My nozzle width is 0.4mm, the shell width is also 0.4, line width is 0.4, I tried 0.35 but it just got way worse. The wall has to be only 1 layer thick because of the weight. Layer height is 0.15, but i tried everything from 0.1 to 0.2. Print speed did not make any difference, I also tried every possible speed. The stl-file is a closed model, which is printed without top/bottom layers. The thickness is not a part of the model.
I tried printing the wing of the Stearman provided by 3DLabprint, but I keep having this problem. I am using Cura, but it also appears when using other slicers. I´ve printed several 3DLabprint planes before, but never had this issue. I am using a Creality cr-10.