What is it about the GT40 monocoque chassis?
- Thread starter Bill D
- Start date
Bill, You have really answered your own Question. When you look at the mono,s that follow the original design ' as close as possible ' you can see that virtually every single pressing is shaped to fit around all the other parts yet be as light & strong as possible. All the flat panels have a triangle within them to feed loads from suspension components into the tub without deflection etc.
So yes it is a 'piece of art' but it also has function and can be driven which to us old petrol heads is probably the ultimate in 'Art'.
Jac Mac
Bill D, let me have a stab at it. The chassis has a huge mystique factor. It's a guy thing! It's the heart and soul of the GT40 or, it's so hard to obtain! I look at the chassis in amazement asking why was it designed that way, why is this and that shaped that way and say; so this is why it's so fast! I'm assuming most guys like mechanical objects and some objects just hit on something that turns you on. It's alot like looking at women. I don't have to say anything about the body of the GT. I think we are all in agreement about the mystique and aesthetics.
I just caught this thread, and that was a big reason I went with the Mono, looks and engineering design. I have one of Herb's VSE cars and many of the reason why I got it was the chassis, not the beloved cobra body. When I saw the RCR, it was pretty much the same feeling, have to have a car with the mono.
For anyone that doesn't know what the VSE cobras were essentially a backbone frame as Herb calls it. Available in steel and aluminum. The chassis is very light either way and stiff.
Some pics here - VSE Cobra Look in the gallery.
So yes the mono and art of it is what moved me. The 'Art of Engineering' as I'll call it. Some folks may not see it, some do, but it depends what you see when you look at it
Sandy
The mono is loved because it looks brilliant and is rarely attainable by those who want a replica. The other reason is that it is dynamically superior to a spaceframe if properly designed.
The double D style mono used for the GT40 will produce a much stiffer chassis than all equivalent spaceframes. I see lots of spaceframes with redundant tubing and more importantly, tubing that sustains bending or shear loads.
A pure spaceframe will consist of tubes that only experience tension and compression loads. I've yet to see a GT40 spaceframe that matches that ideal in all areas.
The main issue is stiffness. A chassis that is stiff enough is almost (I did say almost) always strong enough, but a chassis can easily be strong enough but not stiff enough. There's nothing weak about the twin 4" round tube chassis of the Cobra but even FFR add the centre backbone for stiffness.
Essentially, the stiffer the chassis, the more predictable the suspension control and therefore the better the acceleration, handling and braking.
To achieve this, a spaceframe must be fully triangulated and this is the difficult bit. You need "holes" for the driver and all other bits where triangulation gets in the way and when left out, these are weaknesses in the spaceframe.
With a mono, the chassis can be designed with two load bearing structures and a massive hole in the middle (Lotus 23, GT40 and so on) and manage huge torsional stiffness. This gives better suspension control and therefore better handling and hopefully lower lap times.
For the same structural weight, the well designed mono will provide the stiffer structure. For example, the Lotus 24 (spaceframe) of 1962 managed 1000 ft.lb/deg and the Lotus 25 (mono) of the same year managed 2400 ft.lb/deg. The Lotus 25 chassis was 2 lbs lighter than the Lotus 24 (70lb vs 72lbs).
However, spaceframes are easier to design and cheaper to prototype which is why they're so popular for low volume production.
I want a mono but will likely end up with a semi due to the limits of my one-off garage production.
The double D style mono used for the GT40 will produce a much stiffer chassis than all equivalent spaceframes. I see lots of spaceframes with redundant tubing and more importantly, tubing that sustains bending or shear loads.
A pure spaceframe will consist of tubes that only experience tension and compression loads. I've yet to see a GT40 spaceframe that matches that ideal in all areas.
The main issue is stiffness. A chassis that is stiff enough is almost (I did say almost) always strong enough, but a chassis can easily be strong enough but not stiff enough. There's nothing weak about the twin 4" round tube chassis of the Cobra but even FFR add the centre backbone for stiffness.
Essentially, the stiffer the chassis, the more predictable the suspension control and therefore the better the acceleration, handling and braking.
To achieve this, a spaceframe must be fully triangulated and this is the difficult bit. You need "holes" for the driver and all other bits where triangulation gets in the way and when left out, these are weaknesses in the spaceframe.
With a mono, the chassis can be designed with two load bearing structures and a massive hole in the middle (Lotus 23, GT40 and so on) and manage huge torsional stiffness. This gives better suspension control and therefore better handling and hopefully lower lap times.
For the same structural weight, the well designed mono will provide the stiffer structure. For example, the Lotus 24 (spaceframe) of 1962 managed 1000 ft.lb/deg and the Lotus 25 (mono) of the same year managed 2400 ft.lb/deg. The Lotus 25 chassis was 2 lbs lighter than the Lotus 24 (70lb vs 72lbs).
However, spaceframes are easier to design and cheaper to prototype which is why they're so popular for low volume production.
I want a mono but will likely end up with a semi due to the limits of my one-off garage production.
Jim Rosenthal
Supporter
I think for its time the GT40 monocoque was very advanced in terms of stiffness, driver protection, durability, and handling. However its time was forty or fifty years ago. While I love these cars as much as anyone, and have gone to ridiculous trouble and expense to replicate an original car from the sixties, I think either a modern Porsche or Corvette would blow my car off the road. Of course, it takes a checkbook to get a modern Porssche or Vette, or Ferrari. It takes passion, dedication, and possibly having a few screws loose to try to create a sixties race car from thin air. The only other car from that era that I am aware of which stimulates similar mania is the Cobra.
I have one of those, too. I am incurable.
I have one of those, too. I am incurable.
The Superformance cars use an original-style monocoque chassis. They are delivered as turn-key-minus cars; there is still a fair amount of work required to get one on the road. It's not a true 'kit' in the strictest sense of the term, but that's probably a good thing. I'd guess that less than 10% of the 'kit cars' ever see the light of day--the amount of work required to properly build a car from the ground up is simply overwhelming to most people, and most of them wind up just serving as expensive garage platforms to support boxes, laundry etc. :sad:
Looks beautiful! I have every confidence yours will one day see the light of day--you're an inspired lunatic! :laugh:
I have to ask though--how do you plan to work on the car inside that shoebox? Looks like you'd have to take a step outside just to take a deep breath! :huh:
Keep on going with your build--you're an inspiration to everyone with your absolute fanaticism! :thumbsup:
Dave Lindemann
Lifetime Supporter
Bill Kearley
Supporter
Look at what you started Bill...............
Road America is heaven! Right Rick?
Road America is heaven! Right Rick?
Considering the ambitious scope of your project, the thought occurs that perhaps the walls ought to be padded! :laugh:
Obviously a monocoque laundry basket will work better. A space frame lets bits drop out and the rain get in.
