Thanks for your question. The issue you're seeing is that only a small set of signals have logging enabled by default (they're in the "Visualization" subsystem). If you want to quickly get a bunch of output signals from the simulation, the simplest thing to do is to log the Vehicle Feedback bus. This is the output signal from the "Vehicle" subsystem in the root level of the model. Right-click on that line and select "Log Selected Signal":
Once the simulation is complete, you'll see a bus in the Simulation Data Inspector that includes a lot more signals, one of which is the yaw signal you're looking for, psi (defined as the rotation of the vehicle-fixed frame about the earth-fixed Z-axis).
