On Thursday, 8 January 2004 21:03, Erik Hofman wrote:
Paul Surgeon wrote:
Is position 0,0,0 of an aircraft model the same point as 0,0,0 of the JSBSim FDM in FlightGear?
I know the JSBSim FDM defines everything using the nose as the origin but I'm trying to figure out if my model and the FDM are lined up correctly.
No JSBSim does not. JSBSim uses an arbitrary location and everything else is relative to that location. I for one use the center-front of the nozzle as (0,0,0).
To align a JSBSim model correctly you should place the static Center of Gravity at (0,0,0)
So that's what the AC_CGLOC property is for ...
Ehrm, I just discovered it is not very helpful what I said.
I should have said that the *3d models* origin (0, 0, 0) would be places at the FDM models static CG. The CG of the FDM is (again) relative to the arbitrary reference point (which still could be equal to the CG though).
I thought it was the CG offset from the nose! No wonder the darn thing wouldn't become airborne till it hit 250 knots. :-)
So if I set the JSBSim FDM CG at (0,0,0) and I model my aircraft CG around (0,0,0) in a 3D modeler I won't have to offset anything. Right?
Actually you should the FDM CG at 25% chord on most aircraft (and relative to the arbitrary point you chose as model origin).
Erik
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