What remained of the SBD’s wing center section in the jig during early October. Here we see the wing ribs for Stations 15 Left and Right (and the structure in between) standing vertically from Spar #2. (image via Pioneer Aero Ltd.)
What remained of the SBD’s wing center section in the jig during early October. Here we see the wing ribs for Stations 15 Left and Right (and the structure in between) standing vertically from Spar #2. (image via Pioneer Aero Ltd.)

Overview:

Pioneer Aero's engineers have steadily worked through the disassembly and restoration of the SBD's Wing Center Section over the past year, progressively moving from the trailing edge forwards. They have been methodical in this process, removing and refurbishing/refabricating parts for each section before taking on the next. The engineers carefully back-drilled any newly-made parts against the appropriate mounting holes in adjoining, original components to ensure the structure's proper alignment upon reassembly. This past month saw Pioneer remove the last remaining components from the Wing Center Section jig, this being Spars #1 and #2 (along with the associated interlinking structure) and some residual inter-spar ribs from the rear face of Spar #2. Removal of the latter structure formed the initial step in this task.

The remaining structure still attached to the rear face of Spar #2 prior to its removal. These ribs (#15L and #15R) form the inner boundaries for the Wing Center Section Fuel Tank Bays. The ribs attach to the Spar #2 web assembly via extrusions, which are considered part of the spar, so they will only be removed during the spar’s disassembly. (image via Pioneer Aero Ltd.)
The remaining structure still attached to the rear face of Spar #2 prior to its removal. These ribs (#15L and #15R) form the inner boundaries for the Wing Center Section Fuel Tank Bays. The ribs attach to the Spar #2 web assembly via extrusions, which are considered part of the spar, so they will only be removed during the spar’s disassembly. (image via Pioneer Aero Ltd.)

Central, Rear-facing Interspar Ribs (Spar #2) :

The rear face of Spar #2 still retained the centrally-mounted ribs once linked to the forward face of Spar #3. These ribs (either side of the centerline at Stations #15L and #15R) represent the inner bulkheads for the Wing Center Section Fuel Tank Bays. After de-riveting the sections of extrusion which held this structure to the rear face of Spar #2, Jayden Molloy was able to detach the entire subassembly and move it to his work bench. He then separated it into its component parts, and began assessing them for their potential airworthiness. He started this process by bead-blasting areas of obvious corrosion to determine its severity and whether it was worth continuing to clean the part.

The structure from the previous image following its removal from Spar #2. The horizontal panel linking between the ribs is referred to as Spar #2-1/2, because it lies between Spars #2 and #3. Rib #2-1/2L runs vertically below Spar #2-1/2 in this image; it is offset just to the left of the aircraft’s centerline. Whereas Rib #2-1/2R runs vertically above Spar #2-1/2, offset just to the right of the aircraft’s centerline. (image via Pioneer Aero Ltd.)
The structure from the previous image following its removal from Spar #2. The horizontal panel linking between the ribs is referred to as Spar #2-1/2, because it lies between Spars #2 and #3. Rib #2-1/2L runs vertically below Spar #2-1/2 in this image; it is offset just to the left of the aircraft’s centerline. Whereas Rib #2-1/2R runs vertically above Spar #2-1/2, offset just to the right of the aircraft’s centerline. (image via Pioneer Aero Ltd.)

Rib #2-1/2: This is the small rib which sits between Spars #2-1/2 and #3. It appeared to be salvageable following initial inspection and, after media-blasting the entire component, Molloy determined it could indeed be returned to airworthy condition. Following some minor panel beating, and tweaking flanges into their correct angles, it was ready for primer painting as a serviceable part.

The opposite face of the rib shown in the previous image. Note the two original extrusions clecoed to the rib. Both of these parts were deemed salvageable. They are now awaiting primer-painting. (image via Pioneer Aero Ltd.)

The lefthand side of Rib #2-1/2R after a complete bead blasting. Minor panel beating has also taken place, with the flanges returned to their correct angles. The clecoes are holding the extruded sections for mounting the part to the Spar webs The part is now awaiting primer-painting, after which it will be ready for reassembly once that takes shape. (image via Pioneer Aero Ltd.)

Spar #2-1/2: In contrast, media-blasting Spar #2-1/2 revealed significant corrosion - too much for the part to be reused. A replacement component is being fabricated as a result. Molloy has continued that effort as far as practical, leaving some edges longer than necessary, with a minimum number of holes, to allow adjustments during final-fitting. When the time arrives to install this spar into the Center Section it can jigged up in the correct position, with the mounting holes drilled against existing structure to ensure that the new components fit in precisely the correct spot.

