It's missing some points out, so the patch doesn't match the sketch properly:-
This spline is slightly curved around an imaginary cylinder - if I project the spline to a flat plane, the patch works happily:
but that's no good for me of course - I need that wrap, and this bug should be squashed anyhow.
Here is the sketch in question:
Here is the screencast: https://autode.sk/37cka2o
I can reproduce this, and created bug FUS-75503 for this issue. Not quite sure what the issue is, since an Extrude of that same curve does follow the curve fine.
I would not call this pe-se a bug. Fusion 360 creates a trimmed NURBS surface in cases like this. I verified this in another application by looking a the CV distribution.
For curves that lie flat on a surface that is straight forward and only the simple surface with 4 control points and a trimming loop are needed
However, the airfoil curve does not lie on a plane. It is double curved, so to speak. As such the simple surface that needs to be trimmed is not simple whatsoever.
The airfoil curve is densely and unevenly populated with too many control points (both are deadly when working with NURBS surfaces) , which results in bad curvature.
Now Fusion 360 will have a hard time trying to match that mess with a NURBS surface.
Check the curvature of the splines with the curvature comb tool in the inspection menu. That provides you with all the info you need. The curvature is garbage!
Then perhaps check out the Autodesk Alias Theory builders to learn the basics how technical surfacing works.
Then, at some point in time the practical aspects of technical surface generation may catch up with your mathematical knowledge.
The curvature appears to be irrelevant. This bug still crops up on "perfect" splines in about 5% of cases. It might be related to the angle that the starting and ending points arrive together at perhaps? It's so random it's hard to work out why 95% work and why those 5% fail.
Worse, in about 10% of those 5% - it crashes Fusion 360 dead (locks up forever)
Try surface-lofting these 3 examples to observe the problems - one of the inner splines on the top-left prop blade is broken, and the tip of the bottom-right is too. https://a360.co/2VOwKiW
Fusion 360 crashes for me after I've done the top and middle blade, then try to do the last one.
This is a different problem than initially presented.
I believe in this case the difficulty for FUiosn 360 is to determine the proper location of the twist control handles.
It's a closed spline so might need some user input to work, if it works at all.
In respect to your previous comments, the software you are using is used for technical surfacing in the area of product and industrial design. I had linked to the Autodesk Alias Theory builders to provide you with a background on how that usually works. That is the background for my earlier statements of too many spline control points. Less is more!
Perhaps it's time for your practical knowledge of technical surfacing to catch up with your purely theoretical musings.
Fusion
