Abstract
Designing a prototype for the Shell eco-marathon competition contains a huge amount of different engineering disciplines. The goal in the end is to design and create a prototype that pushes the boundaries of ultra-low energy consumption. This report studies the entire design process of a prototype’s monocoque, built for entering this famous competition. The conceptual design of the vehicle is mostly limited by the competition’s technical regulations. With the concept fixed, the detailed design could start. Since aerodynamic drag is a very important factor in improving fuel efficiency, we decided to use a 2D wing profile from the aerospace industry as a basis for the monocoque’s design. A design loop resulted in a typical airfoil (NACA 0020-65), with minimal drag coefficient, taking into account the vehicle’s low velocities. Revolving this 2D profile basically gives the ideal 3D shape for the prototype. The combination of the monocoque’s main 3D form and wheel fenders then has been subjected to CFD calculations, to verify the 3D design. Some minor changes to the 3D design had to be made, decreasing Cd with 2.4%.
Another important factor for improving fuel efficiency is the vehicle’s weight. To minimize the weight of the monocoque it we had to integrate the subcomponents’ design into the design of the monocoque at a very early stage. This has the advantage that the design of the CFRP monocoque can be optimized already in the design phase.
Concurrent engineering was therefore indispensable to obtain a fully integrated design. Design integration along with some FEM-calculations and a -for the competition- unique fabrication method resulted in a monocoque weight of around 7kg.
Next to the numerous aerodynamical and structural calculations the ergonomics of the vehicle where studied. Focused lied on optimizing the window surface and investigate whether the pilot would be able to reach all necessary controls of the vehicle. All the efforts made during the design process paid off since the vehicle passed the technical inspections on the 2010 Shell eco-marathon without any problems.
Keywords: Composite design, low-speed aerodynamics, fuel efficiency, Shell eco-marathon, monocoque, concurrent engineering