Overview:
Pioneer Aero’s engineers have made a series of major leaps forward restoring the SBD’s Wing Center Section. This report covers the work they have accomplished so far in rebuilding each of the wing’s five, full-length wing spars. While it may seem odd for an airframe of this size to have so many wing spars, one has to remember that the SBD’s primary function was in the dive bombing role. It’s wings needed far more strength than most single-engine combat aircraft types of its day due to the enormous strain placed upon them when the pilot leveled out from a high speed, high-angle attack.
Spar #1:
Spar #1 is the closest of the full-length spars to the leading edge in the SBD's Wing Center Section. It straddles the main undercarriage bays which means there are substantive cutouts in the spar to accommodate the aircraft's bulky main wheels, adding to its complexity. With Spar #1 being the last to leave our SBD's original Wing Center Section, it was obviously the last of the five spar assemblies in the structure to undergo rebuild.
As of now, Pioneer's Hadon Smith reports that his team has refurbished (or refabricated) almost all of the components which form this major subassembly. They have trial fitted these parts together now too, and also completed the assembly and primer-painting of the inter-spar ribs connecting Spar #1 with Spar #2.
A closeup of Spar #1 during the trial fitting process. These are the components which make up the lefthand wheel well arch. (image via Pioneer Aero Ltd.)
Components for the ribs which which fit between Spars #1 and #2 in the paint booth awaiting a coat of primer paint. (image via Pioneer Aero Ltd.)
Another shot of the components for the ribs which which fit between Spars #1 and #2 in the paint booth awaiting a coat of primer paint. (image via Pioneer Aero Ltd.)
The components for the ribs which sit between Spars #1 & #2 following primer painting, and now awaiting assembly and final riveting. (image via Pioneer Aero Ltd.)
The ribs which sit between Spars #1 and #2 at Stations 10R, 0 & 10L (left to right). (image via Pioneer Aero Ltd.)
The ribs which sit between Spars #1 & #2 following the riveting process. Running along the bottom of the image are the ribs for Stations 32L/R and 48L/R, while the ribs for Stations 10R, 0 & 10L are running along the top. (image via Pioneer Aero Ltd.)
Spar #2
We reported on Pioneer’s efforts to remove, disassemble and rebuild Spars #1 and #2 from the SBD’s Wing Center Section jig back in November 2023. It marked a major milestone for the dive bomber's restoration, as these were the final untouched parts to come off that massive jig. Spar #2’s rebuild commenced soon after.
Thankfully, Pioneer was able to return several important parts to flightworthy condition, including the lower spar cap. However, they did have to refabricate the web plate, upper spar cap, and the undercarriage jack shaft support plates. These parts have now been drilled off against one another, with the web plate having also received a coat of primer paint.
These are the undercarriage jack shaft support plates (left) and support rings (right) which mount to the web plate in Spar #2. While the plates are replacement components, the originals being corroded beyond airworthy use, the rings are original. These parts are made from steel, and have now been sent away for cadmium plating, the cadmium serving as a preservative layer which helps prevent the parts from rusting. (image via Pioneer Aero Ltd.)
A view of the lefthand set of undercarriage jackshaft plates and support rings being test fitted. The square mount in the upper left corner is for an electrical box. (image via Pioneer Aero Ltd.)
The righthand forward face of Spar #2. The undercarriage jackshaft plates and support rings are being test-fitted to the spar in this shot. The square mount attached to the spar just beyond the jackshaft plate is for an electrical box. The stiffener across the web just beyond it is an original component. (image via Pioneer Aero Ltd.)
The aft face of Spar #2. The row of clips down the middle hold the fabric strip which prevents the front face of the fuel tanks from rubbing against the spar. (image via Pioneer Aero Ltd.)
Spars #3, #4 & #5:
Pioneer's efforts to rebuild these spars was obviously more advanced than the other two given the order of their removal from the jig. Indeed, Hadon Smith recently reported that they have completed the assembly of each of these assemblies as far as is practical prior to final installation in the Wing Center Section. The images below show some of the work in progress for Spars #3 and #5.
