Subdivision surface problems

I have some issues with the subdivisions.
I would like to know how to go from a curved surface to a cut surface with straight edges without destroying my curved shape.

The simplest example is for example a fuselage with a hole for the cockpit.

I put you 2 images to illustrate my point (you could see the “pinch” mark by an arrow.

Thanking you in advance for your help.

The answer to that is straightforward: use more geometry. If you put high-frequency detail next to low-frequency detail with subsurf (in other words, if you put tiny polygons next to large polygons), you’re going to get pinching.
Use more geometry to define the curvature first, then cut in the smaller details.

shape_no_pinch.blend (161.3 KB)

Thanks a lot for the answer and the file.

The only way I have found to subdivide like you, is to start with 1 plane subdivide(level 2), apply the modifier and then subdivide again(level 1). I saw that you use the “boundary smooth” keep corner. Is this the method?

If I’ll want to modeling with subdivide patch I’ll must use this method?

Thanking you in advance.