Linearize Implicit Nonlinear ODE System in Simulink

Hello,

what I basically want to do is to linearize my 6 Degree of Freedom Aircraft Model. I have the model built in Simulink and also have written a Trim Routine as a Matlab Script to find the stationary points of the Simulink model.

Now i want to linearize around this stationary points, with another Malab script. I know Matlab has linearization functions like linmod,..., but I'm not fully satisfied with them as they assume the ODE System in the form of

• x_DOT = fct(x, u)

I rather want to treat the more general case of

• 0 = fct(x_DOT, x, u)

as some aerodynamic derivatives like the lift also are dependent on these DOT States.

As of now i used commands like

y = feval(Model_Name,0, xB, uB, 'outputs');

to calculate the matrices A, B, C, D. But these executions of some particular phase of a Simulink Model do not give the possibility to specify different State Dots.

Does anyone know how to access these? Or is this just no possible?