Blender Convert To Mesh

To create a beautiful fuselage or wing, for example, mesh, you might consider starting with a cylinder or beveling a cube. Now that's fine, but I suggest for the wings, that you create a cube with such a profile (Fig.1), and then apply a subsurface modifier. Alter the wigns to how you want them. Now, here comes the problem, since you are working with a subsurf mesh, how are you going to knife project your control surfaces? This is also going to make texturing tricky! Here is where Blender's convert to mesh feature comes in handy.

Essentially, what this does is apply the modifier to your object, removing the modifier yet keeping the mesh how you wanted. For example, when subdividing a cube, you'll see its outline in edit mode even if the object looks different when in object mode, thus proving that your cube is still, indeed, a cube (Fig.2)! 

To convert this to a proper mesh with no subsurf modifier as seen in Fig.3, open the object context menu by double clicking and navigate to "Convert To"  > "Mesh". The result will be a proper mesh as seen in Fig.4!