of GT40 et al design.

All this said - I think that there may be some misconceptions, by some, regarding Space Frame design in the cars we are building here.
First off - when you rigidly attach a skin to a framework, you are turning that frame into a monocoque structure. In looking at all the information I could find about MDA, Tornado, GTD, et al - all of them were to a large degree using this design principle. This is called by some semi-monocoque. Frankly I don't think these designs give away anything in terms of strength.

There's only one fault (my opinion) of a monocoque chassis - They are more difficult to properly repair when damaged.
Obviously the difficulty of repair is dependant upon the type and location of the damage.

This said - there are many more advantages of the true monocoque which the aviation and aerospace industries bear testimony to.

I've made my choice based on the Pros and Cons and other factors that were important to me.

That's my story - I'm donning my nomex undies waiting for the fur to fly..

[Scott Calabro]

Good post Randy,

Two huge disadvantages to a monocoque in a street car.....

1). A side impact with an integral fuel tank (sponson
/sill tanks) will most likely result in the death of the occupants. May I suggest to all with these setups is to have the tanks continuosly pressurized (1 psi) with low pressure nitrogen, (a small used O2 bottle would work great charged with nitrogen) also in integral halon bottle for discharge into the tanks and engine compartment. Plus a main DC power cutoff switch located within the drivers reach, or better yet one actived a remote G switch.

2). As aluminum monocoque's age (steel too) they will work harden making them brittle. Then when they are involved in an accident or just from regular use, chances of them cracking at stress points (read suspension pick-up points) becomes a greater possibility.

Thats the way I see it. I have worked on monocoques (aviation) for a LONG time. Don't get me wrong I would love to have a monocoque car, but I will be realistic in my expectations of longevity/reliability/repairability.

Regards,
Scott

[Bill D]

I guess when my aluminum mono wears out, I'll just have to get another

[Scott Calabro]

Bill,
If I had your money I'd burn mine !!!

[Doc Watson]

What would be the comparative weights of a true monocoque vs. a 'semi-mono' (spaceframe with panels). The purpose of the mono was, I assume, to reduce weight, as was seen in the MK IV which used honeycombe sheets bonded together. Its now the norm to have modern cars with carbon monocoques... I again assume that the strength of these new monos is comparable to cars in the 60's (possibly stronger to pass modern chassis tests). Eric Broady, who's lola was the starting point of the GT40 design, has stated that he wanted the original car to be an aluminium monocoque and I think someone out there has a Mk V all aluminium chassis. If you want to go even lighter and still retain the original look of the mono chassis you could always make it from titanium sheet........

[TimB]

Originally Posted by Big-Foot

But it's the Aviation & Aerospace industry that has taken the basic premise of monocoque design to the levels of strength seen today.

Actually beyond airospace I believe the second widest use would be large transport. All over the road busses from the 50's to the present are a stressed skin mono

[Colin Artus]

Citroen were using monocoque construction in the Traction Avant in 1934! This is before most aero designs had got there. Perhaps that is why we use a French word for the design. Race car constuctors were very 'johnny come lately' with regard to this development.

[Bill D]

From Wikipedia

monocoque - French meaning single shell.

First used on aircraft

In 1916 LFG introduced their Roland C.II, which used a fuselage made of "bent" plywood, forming both the external skinning as well as the main load bearing surface. This made the plane immensely strong in comparison with contemporary designs, although it was also quite heavy. Similar designs were also produced by Pfalz Flugzeugwerke, who had originally built the Roland under license.

By the late 1920s the price of aluminium (specifically duralumin) started dropping considerably and many manufacturers started using it to replace the internal framing, and in some cases, the external skin. A classic example of such a design is the Ford Trimotor, which retained the old type structure with new materials. The structure of the plane consists of a trusswork of U-shaped aluminium beams, with a thin skin of aluminium riveted on top, using skin corrugations instead of wing ribs and fuselage stringers.

Bill

[Big-Foot]

Good post Bill (re: Dating of 1916) - But I think the Native American Indians probably had the birch-bark Canoe a bit before then.. One could call the BB Canoe a Semi-Monocoque - but it would be very loosely in that category. Then there was the carved out Tree Trunk canoe which had no framework whatsoever.. I think we're back in the 1400's there.. I'm sure there are other watercraft (Roman? / Chinese?) and perhaps models built by DaVinci that predate them..

Certainly large trailers and busses etc used stressed skin support but when I think of the most extreme test of monocoque design, I think of vehicles like America's Space Shuttles. Not only do they have to be able to take extreme heat and aerodynamic loading, they have to be able to do it again and again while being capable of maintaining a roughly 14psi pressure inside while in a perfect vacuum (outer-space)..

I'm not worried about the chassis in my RCR being able to take whatever grief I or any of my successors will give it. I'm comfortable with the design (which is actually well over-engineered) and while I'm not ready to sacrifice it to side-impact testing to see if it's stronger than a Tube-Frame semi-monocoque design - I feel that it would do very well if it was.
Point in fact - it was the engineering of the RCR that was a key driver in the decision making process.

Now - I don't think Bill or anyone else wants to make this into a contest between Tube-Frame Semi-monocoque and Full Monocoque. They all have their Pro's and Con's..

[Bill D]

No, this isn't a contest between the designs. I just know guys lust after that original mono

[Joe T]

Dont leave out the Vikings, they built a mean mono type Boat, first across the Northern Atlantic etc.

Only point I would make on the monocoque chassis is if it is damaged beyond repair I believe it would take less time to completly replace than a space frame, no making up ally panels drilling and rivetting. I appreciate some would say a slight accident may be able to be repaired with a space frame by chopping out the bent bits and welding new bits in etc but I think that would only make up a small percentage of accidents.
A good design is one where the damage is absorbed in crumple zones etc, otherwise it tends to transmit the impact/damage to the occupants.

I think weight has always been the driving for in race chassis design and that prompted the move to Mono's just like Carbon Fibre has now.

Now a complete Carbon Fibre GT40 Mono, that would be something, I have see some very clever stuff with this material.