Using an imported model: Why does my mesh look like this? [duplicate]

Question

I am using a purchased model, imported as an OBJ. In Blender Object and Render modes, I am seeing a mesh pattern I am not used to seeing on stuff I create myself:

Much of the model, in object mode, has a strange-looking waffle mesh, which affects the render as well as the solid view. In Object properties, the max draw type is set to solid:

... And portions of the mesh appear in a mix of solid (like the area near the front and cockpit door) and waffle mesh.

I suspect I am about to learn something about Blender: Why does my mesh look and render like this?

Thanks rg

EDIT : As requested, here is a small portion of the mesh:

Answer 1

The mesh imported did indeed use custom normals. The solution as posted worked perfectly:

You have Custom Split Normals Data added to the geometry, to fix this, while selecting the object, go to Data Tab in Properties Panel, scroll to find Geometry Data, and click Clear Custom Split Normals Data. enter image description here More information about this issue: Strange black shading. Cannot fully light mesh. (Cycles)