Sometimes both passion and logic influence a decision in equal proportions. Mike Cudahy wanted to go racing. He'd been driving an Alfa Romeo Duetto in local club events and had the bug— passion. He says he wasn't excited about the safety provided by an open car, so he began looking for a closed car—logic. Cudahy was also an Alfa enthusiast; he loves the Italian machines—passion. So, when an Alfa Romeo Alfetta came available near him, he went to look at it—again, passion.With a blown motor, worn-out interior and straight body, it was perfect for a race car project—logic. He brought it home.

"I chose the Alfetta GT for a couple of reasons," says Cudahy. "One, simply because I've been a fan of Alfa Romeo cars since before I had a driver's license. Two, because it provided an interesting platform, in that virtually nobody was running the car in any of the classes.This meant that I had access to an empty canvas in which to create a competitive car by using whatever talents I had, or had access to. It's much more of a challenge to make a car competitive on your own than it is to write a check for someone else's fast car. I wanted to do more than win; I saw it as an incredible opportunity to create, to design, to learn."

Cudahy's second chore was to decide in which class to race. The Alfetta could run in ITB under Improved Touring rules, or it was also eligible in E Production as a full-preparation car (as opposed to the limited-prep later models now included in the class). Cudahy has a propensity for tinkering, so he figured E Production would be more tun— passion. Since he is a prototype model manufacturer, he also had some ability to tinker—logic.

The Alfetta is not the hot choice for EP. It is heavy, not terribly aerodynamic and, with its 2-liter engine, not a powerhouse. But Cudahy says he had some thoughts about how to reduce drag and improve downforce. A friend from the Rapid Prototyping Consortium at the Milwaukee School of Engineering (MSOE) reminded Cudahy that the school had a wind tunnel and senior engineering students looking for an interesting senior project.

Cudahy had graduated from MSOE and was familiar with the technology they had available, so he approached Dr. Robert Kern about making a senior project from aerodynamic improvements to the Alfetta. He was soon involved as an advisor to Mechanical Engineering students Nicholas Kristan and RickWilliams, who were excited to be doing a project that was not purely theoretical. A side benefit was that Williams brought some useful and practical experience to the project—he had been a body man for 11 years before pursuing his degree.The final report for their ME 492 Senior Design III project was titled "A Lighter and Faster Alfetta GT" and provides the details for this article.

MEASURABLE OUTCOMES

When starting a project such as this, it is important to have some measurable outcomes so you know when you have been successful. One important criterion was the weight.The rules say that an Alfetta can weigh 20001bs.; Cudahy's car weighed 2108. So, a primary goal was to reduce the car's weight by 1081bs. Usually that's easy, since all you have to do is replace steel with lighter materials where the rules allow. The driving goal, though, was to reduce the weight in a way that also improved the aerodynamics and downforce of the car, a particularly good thing to do with a car that already suffers from a power deficit.

The approach to aerodynamic gains and weight reduction centered on the redesign of the front and rear quarter panels, header panel and spoiler. Taking advantage of the rules that allowed for flares to accommodate increased track, new panels would be fabricated from carbon fiber to provide the weight savings.

The wind tunnel at MSOE can't accommodate a full-size race car, so the plan was to make a scale model of the car. Ideally, the model would have resulted from a laser scan of the race car, giving a very accurate computer image of the car. Cost being a consideration, Cudahy instead bought a 1/43-scale model Alfetta, which was then scanncd.The scale model was produced from the computer image at a 1/17.2-scale using Laminated Object Manufacturing (LOM). In their final report, Kristan and Williams describe LOM as "a process where a laser cuts the perimeter of a part from sheets of paper (layers of paper glued together) along with a grid between the border and part line. The part is then carefully uncovered by removing the small pieces of the grid, sanding and covering (the part) with a finish to protect the model from humidity." Essentially, the model was a block of carved paper covered with a hard finish. Imperfections were smoothed or repaired using modeling clay.

The scale,1/17.2,seemsanodd number; but it was determined based on restrictions on how wind tunnels can be effectively used. A model cannot exceed 7 percent of the tunnel's cross-section, or it will cause "tunnel blockage."The model of the original car had a frontal area, calculated using SolidWorks engineering software, of 0.05507sq.ft.; the altered body style's frontal area was calculated to be 0.06223sq.ft. The 1/17.2 scale was selected because it produced a model that was big enough to work with but still less than the critical 7 percent of the wind tunnel cross-section.

Once painted and with wheels added, the "stock" model was tested in the wind tunnel to establish the base number for drag. The wind tunnel set up was designed to elevate the model and move it out of the effects of the tunnel's lower boundary layer. Drag was measured from a spring scale connected to the bottom of the model by fishing line run over a fricrionless pulley.

