High Oscillations in 6DOF Aircraft Dynamic Simulation

I am using Simulink to model 6DOF Aircraft Dynamics, and I have confirmed that the dynamics, attitude and environment work correctly by plotting an orbit with no aerodynamic forces and moments. When I introduce the aerodynamic force and moment calculations that come from this source: https://ntrs.nasa.gov/api/citations/20040110310/downloads/20040110310.pdf I start to get incredibly fast oscillations in my states as shown in the image.

I have modelled the F-16 aerodynamics a couple of times and yield the same coefficients, so I am not certain what the cause of this oscillation is.

The integration method used is ode4 with fixed timestep of 0.01.

[John D'Errico]

So, you changed the problem, by adding extra forcing terms, and suddenly, things go to hell? The probem is now probably stiff, and you will need either a solver that can handle a stiff system, or a significantly shorter time step. That presumes you implemented those foring terms correctly.

What solver you should be using, I have no clue, since I'm not a Simulink user. But I would start looking there, at least after you carefully verify how those terms were put into the model.

Answer 1

[Corey Slick]

We had a similar problem recently and realized that the order of our damping terms did not match the order of the output angular velocity terms from the 6DoF block.

Answer 2

[Sam Chak]

Hi @George

Given that an F-16 aircraft is capable of achieving a maximum speed of Mach 2, it may induce the aeroelastic flutter.

Source: https://engineering.jhu.edu/fsag/research/aeroelastic-flutter/

[George]

Since I do not have a controller in the model yet this could be the issue since the F-16 does have pitching instability.