Perhaps this video may help:
I think that the way in which you are building the wing tip (assuming it is that type of structure) could benefit from this type of approach. This is of course assuming that your curvature is good to start with.
So fundamentally, rebuilding the end smoothly, without the many isocurves may help your cause to get smoother results, and then using the trimmed corner method will create the surface result you need.
Hello David53,
thanks for your reply.
This video is how to use some Autodesk plugin for Rhino.
Rhino start looking like Alias Stusio Tools (now Autodesk Automotive).
I was asking how to do things without plugins or subd.
Regards
Did you watch the video? @sgreenawalt uses VSR there, but the process itself can be done without it.
The basic fact of wings is that the tip needs to be handled separately with multiple surfaces, there no aircraft in the world ever that has its wing shape described as a single 2-rail sweep all the way to the tip.
As stated by Gijs, this most certainly can be done without VSR. Infact, these videos are normally explicit in stating that VSR is not needed, it is merely an aid to get to the point.
However, one plugin you will find useful for checking would be the free GlobalEdgeContinuity tool, created by Gijs. This is invaluable for this type of work.
One thing I can see here in your upper wing profile is that it looks almost like you have some form of curvature inversion. The shading towards the centre isocurve contains a bright area, which may be indicative of this curvature inversion. This will cause complication as you are trying to do surface matching towards the tip of the wing.
If you post the file I can show you really quick a better way to structure your patches - as other have noted - it’s best to loft the wing as a clean definition, and then create the tip surfaces after. Trying to do a wing and a tip as one single process will always lead to substandard results.
Thanks for reply guys,
this is the result I achieved after 2 sweep2 rails, merge and rebuild.
I delete manually some points from wingtip blend curves results.
Not sure its perfect. I got some issues loosing surface after "cap"command but all objects are closed polysurfaces now.
Is there something else I can do to get better result?
Thanks for reply once again.
You are right - there is curvature inversion.
Thanks for reply,
can you please tell me where I can get GlobalEdgeContinuity tool?
Regs
@Popoff you can download it through _PackageManager
Let me know if you have any questions regarding its usage. Pls note this is not an official ‘McNeel’ plugin, as I wrote that before I joined McNeel.
I would highly recommend taking @sgreenawalt 's offer of help. You can probably send him the file directly if you feel it is too confidential to post here.
While it looks much clearer on the version closest (left), what you will probably find here with the PointsOn command, is that the control points and the underlying surface have a lack of flow. This may cause issues if you are trying to add detail at a later stage.
While it is often tempting to use a single sweep or a blend to achieve these results, you often are triggering a double-pendulum effect, where the model and surfaces become exponentially harder and chaotic to control as you try and make refinements or add details.
I only know this, as it was only a few months ago I kept doing the same thing, until I was rescued from certain doom. 
Here’s how I would structure this:
Use Loft (Straight) for your root and tip sections, and make your desired wingtip shape with a clean blend curve.
Make a blend from a portion of your wing to your tip curve:
Make a single span curve that describes where this trimmed edge will be. It does not have to perfectly sit on your surface. It’s important to start with a clean curve, even if it doesn’t perfectly match the surface/edge that will be trimmed:
Surface From Edge Curves, using these curves as your input:
Point Edit (MoveUVN) and MatchSrf to get your final desired result to whatever continuity you’re looking for. In this case I’m going for G1/Tangent. To achieve this, I bumped the final surface up to 7/2-5/1 using ChangeDegree and InsertKnot:
-Sky
SimpleRoundedWingtip.3dm (234.0 KB)
Hello Sky G,
thanks so much for your advice, screenshots and 3dm file!
I’ll try your modeling method.
Regards
Hello Sky G,
can you please tell me how you have done this?
I stuck again on this.
Regards
Setting the isocurve density of the wing to, for example, 7, one can extend degree 3 curves off of them, snap them to the outer curve and match G2 to the wing. Isocurve ends are good locations to insert curves, such as the inner one that mimics the outer one. Then it’s easy to build a G2 solution of the same thing ; )
