Carbon Bulkheads and Interfacing

New to Solar Racing? Read What is Solar Racing? for a quick overview.

Scope and constraints

The bulkheads are carbon-fibre sandwich panels that link the aerodynamic shell to every subsystem in the car. The goals were clean load paths, minimal mass and fast service on the side of the road. Key constraints were the occupant cell and roll structure, the external aero shell and keeping ideal subsystem packaging intact where possible. Several bulkhead features also tie into the Solar Array Hinging and Charging Setup and the driver Four Bar Hinges for Egress. For body shape, drag targets and trade-offs, see Solar Car Aerodynamics.

Design

Bulkhead design started as soon as the aerodynamic concept was selected. Early panels were used to let mechanical and electrical teams place their hardware while the aero body matured. We iterated many times in SolidWorks with full-assembly snapshots to surface clashes early, then locked the aero body and drove into detail design.

Load paths from front suspension, steering, the occupant cell and the battery pack drove most geometry. The final layout uses:

• Two longitudinal bulkheads running front to back. These mount left and right front suspension, constrain the battery and form one wall of the occupant cell.
• Two diagonals tying suspension loads into the shell. The rear diagonal also carries hardware for the Solar Array Hinging.
• Several lateral bulkheads that run left to right for remaining mounts and stiffness over the 2.0 × 4.6 m body.

Battery constraint

Rules require the battery pack to be constrained for 20 g in all axes. We explored options to balance removal for service, complexity and mass. Three bulkheads around the compartment plus a local foam-core region in the shell constrained most directions. The final restraints addressed the remaining axes without adding heavy frames.

The final design uses rated eyelets on the aero body and the longitudinal bulkhead with two cam-buckle straps to take the remaining loads. It is fast to remove, light and passes checks. Thermal routing and monitoring are handled by the battery cooling system.

Manufacturing and assembly

Panels are carbon sandwich with local solid carbon in high-load zones. We used secondary bonding to install panels into the shell, then tied in seat mounts, pedals, steering, battery, LV boxes and array feedthroughs.

After bonding, a two week integration push drilled mounting holes and cable pass-throughs and added local reinforcement where needed. Examples include carbon tubes embedded in light core for the rear suspension, and 1 mm monolithic plates under bearing seats. Interfaces for the Four Bar Egress were captured so service stays clean.

Testing and checks

• Fit and access checks for all service panels and pass-throughs
• Torque retention on inserts and hard points after vibration
• Visual inspection of bonds and overlaminate edges
• Dry run of removal and re-install of the battery box

Materials and notes

• Carbon sandwich with foam cores; local solid carbon under mounts
• Structural adhesive with controlled bondline thickness
• Simple drill templates and edge distances to keep holes consistent

What I would refine next

• Capture more mounting holes and pass throughs in CAD before bonding, so less of the integration push happens inside the car
• Cut lightening and service holes earlier where load paths allow
• Standardise insert and hard point patterns so late mounts reuse existing templates

---

Related projects

• Solar Car Aerodynamics
• Solar Array Hinging and Charging Setup
• Four Bar Hinges for Driver Egress
• Transparent Light Covers