Attached Link: http://www.turbosquid.com/gmax

You might want to add 'gmax' to that list of free sw :) (a lot of plane models for flight simulators are done with this package) It's a subset of 3dmax 4, with no rendering capabilities, but has most of the modelling/boning functions of its big brother. And it's free! ps: don't know about import/export possibilities, those are quite limited, but maybe there are some 3rd party plugins that do the job...