Engineering News 2-16-98Engineering News 2-16-98

February 16, 1998

8 Min Read
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February 16, 1998

ENGINEERING NEWS

Sport science propels U.S. into medal contention

A freshly engineered bobsled design makes the U.S. Olympic team a force to be reckoned with

by Laurie Peach, Associate Editor


Oxford, CT--The four-man bobsled careens 90 mph down the 1,700-meter long spiral track located in the foothills of Mt. Iizuna, Japan. The track drops 113 meters from start to finish. The driver deftly pulls the ropes left, then right to steer through the 15 sharp curves. As the sled speeds across the finish line, the brakeman expertly pulls the lever, praying that their time was within that 1/100 of a second needed to take the lead.

All crew members except the driver crouch down, reducing air resistance. They tilt their heads about five degrees helping to turn corners. Nicknamed 'Spiral,' the 1,700 track in Nagano has 15 curves.

For the first time in almost 50 years, the U.S. bobsled team is in contention for an Olympic medal, thanks to the Bo-Dyn sled, a new design by Bob Cuneo, president of Chassis Dynamics. With an infusion of $200,000 of personal funds, NASCAR racer Geoff Bodine sparked the project that led to the U.S.-built machine, now racing in Nagano, Japan. "Prior to this, we were using old European sleds that we had to weld back together," says Tim Conrad, principal engineer of the U.S. Olympic Sport Science Technology Division in Colorado Springs.

The Bo-Dyn, originally introduced at the Lillihammer Olympics in 1994, has undergone major revisions in the last four years. "There were many factors we didn't understand then that we do now," says Cuneo. "We realized we hadn't taken into account the ergonomics of the athletes' bodies. So we redesigned the frame and cowling (the body) because the way the athlete rides in the sled has a large effect on the performance of the sled both aerodynamically and mechanically." To develop a more aerodynamic design, Cuneo viewed both the athletes and sled as a single unit. "These weren't two separate items--they were one and the same," he says.

The key engineering issue was control. "There are two elements of control--actual control and perceived control," says Cuneo. It is actual control when the car or sled does what the driver wants it to do at a specific speed. It is perceived control when the driver feels that he has dominion over the machine and, as a result, will take more chances. Cuneo sees a definite gain in racing performance when perception is increased.

A bobsled's speed is affected by three factors: the start (push), weight, and ice friction. To increase confidence in the sled, the athlete has to "feel" the track. In other words, there must be communication between the ice's surface and driver's body, "and it has to be friendly," says Cuneo.

Much of this communication is transferred through the sled's runners. "Runner technology really is a black art," says Cuneo. "Many athletes will have 20 or 30 sets of runners per sled depending on conditions." Ice surface, sun or clouds, humidity, and temperature--even changes of a degree or two--will affect the speed of a race. Each set of runners is designed with a slightly different curvature, cross sectional radius, or chemical composition that corresponds to the situation. Although no one yet exactly understands why a particular shape or metal works differently under varying conditions, Chassis Dynamics is "trying to turn the black art into science," says Cuneo.

Another aspect of the ice-to-driver relationship is sled stiffness. Because of the tight constraints set by the International Bobsled Federation, there are few components one can alter to improve the design, says Conrad. Olympic rules confine the construction of sled bodies to carbon fiber, Kevlar, or fiberglass. Only steel can be used for the chassis and runners. By altering the thickness and composite of the various materials on the cowling, stiffness of the machine can be refined.

The thickness of the frame, shell, and runners all contribute to the rigidity of the sled, says Conrad. Because one can't build the frame stiff enough, body hardness has to be added, while maintaining flex in the machine. If the body is too stiff, the bobsled bounces all over the track. If too soft, it is uncontrollable.

Chassis Dynamics worked with Ken Armstrong of Creative Instrumentation (Davidson, NC) to develop an elaborate testing package that helped determine the optimum design. The system monitors articulation, front axle swivel angle, rotation of runner shoes on axle, the lateral G's on the machine, speed, acceleration, as well as vibration on all parts of the sled. Any motion-control technology was fair game--computer simulations, gyros, accelerometers, and IR lasers, were all included in the test program. The sled was originally designed using CADKEY, a CAD software package from Baystate Technologies (Marlboro, MA).

