Overview:
In celebration of our 90th SBD Restoration Update, we thought our readers might enjoy seeing the extensive progress which Pioneer Aero has made in rebuilding the fuselage structure lying between Fuselage Frame #1 and Spar #1 in the Wing Center Section jig.
Fuselage Frame #1: Middle and Lower Sections
Fuselage Frame #1 is the forward-most structural bulkhead in the SBD's fuselage. As discussed in Restoration Update #74, this structure comprises three primary sections (lower, middle & upper) with the interior gap between them sealed by the fire wall. During the aircraft's original construction, the lower and middle sections were riveted together before being mounted in the Wing Center Section, since the aircraft's lower forward fuselage is integral to that major subassembly. They are reunited with their topmost element, however, only during final reassembly with the upper fuselage.
Pioneer's Craig Cunha refurbished/remanufactured most of the parts for Fuselage Frame #1's lower section earlier this year, but the newly-made middle section only recently arrived following heat treating. With its return, Cunha could continue rebuilding Fuselage Frame #1. Before he could begin, however, he first needed to straighten a minor twist in the middle section. Such warping is not unusual following the heat treating process—considering that the part is baked in an oven not far below its melting point, then rapidly cooled (quenched) to retain the superior mechanical properties its high-temperature crystalline state permits. Deformations are usually correctable without much difficulty, so long as the rework occurs reasonably soon after heat treating (i.e. before age hardening is complete).
With the middle section once again in its correct shape, Cunha trimmed the flange to its final dimensions then attached the part to the Frame's lower section. He then laid out the precise positions for the engine bearer attachment brackets on the frame, then marked, drilled and reamed the holes to the appropriate size.
Cunha then positioned the Fuselage Frame #1 subassembly on the SBD's Wing Center Section datum plate, with the engine bearer mounts and temporary bolts holding the it in place. He also added a new cross beam to the jig to hold the middle section (Fuselage Frame sides) in their correct locations.
The aft face of Fuselage Frame #1 seen with its lower edge nearest the camera. The lower half of the SBD’s fuselage—from the firewall to the wing’s trailing edge—is built integrally to the aircraft’s Wing Center Section, which is why this area is being restored now. It will be installed at the same time as the wing leading edges during final assembly. Note the lowly wooden support holding the lower edge of the fuselage frame—this will be replaced with dedicated steel jig structure, as seen in subsequent images. (image via Pioneer Aero Ltd.)
In this shot we can see that dedicated support plates and an extra cross beam have been fabricated and added to the Wing Center Section jig structure to help support the upper ends to the middle section of Fuselage Frame #1. The large flat plate towards the top of the image positions the lower engine bearer bolts and the datum point for Fuselage Frame #1 relative to the wing spars. (image via Pioneer Aero Ltd.)
A closeup showing the aft face of the join between the middle and lower sections of Fuselage Frame #1—the upper channel being from the middle section whilst the remainder belongs to the lower section. Also visible are two pulley brackets being trial-fitted. (image via Pioneer Aero Ltd.)
A similar view of the structure shown in the previous image, albeit from a different angle. (image via Pioneer Aero Ltd.)
A similar view to the previous image, albeit from a different angle, showing one of the pulley brackets being trial-fitted. (image via Pioneer Aero Ltd.)
Structure Between Fuselage Frame #1 & Spar #1:
With the lower sections of Fuselage Frame #1 positioned properly in the SBD's Wing Center Section jig, it was then possible to trial-fit and complete the internal structure linking this frame to Spar #1. This included the two ribs which comprise the Bomb Displacing Gear supports. Regular readers will remember that we covered the restoration of these components last October in Update #59—well, the time had arisen for Craig Cunha to locate them precisely against adjacent structure and drill them off. The bomb aiming window support bracket assembly (covered in Update #74) could then be positioned between these two ribs (and the support bracket on Spar #1), then drilled off.
The righthand Bomb Displacing Gear mounting bracket which attaches its rib to Fuselage Frame #1 is an original item from B-22, although its opposite on the lefthand side had to be refabricated. These two brackets were positioned and drilled off to their respective ribs and Fuselage Frame #1.
And finally, the SBD's righthand inboard leading edge assembly was temporally refitted to the Wing Center Section jig to confirm its clearance with Fuselage Frame #1. Some of the images below show just how tightly it squeezes into this section of the Dauntless!
A slightly different angle of the main structure between Fuselage Frame #1 and Spar #1. The righthand Bomb Displacing Gear mount bracket which attaches the rib to Fuselage Frame #1 is an original item from B-22. (image via Pioneer Aero Ltd.)
