I am trying to discover why the principal axes of inertia that solidworks calculates does not align with the coordinate system. Why doesn't Iy align with the Y axis in the the attached picture. Any help would be greatly appreciated!

I am trying to discover why the principal axes of inertia that solidworks calculates does not align with the coordinate system. Why doesn't Iy align with the Y axis in the the attached picture. Any help would be greatly appreciated!

Correct. I would say that an aircraft is generally symmetric about the axis that runs nose to tail, so the weight distribution is symmetric about that axis, which is the roll axis, and therefore that axis and one of the principle axes should be concentric, right?

What I was trying to suggest is that the model is not symmetric.

Try cutting the model in half along the central axis, and mirroring the result. Then run the Mass Properties again.

EDIT: Of course it could also be a bug/glitch or some crazy intended functionality caused by using the Centre of Mass in a mirror illogic.

After a meeting with another colleague, I think I figured out what is going on. I think SolidWorks makes Ix the principle axis with the least rotational torque needed to rotate the mass. In my picture shown above, the majority of the mass is located on the wings, and since the CG is located within the wings, the pitch axis requires the least torque to rotate, compared to the roll and yaw axes. I have made a couple of masses and this keeps proving true. That being said, the axes will default to the output coordinate axes if you have a homogenous isotropic mass with the origin at the center of mass. Thanks for the help Kelvin!

You wouldn't know how to export reference points in a sketch to excel or notepad would you on a side note?

Could it be that the weight or mass distribution is not symmetric about the co-ordinate system?