Question on AR_3D_factor usage in compute_section_aerodynamics within wing_aerodynamics in the AeroBuildup class

[willjrh]

Hi Peter,

I was hoping you could help me understand the usage of AR_3D_factor within the compute_section_aerodynamics method. This lives within the compute_section_aerodynamics in the wing_aerodynamics method of the AeroBuildup class (line 816 of aero_buildup.py on your current master branch at the time of posting).

I realize this is a 2D -> 3D correction, taking into account some basic geometry parameters, coming from aerolib.CL_over_Cl. When calculing the sect_CL, we take the AR_3D_factor and raise it to the power of 1/5. I was wondering why we don't use the parameter as-is, and why the fifth power is used?

I looked at comparing an alpha sweep against higher fidelity analysis (outside of asb) and it does seem to be quite far off. Admittedly it was for a wing with an aspect ratio of two, so this is likely pushing the correction pretty far!

Just wondered if you could give some reasoning on the 1/5 power.

Thanks for all your ASB work, really an amazing tool!

Will