In order to decide on what alterations to test, Cudahy studied the shapes of altered Alfetta race cars, including a number of cars raced successfully in Europe. However, Cudahy also made sure he understood the SCCA's General Competition Rules. This is a critical step in any race car development process. It' you don't understand the rules, you could have a very unpleasant season in the tcch shed. The aesthetics of the shapes he reviewed and the reality of the OCR requirements produced the prototype shape to test; once again passion and logic collide.

IN THE WIND TUNNEL

With the potential shape selected and the test procedure designed, it was time to run the tests. After the model was mounted in the wind tunnel, temperature and atmospheric pressure were recorded. This is critical, since you can't compare data from multiple tests if the ambient conditions, which can vary considerably, arc unknown. The tunnel fan was then brought up to 50 Hertz (1Hz = 1 cycle per second), drag force recorded from the spring scale, and wind speed measured using a Pilot-static tube. The runs were repeated at 1Hz intervals until a fan speed of 60Hz was reached.

This entire process was repeated three times for both the stock body shape and the race car body.

The final results of the tests showed that, when drag force was plotted against velocity, the altered body had a higher drag force at lower speeds than the original, but that the force on the stock body increased more rapidly than that on the altered body, finally resulting in a lower drag force on the race car shape at me maximum velocity of the wind tunnel. Higher drag on the race car body shape at lower speeds is likely related to increased downforce—a good thing when cornering.

Downforce measurements were made during the fabrication of the new body panels because downforce improvements, while important, were secondary to weight reduction and drag improvements.The setup for measuring downforce was innovative but not very successful. A false floor, similar to the one used for the drag measurements, was constructed; but it was allowed to rest, through narrow slots cut in the wind tunnel floor, on a scale.
The results showed that the new body shape had more downforce at low speeds, and both body shapes produce similar downforce as speed was increased from about 67-72 ft/sec (45.7-49.1mph). Above 72 ft/sec, the new shape had less downforce than the original shape, the result of improved airflow over the more aerodynamic body shape. At the highest fan speeds, approaching 80 ft/sec (54.5mph), downforce on both bodies was again the same.

While the data looked reasonable, analysis of the testing procedure raised some questions. It was feared that the negative pressure created by the moving air inside the wind tunnel, and causing an uneven distribution of force on the model, was too much for the model to overcomc.The results, therefore, were suspect. A more accurate procedure was devised, but the reality of anapproaching race season prevented it from being tested.

FROM THEORY TO PRACTICE

After validating the performance of the new body shape, the next step was to produce new body panels for the race car. To help the process along, Cudahy bought another Alfetta to construct the buck from which the molds for the new panels would be taken. Kristan and Williams reported on this process: "By using aluminum templates and Styrofoam, the new design features were roughly shaped on the duplicate car. Application of polyester body tiller and grinding to desired shape resulted in the final design. Once this was complete, the panels were painted for a smooth finish so that molds could be taken."

This was a time-consuming process, because imperfections in the buck would appear in the molds and, therefore, the new carbon fiber body panels. The finishing process involved priming, sanding and waxing the surface to make sure it was very smooth.With one side completed, cardboard templates were cut for several sections of each panel.

"The sections were then used on the opposite side for an identical match." The final step was to spray the surfaces with polyvinyl alcohol, a treatment that made it easier to remove the mold once the mold material had hardened.

The mold material proved to be another critical piece of the project. It needed to be easy to use and relatively inexpensive. Cudahy's business. Prototype Techniques, builds prototypes, so he was familiar with the materials that were available. He settled on Epopast 400, a molding material that is easy to use, good for five or six sets of body panels from each mold, and costs about S120 per mold. It is produced by Axson North America, Inc., and one of Cudahy's sponsors, Thyssen Krupp/AIN Plastics (800-544-0597), which distributes AXSON Epopast 400 and provided die material for the project.
"The AXSON Epopast 400 laminating epoxy paste gave us all kinds of advantages: It's very inexpensive, it's really easy to use— kind of like playing in the mud at kindergarten—and best of all, gives you a useable mold in 24 hours!" explains Cudahy.

Cudahy's first season with his newly modified Alfetta included many of the problems associated with racing a significantly altered car, but the overall results of the project were positivc.The handling and downforcc of his lightened race car were noticeably better, with no affect on the car's top speed. Even with the increase in frontal area, the newly designed pointy end of the car helps keep the car's nose planted better on the track.

Alfettas, with their high front end, develop lift at the front because they channel air under the car. The new design directs the air over the hood of the car and around its wheels, improving aerodynamics and downforce. The results were quantified at Road America, where Cudahy says his lap times dropped two seconds a lap with the reshaped car. His results in 2003 were better than they had been, but the Alfetta is a big car that Cudahy believes has an unfavorable power-to-weight ration compared to many of his EP rivals, so he remains an underdog in the class.

Sometimes, though, you just have to go with your passion.