Safety first at Formula SAE

  • 09-Jun-2010 01:20 EDT
Laval (FSAE10).JPG

The racecar for Canada's Universite Laval is on the tilt stand, a test for determining whether fluids are leaking from a vehicle.

Collegiate engineering students design and build open-wheel racecars with visions of demonstrating blazing speed on the acceleration pad, superior vehicle handling on the autocross course, and reliability in the endurance event. But safety overrides everything.

Just days before arriving at the Michigan International Speedway for the May 12-15 Formula SAE event, flames were licking the wiring harness and intake manifold on the University of Windsor's racecar. "No one was hurt thankfully, and the fire was quickly put out," said Sean Maloney, the Canadian team's technical director.

Team members later determined that the fuel injector seat had worn away, so fuel was spraying onto the engine.

"We used a rapid prototyped intake manifold and the material [polycarbonate ABS] is not very resistant to fuel, so it tends to gum up when it comes in contact with fuel. When the material softened that contributed to the injector falling into its seat," said Maloney.

After making repairs using aluminum runners to replace the polycarbonate ABS intake manifold runners, the team focused on testing the racecar. "We didn't end up doing nearly as much physical testing as we wanted to, but later in the summer we'll run tests and correlate those tests back to the simulations that we did so that next year's team has all of that information," Maloney said.

Messages of what did and did not work also will be passed along to next year's team. "What it really comes down to is you need to follow best engineering practices while you're doing things. You also have to take the lessons learned from mistakes and turn those into successes," said Maloney.

During the run-up to the 2010 Formula SAE Michigan competition, Graz University of Technology's team was on a crash course to gather information. "We wanted to know more specifically what happens to the monocoque during a frontal impact, so we did two tests with the monocoque," said team manager Stefan Pressl.

Austria's TU Graz Racing Team is likely the first Formula SAE team to do crash tests using a rebuilt monocoque.

For the first crash test, a front bulkhead monocoque and its crashbox traveled 7 m (23 ft) per second until crashing into a wall. "We got the expected result. The crash foam absorbed the energy without intrusion through the composite plate," said Pressl, who was also in charge of the racecar's chassis design/development.

A second crash test was done at double the required velocity. "At 14 m/s, that increases the energy going into the monocoque by a factor of four. There was only a little deformation to the carbon-fiber monocoque at the higher speed," said Pressl. "The whole package was still alive with only about 20 to 25 mm of intrusion, which means the driver's feet and legs would be several millimeters away from the crash intrusion."

The 2010 racecar had a foam crashbox and an anti-intrusion plate comprised of a sandwich structure with aramid and carbon fibers. The crashbox and intrusion plate together weighed 1.4 kg (3.1 lb). In contrast, the 2009 car's crashbox—a 10-layer aluminum-honeycomb structure—and the 1.5-mm (0.06-in) steel anti-intrusion plate together weighed 2.1 kg (4.6 lb). "So we decreased the weight, but increased the safety for the driver," said Pressl.

Weight reduction for this year's University of Texas at Arlington's racecar was fairly minimal in the frame, going from 80 lb (36 kg) to 74 lb (33.5 kg), but the team netted substantial weight savings with an engine change. "One of the biggest weight reductions came from the engine package as we switched from a Honda CBR600 F4i 600cc four-cylinder to a turbocharged Honda CRF250X 250cc single-cylinder engine," said Blake Hinsey, UT at Arlington's team captain.

Replacing the 120-lb (54-kg) engine used in 2009 saved 70 lb (32 kg). "Our preliminary analysis showed that going with this single-cylinder engine would significantly improve the car's center of gravity," Hinsey said. With the same driver, the center of gravity went from approximately 12.25 in (311 mm) to 11 in (279 mm). "We spent a lot more time rethinking the chassis packaging with respect to the driver's cockpit because one of the goals this year was to improve the driver's visibility," said Hinsey.

Global Formula Racing's car, jointly developed by Oregon State University and Germany's Duale Hochschule Baden Wuerttemberg-Ravensburg (DHBW-R), won the American Society of Body Engineers (ASBE) Foundation's Formula SAE Michigan award for outstanding design relative to aerodynamics, structure, panel breakup, and manufacturability. According to ASBE Foundation judge David Barran, the car also "incorporated a unique side pod design that not only gave the racecar a better air induction point, but it made the car less prone to scraping the ground in a body roll situation. That converts to a safety feature because the car is less likely to hit the ground in a turn and take control away from the driver."

Severe torque spikes can be extremely challenging to a driver, which is why Canada's McGill University team focused on finding ways to prevent dramatic engine power surges. "You want the torque curve to be as smooth and as flat as possible. We tuned the four-stroke, four-valves-per-cylinder, twin-spark Rotax 450cc engine to have approximately 80% of the peak torque available starting at 3000 rpm," said team captain William Kerley.

"And then the maximum torque of 28 lb·ft is available from 6000 rpm to 9000 rpm, which is almost the entire power band used for racing our vehicle at Formula SAE. With a relatively flat torque curve from 6000 to 9000 rpm, that helps an inexperienced driver extract almost the same level of performance from the racecar as an experienced driver," Kerley explained.

From a driving perspective, the racecar should handle well whether an experienced professional or an amateur driver is behind the wheel. "You want the driver to hop in, strap in, and go racing," said Kerley.

Safety considerations for the McGill team go beyond the actual racecar. "You're designing, developing, and building the car over several months, so workplace safety is paramount," Kerley said. Instead of a haphazard maze of parts and tools, the team's work environment is structured. "We make sure to hold workplace safety in the highest regard. That's really important because your work habits are reflected on the final product: the racecar."

Formula SAE representatives registered 102 teams on-site at this year's competition. Oregon State University/DHBW-R was the overall first place winner.

Rounding out the top 10 in order of finish were the University of Michigan-Ann Arbor; Austria's Graz University of Technology; University of Maryland-College Park; Rochester Institute of Technology; University of Texas-Arlington; Technical University of Munich; University of Michigan-Dearborn; Cornell University; and Kookmin University of South Korea.

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