This view of the SBD's internal rollover structure from last fall reveals that the subassembly's strength centers primarily upon the four extruded beams which come together at a single node to form a rigid, pyramidal shape. At that point in the restoration, the primer-painted beams extending from Fuselage Frame #5 had been restored to airworthy condition, whilst the unpainted elements were damaged originals, temporarily holding the other parts in place for trial-fitting. The non-airworthy parts have now been replaced, as this article will explain. (image via Pioneer Aero Ltd.)
This view of the SBD's internal rollover structure from last fall reveals that the subassembly's strength centers primarily upon the four extruded beams which come together at a single node to form a rigid, pyramidal shape. At that point in the restoration, the primer-painted beams extending from Fuselage Frame #5 had been restored to airworthy condition, whilst the unpainted elements were damaged originals, temporarily holding the other parts in place for trial-fitting. The non-airworthy parts have now been replaced, as this article will explain. (image via Pioneer Aero Ltd.)

Overview:

As we have discussed in previous articles, the rollover structure which protrudes from behind the pilot’s seat is, by necessity, a sturdy affair, since it is designed to help protect the aircrew if the aircraft accidentally ends up on its back during landing or takeoff. At the time the image above was captured during the fall of 2024, Pioneer Aero's engineers were in the process of trial-fitting restored elements of the original rollover structure (painted in primer), using the damaged original elements in the foreground to hold them accurately in place. They have since refabricated these damaged parts, as this article will reveal. While Fuselage Frame #4 could be remade in-house from sheet aluminum relatively easily, the replacement beams extending up from it required a hard-to-find bulb extrusion - which took some time to arrive in stock.

The replacement, lefthand upper section of Fuselage Frame #4 is seen here positioned against the replacement forward rollover beam, which extends up towards the top right of the image. Lowen created a drilling template using the non-airworthy, original frame to correctly position the rivet holes in the new frame. (image via Pioneer Aero Ltd.)

A view of the replacement, righthand upper section of Fuselage Frame #4 is seen here positioned against the replacement forward rollover beam. As with the other side, the original component served as a template for drilling the holes accurately in the newly-fabricated rollover beam running from behind the fuselage frame up to the top left of the image. (image via Pioneer Aero Ltd.)

Rollover Beams:

Pioneer's engineer, William Lowen, has carried out much of the work to restore the SBD's rollover assembly. After the long-awaited bulb-channel extrusion arrived, he was able to remanufacture the two forward rollover beams for attaching to the newly-made Fuselage Frame #4. He trimmed these components to the appropriate size and trial-fitted them to the fuselage (as seen in the above two images) using a template to correctly position the rivet holes. The parts were then ready for primer painting.

Working with Pioneer Aero's Chief Engineer, Martin Hedley, Lowen then riveted the forged fittings to the top of each rollover beam. This required the use of 1/4" diameter, 'icebox' rivets, some of the largest in the SBD's entire upper fuselage.

A view inside Pioneer Aero's paint booth after primer-painting several parts for the Museum's SBD. Closest to the camera at left is the replacement upper section of Fuselage Frame #4. Nearby are the two replacement forward rollover extrusions. Also visible are components from the Wing Center Section leading edges and the tail plane fairings, which will be discussed in a subsequent article. (image via Pioneer Aero Ltd.)

The replacement forward rollover beams are seen here following the application of primer paint. While the forged fittings are held in place with temporary bolts, they were ready for riveting together at the time this image was captured. (image via Pioneer Aero Ltd.)

This image shows the rear fittings (original) after after William Lowen and Martin Hedley riveted them to the original rear rollover extrusions. The 1/4" rivets used are the largest diameter rivets in the Dauntless and, due to the thickness of the fittings and the extrusion involved, some of the longest too. They are also "DD" grade rivets too, better known as ‘icebox rivets’… This means that they are first annealed (heat treated) in an oven before immediately being placed in a freezer a short period before they are needed. When it's time to shoot such rivets, they are removed from the freezer, but they must be used within about 10 minutes or they will return to their hardened state before they can be formed into shape. This process ensures they are soft enough to be formed in their operational window, but they age harden to their final strength fairly quickly afterwards. (image via Pioneer Aero Ltd.)
This image shows the rear fittings (original) after after William Lowen and Martin Hedley riveted them to the original rear rollover extrusions. The 1/4" rivets used are the largest diameter rivets in the Dauntless and, due to the thickness of the fittings and the extrusion involved, some of the longest too. They are also "DD" grade rivets too, better known as ‘icebox rivets’… This means that they are first annealed (heat treated) in an oven before immediately being placed in a freezer a short period before they are needed. When it's time to shoot such rivets, they are removed from the freezer, but they must be used within about 10 minutes or they will return to their hardened state before they can be formed into shape. This process ensures they are soft enough to be formed in their operational window, but they age harden to their final strength fairly quickly afterwards. (image via Pioneer Aero Ltd.)

Splice Plate:

William Lowen also fabricated a replacement splice plate which sits between the parallel sets of forged aluminum fittings which knit the four extruded beams together at the top of the pyramidal rollover structure.

A view of the original, 1/4" thick splice plate (left) positioned next to its newly-fabricated replacement. This part sits between parallel sets of forged fittings at the top of the rollover structure where the four extruded beams come together. Significant corrosion damage to the original part is in ample supply, explaining why a replacement proved necessary. (image via Pioneer Aero Ltd.)

The replacement splice plate is seen here after receiving a coat of primer paint. It is now ready for final installation. (image via Pioneer Aero Ltd.)

