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Implementing VNAV support in FlightGear: Difference between revisions
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Implementing VNAV support in FlightGear (view source)
Revision as of 05:50, 4 December 2013
, 4 December 2013→Parent & Child FDMs
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=== Parent & Child FDMs === | === Parent & Child FDMs === | ||
The whole VNAV effort would be simplified if we could directly | The whole VNAV effort would be simplified if we could directly run and query the FDM for some future point in time. This isn't directly supported by JSBSim. However, as a workaround, we could run a "simulation inside the simulation" by instantiating the JSBSim FDM recursively: | ||
As in, run an independent instance of the FDM as part of the FCS, to solve for specific pitch/thrust settings. | |||
And as it turns out, this is another long-standing idea/feature request, i.e. supporting recursion in FDMs and having multiple instances per process. | |||
Meanwhile, since around ~2009, this has been partially implemented in JSBSim, which now contains support for a '''<child>''' FDM element that is mated/coupled to the main FDM. The feature is still considered experimental and unsupported by JSBSim developers, it is also currently disabled by default - especially in FlightGear, where it's causing problems/segfaults. However, we can look at the corresponding code in order to learn how to instantiate an '''FGFDMExec''' instance as part of '''FCS''' system/channel in order to run an identical FDM instance in look-ahead mode, see $JSBSIM_SRC/FGFDMExec.cpp: '''bool FGFDMExec::ReadChild(Element* el)''' | |||
{{cquote|One feature in JSBSim that I began and have not yet finished (pending other things) is a parent/child capability. You can (for instance) load a Mk82 on | {{cquote|One feature in JSBSim that I began and have not yet finished (pending other things) is a parent/child capability. You can (for instance) load a Mk82 on | ||