[Jsbsim-devel] Datcom and coefficient conversion

[Elias T. <eli...@gm...>]

Hello!
Situation: Datcom produces coefficients in the stability axis system.
JSBSim requires it to be in a body or a wind axes.
Since body differs from stabilty only at the AoA, it seems rationally to
convert stability to body.
The way to convert (assumption):
1. Get coefficients from <Airplane_Name>.out file, produced by Datcom.
2. Evaluate respective force or moment.
3. Convert F or M into Body axis.
4. Evaluate coefficients form the F or M that now in a body system.

Is that way correct? Or there are some other ways do exist?

The problem i have encountered:

Since for instance F = qbar * S* C, then qbar is an obvious vector.
qbar = (1/2)*density*V^2.
So:
1. When we do a step №2 and evaluate the Force wrt to Stability axis do we
have to express V as a vector wrt to Stability?
2. When we do a step №4 and evaluate the coefficients wrt to Body axis do
we have to express V as a vector wrt to Body?

These 2 questions seems an obvious, but since in Datcom we cannot input
Beta, and don't have it in an output file, that means we
can't get or calculate the components of V and therefore can't get qbar wrt
Body or Stability axes.

Cannot find the solution at Stevens and Lewis and Datcom User Manual.
Can anybody point how to solve that problem?

Thanks a lot and best regards.