Building the Perfect Beast

7/10/2015

Version 12.2

Follow Vermont SportsCar as they collaborate with Subaru Tecnica International (STI) to create a championship 2015 Subaru WRX STI rally car

Balance is the key – making everything work together.

Lead Fabricator Mike Bacigalupo is adjusting the position of a transmission mock-up – a 3-D printed plastic replica of the actual gearbox – trial-fitting it to a Subaru rallycross car. It should be as low as possible, but ground clearance is an issue and the driveshaft angle has to be less than 3 degrees. An angle of even 3.1 degrees could lead to premature driveshaft failure – disaster in the middle of a race. “We’re constantly looking at little tweaks and changes,” Bacigalupo says.

In the assembly area, Lead Technician Shaun Jacobs is doing a “dry build” of the battery bracket and co-driver’s seat in David Higgins’ Rally America car, making sure the battery location won’t interfere with other components and will be easy to service on the spot. “The shape and dimensions of this new 2015 rally car are longer, so we have to refine everything – not start from scratch, but look carefully at where to put the weight,” Jacobs explains.

Meanwhile, Design Engineer Winston Hale is conducting a computer stress analysis of a new aluminum-alloy mounting bracket for the rear suspension. The previous supplier no longer produces this part, so the timing is ideal to take a fresh approach to the design, materials, and construction of the bracket. “Just about everything on the car gets computer-modeled in some way,” Hale notes.

All of this is taking place simultaneously as the team at Vermont SportsCar, the official technical partner of Subaru of America rally efforts, works with Subaru Tecnica International in the off-season to increase their competitive edge. In each case, increments of millimeters, tenths of a degree and fractions of a kilogram are everyday challenges. Starting with the more-rigid 2015 WRX STI chassis, each seemingly minor modification is designed to create a faster, stronger, and more competitive Subaru rally car.

Engineering Teamwork

Few people passing by the nondescript industrial park on the outskirts of Burlington, Vermont, would imagine the race car engineering going on inside. The work spaces at Vermont SportsCar are spotlessly clean and highly organized, with specific rooms dedicated to each specialized task. The other thing that’s apparent when talking to the employees is you rarely hear the word “I.” Teamwork seems ingrained and natural. While every person may have a specific role, the group’s ultimate goal is the same – producing a championship car.

“The 2015 car, with its many advancements from the factory, is like a clean slate for us,” explains Engineering Manager Dan Farley. “We have to take what we know worked, and with the help of Subaru of America, evolve it to fit the new car, hopefully making it better along the way.”

Simplify and Consolidate

Let’s go back to Hale, who’s finalizing the computer-aided design (CAD) work on the rear suspension bracket. “After each event, we do a debriefing and look at performance and reliability issues. One of the things we try to do is simplify parts, to consolidate them where possible.” It helps to have a great chassis to start with.

The suspension mounting bracket Hale is working on used to be fabricated from steel. There were several issues with that approach. “Each part might be slightly different, and we thought we could make one out of aluminum-alloy billet that would be stronger and more precise.” The end result is a better piece that meets all of those goals, and is less than half the weight of the old part. “Removing unsprung weight from the suspension is always a plus,” Hale notes.

“There are so many variables, and there’s a domino effect where tweaking one thing affects the other,” he says. “It’s a real two-way street between my work and the fabrication shop.”

Each Piece Impacts Another

“Everything that bolts onto the body shell is fabricated,” explains Bacigalupo. “It’s all-new for 2015, so working closely with Subaru Tecnica International, we’re dealing with making things lighter, stronger, and faster.”

On-the-spot serviceability is also a concern. “When we fabricate a new part,” Bacigalupo explains, “we have to consider making it easy to remove and replace if it’s damaged in a race.”

Moving the mounting points for different components is “a big challenge,” Bacigalupo says. “We start with what we consider an ‘ideal’ placement, and then see how it fits in the car and how it impacts other components.”

The use of a 3-D printed, plastic transmission replica was a huge time-saver, because the custom-made transmission was still in production. “We work with race-transmission specialist Sadev in France, and they took the CAD data that’s used to make the transmission housing and then 3-D printed a plastic replica for us. When the actual transmission comes in, most of the issues relating to its placement will be taken care of in advance.”

Minor adjustments to make the driver and co-driver more comfortable are accommodated wherever possible. Since Subaru Rally Team USA driver Sverre Isachsen prefers a gas pedal that’s at a flatter angle, while his fellow team member Bucky Lasek wants it more vertical, “we can accommodate those preferences with an adjustable pedal assembly,” Bacigalupo notes.

Different Formulas for Different Parts

The area where the driver’s feet are positioned is called the “footrest,” and in the Subaru rally cars it’s made of a carbon-fiber composite. At Vermont SportsCar, these advanced materials are handled by “Mr. Composites” WeeGee Smith. “Carbon makes it strong – stronger than steel and lighter – and the resin bonds it together and enables it to retain its shape,” Smith explains.

The driver’s door and co-driver’s door have to be steel, per the rules, but Vermont SportsCar sandwiches a honeycomb structure to the inner door panel behind the steel for impact protection. Other parts are made of a carbon/Kevlar® hybrid, which is less susceptible to fracturing than typical carbon-fiber pieces.

“For some parts, we use a thermoplastic material that has more ‘give’ and more memory,” Smith says. “Damaged thermoplastic parts often can be remolded and used again.

“We look at different materials based on how the piece will be stressed and in what direction it needs to be strong,” he says. “It’s an ongoing process to tweak the formulas. The more time we put in here, the less work we have to do at an event fixing or replacing pieces.”

The Shakedown

After an entire car is designed, engineered, and assembled, Vermont SportsCar does a shakedown run. That leads to further testing and tweaks, “getting the low-hanging fruit first and then doing a run versus the ‘old’ car to check for areas of improvement,” explains Farley.

The Incremental Road to Success Millimeters

Tenths of a degree. Fractions of a kilogram. A ferocious attention to even the most minute parameters is one of the key secrets to success for Subaru Rally Team USA and Vermont SportsCar. None of it comes easily, and every small change to one component impacts another. It’s only when all the pieces work seamlessly together – like the people do at Vermont SportsCar and Subaru of America – that a winning rally car is created.