Overview:

Our most recent restoration report featuring the Museum's Douglas SBD-5 Dauntless described Pioneer Aero's progress rebuilding the five primary spar assemblies for the aircraft's Wing Center Section. At that time, the restoration team had completed work on Spars #3, #4, and #5 as far as practical, with the remaining work awaiting the moment when reinstallation could occur. Work on parts for Spar #2 was also nearly complete, but Pioneer needed to acquire a section of specialized extruded aluminum to replace the damaged original upper spar cap. Well, thankfully this extrusion arrived recently, allowing refabrication of the new spar cap. Soon after, Martin Hedley and Craig Cunha got to work reassembling Spar #2.

 

Spar #2 on the bench ready to have rivets installed. In the background, Jayden Molloy is giving a "thumbs up" to say that everything is ready to go. The orange masking tape which is visible in several spots along the spar indicates the locations where rivets should not be installed at this stage. Typically, the tape covers attachment holes where other components will be installed at a later date, but it can also indicate where rivets need to be installed in a certain order. (image via Pioneer Aero Ltd.)
Spar #2 on the bench ready to have rivets installed. In the background, Jayden Molloy is giving a "thumbs up" to say that everything is ready to go. The orange masking tape which is visible in several spots along the spar indicates the locations where rivets should not be installed at this stage. Typically, the tape covers attachment holes where other components will be installed at a later date, but it can also indicate where rivets need to be installed in a certain order. (image via Pioneer Aero Ltd.)

Top Cap Arrives:

As Craig Cunha noted, "With the arrival of the replacement top cap, the restoration of Spar #2 could advance significantly." Cunha and Martin Hedley positioned the extrusion against the associated web plate, and drilled off the necessary attachment holes, using the pre-drilled holes in the web as a guide. The spar cap then received a coat of primer paint. After it dried, Cunha and Hedley got to work riveting the parts together.

However the rivets which hold the spar caps to the web are all of the so-called "icebox" variety, meaning that they require heat treating to put them in a more malleable state when they are used. After heating, these rivets must immediately be placed in a freezer to slow down the return to their natural, higher hardness state - hence the name, "icebox" rivet.

The forward face of Spar #2 having rivets installed in the upper and lower spar caps. A combination of clecos and bolts are holding the cap to the web plate, ensuring that it remains in the correct location during the assembly process. Mostly obscured by the spar, Chief Engineer Martin Hedley is focused upon trimming the next group of rivets to the correct length ready for shooting. These 3/16" and 1/4" diameter rivets require a big rivet gun and a heavy dolly/bucking bar to form the tails correctly. The dolly in this case is the block of steel in the middle of the image. (image via Pioneer Aero Ltd.)
The forward face of Spar #2 having rivets installed in the upper and lower spar caps. A combination of clecos and bolts are holding the cap to the web plate, ensuring that it remains in the correct location during the assembly process. Mostly obscured by the spar, Chief Engineer Martin Hedley is focused upon trimming the next group of rivets to the correct length ready for shooting. These 3/16" and 1/4" diameter rivets require a big rivet gun and a heavy dolly/bucking bar to form the tails correctly. The dolly in this case is the block of steel in the middle of the image. (image via Pioneer Aero Ltd.)

The aft face of Spar #2 part way through having rivets installed in the lower spar cap. Martin Hedley, whose hands are visible at left, is in the process of trimming AN430 D6 rivets to the exact length required using a set of rivet shears. Hedley’s gloves are padded on the palms and inside of the fingers; this helps absorb some of the rivet gun vibrations. (Image via Pioneer Aero Ltd.)

Spar #2 part way through having rivets installed in the lower spar cap. The random nature of the rivet installation prevents the two pieces of aluminum from walking in relation to each other, something which would happen if the rivets were installed sequentially from one end to the other. (image via Pioneer Aero Ltd.)

The aft face of Spar #2 part way through having rivets installed for the lower spar cap. The clear plastic tray at left holds some rivets which are still full length, while the others have been trimmed to the exact length required - you can see some of the trimmings scattered over the bench. The rivets being installed here are AN430 D6 rivets. 'AN430' refers to the head style, while 'D' is the material specification - in this case, it was annealed on site and then placed in a freezer. These rivets must be used within 1/2 an hour of their removal from the freezer. And finally, ’6' refers to the rivet diameter in 32nds of an inch - i.e. these rivets are 3/16” in diameter. (Image via Pioneer Aero Ltd.)

