How to slice this wing so it has a smooth infill like perimeters
I found a great solution!

In Cura, there is a setting under Shell called Horizontal Expansion. What this does is it controls the distance between the two perimeters. A negative value in this field will make them come closer together, thus removing the gap between them.



I found that -0.1 is the perfect value for 1 mm thick walls like the ones in my design. So I set it to -0.1, then set the infill to 100% because in some spots the thickness is a little bit more than 1 mm, so the infill closes the gaps in those places. Here is the result:



You can see the perimeters are now sticking to each other and there is no gap between them. The result estimated weight is 71 g, which is a quite good reduction from the estimated 92 g when not using horizontal expansion.