VSP AERO - ERROR IN STEADY MODE

[Miguel Aguirre]

Hello,

In previous versions of VSPaero, the derivatives computed in steady mode used the following values for adding perturbations to the base condition:

Alpha                  +1.000 deg        
Beta                   +1.000 deg        
Roll__Rate             +1.000 rad/Tunit  
Pitch_Rate             +1.000 rad/Tunit    
Yaw___Rate             +1.000 rad/Tunit

But in the latest version (3.46)  it now uses:

Alpha                  +0.010 deg          
Beta                   +0.010 deg          
Roll__Rate             +0.010 rad/Tunit    
Pitch_Rate             +0.010 rad/Tunit    
Yaw___Rate             +0.010 rad/Tunit

Since the perturbations are very small, the changes in forces and moments are also very small (in the order of the numerical error) thereby leading to erroneuous values in the derivatives.

How can I modify/increase the perturbation values for the derivatives? 

Thanks

Miguel AGUIRRE

[Rob McDonald]

There is no way for the user to change the size of the perturbations.

The perturbations were reduced to generally give better results (for testing during development of the adjoint derivative capability).  However, when using small perturbations, you may need to tighten down some of the other tolerances and make sure you have good wake convergence.

The best solution is to use the "Steady Adjoint" method for calculating the derivatives.  You may still want to tighten down some of the convergence stuff (and make sure the wake is converged), but it will calculate an exact derivative for the case.

Rob