Obviously, such rivets must be used pretty soon after heat-treating - typically no more than an hour after removal from the freezer. Thankfully, Pioneer is able to perform the heat treating on site, minimizing the delay before the rivets are used. Cunha and Hedley riveted the spar cap to the web plate, along with several ancillary components. The short series of videos below show the process, which also included shortening some of the rivets, since they were unable to acquire examples of the correct length. This is not an unusual procedure.

Jack Shaft Support Plates:

The jack shaft support plates returned from the cadmium plating facility. The chemical process involved passivates the part's steel surface so it is less likely to corrode. The process also reduces the possibility of galvanic reaction when the part is placed against dissimilar metals, like the 2024 aluminum web plate it attaches to. After riveting these components to the web plate, the restoration team had installed everything on the spar which was necessary for this stage of the project.

The righthand, aft face of Spar #2 most of the way through rivet installation. Note that the steel, cadmium-plated jackshaft mount is visible, with most of its rivets installed. (image via Pioneer Aero Ltd.)

The righthand, forward face of Spar #2, most of the way through rivet installation. The rectangular patten of rivets towards the left of the image affixes the jackshaft mount to the reverse side of the spar web, while the ring of holes in its midst (with four, temporary bolts in place) will attach a ring, on this face, that will hold the end of the jackshaft. (image via Pioneer Aero Ltd.)

The lefthand, aft face of Spar #2 most of the way through rivet installation. Note that the steel, cadmium-plated jackshaft mount is visible, with most of its rivets installed. Having some rivet heads on one side and some on the other replicates wartime production techniques. This procedure normally occurred due to access issues related to the rivet snap/gun combination. (image via Pioneer Aero Ltd.)

The lefthand, forward face of Spar #2 most of the way through having rivets installed. The rectangular patten of rivets towards image right hold the jackshaft mount to the reverse side of the web plate. AN470 DD8 and MS20426 DD8 rivets are being shot on this spar, where the 'AN470' variety has the so-called 'universal' rounded head and the "MS20426' employs a 'countersunk' head. 'DD' refers to the material specifications and, in this case, the rivets are annealed on site and then placed in a freezer. Once removed from the freezer, there is a roughly 5 minute window to use them before they return to their original hardness, which would render them too hard to shoot. For both rivet styles, ’8' refers to the diameter, which in this case is 8/32”… or, in other words, 1/4”. (image via Pioneer Aero Ltd.)

Spar #1 and Other Components:

After riveting Spar #2 together, the restoration team continued their work on components for Spar #1, along with the inter-spar ribs which link these two major subassemblies together. They also began manufacturing new nut-plate assemblies for Spars #1, #2 and #3. These particular nut plate assemblies help anchor splice plates firmly linking the SBD's outer wing panels to its Wing Center Section at the ends of the aforementioned wing spars. Unfortunately, these particular nut plates are specialized Douglas products, making them almost impossible to source. Furthermore, those examples which came with our project are no longer refurbishable, so Pioneer had to refabricate them.

These are the main load-carrying structures for the front portion of the SBD’s Wing Center Section. Top to bottom: Spar #2 (aft face visible), then all-but-one of the inter-spar ribs linking Spars #1 and #2 (not in order, remaining rib in paint booth), then a few components for Spar #1 (including replacement undercarriage torque tube mounts which attach to the spar ends), and finally Spar #1, which is in the last stages of component work before its parts head to the paint booth for a coat of primer. (image via Pioneer Aero Ltd.)
These are the main load-carrying structures for the front portion of the SBD’s Wing Center Section. Top to bottom: Spar #2 (aft face visible), then all-but-one of the inter-spar ribs linking Spars #1 and #2 (not in order, remaining rib in paint booth), then a few components for Spar #1 (including replacement undercarriage torque tube mounts which attach to the spar ends), and finally Spar #1, which is in the last stages of component work before its parts head to the paint booth for a coat of primer. (image via Pioneer Aero Ltd.)

The Douglas Dauntless employs splice plates at several locations bridging the divide between the Wing Center Section and the Outer Wing Panels. The majority of these splice plates attach to each center section wing spar at Station 66 (i.e. 66” from the airframe centerline). These tie the spar ends and match angles together, helping to strengthen the wing. An anchor nut channel is mounted to the end of Spars #1, #2 and #3 to hold the splice plates and spars together. None of B-22’s original channels or anchor nuts were salvageable, so needed replacing. However, these parts are Douglas-specific and no longer available, so Pioneer resorted to refabricating them. (image via Pioneer Aero Ltd.)

Another shot of the anchor nut channels which hold the splice plates and spars together. The nuts are Douglas specific, so had to be custom-made; the channel needed refabricating as well. (image via Pioneer Aero Ltd.)