The original aircraft was constructed from metal tubing and canvas. In the model, to get enough strength, I have decided to use a square internal truss. The formers are only there to give the correct fuselage shape. This has the benefit of easy construction, whilst still allowing the exterior to look like the original aircraft. The much stronger internal truss will also be able to properly support the elevator and rudders. Both the longerons in the truss, and those used to get the external shape are spruce.