Rebuilding Spar #4:
In a similar fashion to Spar #5, which we covered HERE, Pioneer’s Craig Cunha and a colleague carefully removed Spar #4 from the wing center section structure. They then disassembled it into its component parts, assessing each for its potential airworthiness. Bead-blasting each part revealed a good number which could be restored to flightworthy condition, while those too corroded for reuse still served as excellent patterns for manufacturing their replacements.
SPAR CAPS AND WEB:
While both spar caps proved to be restorable, several areas of significant corrosion on the web meant that Pioneer’s engineers had to refabricate the part, using the original as a guide. The pulley brackets riveted to the spar have also been disassembled, bead blasted and inspected. The upper sections for each of these components were corroded beyond use, so replacements were made.
A close up view showing a pair of stiffeners riveted to the aft face of Spar #4. Sadly both of these components needed replacing due to corrosion damage. The one on the right also had a significant crack near the lowest rivet hole. (image via Pioneer Aero Ltd.)
An image captured during the disassembly of Spar #4. Shown here is the large pulley bracket still riveted to the spar web. Visible in the bottom portion of the photo is the lower left hand section of Frame #6. This frame normally sits through the upper skin of the wing center section. (image via Pioneer Aero Ltd.)
A close up view of the large pulley bracket riveted to Spar #4. The light grey arc of corrosion beside the remains of the pulley mounting bolt is what rendered the upper piece unserviceable. (image via Pioneer Aero Ltd.)
Components from the large pulley bracket (see previous image) which mounts to Spar #4 are ready for re-assembly. The upper piece is a replacement while the lower is the original. (image via Pioneer Aero Ltd.)
An original part (left) and its replacement (right). The component is part of the small pulley bracket which mounts to Spar #4. The original part seemed usable initially until bead-blasting revealed the corrosion around the raised boss. (image via Pioneer Aero Ltd.)
FRAME #6:
The lower sections of fuselage Frame #6, which rivet on to Spar #4, were removed, bead-blasted and checked over. Unfortunately, the left hand frame was corroded beyond limits, as per the SBD’s Structural Repair Manual specifications. To manufacture its replacement, Craig Cunha created a forming block which fit within the original frame, using the block to shape a duplicate frame section.
The lower half of fuselage Frame #6 rivets directly to Spar #4. While the right side was salvageable, the left was not. This image shows the replacement component (with its forming block sitting inside it) beside the original component. It is hard to show in this image just how deeply the corrosion ate into the original component, but it was too severe for its airworthy reuse, but the hand written notes point out the areas of corrosion damage. (image via Pioneer Aero Ltd.)
Another view of the replacement Frame #6 component beside the original. The grid of holes at the end of the original component show were it once riveted on to Spar #4. (image via Pioneer Aero Ltd.)
Another view of the replacement Frame #6 component beside the original. The grid of holes at the end of the original component show were it once riveted on to the upper half of the frame via a joiner angle. (image via Pioneer Aero Ltd.)
PAINTING & REASSEMBLY:
With each part either refurbished or replaced, it was time to prepare them for primer painting and reassembly. The small pulley bracket was also reassembled, with its small tabs riveted to the spar web.
The small pulley bracket has been restored and is shown being test fitted onto Spar #4. (image via Pioneer Aero Ltd.)
A close up showing the replacement pair of stiffeners fitted to the aft side of Spar #4. The spar caps viewed to their top and bottom are both original. (image via Pioneer Aero Ltd.)