 

Spar #2-1/2 just prior to its disassembly and inspection. For reference, the exposed surface is the forward face, while the horizontal flange nearest the camera runs along the bottom side of the wing. The areas shaded white/light grey show signs of aluminum corrosion, while those tinted red/brown are the result of staining from corroded steel fasteners nearby. (image via Pioneer Aero Ltd.)
Spar #2-1/2 just prior to its disassembly and inspection. For reference, the exposed surface is the forward face, while the horizontal flange nearest the camera runs along the bottom side of the wing. The areas shaded white/light grey show signs of aluminum corrosion, while those tinted red/brown are the result of staining from corroded steel fasteners nearby. (image via Pioneer Aero Ltd.)

Spar #2-1/2 following disassembly. The areas of corrosion noted in the previous image proved too severe for salvaging the part, so Jayden Molloy had to fabricate its replacement and new extruded sections too, as these were beyond airworthy use as well. (image via Pioneer Aero Ltd.)

The replacement for Spar #2-1/2 during the fabrication of its web and extruded sections. (image via Pioneer Aero Ltd.)

The opposite side of replacement Spar #2-1/2 to that shown in the previous image. The image was captured during the fabrication of the web, doubler plate and extruded sections. Of the parts shown here, only the righthand extruded section is original. The phenolic pieces (brown squares) are pipe guides; these also required replacement. (image via Pioneer Aero Ltd.)

Disassembling what remained in the Jig:

After Jayden Molloy drilled off the rib assembly described in the previous section, the structure between Spars #1 and #2 was all that remained in the SBD's Wing Center Section jig. Engineers Craig Cunha, Jason Harris and Hadon Smith soon got to work on this. Their first task involved drilling off the twisted, forward remains of the central bomb rack fairing on the bottom side of the airframe. With that removed, they could then access (and drill out) all of the rivets holding the lower skin panel spanning Spars #2 and #3. They also de-riveted the topside skin panel, exposing the ribs linking the spars together. With the skin panels removed, it was then possible to drill off the rivets holding Spar #2 to inter-spar ribs, and then lift the spar free for further disassembly.

A closeup view of the upper skin panel linking Spar #2 (shown) to Spar #3. Note the significant kinking in the skin, damage caused during the SBD’s wartime crash. (image via Pioneer Aero Ltd.)
A closeup view of the upper skin panel linking Spar #2 (shown) to Spar #3. Note the significant kinking in the skin, damage caused during the SBD’s wartime crash. (image via Pioneer Aero Ltd.)

A closeup view of the lower skin panel near the lefthand wheel well showing some of the bomb fairing remains standing proud of the surface. Note the pencil markings exposed on the skin usually covered by the fairing, likely marked on the airframe by a wartime factory worker. The bomb fairing was in the process of being removed at the time this image was captured. (image via Pioneer Aero Ltd.)

An even tighter closeup of the structure shown in the previous image. The corrosion to the spar cap and lower skin is clearly evident. (image via Pioneer Aero Ltd.)

This is a view inside the lefthand wheel well looking towards the upper skin panel. The light streaming through the numerous empty rivet holes indicates that the skin is almost ready to be removed. Note the badly crushed interior ribs, further evidence of how Spar #1 flexed inwards when the aircraft crashed into Lake Michigan during 1944. (image via Pioneer Aero Ltd.)

Craig Cunha drilling out the rivets holding the upper skin panel to Spar #2. Note the the structure jutting from Spar #2 at the lower right; this is a component belonging to the righthand side of Fuselage Frame #3. (image via Pioneer Aero Ltd.)
Craig Cunha drilling out the rivets holding the upper skin panel to Spar #2. Note the the structure jutting from Spar #2 at the lower right; this is a component belonging to the righthand side of Fuselage Frame #3. (image via Pioneer Aero Ltd.)
Drilling off the rivets connecting Spar #2 with the underlying structure. This closeup shows the spar’s lefthand, aft face. Note the two whitish bands of corrosion running along the web plate where the fuel tank support straps once lay. Evenly spaced along these bands of corrosion is a series of small, squarish channel sections; these once held the tank straps against the web. (image via Pioneer Aero Ltd.)
Drilling off the rivets connecting Spar #2 with the underlying structure. This closeup shows the spar’s lefthand, aft face. Note the two whitish bands of corrosion running along the web plate where the fuel tank support straps once lay. Evenly spaced along these bands of corrosion is a series of small, squarish channel sections; these once held the tank straps against the web. (image via Pioneer Aero Ltd.)

Rib Removal and Inspection:

After the team detached Spar #2 from the SBD's Wing Center Section, they lifted the remaining structure from the jig and placed it on a workbench for further disassembly. This involved removing all of the ribs which once linked Spar #1 to Spar #2. Each rib went through inspection to determine its potential future airworthiness.

Spar #1 sitting on the workbench awaiting the removal of the ribs linking it to Spar #2. The spar’s forward face is exposed, with the righthand edge closest to the camera. (image via Pioneer Aero Ltd.)
Spar #1 sitting on the workbench awaiting the removal of the ribs linking it to Spar #2. The spar’s forward face is exposed, with the righthand edge closest to the camera. (image via Pioneer Aero Ltd.)

