To generate rear downforce, to set the rearward end of the aerodynamic balance, and to keep the car stable at the speeds and yaw angles seen in autocross and endurance.
A multi-element stack on a 'reverse-spoon' main element with variable spanwise twist. The reverse spoon exists because the freestream behind the driver and the freestream near the endplate arrive at very different angles; twisting the main element moves the stagnation point off the top surface across the whole span rather than only in the middle. Aluminium swan necks take the drag load, carbon fiber rods resist the lift load, and cables provide lateral stability, so each member carries one thing.
Simplify load paths so each structural member has a single job. That is what allows the mounting to stay at 0.94 lb while the wing itself is the heaviest aerodynamic assembly on the car. Element count is a live trade, not a default. CR26E compared 2-element (9.52 lb, half-car CLA 2.9735, rear wing efficiency 2.948) against 3-element (9.87 lb, CLA 3.1824, efficiency 2.299) and against the CR25 baseline (11.58 lb, CLA 3.2327, efficiency 2.26). 1. 2D ANSYS sweeps to optimise element positions and angles of attack for each candidate element count. 2. Verify positions in 3D and increase stack angle of attack where 2D over-predicted. 3. Run integrated half-car runs with the current undertray iteration so element interaction is captured rather than assumed. 4. Full-car yaw runs to check performance when the front stack is reduced. 5. On-track validation with tufting on both surfaces and Flo-Vis oil during constant speed and skid pad.
- Increase rear wing efficiency, which is the weakest link in the package (CR26I overall efficiency 2.46 in the worst-case corner, rear wing only 2.25). - Reduce subsystem weight by 1.1 lb (CR26E goal). - Keep the center of pressure inside the 40-50% front loading window. - Move the wing forward where smaller tires allow it, without compromising the undertray outlet.
- Flow detachment behind the driver's head, visible in constant-speed tufting on the upper surface. Small but repeatable. - Leakage around rear wing elements from manufacturing tolerance and mounting wake, visible in Flo-Vis on the bottom surface. - Turbulent air from side aero devices reducing rear wing downforce and raising its drag. This is the main reason side aero is designed with the rear wing as its first constraint. - Warped fiberglass main element molds pulled from CNC foam plugs, with a visible gap at the leading edge. Fixed by machining molds directly from higher-density tooling board.
ANSYS Fluent 2D sweeps and 3D integrated half-car runs, full-car yaw runs. SolidWorks FEA for mounting (110 mph, 115 lbf drag load, 8.31 ksi peak stress, FoS 4.80) and rod buckling. Tufting and Flo-Vis for on-track flow visualisation.