A view from September 13th, 2024 showing Pioneer Aero's Craig Cunha holding Spar #3 soon after removing it from the SBD’s Wing Center Section. Craig and his team have stripped down this subassembly in subsequent weeks and begun restoring or remanufacturing its various components, as described in the current article. (image via Pioneer Aero Ltd.)
A view from September 13th, 2024 showing Pioneer Aero's Craig Cunha holding Spar #3 soon after removing it from the SBD’s Wing Center Section. Craig and his team have stripped down this subassembly in subsequent weeks and begun restoring or remanufacturing its various components, as described in the current article. (image via Pioneer Aero Ltd.)

Overview:

Pioneer Aero’s restoration team detached Spar #3 from the SBD’s wing center section back in September. Since that time, Craig Cunha and Rod Hanson have disassembled this major subassembly and got to work refurbishing what can be returned to airworthy condition and refabricating those parts which cannot. Sadly the web section was too corroded for reuse, however both of the spar caps were refurbishable. Each of the latter had a minor area of corrosion, which Cunha was able to mitigate in accordance with the Structural Repair Manual. The images below reveal just what was involved with performing those tasks.

The lower cap for Spar #3 had only one area of corrosion concern following media blasting and inspection. Thankfully, Craig Cunha was able to develop a permissible damage mitigation strategy using the aircraft’s Structural Repair Manual as a guide. This involved milling the spar cap surface at a constant, shallow depth around the affected area to remove the corrosion. The missing material could then be replaced with a shim, cut precisely to fit the empty space. This image shows the spar cap after Cunha excised the corrosion with a vertical milling machine. (image via Pioneer Aero Ltd.)
The lower cap for Spar #3 had only one area of corrosion concern following media blasting and inspection. Thankfully, Craig Cunha was able to develop a permissible damage mitigation strategy using the aircraft’s Structural Repair Manual as a guide. This involved milling the spar cap surface at a constant, shallow depth around the affected area to remove the corrosion. The missing material could then be replaced with a shim, cut precisely to fit the empty space. This image shows the spar cap after Cunha excised the corrosion with a vertical milling machine. (image via Pioneer Aero Ltd.)

This image shows the insert which Craig Cunha fashioned to fill the section of lower spar cap he had previously milled to remove a small area of shallow corrosion. (image via Pioneer Aero Ltd.)

The shim, seen here temporarily clecoed in place, will fill the void in the spar cap for Spar #3 following corrosion removal. To complete the repair, Cunha will fabricate a steel strap to straddle the shim and return the spar cap’s strength to its requisite levels. (image via Pioneer Aero Ltd.)

The upper cap for Spar #3 had only one area of corrosion concern following media blasting and inspection. Thankfully, Craig Cunha was able to develop a permissible damage mitigation strategy from the aircraft’s Structural Repair Manual. This image shows the corroded area after it had been ground down a little to determine its extent. The chosen repair technique involved milling away the corrosion, fitting a shim and then overlaying the affected area with an aluminum strap to rebuild the spar cap strength. This is the same method which military personnel would have employed in WWII to repair a bullet-damaged spar cap. (image via Pioneer Aero Ltd.)

The upper cap for Spar #3 after the corrosion has been removed by cutting a small notch in the edge. The resulting void is now filled with an insert (clecoed in place here). In this image, Craig Cunha is displaying the excised section of spar cap beside the repairs. (image via Pioneer Aero Ltd.)

This image shows the reverse side of the spar cap depicted in the previous image. Here we can see the lengthy aluminum strap used to rebuild the spar cap’s strength after Cunha cut away the corroded section. The notch on the left side identifies the insert’s location. (image via Pioneer Aero Ltd.)

Stiffeners, Channel Sections and End Angles:

Ten of the twelve extruded stiffeners which run vertically along the rear face of Spar #3's web proved to be in restorable condition. These have been media-blasted to remove grime, old paint, and minor surface corrosion; a fresh coat of primer paint has also been applied. Cunha also inspected the channel sections which support the fuel tank on the forward face of Spar #3. He found that the two righthand examples were salvageable, but had to remanufacture the lefthand units. A similar situation arose with the end angles as well; one being reusable and the other not.

