> FWIW, the turn coordinator ball behaves *very* differently between > JSBSim and YASim and another FDM I am playing with. All supposedly > return accelerations in body axis in ft/sec squared. This means we > can't create a single turn coordinator instrument who's ball behaves > reasonably well for every FDM.
Body axes must be the coordinate frame used here, IMHO: +X forward, +Y out the right side, +Z down. The issue of whether to include the local acceleration due to gravity I'll leave for Tony to address - this is probably an issue, if my hunch is correct. > Would it be better to force the FDM's to calculate a ball deflection > in degrees/radians, No. That's not the job of the FDM, IMHO. > or do we need to investigate why the body axis > accelerations are so radically different for 3 different FDM's Yes. > (who > all are trying to model a C172.) If the FDM's do the work, then they > all have to do the failure modeling too. No! > It would be nicer to figure out what's going on ... Yes. > it seems to be more than a simple coordinate > system difference, unless JSBSim/YASim swap X/Y axes or something > strange like that. I believe we do. JSBSim uses the industry standard body axis system as described above. Jon
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