FSAE Drag Reduction System
The rear wing on the 2019 car had 5 airfoils to direct airflow and improve the downforce on the rear wheels during cornering. During straightaways, it would be advantageous for the two airfoils at the back of the wing with the steepest angles of attack to not produce as much drag. The team developed a design where those two airfoils were mounted on pins and bearings, and an air piston would tension a cable that rotated the airfoils to a 0˚ angle of attack.
The cables were designed to be attached to the airfoils with plastic rockers that mimics the airfoil cross-section but with offset mounting points for the cables. The rockers would also house bearings that would be fixed to both ends of both airfoils for easy installation. The positions of the cable mounting points were determined by analyzing the system as a 4-bar linkage. End-stops were positions to mechanically prevent over-rotation of the airfoils that could cause them to break or fall off of the rear-wing.
A prototype to test the linkage system and modified airfoil rocker cross-section was lasercut out of wood and acrylic. Plastic dowels and holes were used in place of precision pins and bearings. Rubber bands were used in place of metal springs to mechanically failsafe the system to the inactive position with the airfoils in the default position with the larger angle of attack. Nevertheless, the positions of the end-stops and cable mounting points produced a linkage system with the correct and synced rotation of the 2 rear airfoils.
For EID-101, teams of students collaborated with Cooper Union's FSAE to develop and prototype different models for a drag reduction system (DRS) for the race car. Airfoils on the front and rear wing of the car improve wheel traction by producing an aerodynamic downforce. This improves the cornering performance of the car, but it also reduces top-speed and acceleration because of the aerodynamic drag from the airfoils. The DRS aims to mitigate the drag during straights to improve top speed and maintain the downforce and improved traction before and during cornering.
To simplify the design, only a single actuator to tension a cable was designed to be mounted on the lower part of the rear wing away from the airfoils. However, two airfoils needed to rotate with this single actuator. Therefore, a cable needed to connect the two airfoils and sync their motion such that both airfoils rotated to positions with 0˚ angles of attack with a single cable retracting.
The proposed prototype design utilized a bicycle shifting cable to actuate the rotation of both rear airfoils. Experimental testing with an INSTRON machine was used to test and characterize the tension behavior of the cable to verify it would not fail during operation. The cable began to fail at 800 MPa, and because the cable was composed of a dozen individual strands of steel, it incrementally snapped until it was stretched around 4mm.
