Designing and building an open-wheel racecar that is nimble and durable enough for the tough demands of Formula SAE’s autocross, endurance, skid pad, and acceleration performance challenges was no easy feat. But before the dynamic challenges unfolded at the 35th annual Formula SAE Michigan competition teams and their racecars underwent intensive scrutiny during the static judging events.
This year’s 104 competing entries arrived at Michigan International Speedway in Brooklyn, MI, from various colleges in the Americas, Asia, and Europe.
Honda, Kawasaki, Suzuki, and Yamaha sport bike engines or small-displacement engines from other manufacturers had the racecars roaring for four days in May. With no two racecars exactly alike, the technology applications ranged from off-the-shelf to completely customized—like the machine-crafted, 15-in (381-mm) long carbon composite support tube on the Auburn University racecar.
Located on the car’s main roll hoop bracing, this unique carbon composite structure supported the headrest. The lattice structure was fashioned by a modified textile machine invented in the 1700s. “How it’s formed is definitely unconventional,” Austin Gurley, Auburn University’s chief chassis engineer, said during an interview with SAE Magazines.
A maypole braiding process produces the intricate structure. “The bobbins dance around on the machine. Gears carry the carbon fiber tows around a central mandrill to hold the material’s shape, and the braiding occurs as the carbon yarns weave around the mandrill,” Gurley explained, adding that controlling the braid’s shape essentially tailors the structure’s directional strength.
The process of producing the 1.25-in (32-mm) diameter, 1.7 oz (48 g) brace, capable of supporting 200 lb (890 N), required specific material preparation. “We take the carbon composite filaments and create yarns. There’s kind of a special way that we put a jacket on the yarns to protect the material and make it stronger so that it can last through the production process,” said Gurley, who is writing his master’s thesis on the structure’s properties.
Gurley considered using this novel structure elsewhere on the 442-lb (200-kg) racecar. “Several halfshaft samples were made. But we didn’t use this structure because we needed to do more testing to confirm that it could handle the shock loading that would occur in a drivetrain application,” Gurley said.
Although several racecars sported rear wings, Colorado State University’s team opted for a full-vehicle aero package. At approximately 36 in (914 mm) tall and 54 in (1372 mm) wide, the three-element rear wings created 65 lb (289 N) of downforce. Triple-element front wings added another 70 lb (311 N) of downforce.
“Both the front and rear wings use an EPS [expanded polystyrene] foam core wrapped in carbon fiber. Our car’s center section features a mid-wing design, so the racecar has a wing profile that sits under the carbon fiber side pods creating downforce. It’s an uncommon design at Formula SAE, but this approach was done for a brief time during the 1970s in Formula One racing,” said Christian Becker. He worked with teammate Kevin Aiken to develop the car’s aero package.
The 36-lb (16-kg) aerodynamic package provided 160 lb (712 N) of vehicle downforce and 38 lb (169 N) of drag at 30 mph (48 km/h). “We probably did more than 100 design iterations for the front and rear wings combined, plus another 50 design iterations for the mid-wing and the underbody,” Aiken said. The team’s 2012 Formula SAE car had dual-element front and rear wings and a flat underbody tray with a diffuser rear section.
Just as downforce matters in racing, so does braking power. For the University of Florida’s racecar, the stopping technology was a Bosch Motorsport antilock braking system (ABS) M4 unit.
“After looking at vehicle data logs and our own testing, we found that—especially with an amateur driver—the amount of time that the racecar spends locking its wheels increases the braking distance of the vehicle. That’s what prompted us to look at using an ABS unit,” said Dylan Edmiston, the team’s project manager and electrical system leader.
The ABS unit, believed to be the lone application at Formula SAE Michigan in 2013, added girth to the racecar. “The unit weighs about 7 lb, and that’s significant for a car that weighs 445 lb. But we decreased the 2013 car’s chassis weight by 5 lb, which helped offset the ABS unit’s weight,” Edmiston said.
The braking system, which includes yaw rate/acceleration and other sensors, is driver-adjustable. “That’s a benefit if track conditions change or there’s a driver switch,” Edmiston said. In the event of an electronics malfunction, the driver can turn the system off and the racecar’s ABS functions as a conventional master cylinder to brake caliper setup.
Reducing vehicle weight was a key goal of The Ohio State University team. Compared to the school’s previous 513-lb (233-kg) racecar that used a steel frame chassis, this year’s vehicle weighed 473 lb (215 kg)—a reduction of 7.8%, due in large part to its carbon composite monocoque.
“Our steel-frame racecar had 800 lb·ft per degree in twisting, and we increased that stiffness to 1400 lb·ft per degree with the carbon monocoque. That’s a huge advantage in terms of the car’s suspension performance, and on-track tuning is a lot easier with a stiffer chassis,” said Aaron Ressa, the team’s composite leader.
Next year’s racecar entry may be designed using solid carbon hard points in place of the phenolic hard points used for the 2013 car. “It would make it easier to manufacture,” Ressa said, noting that composites usage was just one of the discussion topics the OSU racecar crew had with the University of Stuttgart team.
“This was the first year that Ohio State hosted an international team. It was beneficial for both of us. The Stuttgart team shipped its car to our facility. They worked on their car and tested their car at our facility. We’re also side-by-side in the paddock,” Ressa said, adding, “They’re a top-tier team with many victories, so we really learned a lot from them.”
Following are the top-10 overall finishers at Formula SAE Michigan 2013:
1. University of Stuttgart (Germany)
2. Tallinn University of Technology (Estonia)
3. University of Akron
4. École de Technologie Supérieure (Canada)
5. Université Laval (Canada)
6. Cornell University
7. Graz University of Technology (Austria)
8. Centro Universitário Da FEI (Brazil)
9. Michigan State University
10. University of Florida.