Some blueprints have cross-sections, which can be put to good use. I've tried using them in 3DS Max (not yet in Blender) and can't get a good effect. The trick may be to calculate the number of sides or vertices each cross-section has, and accordingly make cuts elsewhere to keep that number uniform. Some airplane models are tricky, where the wings or engines or both are extensions of the fuselage, so the question is whether to extrude or just adjust. I haven't yet thought of using splinecages, so I'd like to know if that's a viable option in card modelling, as we can get a higher degree of curvature in at least one direction. Polygon/mesh modelling still seems the more preferred method. I have thought of putting to practice the steps mentioned in "Designing without CAD" in 3-D modelling, to create wraps for the fuselage. We'll get more accurate parts that way. That said, I find work at a workshop table more interesting than the computer- just the way I did my first few models.