Monday, March 30, 2009

Our Lady's Skirt

So part of the secret sauce of this project is to do something that nobody in racing has before: build a suction downforce rig that channeled the force directly to the wheels. The Chaparral and Brabham cars came after the rules had tightened, so they used the body of the car as the "manifold" on which the suction forces could act, requiring a very stiff suspension to keep the car from dragging on the ground when the fan was on.

We are building a completely separate manifold. Imagine an upside-down John Boat hanging off of the suspension by shackles near the wheels. Initially I thought we might make it out of plywood like a homemade boat, but the high forces, low profile and proximity of the cat lead to an all steel design. Needless to say it's not light.

I had hoped to use the shock mounts as a mounting point for the manifold. It seemed like a convenient way to hook in to the suspension fairly close to the wheels. Unfortunately in the front there is not a lot of clearance around the shock mounts, and the shackles that support the manifold would rub the front tire. We also noticed that the shock mounts move a bit more than we hoped, about 1" over the full travel of the suspension, which would in turn change the air gap around the manifold. So instead of using the shock mounts we welded sleeves to the lower suspension arm on the wheel side of the shock mount. This gave us more leverage to resist motion and also allowed the front shackles to be better positioned to avoid rubbing the wheels.

Check out the crappy cell phone video of the system in action. I'm pushing on the car to move the suspension, and the front beam of the manifold hardly changes its height relative to the ground!

video

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