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Since we have 3D discretized numerical solution, we can easily integrate over the rocket area and define CP per the classic NASA Beginners Guide. Since the CFD includes viscous effects, I added wall shear stress magnitude into the calculation.

I think this approach make sense, and I think I calculated correctly. Regardless, the X result (Cp) did not change very much due to the addition of wall shear in my test cases.

I compared the CFD outcome to 5 other simulators. The CP locations in the figure below are color-coded to the tool used. CFD uses numerical Navier-Stokes continuum equations governing the air flow around the entire rocket, while all the others are Barrowman-based normal force, part-wise methodology.

The CFD result for CP falls in the cluster of predictions near the leading edge of the fin root. The OR + Base Drag Hack is the outlier since it radically violates Barrowman's theory. This Fat Boy case was the prototype for Levison's hack. I don't think you are doing yourself any favors by artificially moving the CP rearwards with a giant cone stuck to the back of the rocket and giving yourself a false sense of stability.