Paul wrote: > I don't mind if the origin of the FDM and model can be adjustable but once > they are set they MUST be static regardless of CG changes.
The Model Reference Point (MRP) must be static, yes. The CG will change, but so will the vector from the CG to the MRP. It balances out. When the FDM reports the MRP to FlightGear, everything will be OK. > Just because the aircraft may have burnt some fuel off the FDM > should still line up with the model. > From what I understand that is not the case but I'll re-read the > entire thread again to make sure I haven't misunderstood the whole issue. Here's an example (which will also go into the documentation that I am writing as we speak): You are in an A-10 with a maverick on one side. You have an aircraft CG (which the FDM is reporting the position of) and an MRP, which the FDM is also supplying to FlightGear. The MRP is given to FlightGear in lat/lon/alt. The FDM calculates that position because it knows where the CG is absolutely, as well as where the MRP is relatively. Since the 3D model builder and the flight modeler for the aircraft agree on the MRP (we hope!) the aircraft can be placed properly in the scene. Now, say we are stationary on the runway and we drop the missile. The CG shifts instantaneously - however the FDM will not report a different position because no force has caused an acceleration which in turn could not have been integrated to produce ultimately a change in position. This is a flaw that may need to be addressed. In any case, let's assume that the FDM *did* shift the reported lat/lon/alt of the CG as reported to FlightGear by the equal and opposite amount that dropping the Maverick resulted in. The vector to the MRP would be shifted by an equal and opposite amount, and the end result would be that the model would not "jump" and the FDM and the model would agree. In the case of smooth flight where fuel burns off slowly, it's not so critical. Jon _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
