Background - Drag Reduction System (DRS)

A central engineering challenge in high performance motorsports is determining the tradeoff between downforce and drag on vehicle.

We intend on investigating and designing a morphing wing prototype for use in a high-speed SCCA or FSAE track with high-speed corners and short straights. The use of a drag reduction system reduces energy consumption, improves top speed, and produces more predictable driving characteristics in dirty airflow.

Above is a visualized comparison of a formula car with and without a DRS. As seen, in a straight portion of the track, it is advantageous to minimize the drag on the car at the cost of the lost downforce since traction is not of as much value in this instance. This is why the car on the left has its rear wing in the down state, while the car on the right has no choice but to keep its configuration without a DRS.

When it comes to practical application of a DRS, it was heavily debated on our FSAE team. On one hand, it does decrease our drag on straight-track portions, but it also comes with the added weight of the system that toggles the mechanism.  On the larger scale, it would likely be the most effective to use a gas tank to power a solenoid for toggling, but for the scope of the class we wanted to power our linkage with 2 smaller servos.

Foil Design and Angle:

A critical part of the efficacy of the design stems from the actual wing design as well as the angle of attack it is situated at. With existing data from our past years cars, we were able to select an airfoil design we found most suitable as well as collect relevant data pertaining to our choice.  We were able to use Cd and Cl numbers from an FSAE vehicle (Lady Luck, Longhorn Racing Electric) and scale our project targets.

To further support our decision, we used available data to compare the drag coefficient at varying angles of attack.

Note: Each line represents a distinct Reynold's number, but for our low speed (est. 30 mph) the lowest Reynold's number will serve as sufficient.

We were then able to use a Computational Fluid Dynamics (CFD) simulation of the airfoil elements and target Cl (including the main element, which is not included in this project) to target an optimal airfoil angle of attack in the downforce state. This is also covered in a more relevant context in the "Physical Protoype" tab.