Obtaining stability derivatives from forced oscillations

This article explains how to obtain the stability derivatives of a design from forced oscillations

Before performing forced oscillation simulations the location of the neutral point of the wing-tail configuration must be determined. Two simulations at different angles of attack are required to determine the neutral point location. Please refer to the Stability article for more information on how to determine the neutral point.

For a statically stable design the centre of gravity is ahead of the neutral point.

Once the centre of gravity location is obtained, forced oscillation simulations can be performed. Remember to change the x_cg value in the .conf file and to re-run the preprocessor before proceeding. The preprocessor will move the origin of the body-fixed coordinate system to the new location specified by x_cg, y_cg, and z_cg. Please refer to the Configuration file section of the documentation for more information.

Creating a forced oscillation motion file

A motion file describing the translation and rotation of the body-fixed coordinate system is required to perform a forced oscillation simulation. Please refer to the Custom motion section of the documentation for additional information. To obtain the longitudinal stability derivatives of the design, a forced pitch oscillation motion is required. The pitch angle during the oscillation is defined by the following equation:

Obtaining the stability derivatives from the simulation results

The video below shows the development of the wing-tail configuration wake during the forced oscillation simulation.

Verifying the obtained stability derivatives

Last updated