kɹɪstəfɚ hafmɪn
Cross section
The elbow of the black robot arm nests into the groove of the exposed pulley wheel in front of it, which has a 1x1 round on each side. This, combined with the 1x1 brick with studs on 2 sides, the hook, and the way the cannon is attached to both sides, holds the two helicopter blade pieces back to back with enough strength to support the weight of the wings. The technic connector with the T-bar and the horizontal clip with the cheese slope both nest between the two halves. The flashlight piece just below the cockpit fits into the 1x1 brick with studs on 2 sides and helps keep the engine in place. The technic visor technique is slightly modified from Mike Nieves.
P.S.: Flickr really should bring back notes so I don't have to explain all this in words. EDIT: notes added
Cross section
The elbow of the black robot arm nests into the groove of the exposed pulley wheel in front of it, which has a 1x1 round on each side. This, combined with the 1x1 brick with studs on 2 sides, the hook, and the way the cannon is attached to both sides, holds the two helicopter blade pieces back to back with enough strength to support the weight of the wings. The technic connector with the T-bar and the horizontal clip with the cheese slope both nest between the two halves. The flashlight piece just below the cockpit fits into the 1x1 brick with studs on 2 sides and helps keep the engine in place. The technic visor technique is slightly modified from Mike Nieves.
P.S.: Flickr really should bring back notes so I don't have to explain all this in words. EDIT: notes added