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High Oscillations in 6DOF Aircraft Dynamic Simulation

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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.
  1 Comment
John D'Errico
John D'Errico on 6 Jul 2023
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.

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Answers (2)

Corey Slick
Corey Slick on 14 Jul 2023
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.

Sam Chak
Sam Chak on 6 Jul 2023
Given that an F-16 aircraft is capable of achieving a maximum speed of Mach 2, it may induce the aeroelastic flutter.
  1 Comment
George
George on 7 Jul 2023
Since I do not have a controller in the model yet this could be the issue since the F-16 does have pitching instability.

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