A drawing depicting the top surface of the SBD's Wing Center Section showing where the lower halves of Fuselage Frames #2 through #6 protrude through the skin panels. The two circular inset images reveal the fore and aft sides of the diaphragm panel which spans Fuselage Frame #4 in greater detail. (image from p.71 of the A-24/SBD Illustrated Parts Manual)
A drawing depicting the top surface of the SBD's Wing Center Section showing where the lower halves of Fuselage Frames #2 through #6 protrude through the skin panels. The two circular inset images reveal the fore and aft sides of the diaphragm panel which spans Fuselage Frame #4 in greater detail. (image from p.71 of the A-24/SBD Illustrated Parts Manual)

Overview:

The SBD's Wing Center Section assembly incorporates the lower sections of several fuselage frames, including that for Fuselage Frame #4. Together with the diaphragm spanning its forward face, this structure forms the rear wall of the pilot's cockpit. Pioneer Aero's team removed this diaphragm panel during the SBD's disassembly back in late 2023,  partially restoring it soon after.

An aft-face view of the diaphragm panel which spans the lower half of Fuselage Frame #4, seen here soon after its removal from the SBD’s Wing Center Section. The component was awaiting disassembly and assessment at the time. Note the small pulley bracket protruding from the diaphragm assembly near the top of this image (on what would be the lefthand side of the fuselage). This pulley guides the cable for adjusting elevator trim. (image via Pioneer Aero, Ltd.)
An aft-face view of the diaphragm panel which spans the lower half of Fuselage Frame #4, seen here soon after its removal from the SBD’s Wing Center Section. The component was awaiting disassembly and assessment at the time. Note the small pulley bracket protruding from the diaphragm assembly near the top of this image (on what would be the lefthand side of the fuselage). This pulley guides the cable for adjusting elevator trim. (image via Pioneer Aero, Ltd.)

Restoration:

After disassembling the panel into its component parts, Pioneer's engineers found that several pieces, like the channel stiffeners along its lower edge, were too badly damaged to refurbish. As a result, they refabricated these items using manufacturing drawings and the original pieces serving as a guide.

Happily, the diaphragm's main sheet aluminum section was in much better condition, barring one heavily corroded corner. After determining a repair strategy, however, Pioneer cut away the affected area and spliced in new material to replace it, rendering the part airworthy once more. Most of this work took place around the beginning of 2024, after which the team shelved its completion for a later date so that they could continue with more pressing concerns.

A remanufactured stiffener channel from the bottom righthand side of Fuselage Frame #4’s lower diaphragm panel is paired here with the original, sadly non-airworthy part (top) from B-22 which it is replacing. The latter component suffered from corrosion issues which were beyond repairable limits. At the time, the replacement channel was ready for reattaching to the diaphragm during its trial-fitting onto Fuselage Frame #4. (image via Pioneer Aero, Ltd.)

A remanufactured stiffener channel from the bottom lefthand side of Fuselage Frame #4’s lower diaphragm panel is paired here with the original, sadly non-airworthy part (top) from B-22 which it is replacing. The latter component suffered from corrosion issues which were beyond repairable limits. At the time, the replacement channel was ready for reattaching to the diaphragm during its trial-fitting onto Fuselage Frame #4. (image via Pioneer Aero, Ltd.)

The replacement stiffener channels for Fuselage Frame #4’s lower diaphragm panel are seen here in the process of being positioned for drilling off against the bottom edge of the main sheet aluminum section. This image was captured before the main component was repaired—note the corrosion pitting at its lower righthand corner. (image via Pioneer Aero, Ltd.)
The replacement stiffener channels for Fuselage Frame #4’s lower diaphragm panel are seen here in the process of being positioned for drilling off against the bottom edge of the main sheet aluminum section. This image was captured before the main component was repaired—note the corrosion pitting at its lower righthand corner. (image via Pioneer Aero, Ltd.)

