Weird lines appear while applying smooth option.


I am trying to model an aircraft, I am almost done with it, but when I tried to apply ‘Smooth’ to the model, it shows some weird lines. I tried fixing it by adding lines with knife tools…it helped in some places, but still there are more.

I have attached a screenshot. Have a look and lend a hand.



Without a .blend file there’s not much anyone could do now here. But it looks like to me this is a case of a really bad topology. My guess is that you still lack a lot of unconnected edges.

Along with unconnected edges, it can also come from non-planar faces (especially if said face is an Ngon) and zero-area faces.

My advice is to go over the model, redo whatever is causing the smoothing artifact and make sure your vertices are properly welded to one another.