I try to post updates only for completed projects, and since I’ve had several projects in progress it’s been a while since I’ve blogged. The diffuser is finally finished, so here are some pix and a video that explains it all:
After much debugging of the electrical and fuel injection systems, we have ignition!
For the intermediate term I’ll be using a custom-molded seat insert made with readily available (and cheap) two-part urethane foam. I have a kit of the Indy/F1 style foam, but it’s so expensive I’m going to learn what I can from the cheaper seat first. I’ve learned useful things already: on the first pour the bag doubled over or stuck to itself and the foam didn’t make its way to the thigh area, so the first attempt was scrapped. It was also useful, however, in finding out where to slice the foam to get it out of the car easily, and learning how thin the foam will make itself under high pressure areas (zero thickness). So for the second attempt I first lined the entire cockpit with two layers of 10mm energy-absorbing foam before pouring the 2-part foam.
As it expands the foam pushes hard against any constriction, like your body. When it hardens it’s almost too tight to fit back into. Many hours of sanding and cutting are needed to make the fit reasonable and comfortable. As it is, I can’t even get into the seat with my wallet in my pants pocket. At first I couldn’t even breathe in fully with the shoulder harness straps moderately tight.
Building the undertray started with building a surface large enough to hold it. It’s larger than it looks, so we had to laminate decorative plastic laminate onto two 4×8 foot sheets of plywood that had been trimmed to about 3×8 feet each. Then wood to form the side air dams was screwed down, and the radii filled with auto body putty. Next we cut plastic honeycomb and plywood pieces to fit, with the plywood located to pick up the attachment points on the frame and to protect the radiators on either side of the car. I built a hot-wire foam cutter from a tree saw handle, a piece of guitar wire, and an automobile battery charger, which I used to cut foam profiles for the leading edge of the floor. Then we laid the whole thing up with epoxy and two layers of fiberglass on the bottom and one on the top, and vacuum bagged the whole shebang. Vacuum bagging was made more difficult by the random tiny holes in the plastic sheeting, which we expediently fixed by adding a whole second sheet on top of the first.
After debagging we painted it and found out the hard way that you can’t paint enamel over fresh epoxy in a humid climate. It never dried, and had to be scraped off like tar. Epoxy paint worked much better. We then mounted the undertray on the car, drilling mounting points through the plywood in the correct places. We had to fabricate a mount for the front of the undertray, which was a little tricky as we didn’t want to remove the fiberglass body panel under the driver’s legs so everything had to be done from the outside. We fabricated a small pylon from aluminum sheet and pop-riveted and epoxied it to the bottom of the body.
SCCA FB rules require a metallic or composite front impact attenuator. Can’t have cars running around on the track with a battering ram on the front… My impact attenuation structure, or crash box, consists of a carbon-fiber and honeycomb sandwich laid up directly on the inside of the fiberglass nose. The carbon fiber varies from four layers at the front to eight layers around the rear attachment points so that it will crush progressively from the front to the back. Cylindrical aluminum inserts are used in the honeycomb as hard mounting points for the wing to the nose and for the nose to the chassis. This area is designed to be strong enough not just to absorb impacts but to allow lifting the front of the car by the front wing.
Formula 1000 rules require a chain guard equivalent to 1/4″ aluminum to contain the chain in case of a break. I had the blank laser cut, then bent it on my tubing bender. After bending, it was sliced in two parts for easier access to the chain and rear sprocket, drilled and tapped for an overlapping tab, cross-drilled for mounting holes, and installed.