"Last year we were the hottest team on the circuit," says Cuneo. "We've won more metals in the last five years with the new design than we've won in the past 50 years combined."

It began in America

"Bobsledding is the only Olympic winter sport that we can claim is totally American," says Christopher Lindsay, National Director of Youth Bobsled Programs (Lake Placid, NY). Lindsay spent the last three years researching the sport's precise beginnings.

The practical use of bobsleds in the U.S. dates to 1839, when loggers used them to haul wood. "Bob" means "to shorten," says Lindsay.

Competitive bobsledding originated in Albany, NY, in 1886 when the loggers came to the city to sell the wood. In an attempt to show off for the ladies, the men rode the empty sleds through the streets. This event caught the imagination of locals. One businessman, Stephen Whitney, designed a two-section sled. A board, approximately 244 cm wide and 366 cm long, was connected to the rear section with a round bolt. A thick wooden rod running crossways through the front portion extended 20 cm on either side to form the steering handles.

Built of solid oak with tempered iron-clad blades, the original sleds weighed between 500 and 700 lbs empty. Fifteen to 20 men and women added more than a ton of weight to the 30-ft-long sled. An engineer at the time calculated the projectile force of such a machine, traveling at 40 mph, to be sufficient to carry the sled through a two-foot brick wall.

At the sport's pinnacle, 20,000 people gathered in Albany to watch the competition. The killing of a 14-year-old boy by a runaway sled in 1889 put a stop to the sport. Competitive bobsledding continued in Davos, Switzerland, where Stephen Whitney introduced his sled after the New York tragedy.

Volunteers wanted. In order to bring the sport to a new generation, Lindsay is developing a "build-your-own bobsled" education program for junior high and high school students. Mechanical engineers are needed to design blueprints that will be used to build a sled from scratch. If constructed to Olympic regulations, the children will be invited to Lake Placid to run their sled on the Olympic training track. Not only will the children learn about the sport, says Lindsay, they will acquire mechanical engineering skills and master physics laws, vectors, and G-forces while having fun.


Thin-wall bumper fascias save cost, weight

Detroit--For its 1998 LH platform cars, Chrysler wanted a redesign that would differentiate the Dodge Intrepid from the Chrysler Concorde. One component that set the Intrepid apart from its "kissing cousin" is its bumper fascias.

Integral to the new look is a new material developed by Solvay Engineered Polymers (formerly D&S Plastics International), Auburn Hills, MI. The material, SEQUELr 1440 engineered polyolefin, was specifically designed to reduce wall thicknesses in applications intended for thermoplastic olefins (TPOs).

The 1998 Intrepid program includes three fascia tools: two front fascias--one for the base model and one for the ES upgrade--and a rear fascia common to both models. The rear fascia and the base-level front fascia are fully painted, as are dark-color versions of the ES front. Four light colors of the ES front, however, are partially painted, with a blackout panel of bare substrate between the fog lamps.

Choosing the SEQUEL 1440 polyolefin over a conventional TPO, or a competing RIM process, enabled Chrysler to cut costs in several areas. Although all-new in design, the 1998 front fascias are about the same size as their 1997 counterparts molded in a TPO. However, the new fascia assemblies weigh six lbs less than the previous iteration, with most of the weight loss attributed to the thin-wall fascia skin. Victor Liu, engineering manager at the molder--the Plydex division of Magna's Decomma Exterior Systems--estimates the savings to Chrysler over a run of 200,000 parts at more the $1 million.

The rear fascia is "the largest fascia anybody in our company makes," notes Bob Stewart, supervisor of exterior systems for Chrysler's large-platforms. Still, it is much lighter. It also uses less material than had it been molded with a 3.5 mm wall section typical for traditional TPOs. In fact, wall thickness on the rear fascia has shrunk to 2.9 mm, while the nominal thickness for the front fascias now measures a slim 2.7 mm.

"With the higher flex

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