Type: solar-powered composite-built car
Significant date: 2001
After suffering delays in getting the right company to machine their car bodies for participation in the American Solar Challenge, the Arizona Solar Racing Team's futuristic looking Monsoon car project was about to be cancelled for lack of funding to simply pay for the plug machining at full cost. However, thanks to some frantic last minute calling and the tremendous help of STW Composites of Montrose, Colorado, their plugs were able to be machined at the very last minute, getting their project back on track. This was not Scaled's first involvement in molding the frame for a solar car, since the company had worked two years before on the Cal Poly Solar Car.
"Taking the molds to Colorado and back involved a couple 14 hour drives and a little bit of missed class, but the finished plugs have been well worth all the effort put into them" said their spokesman on the web. The team loaded up the plugs into a Ryder truck only a week and a half after the initial call to STW Composites, where four Racing Team members were given a tour of the impressive facility by STW’s plant manager, including an up-close look at the 5-axis gantry router where their plugs were machined into their finished shape. After building a ladder frame base to support each plug and finding time in their machining schedule, the plug machining itself took only two full days, and three weeks after their initial trip to Montrose, two of the team members were back in a Ryder truck, driving to Montrose in western Colorado, through some of the most beautiful scenery in the US.
While the plugs were away, the team constructed two supports that fit to the shape of each plug, which were to be used to support the body shape as a body is manufactured from it. Built of the same composite panels used to construct the chassis of Monsoon, the support structure was designed to withstand the elevated temperatures required to cure the epoxy matrix for the carbon fiber material that would be used to manufacture Monsoon’s bodyshell.
One of the hardest parts of getting the molds to and from Colorado was having to rent a Ryder truck for each leg, moving the molds out of their race trailer and cutting down the mold stacking structure to fit the narrower Ryder. This was made necessary as neither the team nor any of its members had a truck capable of pulling our race trailer, and neither University vehicles nor any rental vehicles they had found were allowed for towing. This was becoming a major problem for the team, as they had had to turn down opportunities to showcase their other race car Daedalus at several events around Tucson and were not able to take the car to sponsors who supported that car prior to Sunrayce.
This problem was now becoming more severe, as the team needed to move the plugs, molds and eventually the body to and from Phoenix and around Tucson for several steps necessary in its completion. Later it would become even more critical when Monsoon was completed and ready for testing, as renting a Ryder would not be an option when the solar car must be rolled into and out of our race trailer. Testing is extraordinarily critical to race success, and it is not feasible to drive away from the lab with no trailer nearby in the event of reliability problems or a sudden storm. If the team had not made arrangements for a truck before July, they would not be able to go to American Solar Challenge.
The team worked hard on finding a solution to this problem for months, and nearly every car dealership in Tucson, and a few in Phoenix, were now intimately familiar with the intricacies of solar racing. The team was working even more frantically now, talking to the City of Tucson, the State of Arizona, Tucson Electric Power, several more dealerships, and more University officials. Friends of team members with trucks were also getting an earful, but a simple solution didn't seem to be on the horizon.
However, once the plugs were back in their lab, the Racing Team were encouraged to find that the composite supports fit the plugs very well, though they were created from CAD drawings before the body was even machined. Intensive surface preparation of the plugs ensued. Then the team worked hard to turn the plugs into a finished car body. The usual method for this is to create female molds from the male plugs, which are then used to create the finished part. This requires sealing the surface of the plug and sanding it to perfection, waxing the surface and spending several thousand dollars on mold-making materials. The team had planned about two months of the project timeline to completing the molds and the finished car body from them, but the delay in plug machining forced the team to reconsider its options.
After investigating several options and making several test pieces, it was instead decided to use a different method to create the car body, using the plugs to create the body directly. After some finish sanding of the plug by hand and filling some small holes with a mixture of epoxy and glass silicate, pre-preg carbon fiber material was layed directly onto the plug, which was then vacuum-bagged and prepped for curing.
Curing the carbon fiber sheets, which have been pre-impregnated with the correct amount of epoxy and frozen, required using a huge oven to heat the plug to 220 degrees F; these ovens aren’t found just anywhere! The team was able to use the facilities at Boeing Helicopters in Mesa, AZ, which also donated several thousand dollars worth of carbon fiber materials for use in the car. The carbon fiber was layed-up and vacuum-bagged in the Racing Team's own facilities and then transported up to Boeing in Mesa the next day.
With the curing completed, the team not only had a completed outer surface of the car, but each half still weighed more than 300 lbs, a little heavy for a solar car! The next task was a tedious one: carving out the foam to a thin, uniform thickness, before applying more carbon fiber as an inner layer. This process of sandwiching a lower density material between composite face sheets is known appropriately as sandwich composites, and it creates panels with high bending stiffness at much lighter weight than would be possible without the inner core of material.
Ordinarily, had a true mold been used to create the car, the team would have used Nomex honeycomb for this core material, as used in Hexcel panels found in the chassis of Monsoon. However, the team was lucky that the low-density foam material used to create the plug is also commonly used for sandwich core construction. With a secure bond between the outer layer of the car and the foam plug, all that was required for the core material was to carve out the foam of the already hollow plug to the right thickness using depth gauges and any sanding materials the team could get its hands on.
Once the foam was carved to the correct thickness in the correct areas, carbon fiber was then applied as an inner layer of the car body, in a repeat of the process used for the outer layers of the car. First the layers of carbon fiber were applied, followed by the requisite vacuum bagging materials. The team would like to thank Airtech International for donating all of the necessary vacuum bagging materials used to create both the inner and outer layers of the car body. Next came a second trip to Boeing in Mesa to have the new carbon fiber cured. On this second trip an autoclave was also used to cure one half of the body, but no positive pressure was used.
The Arizona Solar Racing Team once more obtained the help and sponsorship of Scaled's STX Composites (this time alongside Boeing and others) for their next solar vehicle, the Turbulence.