creation of a bus problem

Hello,

I am creating a bus, and when tested in OMSI I see the different parts that I enter the model file.
As soon as I rotate the view to different parts disparaisent .....
Does anyone know how to make the parties remain visible regardless of the angle of view?

Thank you in advance

Here are two photos (the first opn see the three sides and the second that I rotate the view I see more than 2)

i recommend you check the options in your 3D moddler

Small

A polygon is only one-sided; if you want to see the other side then you must also make polygons facing the other direction and sandwich them together An easy way to do this is to make a second copy of the whole side and then flip the direction (there is a different way to do it for each modelling program, but ZModeller for example I think is Modify -> Rotate -> Flip).

ok thank you