The bottom righthand corner of Fuselage Frame #4’s lower diaphragm panel. The corrosion visible here is the only area on the diaphragm itself requiring repairs. For reference, this is the diaphragm’s aft face, with the top of the image pointing towards the SBD’s canopy. (image via Pioneer Aero, Ltd.)

The same area of the diaphragm shown in the previous image, but with the newly-fashioned repair positioned over the area which needed replacing. After having its outer edges trimmed to size, the patch was ready for primer painting and attaching. (image via Pioneer Aero, Ltd.)

Parts from a pulley bracket which attaches to the lower diaphragm panel spanning Fuselage Frame #4 are pictured here to the left of their partially completed replacements. After bead-blasting, the original components were found to have corrosion beyond usable limits. The first steps in refabricating the parts involved folding the mounting edge, then pressing in the dimpled shapes — as shown here. They were then cut to shape and heat treated before primer painting. Note, this component is visible protruding in situ from the lefthand edge of the diaphragm panel in an earlier image just prior to the component's disassembly. (image via Pioneer Aero, Ltd.)

Riveting and Trial Fitting:

With the restoration of the lower fuselage components incorporated within the SBD's Wing Center Section fast approaching their completion, as related in Update #105, it became time to finish up the effort on the diaphragm spanning Fuselage Frame #4. This included riveting the parts together and trial-fitting the subassembly onto the airframe to confirm dimensions and clearances with the associated surrounding structure. The following images describe this process.

The forward face for the lower half of the diaphragm spanning Fuselage Frame #4 after the restored and remanufactured parts were painted and riveted back together. The various holes in this structure permit plumbing and control cables to pass through it, while the large notch along the lower edge accommodates the interconnect tube linking the control columns in the fore and aft cockpits. Note the small rectangular section of sheet metal at the far left with four round holes in it and a slightly different shade of primer paint; this is where the corroded original material was cut out and replaced with a patch, as described earlier in this article. (image via Pioneer Aero Ltd.)
The forward face for the lower half of the diaphragm spanning Fuselage Frame #4 after the restored and remanufactured parts were painted and riveted back together. The various holes in this structure permit plumbing and control cables to pass through it, while the large notch along the lower edge accommodates the interconnect tube linking the control columns in the fore and aft cockpits. Note the small rectangular section of sheet metal at the far left with four round holes in it and a slightly different shade of primer paint; this is where the corroded original material was cut out and replaced with a patch, as described earlier in this article. (image via Pioneer Aero Ltd.)
A closeup featuring the bracket mounted to the upper left corner of the diaphragm’s aft face. The bracket will hold a pulley guiding a cable to the fuel selector. (image via Pioneer Aero Ltd.)
A closeup featuring the bracket mounted to the upper left corner of the diaphragm’s aft face. The bracket will hold a pulley guiding a cable to the fuel selector. (image via Pioneer Aero Ltd.)
An image showing the lower half of the diaphragm spanning Fuselage Frame #4 during its trial fitting onto the SBD’s Wing Center Section. The subassembly’s forward face is on view, demarking the rear bulkhead for the pilot's cockpit. (image via Pioneer Aero Ltd.)
An image showing the lower half of the diaphragm spanning Fuselage Frame #4 during its trial fitting onto the SBD’s Wing Center Section. The subassembly’s forward face is on view, demarking the rear bulkhead for the pilot's cockpit. (image via Pioneer Aero Ltd.)
Another perspective of the Fuselage Frame #4 diaphragm (forward face on view). Much of this subassembly comprises restored original material from B-22. This diaphragm forms the dividing line between the SBD’s two cockpits, the rear gunner’s compartment being to its rear. (image via Pioneer Aero Ltd.)
Another perspective of the Fuselage Frame #4 diaphragm (forward face on view). Much of this subassembly comprises restored original material from B-22. This diaphragm forms the dividing line between the SBD’s two cockpits, the rear gunner’s compartment being to its rear. (image via Pioneer Aero Ltd.)