Motivation
The McGill Baja SAE Team is comprised of approximately 40 undergraduate Engineering students that design, build, and race an all-terrain vehicle every academic year. The team’s objective is to optimize characteristics such as acceleration, lap time, manoeuvrability, handling, and hill climb abilities through an engineering approach to the design and manufacturing of every component of the vehicle.
The spirit of this design project is to look at a characteristic of the Baja that have never been studied by the McGill Team: aerodynamics. While not critical to the core function of the Baja, with a top speed of 65 km/hr it may be a viable way to reduce lap and acceleration times. Some successful SAE Baja teams have introduced streamlining elements on their vehicles, such as rooftops, curved body panels and rear side panels. Furthermore, the exploration is expected to provide insight in to the real-world application of reducing drag on transport trucks.
The objective of the project is to improve lap times and acceleration performance through study of aerodynamics and reduction of drag coefficient of the Baja.
Method
Process
Problem Definition
Firewall Drag
The firewall separates the cockpit from the engine compartment and protects the driver in case of a fire or explosion. It’s location and dimension are fixed by regulation. Unfortunately, it is also the main drag producing element of the car since at higher speeds it acts as a large bluff body creating drag dominated by pressure losses in the wake.
Visibility
Accessibility
Panels behind the firewall should not obstruct access to the engine of gas tank as the pit crew must have rapid access to these parts during pit stops.
Elements that would reduce visibility for the driver cannot be considered.
Concept Generation
Inspiration
Sketches
CAD
Concept Evaluation
CFD
Computational fluid dynamic (CFD) analysis of the concepts was performed to quantitatively compare the performance of the various concepts. Using the Flow Simulation tool inside NX, we obtained plots of flow velocity, directions of streamlines, and the drag forces acting on the vehicle.
Wind Tunnel Testing
To validate our CFD results, small scale wind tunnel testing was performed. Using an Armfield subsonic wind tunnel and a 3D printed model of the Baja’s frame and body panels the drag force was measured at various wind speeds for concepts 3 and 4. The results confirmed that both concepts succeed at reducing drag with concept 3 once again performing better than concept 4.
Fabrication
To fabricate the panels, MDF molds were designed and routed using CNC tool paths generated using NX CAM software. These molds were then used in a hand lay-up process in which 5 plies of biaxial carbon fiber were laid down one by one, impregnated with resin, and left to cure in a vacuum for 36 hours.
The Parts
Results
