Illini Electric Motorsports FSAE Team

Design and Analysis

The core structural challenge was resisting spanwise bending, torsional twist, and localized loads at mounting interfaces, all within a tight mass budget. Previous internal components were complex curved 3D geometries that required separate molds, were difficult to layup consistently, and relied on sequential bonding that introduced tolerance stack-up. Compensating with adhesive and filler to close gaps added weight and undermined the design intent. To address this, the internal structure was redesigned around a flat-stock strategy: ribs and spars manufactured as flat carbon fiber plate and waterjet-cut to final geometry. This removed the need for mold tooling, reduced layup complexity and scrap rate, and ensured dimensional accuracy at cut edges. Assembly tolerance was addressed through an interlocking cross-lap joint system, where opposing slots in the ribs and spars allow each component to self-align onto the main spar rather than accumulating positional error through sequential placement using things like jigs.

Structural concepts were developed in CAD and evaluated using FEA to identify stress concentrations and excessive deflection. Early designs showed localized stress near mounting features, which were resolved through changes in rib geometry and laminate thickness. The final design reduced mass by from 7.5lb in previous seasons to 5.86lb while also improving strength, achieved by removing material in low-stress regions and reinforcing areas of concentration.

As part of a broader team effort, I contributed to developing an FSI workflow using ANSYS Mechanical and STAR-CCM+. The workflow moves beyond static deflection targets by capturing how 3D wing deformation affects aerodynamic performance. Spanwise bowing closes slot gaps, torsional twist shifts angle of attack, and surface deformation alters the airfoil shape. Pressure field data is exported from CFD as a point cloud and mapped directly onto the structural mesh, providing significantly higher fidelity than averaged surface loading.

Manufacturing

Manufacturing decisions were driven by FEA results and the need for repeatable fabrication within a tight production timeline. Composite layups were optimized for each structural member based on stress distribution and stiffness requirements. The ribs use a [0/C/0] symmetric layup with carbon plies on either side of a Nomex core, while the spars use a five-ply carbon [0₅] layup. The five-ply spar maintains adequate geometric stiffness in the flat-stock configuration, while the cored ribs place material only where structurally necessary. All parts are laid up flat and waterjet-cut to final geometry, eliminating mold tooling and ensuring edges are dimensionally accurate.

The front wing mainplane leading edge presented an unexpected challenge. The original design called for a high-density foam core to distribute aerodynamic loads and absorb impact energy during cone strikes, but budget constraints made the specified foam unavailable. Rather than compromise on structural performance, the team pivoted to a 3D printed core designed to replicate the deformation and energy absorption behavior of the original foam. The geometry is tailored to deform and spring back under impact in a similar manner, maintaining the survivability goals of the original concept. To validate this approach, the printed core is modeled as an anisotropic material in ANSYS, allowing the simulation to account for the directional stiffness properties introduced by the print geometry and infill structure.