Direction Finder Tray:

Straddling the rollover structure (level with the Upper Longerons) is a set of deck panels which extends from the top of Fuselage Frame #4 to the top of Frame #6. Most of the original parts which comprise these panels were too damaged for re-use, however William Lowen was able to salvage the Direction Finder mounting tray (discussed in Restoration Update 57), with the fully restored subassembly seen in the images below).

The Direction Finder mounting tray after primer-painting and reassembly (note that the repair patch has been riveted in place. The side ribs will be riveted in during the process of fastening it to the upper fuselage near the front of the gunner’s cockpit. (image via Pioneer Aero Ltd.)

A closeup of the repair patch riveted into the Direction Finder mounting tray. (image via Pioneer Aero Ltd.)

Deck Panels:

Since B-22's central deck panel was too damaged for reuse, it required remanufacturing. The two images of the skin section immediately below this text reveal the extent of the corrosion. Lowen fabricated replacement skins, trial-fitting them onto the fuselage as shown in subsequent images.

A corroded section of the original decking skin which sits between the four extruded sections forming the pyramidal rollover structure; it spans Fuselage Frames #4 & #5 and lies atop the upper longerons. The decking itself comprises two reinforcing rails and a skin. The original skin, seen here, is corroded beyond airworthy limits. Of note is the circular hole in the middle; it is non-standard, so will not be replicated on the replacement part. (image via Pioneer Aero Ltd.)

The opposite surface of the decking skin seen in the previous image. Ample corrosion is evident here too, which is why a replacement part was required. (image via Pioneer Aero Ltd.)

An image showing the replacement decking (now primer-painted) in position behind two of the extrusions forming part of the rollover structure. Note also that the Direction Finder tray has also been installed at center left. (image via Pioneer Aero Ltd.)

Another view of the decking structure in place beneath two of the rollover bars. The decking is in the process of being fitted atop Fuselage Frames #4 & #5 and the upper longerons; Fuselage Frame #4 is to the right of the image. (Image via Pioneer Aero Ltd.)

A view of the decking during trial fitting in the SBD's rollover structure. Note that one of the side panels for this structure is also being trial-fitted in position. (image via Pioneer Aero Ltd.)

Reinforcing Rails:

The central decking panel also required two new reinforcing rails for stiffening the skin; the original pair had suffered from both corrosion and cracking. Lowen folded new examples from 2024-T0 aluminum, and then had them heat-treated to return their strength to appropriate levels.

As noted in a previous caption, the decking comprises a section of skin with two reinforcing rails lying beneath it. This image shows the original rails and their newly-made replacements. While the original rails (seen here with attached T-extrusions) appear fully intact in this image, corrosion and cracking proved too extensive for their airworthy re-use. The new rails had been heat treated at the time this image was captured, and they are ready for trial-fitting between Fuselage Frames #4 and #5. (image via Pioneer Aero Ltd.)
As noted in a previous caption, the decking comprises a section of skin with two reinforcing rails lying beneath it. This image shows the original rails and their newly-made replacements. While the original rails (seen here with attached T-extrusions) appear fully intact in this image, corrosion and cracking proved too extensive for their airworthy re-use. The new rails had been heat treated at the time this image was captured, and they are ready for trial-fitting between Fuselage Frames #4 and #5. (image via Pioneer Aero Ltd.)

Reinstallation:

With Fuselage Frame #4 trial fitted to the associate rollover beams, the parts have since been primer painted and re-installed back in the upper fuselage. The deck panel skins have also now been drilled off to match their appropriate positions atop Fuselage Frames #4, #5 and #6. The reinforcing rails supporting these decks have been test fitted too. The "T" sections which help support the pilot's seat and upper armor plate have also been fabricated and drilled off. The rollover structure is now very close to being fully assembled!

A view of the rollover structure looking aft from the cockpit. The replacement for Fuselage Frame #4 has now been primer-painted, as has the deck skin which sits between the rollover extrusions atop the longerons. Looking further aft, the deck which surrounds the Direction Finder Mounting tray (also described in the October 14, 2024 post) has been fabricated and is in the process of being trial-fitted. (image via Pioneer Aero)

Another view of the rollover structure, this time revealing progress on the deck skin which surrounds the Direction Finder tray. The decking sits atop the longerons and is in the process of being trial-fitted, as noted in the previous image. Installing these decking panels will lock the upper edges of Fuselage Frames #5 and #6 in place; it is the final large piece of structure for the rollover area. (image via Pioneer Aero)

A closeup image showing a replacement T-section inside the upper fuselage. This particular fitting attaches the forward end of the lefthand decking support channel onto Fuselage Frame #4. It is also an attaching point for one of the mounts which holds both the pilot’s upper armour plate in place and a mounting tube (upper) for the seat. (image via Pioneer Aero)

A view of the rollover structure looking aft from beneath Fuselage Frame #4 within the pilot’s cockpit area. The two reinforcing rails which support the sections of decking between Fuselage Frames #4, #5 and #6 are in the process of being trial-fitted here - note the two, unpainted, folded sheet metal sections running below the decking skin towards the top of the photograph. (image via Pioneer Aero)
A view of the rollover structure looking aft from beneath Fuselage Frame #4 within the pilot’s cockpit area. The two reinforcing rails which support the sections of decking between Fuselage Frames #4, #5 and #6 are in the process of being trial-fitted here - note the two, unpainted, folded sheet metal sections running below the decking skin towards the top of the photograph. (image via Pioneer Aero)