Strengthen wing skin 3-4 connection - part 4 - construction of shims and doublers

The skin 3-4 doubler is constructed from 0.8mm 6061-T6. The skin 3 shim is made from 0.63mm 6061-T6, to match the thickness of skin 4.

There are three shims and doublers per wing: front, middle, and back. The reason for having to split this strengthening system into three parts is to allow for the uninterrupted placement of the stringers. The front doublers are 197mm long and 60mm wide, while the middle and rear doublers are 194mm and 60mm wide. The matching shims have the same lengths, with a width sufficient to allow them to protrude out from under the doubler to allow some degree of manipulation while they are being slotted into place. Mine were 23mm wide. The shims are given a precise straight edge so they can butt closely with the edge of skin 4. This is thought to improve resistance to deformation of the metal at the edge of skin 4 under load.

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