Re: [Jsbsim-devel] Slaved FDM

[Jon S. B. <jon...@co...>]

> I was visiting the openAE website and the image of Virgin Galactic's
> launcher/spaceship duo reminded me of earlier dicussions here
> concerning running JSBSim in a slaved mode.  To be clear, by "slaved
> mode" I mean running the FDM for the carried object, in this case the
> spaceship, in a mode which looks to an outside application for position
> and orientation.  In this case the slaved object would run the EOM
> backwards to keep the velocity and acceleration values populated with
> meaningful values, so that at the time of release (when the object is
> un-slaved) the EOM can then be run normally with proper initial values
> all along the EOM chain.
> 
> Would this be a good time to renew discussion?
> 
> Note:
> In this scenario I see the launcher as an AI object only, not as a
> JSBSim-powered object.


It has long been my hope to develop the "child" modeling capability that
currently has "stubs" set up in JSBSim. The idea is that a <child> element
within a "master" aircraft config file would cause the instantiation and
loading of an FGFDMExec instance that is controlled by the master FGFDMExec
instance. The child vehicle would update its state vector (location,
orientation, velocity, attitude rates) based on the master (parent) vehicle.
The child vehicle would be placed at a known location that relates the
Vehicle Reference Point (VRP) of the parent and child vehicles. But, there
are a lot of details that would need to be worked out for this to work. I
think Dave is proposing something different than the multi-body sim
capability that I am describing.

For all cases, though, there does need to be a way to set the state vector
for a given vehicle. That would have to include setting past values, as
well. Then there's the question of how you detach a child vehicle. And lots
of other questions.

Jon