Hello,

for the coupling of FAST with another program I need the aerodynamic forces on every blade element in the global (inertial frame) coordinate system.

I have been digging through the source code but I am still not sure on how to interpret the things I have found.

In the “AD_CalculateLoads” function (AeroDyn.f90) the forces calculated in the “ELEMFRC” function are written into the blade load structure:

```
...
ADCurrentLoads%Blade(IElement,IBlade)%Force(1) = ...
...
```

Then the forces are multiplied by the local axes of the trailing edge coordinate system (FAST.f90):

[code] …

! Call AeroDyn through AeroCalc() and fill FSAero() and MMAero() with

! the resulting forces (AeroForces(:)):

! NOTE: AeroForces(1) = element normal force per unit span in the m1 direction (N/m).

! AeroForces(2) = element tangential force per unit span in the -m2 direction (N/m).

! AeroForces(3) = element pitching moment per unit span in about the m3-axis (N-m/m).

FSAero(K,J, = ADAeroLoads%Blade(J, K)%Force(1) * te1(K,J, + ADAeroLoads%Blade(J, K)%Force(2) * te2(K,J,

…[/code]

But in the comments it says that the AeroForces are given in the m-coordinate system (see above).

All the coordinate systems axes seem to be defined with respect to the inertial frame.

Therefore I think the forces in the FSAero matrix are the forces in the intertial frame and therefore the ones I need.

But then still the comment about the m-coordinate system confuses me.

Are my assumptions correct or am I totally off track?

Best regards

Marc