Close-up of the lower wing looking towards the trailing edge. The front wing spar is seen with plywood reinforcement (note beveled ends), metal spar fitting with hole for landing wires (left hole) and interplane strut (right hole) and compression tube, and below is a wood anchor block with internal brace rods.

The plywood reinforcement is a critical part of the wing, helping the main spar carry the load from the landing wires and interplane strut.