Spar #3 during its reassembly phase. The original, unusable spar web (aft face up) sits to the left, with the refurbished, primer-painted spar caps and stiffener angles lying atop it. The corroded, lefthand fuel tank support channels are also sitting on the old web, while their replacements and the restored righthand examples are resting on the newly-made spar web (forward face up) to the right of the image. (image via Pioneer Aero Ltd.)
Spar #3 during its reassembly phase. The original, unusable spar web (aft face up) sits to the left, with the refurbished, primer-painted spar caps and stiffener angles lying atop it. The corroded, lefthand fuel tank support channels are also sitting on the old web, while their replacements and the restored righthand examples are resting on the newly-made spar web (forward face up) to the right of the image. (image via Pioneer Aero Ltd.)

Two channel sections sit at either end of Spar #3 (forward side). Rubber fuel tank supports lie along the raised faces of these components. Shown here are the two, badly corroded lefthand examples along with their newly-fabricated replacements. (image via Pioneer Aero Ltd.)

One end of Spar #3 during its rebuild. The web and end angle are both newly-fabricated components, while the two spar caps are original to B-22. (image via Pioneer Aero Ltd.)

Fuselage Frame #5:

As some may recall, part of Fuselage Frame #5 attaches to Spar #3 (see the lead image). The left and righthand sides of Frame #5 each consist of two primary pieces. Of these, only the lower section of the righthand example was salvageable. Cunha has machined forming blocks to remanufacture the other components.

The left and righthand lower sections of fuselage Frame #5 each comprise two primary parts, one riveted to the spar and the other mounted above it (ending at the fuselage split line). The original top pieces (seen at left) both needed replacing as corrosion rendered them beyond salvage. This image shows the forming blocks for their replacements, along with an aluminum blank (center) for shaping into the righthand example and the newly-fabricated lefthand unit. (image via Pioneer Aero Ltd.)
The left and righthand lower sections of fuselage Frame #5 each comprise two primary parts, one riveted to the spar and the other mounted above it (ending at the fuselage split line). The original top pieces (seen at left) both needed replacing as corrosion rendered them beyond salvage. This image shows the forming blocks for their replacements, along with an aluminum blank (center) for shaping into the righthand example and the newly-fabricated lefthand unit. (image via Pioneer Aero Ltd.)

Skin Panel:

At around the time Pioneer pulled Spar #3 from the SBD’s wing center section, they also removed the upper skin panel assembly which lies between that bulkhead and Spar #2. Cunha's team has begun the restoration process for this component too, removing the skin from the structure. The next steps will involve remanufacturing the skin, using the original as a template. He will also dismantle and assess the underlying components as well… refurbishing what remains viable and replicating the rest.

This image shows what remains of the SBD’s wing center section in the jig. Here we see the wing ribs for Stations 15 Left and Right (and the structure in between) standing vertically from Spar #2. These ribs comprise the inboard bulkheads for the inner fuel tank bays. The skin panel which lay atop these ribs is currently being disassembled. (image via Pioneer Aero Ltd.)
This image shows what remains of the SBD’s wing center section in the jig. Here we see the wing ribs for Stations 15 Left and Right (and the structure in between) standing vertically from Spar #2. These ribs comprise the inboard bulkheads for the inner fuel tank bays. The skin panel which lay atop these ribs is currently being disassembled. (image via Pioneer Aero Ltd.)

The topside skin panel spanning Spars #2 and #3 of the SBD’s wing center section covers a significant area. Many hundred rivets hold the skin to its underlying tangle of stringers, match angles and top hat ribs. With careful planning, Pioneer’s restoration team was able to remove the skin while leaving the underlying structure as a single unit. This image shows Jason Harris drilling out rivets attaching the skin to one of the stringers towards the panels righthand edge. (image via Pioneer Aero Ltd.)

Jason Harris drilling out the last rivets attaching one of the stringers to the skin. (image via Pioneer Aero Ltd.)

The structure for the upper panel lying between Spars #2 and #3 following the removal of the skin (which can be seen propped up against the center section jig in the background). The corrosion pattern on the skin where the structure once touched it is quite evident. (image via Pioneer Aero Ltd.)

Another view of the underlying structure from the upper panel lying between Spars #2 and #3 following skin removal. This image reveals how corrosion appeared (note the whitish powder) prior to the inspection process. (image via Pioneer Aero Ltd.)