Strange sharp edges appear on lofts

[Anonymous]

-Inventor 2017-

Hi, I've make this wing extension and winglet almost successfully.  The last two lofts were formed OK with my 4 rail lines, but there is a thin sharp edge seen at the back edge of Loft 6 (the dark part with a straight edge in the first photo):

If I zoom in one more click, I see more crazy edge appearing on the rear of the upper part (loft 7):

One note.  I wanted to make a single loft instead of loft 6 and 7, but it complained that the transition was not smooth enough. 

I've attached the inventor part file if anyone can take a look (-Inventor 2017-).

Thanks,

Bret

[WHolzwarth]

I didn't test it for myself, but IMO the problems is caused by the closed Loft along the airfoil's trailing edge.

Split it there, or use two separate lofts, one for top, one for bottom.

You know, that you can get a perfect loft with fewer points, too?

Walter

[Anonymous · Accepted solution]

Thanks Walter. Per your suggestion I experimented with splitting the
spline at the trailing edge. To make things faster I extruded a cut to
take off the last 2.8 mm (anything less left a portion of the crazy
surface) of all the trailing edge at once. That worked great and the
designed edge was too thin anyway to manufacture.

Bret

[Steven_Gao]

It may be caused by the irregular transition in the sharp side. Can you try to adjust the position of adjacent points slightly(even a very small change) to get smoother profiles?

[Anonymous]

In the end, I rebuilt the splines: I removed the last 6 points of the sharp edge of the spline (3 on top and bottom) with the trim tool, and closed the spline with a straight line or a tangent arc. Both of these worked to give me lofts with no strange edges. 

[Steven_Gao]

Great, you may change the loft's conditions to get more smoother result. Refer to the attached picture.