Xnp shifts back by 17% cref in newer versions of OpenVSP
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Mike Kelly
Nov 13, 2025, 11:37:03 AM (13 days ago) Nov 13
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Starting with OpenVSP version 3.45.0 the Xnp result after a steady stability analysis shifts rearward by 17% of the reference chord. Using the attached model I am seeing the following results for Xnp in the stab file:
OpenVSP 3.43.3 - 3.44.5: Panel: 7.71, VLM: 8.07
OpenVSP 3.45.4 - 3.46.0: All thick: 10.43, Mixed: 8.81, All thin: does not finish
The results prior to version 3.45 are reasonable with the panel method showing a more forward result probably due to fuselage effects. In versions 3.45 and beyond the result of Xnp being 66% of MAC behind the root L.E. does not seem correct.
OpenVSP 3.43.3 - 3.44.5: Panel: 7.71, VLM: 8.07
OpenVSP 3.45.4 - 3.46.0: All thick: 10.43, Mixed: 8.81, All thin: does not finish
The results prior to version 3.45 are reasonable with the panel method showing a more forward result probably due to fuselage effects. In versions 3.45 and beyond the result of Xnp being 66% of MAC behind the root L.E. does not seem correct.
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