Stability analysis

[Simon Boudoux]

Good afternoon, 

I have a few question about VSPAERO and stability analysis. When I run VSPAERO with the Steady option in the Advanced option i have my stability files but i wanted to know when i checked my values in the file specifically for the q section i have really strange values (cf files), specifically for CMn. In that case, i have few question to be sure also to run the analysis well :

- First, what center of reference use VSPAERO to perform every measurement on my model ?
- Secondly, what is the orientation of x, y, z needed to have a flow going into my model ? 
- Finally what is the difference between CFx and Cd and same for every others like CFz and CL or CMx and CMl ?

I will put attached my model and the stab file

Sincerely yours,

Simon Boudoux

[Brandon Litherland]

1. The X, Y, and Z ref values define the moment reference in VSPAERO.

2. Typically, a model will be aligned with the X-axis along the fuselage.  This is not a requirement, however.  In OpenVSP, positive X is aft or in the freestream direction at zero angle, positive Y is right as the pilot sits, and positive Z is up relative to the ground.

3. Cartesian coordinates transform to the aircraft lift/drag/side directions according to the angle transformations as expected.  

[Simon Boudoux]

Ok thanks for the answer I understand. So just to be sure along x-axis on the positive side it is front to the back ? And for the 3, it is the transformation from the wind axis if there is any alpha or sideslip to the body axis ?