Thread: Problem with yaw moment diagram

1. Problem with yaw moment diagram

Hi everyone,

my name is Alexander and I write from Lund Formula Student in Sweden. I'm having some difficulties producing yaw-moment-diagrams with constant corner radii. As can be seen in the picture below, the diagram with infinite corner radius looks reasonable(?) (I'm using the SAE-axes convention), however, the one with a constant corner radius (and therefore varying yaw-rate which affect slip-angles) seems incorrect to me. For example, when beta=0 and delta=0 the yaw-rate should be zero(?) and therefore all slip-angles should be zero as well (which also means that all isolines should be shifted vertically compared to the current diagram). Therefore, it seems to me that the yaw-rate converges to an incorrect value in my iteration loop. When there is no yaw-rate (infinite corner radius), the slip-angles and lateral acceleration converges to reasonable values. Any hints as to what I'm missing? How do you correctly calculate the slip-angles iteratively when they depend on vehicle speed and yaw-rate? I'm using a four-wheel bicycle model with parallell steer and equal slip-angles left to right on each axle.

Some car parameters and the beta/delta sweep range differ between the diagrams, so don't compare absolute values. The solid lines are the delta isolines and the dashed lines are the beta isolines.