Thank you for the kind help!
@m_adam: The plug-in you have linked is very useful. I could fix some problems with the "Select polygons by normal direction" function.
Working with badly constructed meshes is no fun job either way.
is there a way to flip all the face normals for selected polygons in one direction, especially in python?
The intended purpose is to fix a completly "broken" mesh to correct the background culling for Unity.
Thanks in advance!
All stair polygons should face upwards.
Tried align normals and optimize commands, but they did not work with this mesh.