Another angle of the main structure between Fuselage Frame #1 and Spar #1. The bomb aiming window (the rectangular, bare aluminum opening closest to the camera) was designed to allow the pilot to look between his feet and sight the target before beginning his dive attack. Numerous naval types had such windows in WWII, including early models of the F4U Corsair, but their efficacy proved marginal as oil from the engine often clouded the plexiglas, making them hard to see through. (image via Pioneer Aero Ltd.)
This image shows the same structure depicted in the previous shot, albeit from a different angle which provides a slightly better view of the framing for the bomb aiming window which slots between the two Bomb Displacing Gear support ribs. (image via Pioneer Aero Ltd.)
A view from the lefthand side of the main structure between Fuselage Frame #1 and Spar #1. If you look carefully to where the lefthand Bomb Displacing Gear rib meets Fuselage Frame #1, you can see a forged attachment bracket temporarily clamped in place with a vice grip tool. This bracket is an original item from B-22. Sadly, it was damaged beyond airworthy limits, but it did prove very useful in positioning surrounding components—as depicted here. (image via Pioneer Aero Ltd.)
A closeup view of the join between the lefthand Bomb Displacing Gear rib and Fuselage Frame #1. Seen in Craig Cunha’s hand is the original, albeit non-airworthy, mounting bracket from B-22 described in the previous image; it has now been replaced by a newly-fabricated part. As noted previously, the original bracket was damaged beyond airworthy limits due to corrosion (visible on the right arm) and impact distortion. (image via Pioneer Aero Ltd.)
A closeup view of the replacement lefthand Bomb Displacing Gear mounting bracket which attaches the rib to Fuselage Frame #1. As noted earlier, the original item from B-22 was damaged beyond airworthy limits due to corrosion and distortion, but it did serve as a useful tool in accurately aligning nearby components. (image via Pioneer Aero Ltd.)
A closeup looking of the join between the lefthand Bomb Displacing Gear rib and Fuselage Frame #1 showing the replacement mounting bracket after trial-fitting—all of the rivet holes having been drilled in. (image via Pioneer Aero Ltd.)
A view of the same structure depicted in the previous image, albeit from a different perspective revealing more of the Bomb Displacing Gear support (upper side) and Fuselage Frame #1. (image via Pioneer Aero Ltd.)
A view of the same structure as shown in the previous image, but looking from the lower side of the SBD’s Wing Center Section. (image via Pioneer Aero Ltd.)
Another view of the structure depicted in the previous image, albeit from a different angle, which reveals a clearer perspective of the D-shaped cutout in Fuselage Frame #1 for accommodating the wing leading edge. (image via Pioneer Aero Ltd.)
Another view focusing upon the structure described in the previous two images, albeit from the topside of the wing in this instance. (image via Pioneer Aero Ltd.)
Bomb Displacing Gear Support Ribs & Fuselage Frame #1:
After the parts described in the previous section were trial-fitted and drilled off against one another, it was time to disassemble them for primer painting the individual parts. Once the paint had cured, each of the separate subassemblies was riveted together, then clecoed back onto the Wing Center Section jig to await the eventual addition of other components for trial fitting and drilling off.
From right to left, this image shows the lower and middle sections of Fuselage Frame #1 drying in the paint booth after receiving a coat of primer. They are now ready for riveting together. (image via Pioneer Aero Ltd.)
This view shows the web section for the righthand Bomb Displacement Gear support rib drying in the paint booth after receiving a coat of primer. It is now ready to have all of the smaller components riveted to it. Note: the lower section of Fuselage Frame #1 is visible to its right. (image via Pioneer Aero Ltd.)
After the lower and middle sections of Fuselage Frame #1 were riveted together, the subassembly was trial-fitted into the SBD’s Wing Center Section jig, as seen here. Note that the refabricated lower engine mount fittings have also been temporarily fitted. The lefthand example is seen at image left, offered up beside the replacement stiffener plate (running vertically in the image), while an original (non airworthy) righthand stiffener plate is seen temporarily attached to its engine mount fitting. The stringers seen clecoed vertically to the rear face of Fuselage Frame #1 are being positioned, awaiting fitment of the bomb displacement gear supports ribs. (image via Pioneer Aero Ltd.)
This image shows the freshly-finished left and righthand Bomb Displacement Gear support ribs in position on the SBD’s Wing Center Section jig during trial-fitting between Fuselage Frame #1 and Spar #1. It is now relatively easy to picture the curvature of the lower fuselage. (image via Pioneer Aero Ltd.)
