Rib #7

While all the other wing ribs are made from simple plywood panels with spruce stiffeners, Rib 7 is of a particularly robust construction. It absorbs a large proportion of the loads transmitted by the main landing gear and transfers them into the wing structure. Its box construction is therefore made from walnut (!), plywood stiffeners and multiple layers of plywood. It is also connected to Rib 6 by means of plywood gussets.

The search for walnut of the highest quality led me to Mr Bider of Aecherli in Regensdorf. This resulted in a remarkable connection with aviation history: Mr Bider is a descendant of Oskar Bider, the Swiss aviation pioneer. In this way, the construction of this rib brought a family tradition in aviation full circle.

Construction of the rib began with the upper and lower caps, made from walnut. These were laminated from individual boards and assembled with plywood stiffeners to form a sturdy box. All corners were reinforced with poplar strips, after which the first plywood side panel was bonded in place, giving the structure its basic shape and strength.

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The outer contour of the box was then machined to the required wing profile on a five-axis milling machine. Next, the full-length rib caps, made from laminated spruce, were fitted, together with the plywood gussets connecting Rib 7 to Rib 6.

Finally, the completed rib was machined once more on the five-axis CNC milling machine to achieve the exact final wing profile.