RE: Ground limit and 3D model

> Cool I get the idea... it makes sense!
>
> The only problem is that I am modeling an RC aircraft weighing 6.5 kg
> and 2.2m span. Any idea what the spring constant and damping
> coefficient of the wing tips and tail skid could be?
> My under-carriage has a spring constant of 20 and a damping
> coefficient of 10 (from a quick differential equation calculation).

That's an art form in itself: calculating spring/damper coefficients for contact points.
:-) You sort of have to do trial and error testing to find the right values.

All coordinates mentioned in the JSBSim configuration file should be done in structural
frame: X axis positive towards the tail and out the back, Y axis positive out the
right-hand side of the aircraft, Z axis positive to complete a right-hand system (positive
upwards). The origin technically _can_ be anywhere. The reason for this is two-fold:

1) The FDM itself only needs _relative_ positioning. That is, how far the landing gear
bogies are from the CG.

2) The FDM can report the VRP to FlightGear.

To expand on this: the FDM calculates the lat/long/alt of the CG - that's what the
equations of motion deal with: the motion of the CG of the aircraft. When the initial
conditions are set within the FDM, and as new velocities and accelerations are integrated,
a new lat/long/alt for the CG is determined. However, since the CG moves over time, we
decided we needed a better way to report position to FlightGear, and after much lengthy
debate, decided that the VRP is one way that could make this work. What the VRP does is to
give a way to report the location of a particular point on the aircraft - a conventionally
and mutually understood (between the flight modeler and the 3D modeler) point on the
aircraft (such as the tip of the nose) so that the VRP location as reported by the FDM can
be used to place the 3D model in space.

So, my feeling (and others may have a different point of view) is that a JSBSim aircraft
model can be defined using the structural frame where teh origin can be anywhere, but
perhaps should be at the nose of the aircraft. The VRP should be in that case defined to
be (0,0,0) at the nose, also.

I'm not a 3D guy, and not familiar with the FlightGear Way of placing 3D models into a
scene, but there are others here who can expand on that.

Jon


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