Thanks for bringing up this issue. You can try a few workarounds:
- You can change the model reference block's simulation mode to accelerator mode. Check the doc page for reference.
set_param('ParentMdl/UAV1', 'SimulationMode', 'Accelerator');
set_param('ParentMdl/UAV2', 'SimulationMode', 'Accelerator');
This should let you simulate from parent model.
2. Alternatively, you can use the fixedwing MATLAB API in a MATLAB function block. This should let you compute the derivatives of the equation of motion. You can then use integrator block to get the UAV state.