Working in Rhino 5. This is a one-rail loft of a curved duct. Per the image, the basic shape is achieved, but there are two choke points where the duct is pinched closed. I also include a .3dm file. Where did I go off the track?
Hello - when lofting closed curves, you need to get all the direction arrows lined up and pointing the right way - that is what comes to mind anyway. Note Loft gives you an align button that lets you adjust if the preview looks wrong.
