Parameters measuring Axes from OpenVSP

[KAVIN P AERO]

Hello,

I have a clarification regarding the reference axes used by OpenVSP/VSPAERO for calculating (C_L) and (C_D).

If a wing is analyzed without any rotation in the XForm, I understand that (C_L) corresponds to (C_{Fz}) and (C_D) corresponds to (C_{Fx}).

However, if the wing is pitched and rolled using the XForm rotation, are (C_L) and (C_D) calculated with respect to the global X-Y-Z axes, or are they resolved along the local axes normal and tangential to the rotated wing?

Could you please clarify how OpenVSP/VSPAERO defines and calculates (C_L) and (C_D) in this case?

Thank you. Regards

Kavin P

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[Rob McDonald]

Your message footer is inappropriate for this venue.  Clearly, you have posted this message to a public forum and this message is not confidential.  Please strip such blather from further postings to this group.

CL is perpendicular to the free stream velocity -- always.  CD is parallel to the free stream velocity -- always.

VSPAERO takes a geometry - with no knowledge of how it was created - and then rotates the free stream velocity using alpha and beta.  Those are inputs to VSPAERO for the flow condition, they have nothing to do with the geometry.

VSPAERO starts with an XYZ coordinate system with X running nose to tail, Y out the right wing, and Z up.

When you rotate an individual component with XForm, you are orienting it within the global XYZ coordinate system, so you are changing its orientation at zero angle of attack.

Rob