9 September 2016
Some ideas for making dihedral joints for shallow spars. The last one is paired with the fuselage:
- Rely on wire. Length of spar with a steel wire heat shrinked at the dihedral joint. Crack and bend the spar. The wire holds the dihedral. Advantages: easy, accurate, adjustable. Disadvantage: it relies on steel wire, so it may be too ductile or springy and perhaps it will peel away from wing because there is not much gluing area.
- Spar doubler. This is applicable to flat spars placed horizontally. A short piece is positioned against the spar at the dihedral joint. The two pieces are forced to a curve and then glued together forming a two layer ply. The main disadvantage is to fabricate a jig to hold the two pieces until the glue is set, there may also be some spring back.
- Baseplate. In the Spar doubler, both pieces were bent, but in this application, the baseplate provides a flat compressive member so it has to be stronger than the spar. The spar is tied securely to the middle of the baseplate, small shims are added between the spar and the edges of the baseplate to form the dihedral angle. Baseplate can be substituted with a rod or tube, or a fuselage former.
- Compression/tensile truss. Length of spar is cracked and glued to the underside (compressive truss) of a slim triangular former or a small rhombus former or a fuselage former. Gluing to the upperside (tensile truss) of a V-notched fuselage former is also possible.
