Super Seven chassis design 5

[sacem1]

I'm starting to build myself a Lotus Super Seven replica but am starting from scratch not buying a kit from any supplier, I already got hold of Ron Chapman's book for the Locost S7 but find the design too fragile for fiting a Toyota 2 liter twin cam engine. The original chassis was 1" square tubing 16 swg thick with some reinforcement struts 1n 3/4" square tubing same gauge.
I think we need to raise torsional stiffness found a web page from Australia that stated minimum torsional stiffness requiered there was 4000 Nm/degree and that the Locost design did not reached it.
Got another data from someone in NZ to add some braces to raise torsional stiffness and that can also be done.
I am willing to even build several different chassis and test them to check results but would like your help in the following points:
How can I measure the torsional stiffness of a chassis after finishing the welding but with out having assembled all the other components?
I was thinking of bracing to a solid rigid heavy welded sawhorse lets say the back of the chassis, supporting the front on a center pivot point and fixing a lever to one side and measure the deflection with dial indicators as load is applied to the "torsion lever" then simple math will do, but is this the correct reading of deflection?
The same process could be applied to different planes across the chassis and we could in that way find the deformation loads that are needed for each degree of deformation found.
As all chassis are going to have the same aluminuium sheet cover applied over I want to study bare tube chassis first then after finding the best setup or construiction found, proceed to investigate if its better to pop rivet the Al sheets (like almost all S7's are built) or try some new bonding agents that did not exist in Colin Chapmen's days and that may give better results today.
Any help would be appreciated.
SACEM1

 

[sacem1]

I will like to see photos posted along as you go along your project.

Fine idea for saving weight, would like to know if you have calculated your torsional resistance

SACEM1

 

[benno]

I built a locally produced (Sydney Australia) '7' replica and fitted it with an Isuzu 2 litre twincam. I sold the car many years ago. The construction was in probably 1" RHS 16 gauge and as a matter of preference I glued and rivetted the aluminum panels. I used a building construction adhesive that goes under the name "Liquid Nails" and used wterproof pop rivets probably 3 or 4mm. Primarily I used the glue to surpress vibration on the panel edges and looked upon the added mechanical strength as a bonus. The car was called the "Amaroo" clubman and was really about as basic as you could get. Non adjustable suspension with Spax coilovers. The front uprights were Ford Cortina as were the brakes. Rear Axle was Ford Escort live axle with drum brakes. As a package it wa really terriffic. Very quick and agile. I never got it weighed but it must have been sub 700kg. As far as torsional strenght was concerned, in real driving conditions I don't think it displayed any torsion effects. It felt very tight and turned and tracked superbly in a corner.

Ben Roberts

Broadcast Engineer

Sentient being.