We continue extruding, grabbing and scaling until finishing the fuselage.
Then we go to the side view (NUM3), load the side background and select all the vertices of one cross section (The best way to do this is with the BKEY and drawing a box around the section, but you must ensure you are not in solid mode. If this were the case, you should go to object mode with TAB, press ZKEY and return to edit mode with TAB).
We adjust the section to the side profile by grabbing and scaling it RESTRICTING these movements to the Z axis.
