A BMW AG-designed carbon fiber bobsled carried Team USA to a record year at the 2014 Sochi Winter Olympics. Americans won silver and bronze medals in women's two-person bobsled Feb. 19; and two days earlier, a men's two-man team won the bronze, America's first medal in that event since 1952.
Their achievement was thanks in part to a new fleet of sleds developed by engineers from the German automaker's North American arm and built from a material BMW sees as the future of automotive design.
Hans deBot, one of BMW's manufacturing partners on the sled, has been lending his expertise in composites to Olympic sliding sports since the early 2000s, when a bobsled driver approached him about building a four-man bobsled for the 2002 Olympics.
"I had no idea anything about bobsledding, didn't know the sport, didn't have any involvement in the sport at all," said deBot, who is president and CEO of Mooresville, N.C.-based carbon fiber parts manufacturer deBotech Inc. "But because there was the Olympics and it was exciting, and [the driver] came with a lot of desire, didn't really have any backing or any money or anything else, but still a big desire to build a bobsled, so I took on the challenge."
His work drew attention when a four-man sled he built won gold at the 2010 Olympics in Vancouver for Team USA. He was tapped to build custom carbon fiber saddles for several of the U.S.'s Olympic skeleton team as well.
BMW of North America LLC got involved in 2010 through a sponsorship agreement with the U.S. Olympic Committee. BMW engineers tackled the two-person bobsled, developing a 3-D model designed specifically to be built from carbon fiber-reinforced plastic, similar to the material used in the all-electric BMW i3. Again, deBot was asked to help.
"They had made some wind tunnel models, a full-scale wind tunnel test model that they had done early on, and then it came to the point where they needed a true composite guru to build these new two-man bobsleds," deBot said.
BMW has used carbon fiber elements in its M series of vehicles and used the material extensively in the structure of its electric i3 and the i8, its hybrid sports car. Its carbon fiber plant in Moses Lake, Wash., is ramping up production capacity in anticipation of increased future demand, with the promise of more carbon fiber in future models.
DeBot was able to apply his experience with race car design to work on the bobsled, but he found bobsledding comes with its own set of challenges.
"They are two very different animals. It's a very different bird driving a car on a racetrack than driving a bobsled on ice going 80 miles an hour. It's very violent, it's abrupt, it's got very high G-loads. As people have described it, it's terrifying," he said.
Past sleds were commonly built with gel-coated, wet-laminated fiberglass or wet-laminated Kevlar, which often ended up using more resin than necessary, so they were heavier than necessary, deBot said. Engineering developments were typically focused on the chassis, with the body as an afterthought.
"It was just … let's get a body built, do it the quickest way we can, get a body built, put it on the chassis," deBot said. "… We were allowed to bring a lot of composite engineering expertise to step it up and take it to the next level."
Carbon fiber is very lightweight, which gave the designers flexibility to add weight where it would most help maneuverability. The nature of carbon fiber allows it to be tailored to provide the properties needed in each specific area of the body, without adding what deBot calls "parasitic weight." Unlike other materials that require a uniform thickness, carbon fiber can be tailored — even by orienting the fibers themselves — to provide strength where required, and reduced weight in areas of low stress.
"The resin content is weight-optimized, the product is weight-optimized, so when we build it, we're getting a much more structurally sound product for a lot lighter weight, so the strength-to-weight ratio is much better," deBot said. "So you get a stronger structure with lighter weight, hence better performance, because all the weight that we save in a body can be translated into ballast."
Olympic bobsleds are subject to minimum weight regulations, but choosing where that weight will go is an advantage. Since bobsleds don't have an accelerator, a good run relies on steering and smooth handling to make winning times; lowering the sled's center of gravity by paring weight off the body improves its handling. Because of carbon fiber weight reductions, the Olympic team was adding more than 80 pounds of ballast just to make minimum weight, deBot said.
"We had a substantial weight savings, with obviously an increased ability in strength and structure," deBot said.
DeBot's group built a fleet of six bobsleds — three for the men's teams and three for the women's. They took BMW's designs from computer model to physical part, manufacturing all the tooling themselves.
Though a bobsled is hardly a luxury ride, deBot sees a big opportunity for carbon fiber in the automotive market.
"I think it's a big driver that we have to try to save weight in these vehicles, obviously make them safer in racing," he said. "… Composites have played a big role in increasing the safety of the vehicles; that can all be transformed into increasing safety in everyday vehicles."
And he's looking forward to the next generation of carbon fiber bobsleds.
"I'm ready to start tomorrow to start working on the next rendition to go back and win more medals," he said.