The rib from Station #32L (i.e. from 32” left of the aircraft’s centerline) as removed from between Spars #1 and #2. The rib had yet to undergo bead blasting and assessment regarding its airworthiness potential. (image via Pioneer Aero Ltd.)

Here is the rib from Station #10R following bead blasting. Unfortunately several areas of deep-rooted corrosion were found, rendering the rib beyond airworthy use. That being said, some of the fittings attached to it were salvageable. (image via Pioneer Aero Ltd.)

Waiting to be disassembled into their component parts, Spars #1 and #2 lie atop the workbench following their removal from the SBD’s Wing Center Section jig. Spar #2 is closest to the camera, with the left end nearest. (image via Pioneer Aero Ltd.)
Waiting to be disassembled into their component parts, Spars #1 and #2 lie atop the workbench following their removal from the SBD’s Wing Center Section jig. Spar #2 is closest to the camera, with the left end nearest. (image via Pioneer Aero Ltd.)

Disassembling and Rebuilding Spar #1:

With the ribs removed, it was now possible to disassemble Spar #1 into its component parts. The upper spar cap, bent and corroded, needed refabricating, but the lower spar caps (partial), along with several extruded stiffeners and fittings, did prove to be salvageable. The original web plate, much like the upper spar cap, sustained too much damage in the crash to allow its reuse. With factory drawings to supply missing data in the distorted areas, however, it did serve as an excellent template for tracing out its shape and transferring rivet and bolt holes onto new metal for the manufacture of its replacement. And lastly, some of the damaged formed, sheet metal spar fittings have been shaped and now await heat treatment.

The righthand forward face of the web assembly for Spar #1. The unpainted area at the far right is where the undercarriage mount once sat, whilst the circular hole to it its left is where the mount for the undercarriage retract ram attaches. (image via Pioneer Aero Ltd.)
The righthand forward face of the web assembly for Spar #1. The unpainted area at the far right is where the undercarriage mount once sat, whilst the circular hole to it its left is where the mount for the undercarriage retract ram attaches. (image via Pioneer Aero Ltd.)

The web plate from Spar #1 needed replacing due to crash damage, which also rendered parts of it too distorted for service as a template. However, with assistance from factory drawings to confirm details in the uncertain areas, Pioneer’s engineers were able to fashion a new spar web based upon the original one. While perhaps difficult to discern, this image shows the righthand side of Spar #1’s web (aft face) being used to mark out the various rivet holes and fitting locations on a new sheet of aluminum. Note the original undercarriage mount forging sitting on the table nearby with a yardstick perched atop it. (image via Pioneer Aero Ltd.)

The lefthand end of Spar #1 following the removal of the web assembly. The upper spar cap (top) sustained bending damage during the aircraft's wartime crash, so needed replacing. However, the lower, partial spar cap running from the wing join to the wheel well proved to be in airworthy condition, as did the vertical stiffener at Station #56 (far left). Sadly, corrosion damage to the three remaining components in this image rendered them beyond salvage. Note: parts of the spar web assembly are visible at the top of this photograph. (image via Pioneer Aero Ltd.)

The replacement web plate for Spar #1 during its remanufacture. Pioneer’s engineers have cut out the basic exterior shape, including the large rectangular voids for the wheel wells, but have yet to complete some interior cuts. A careful inspection of the image will reveal that they have drilled numerous rivet and bolt holes into the plate as well. The smaller cutouts at each end make room for the undercarriage mounts. Note that Spar #2’s original web plate lying on the same table (at right) as are the lower sections for Fuselage Frame #3 (far end). (image via Pioneer Aero Ltd.)
The replacement web plate for Spar #1 during its remanufacture. Pioneer’s engineers have cut out the basic exterior shape, including the large rectangular voids for the wheel wells, but have yet to complete some interior cuts. A careful inspection of the image will reveal that they have drilled numerous rivet and bolt holes into the plate as well. The smaller cutouts at each end make room for the undercarriage mounts. Note that Spar #2’s original web plate lying on the same table (at right) as are the lower sections for Fuselage Frame #3 (far end). (image via Pioneer Aero Ltd.)
In addition to the web plate, Pioneer’s engineers have also been working on some of the ancillary parts for Spar #1. This image shows two of the original fittings (and their replacements) which form the arch in the spar making space for the lefthand wheel well. The pair to the left (original and replacement) forms the outer arch, whilst the other pair (replacement and original) forms the inner arch. Thankfully, the complementary fittings for the righthand wheel well both proved to be airworthy. (image via Pioneer Aero Ltd.)
In addition to the web plate, Pioneer’s engineers have also been working on some of the ancillary parts for Spar #1. This image shows two of the original fittings (and their replacements) which form the arch in the spar making space for the lefthand wheel well. The pair to the left (original and replacement) forms the outer arch, whilst the other pair (replacement and original) forms the inner arch. Thankfully, the complementary fittings for the righthand wheel well both proved to be airworthy. (image via Pioneer Aero Ltd.)