Polystrand GT-Lite CRX – Part 2

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The software showing different views for clarity.

The biggest challenge was figuring out the best way to incorporate our composite materials into the design. Since this was a racecar, and not an OEM application (yet), I also wanted to make sure we had plenty of adjustability so we could tune it when necessary. Good geometry was paramount, and having the luxury of an independent suspension setup gives us the opportunity to really create something that handles well. So, out came a clean sheet of paper. Well, actually a blank computer screen (I have nothing against paper – but I am a notoriously bad sketch artist. I can’t draw a straight line, even with a ruler). If you know what you want, actually laying out suspension geometry is not horribly complicated. It’s all about connecting the dots, projecting lines, and drawing some arcs. Almost thirty years ago, before I had the use of CAD software, I had a suspension modeling secret that served me incredibly well, and with today’s availability of inexpensive and even shareware CAD programs, I guess I can finally let the cat out of the bag: Tinkertoys. No kidding. Not those newfangled plastic ones, either – the original wooden ones. You can model some pretty sophisticated working suspension geometries with those things, and then you really get a feel for what happens when things move up and down. Laugh all you want – this was solid modeling at its finest.

A view of the rear suspension looking down through the hatch.

In the meantime, I received a cryptic email from “Goggles” Paisan back in Michigan. Subject: “Oops!” and three words in the body of the email: “No turning back!” The message was accompanied by a single image – that of a view looking down through the rear hatch opening. Where once was a trick rear suspension, there was now nothing but a big empty space. Tony had gotten out the old hot wrench and cutting goggles, and completely cut out the rear suspension and supporting framework from the car. Chris saw him in his torch-wielding attire and immediately christened him with the new moniker. There was no doubt that these guys were eager and committed to getting the job done.

Tony Berlingieri (aka “Goggles” Paisan) skillfully wielding the hot wrench. We have reached the point of no return!

After laying out the desired geometry in a 2-D computer sketch, it was time to figure out how best to use our materials in conjunction with the design. Metals are generally isotropic materials, which means they have the same properties regardless of which direction you measure them. The continuous fiber composites we are using are orthotropic, which means the properties differ depending on the direction you measure them. Without going into too much detail, it means that we can design a part to be stiff, strong, or flexible in a specific direction (determined by the direction we orient the fibers), without unnecessarily wasting extra material providing properties in other directions where we don’t really need it. This is one of the ways we can really reduce mass – it allows us to create a very efficient design. One of the most efficient ways to use continuous fiber composites is to design our system to exploit the properties of our materials in the direction of the fiber orientation, which is a straight line. Our materials are not only stiff and strong, but they are also very good under deflection – which means they can be bent a long way and still spring back without being harmed. Operative word in that last sentence – spring.

Here’s what’s left after Tony's efforts with the torch – a whole lotta nothin’.