Thanks for the tip about getting a MoI model into Autodesk 123D. That could be useful in the future. I uninstalled Autodesk 123D however. I didn't care for it much. I was eventually able to figure out how to fillet in MoI. One thing I can say about how you describe Autodesk 123D is that its convenient from a modelling perspective because it does what you want the first time. But fighting with MoI I came to understand what does and does not work. In the case of the wing example how burrman showed it makes a lot of sense from a real life perspective. They would piece the wing together from sections that extend from leading to trailing edge then apply the fillet. Rather than have a narrow wing and extend the fillet. I found this type of thing with my trial of MoI. It will work in situations where you have specified things in a manner close to reality. But having it mystically determine how surfaces that haven't been drawn should look is outside its capability. From an engineering perspective you want the human determining how things should look rather than a piece of software you may know nothing about determining it for you. The wing and the blend to the body and the body itself in reality would all be determined by careful analysis and/or testing. So those surfaces would be modeled precisely in reality. Since they all affect the performance. There wouldn't have been any question in the original engineers mind as to how those surfaces and blends would be defined. So I don't think this is something outside of MoI's capabilities. As burrman shown, once you define the wing and body, then union them together, the fillet function works just fine. I found the same method works for propellers too. Granted MoI can't fillet a surface that hasn't been defined, but to me that is a situation you should never be in anyway, so it's trivial in my eyes. Not to mention the gigantic install and goofy interface of Autodesk 123D. MoI is the better solution by far.