Over the past few days I have been fitting the 18x9 longerons to the fuselage. The longeron notches in the bulkheads were deliberately left undersized initially, as recommended in the manual. When the longerons are fitted, their bending curve will differ slightly from build to build, depending on wood quality, grain direction, and similar factors.
The work requires a lot of measuring, manual correction, symmetry checks, and more measuring. I took my time with this process; and I am still not done. I have now fixed the lateral position of the lower two longerons (the ones on top in the pictures; the fuselage is inverted on the strongback). The notch depth still needs adjustment, which requires a bit more sanding and rasping. The most effective tools for this job turned out to be a Japanese pull saw and a set of coarse wood rasps.
In the photos you will notice that bulkhead C8 has been removed from the strongback. As noted in the manual, its longitudinal position is not rigidly defined and should be adapted to follow the natural curvature of the longerons. This is indeed the case: the entire aft section of the longerons follows a smooth, fair curve. Forcing them onto C8 at its theoretical station position distorts this fair line. Even a deviation of just 2 mm is visually apparent; the wood is clearly forced into an unnatural shape. The best way I can describe it: introducing a fixed constraint at C8 adds two inflection points to what should be a single clean arc. Rather than one fair curve, the longeron would have to reverse its bend direction locally at C8 to satisfy the constraint. Even the slightest deviation is immediately visible — it simply looks wrong.
