Body Design for Zephyr (Almost) Complete!

While many other Bear Engineers were taking a break from the rigors of UC Berkeley during Winter Break, the CalSol Shell team was busy optimizing the aerodynamics of its latest car, Zephyr.

Side View of Zephyr
The flow around the top of the car. Note blue areas depict regions of low pressure and red areas depict regions of high pressure.


Since building a model for each iteration of the design would be incredibly costly, we use a software called Computational Fluid Dynamics (CFD) to simulate the conditions our car would encounter in the real world, such as turbulence and crosswinds. We model our car in SolidWorks, run CFD, analyze the results, and make the necessary modifications before starting the process over again, with each iteration taking about 5-7 days to complete.

Solar cars produce a fraction of the power of gasoline-powered vehicles, and consequently, it’s of paramount importance to have a well-designed body. We began the process in May 2012 by identifying the aerodynamic shortcomings of our previous car, Impulse. The aerodynamics team then spent the summer learning the intricacies of CFD and surface modeling by testing out numerous different airfoil bodies. Once we returned to Cal in the fall, we hit the ground running by splitting up our team into smaller subteams responsible for the design of different components of the car, like the wheel fairings, canopy, and airfoil body. Once we integrated all the different components, we began the nearly two-month process of running CFD and making changes to the aerodynamics.

To put our predicted performance values into perspective, Zephyr is 250% more aerodynamic than the Volkswagen Beetle, 182% more aerodynamic than the Toyota Prius, 133% more aerodynamic than the Ferrari California & McLaren, and 25% percent more aerodynamic than our previous solar car, Impulse.

Canopy Flow Trajectories
The colors reflect the different pressure values on the canopy as the air flows around it. Each line represents a “stream” of air.


We are pretty much done with the design of our new car and will be changing our focus to manufacturing in the coming weeks and months. Unfortunately, our predicted drag performance is, well, just that—predicted. Imperfections in manufacturing and real-world annoyances (splattered bugs) will inevitably increase our net drag. But our goal for this semester, as we begin the building process, is to minimize the number and impact of those imperfections as much as possible (bugs will still be bugs and splatter on our car).

Steering Wheel Molds

Sam Cohen with Steering Wheel Mold Designed by Parker Schuh
Sam Cohen with Steering Wheel Mold Designed by Parker Schuh

CalSol has been hard at work over our Winter Break touching up the designs on our shell, chassis, and suspension but in particular Sam Cohen and Parker Schuh on the Controls team have been working on creating a lightweight, carbon fiber steering wheel. To do this we first needed a 3D model of what we wanted the wheel to look like; this was designed by Parker and is shown below.

Steering Wheel 3D Model Designed by Parker Schuh
Steering Wheel 3D Model Designed by Parker Schuh


Once we had the model we needed to CNC (Computer Numerically Controlled) out the molds for the wheel in a high density tooling foam. This is a complex process using a 3-axis milling machine in the Etcheverry Student Machine Shop on campus. The bottom photo shows the process of spiraling inwards removing the proper amount of material as the ball end mill progresses. You can see Sam here holding one of the two molds that we machined – corresponding to the top of the steering wheel.

The next steps are to prepare the molds for the carbon fiber layup and for layup itself, stay tuned for updates on this awesome project!

Great work gentlemen!

CNC Machining of the Molds
CNC Machining of the Molds