Installing the wing centre section
Friday, 30th May, 2014
By mid-April, with the woodwork for the port and starboard main planes mostly complete, it was time to consider joining the major sub-assemblies together, starting with the wing centre section and fuselage. First I needed to do a preliminary check on the dihedral. The process is simple enough: I mounted the flat base of the centre section on a raised plinth of 2-in. thick model board (the lower half was left unfinished for this very purpose), clamped the outer wing panels securely in position and measured the height of each wing tip relative to my building table. If the surface of my table is true – and I have checked it – then the outcome is encouraging: just 1.5 to 2 mm difference over a span of some 7 ft!
Thus reassured, I resurrected the six plywood half-sections cut a year or so ago, and finally completed the centre section, a task that included grafting into the leading edge the tubular housing for the gun camera, complete with its plug of clear plastic turned and polished to simulate a lens cover. This was also the final opportunity to mark and drill the protruding ash stub spars for the all-important wing bolts, since with the centre section permanently in place this operation would be impossible. There are seven bolts per wing: two pass horizontally through the main spars with a single equivalent for the rear spar; there are also four smaller bolts set vertically to consolidate the dihedral angle by pinching the centre section’s stub spars tight to the plywood basal web of the wing panel. Over-engineered? Almost certainly, but better safe than sorry!
The wing centre section is designed to slot onto the sturdy 4mm ply web embedded into the mid-line of the fuselage, and is held by two bolts passing through its transverse spar and into the fuselage structure. But that’s not the entire story: significant lateral strength and rigidity is gained by means of a set of alloy right-angle brackets, which are bolted two each side. These join the centre section’s basal web to the protruding vertical extensions of fuselage sections 10 and 7, and thus are made to serve as attachment points as well as playing their part in defining the shape of the wing root fairings.
With the two sub-assemblies now bolted tightly together, I set the entire fuselage up on my building table with its vertical datum set true. With the wing panels reinstalled and clamped, I checked the dihedral once more before drilling through all the wing-bolt holes, using my recently pre-drilled holes in the stub spars as a guide.
This had been a make or break stage, since it put to the test the methodology I had contrived for mounting the wings to the fuselage – a moment of truth for the model! Happily, everything seems to be working as planned: the dihedral in both wings sets true, the trailing edges of the centre section and outer wing panels marry up beautifully and the whole assembly is proving extremely strong and rigid. At this stage at least it appears that I’m on track.