Main wing spar Issue 1 - misalignment of inner layer clearance holes

An earlier posting documents those main spar inner flanges which require counterboring

A survey of clearance holes so affected:

Right wing:

forward top flange - all fully offset

forward bottom flange - 3 outboard moderately offset,

Left wing:

forward top flange - 2 outboard moderately offset,

rear top flange - all moderately offset

Even with the right-angle tools, access to holes was improved by unbolting the spar caps. With the left wing rear facing flange, access was further improved by removing those stiffeners attached by aluminium rivets. Of course the solid-rivet fastened stiffeners were left in place. Only 4 clearance holes directly lined up or adjacent to those stiffeners could not be accessed.

A 1/4" counterbore with #21 pilot was used to recentre the clearance holes, providing optimal clearance for rivet tail expansion. In many cases, where a slight gap existed between the spar layers it was possible to clean out this hole completely while not contacting the outer flange layer. For the rear facing flange, the layers were in contact and in this case it was usually not possible to reliably clean out the clearance hole layer (so as not to leave a wafer-thin layer of metal which could cause problems later) without contacting the outer layer to some degree. Given that this outer layer is 3.2mm thick and given that in the TSi such a layer is considerably altered by countersinking (albeit from the exterior), it was judged acceptable if not more than 0.2mm or so of the outer layer was removed ("touched"). A rubber-grit bit was used to smooth/polish any notable evidence of chattering or roughness left by the counterboring bit, particularly if the finishing operation was done by hand-twirling.

In these cases the anodizing was stripped away - a alodine pen was used to reapply some level of protection to the metal. This will be combined with Duralac Yellow for the inboard stainless steel rivets, and Duralac Green as usual for all the other rivets.