Craig Cunha (left) and Hadon Smith are seen here in the process of installing rivets connecting the lower cap to Spar #3’s web plate. In this shot, Hadon is ‘clearance drilling’ a hole prior to fitting the rivet. During fabrication, the holes are drilled to nominal size, with the rivets also being nominal size. To allow the rivet to fit, therefore, it is necessary to widen the hole diameter by a few thousandths of an inch. This occurs just prior rivet fitment. (image via Pioneer Aero Ltd.)
Craig Cunha (left) and Hadon Smith installing rivets connecting the lower cap to Spar #3’s web plate. Hadon is operating the rivet gun, which is a little like a portable power hammer, propelled by compressed air. It drives a mandrel which repeatedly strikes the rivet head in short, rapid bursts. The rivet’s tail end is buttressed by a bucking bar held either by the riveter or a fellow engineer. The mandrel, its impact face customized to fit the specific rivet head being used, thrusts the other end of the rivet into the bucking bar, flattening the rivet end until the operator decides it has achieved an appropriately sized ‘rivet tail’… after which the team moves on to shooting the next rivet. (image via Pioneer Aero Ltd.)
Another shot of riveting operations for Spar #3. Here we see Craig Cunha holding the bucking bar which shapes the rivet’s tail. Using a bucking bar of the correct shape (and weight) is essential to the completing this process effectively and efficiently. (image via Pioneer Aero Ltd.)
The aft face of Spar #3 part of the way through the riveting phase. (image via Pioneer Aero Ltd.)
Spar #3 following the completion of the riveting process as far as possible before installation. The triangle patterns of empty rivet holes close to the camera are where Fuselage Frame #5 attaches. (image via Pioneer Aero Ltd.)
A closeup showing the aft face of Spar #5 part of the way through riveting in the lower spar cap. Note how clecos are fitted into most of the holes; they help hold the cap in the correct position while the empty holes are systematically filled with rivets. Once those rivets are installed, additional clecos are removed so the riveting process can continue, a step which is repeated until all of the rivets are fitted. Temporary 'pop' rivets (visible silver rivets) were also fitted during initial assembly to help ensure each part remains in the correct position. These 'pop' rivets are eventually removed and replaced with the correct rivets once sufficient conventional rivets are in place. (image via Pioneer Aero Ltd.)
The forward face of Spar #5 during the process of riveting in the lower cap. Note how the upper cap has already been fitted, although the temporary, silver-colored pop rivets have yet to be replaced. Note how you can see the tails of conventional rivets, pop rivets and clecos interspersed along the lower cap. (image via Pioneer Aero Ltd.)
An overall view of Spar #5’s forward face during the riveting process. Note the plastic drum at the top of the image. Filled with steel shot to weight it down, it is tied to the spar to hold it rigidly vertical during riveting. (image via Pioneer Aero Ltd.)
Of these spars, Spar #3 was the most recently completed. The video below shows Craig Cunha (left) and Hadon during the process of fitting a rivet into Spar #3’s lower cap. Hadon begins the process by first drilling a clearance hole. The drill bit he uses is a few thousandths of an inch wider than the hole drilled in the part during fabrication. This allows sufficient space for the rivet to slide in. Naturally, the rivet diameter expands into this extra space when it is driven home. Cunha uses a tungsten ‘dolly’ (better known as a bucking bar in the USA) to buck the rivet’s tail while Hadon fires the gun. Choosing the correct dolly is essential to the process of forming a rivet tail of the correct dimensions. In the video, you can hear Craig calling out to Hadon, using a few carefully selected words to explain precisely what he needs his riveting partner to do. Good, clear communication between them is essential to forming each rivet to the appropriate size each time.
Spars UP!
Spars #3, #4, and #5 lying right to left on the work shop floor after completion of the riveting process, albeit with some rivet holes left empty until the reassembly of the SBD's Wing Center Section. This marks the completion of a major milestone for the project!
