Lay one of the 12x12x18-inch boxes out flat and cut 8 inches off the end all the way through both thicknesses. Draw a line 1.5 inches from the cut edge. Score this line. Cut out a 9x5.5-inch rectangle on a 12-inch side of the box between the line you drew and the fold flap of the flat box. Use this piece as a guide to cut the same shape out of the 18-inch side of the box starting at 1.5 inches from the side. Reverse the pattern on the opposite 18-inch side. Cut down the middle of the remaining 12-inch side. Assemble the box, overlapping the pieces of the 12-inch side to create a taper to the cockpit. Set this piece aside for later installation.