As previously recorded I'd made a decision early in the build to final weld the fuselage, including the wing mounts, before starting on the wings so would have to make sure that the wings would fit the fuselage rather than the other way round. The key issue seemed to be to ensure the wing incidence (angle to the air) would be precisely the same on both sides. The root ribs have cut outs that precisely locate vertically the spar brackets that in turn bolt to the fuselage. and therefore set this incidence
http://tailwindbuild.blogspot.com/2008/10/8th-october-2008-right-wing-attach.html
So a few days ago I took the first completed root rib to where the fuselage is stored to measure up. Unfortunately, what I hadn't really considered is that not only does the vertical location of the wings need to be correct but the horizontal spacing between the brackets that bolt to the wing spars has also to match the fuselage very very precisely. In fact this spacing was correct on the left side of the fuselage but there was a difference of about 3/32" on the left side. When I then compared the spacing on a main rib I found that it was about 1/32" longer than the root rib/left side fuselage and so about 1/16" shorter than the right side fuselage. The good news was that the wing incidence was correct on both sides to within 0.1 of a degree - the limits of measuring accuracy.
So, in summary, the spacing of the spars on the plans for the ribs were about 1/32" different between the root rib and the main ribs and I'd built to the plans. Also I'd welded the fuselage brackets about 1/32" shorter than the main rib on the left side and 1/16" longer on the right side. These are small differences in welding terms but would mean that the wings would not bolt up correctly if the wings were constructed to the original spacing.
The solution was as follows:
The first root rib is correct on the left side of the aircraft so leave as is.
Modify the nine finished main ribs by removing 1/32" from the front of the rear spar slot and gluing a section of 1/32" ply to the rear of the slot (4 completed so far). Modify the main rib jig to match and then construct 3 additional ribs which will complete the requirement for the left wing.
Modify the root rib jig to construct the right wing root rib with an inter-spar spacing 3/32" longer than the left and build the right root rib (completed).
Then re-modify the main rib jig to match the right root rib and construct 12 right wing ribs.
Of course the external outline of all the ribs and therefore the wings will be precisely the same only the spacing of the spars internally will vary very slightly.
Perhaps I should after all have built the wings first, but logistically this would have been very difficult.
