You can inadvertently cause a conflict between design variables by choosing inactive or “dead” parameters that don’t have any control over your model or by adding multiple interconnected parameters to the same design variable list. For example, under the Wing Sect tab, if Span, Taper, and Root C are active, all other section planform parameters are deactivated. So just like trying to adjust the Area slider in this scenario, nothing will happen from the design variable window or files. However, if you were to add the Planform Total Area, Total Chord, and Total Span to the list, you’ll find that the values will be based on whichever parameter was changed last. Furthermore, if you try and alter the *.des text file and load values that are in conflict, your model will only update the values of some of the parameters.
One handy way of identifying potential conflicts among parameters is to see which values are updating automatically when you change a given parameter. In the above example with Span, Chord, and Area, you’ll find that adjusting the Area slider will update both Span and Chord automatically to new values. If you see this behavior, avoid adding one of these.