The yaw angle is the difference in direction between the direction of movement and the direction in which the car is pointing. A few similar topics that may go hand in hand with this study are the roll and pitch angles of the vehicle. The yaw angle is about the rotation in the z-axis (vertical axis), the roll angle is about the rotation in the x-axis (through front of the car and out the tailgate), and the pitch angle is along the y-axis (from the right car doors to the left car doors). All axis pass through the centre of mass of the vehicle.
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Yaw specifically comes into play when cornering or when cross-winds are introduced. The greater the yaw angle is the sharper the car turns.
One purpose of this study is to figure out the optimal yaw angle that will generate the most speed while our vehicle is cornering. The second purpose is to research and decide on an optimal aero-body of the car to achieve our goal of increasing speed.
Sources:
Basic overview - https://www.youtube.com/watch?v=1GEQwWGUEBI