
Overview:
In addition to their herculean efforts concerning the SBD's Wing Center Section, the restoration team at Pioneer Aero Ltd. has been working hard on the aircraft's upper fuselage over the past several months as well. They have repaired or remanufactured many of fuselage frames in this process. This particular article covers the work Pioneer's Martin Hedley has performed so far on the upper section of Fuselage Frame #4.

Refabricating Fuselage Frame #4
The original upper section of Fuselage Frame #4 displayed several areas of corrosion. After bead blasting the part, it was clear that the damage rendered it beyond airworthy limits; a new part therefore had to be made. Pioneer's Chief Engineer Martin Hedley carried out this work. He first had to perform a 3D scan of the original part to get precise data regarding its shape; this allowed him to create a wooden forming block for shaping the new part.
Unlike most of the SBD's other fuselage frames, Frame #4 sits in the fuselage at an angle with respect to the aircraft's centerline. This, coupled with the fuselage's exterior curve, means that the flanges around the outer edge of Fuselage Frame #4 are not folded at a constant angle, but rather one which is constantly changing. These had to be shaped into the form block, as well as the various heights along the upper edge. Thankfully, however, the inner flange angle is constant around its perimeter, making it much easier to recreate.
Hedley cut a blank for the new part from a sheet of 0.063" thick 2024-T0, then clamped it between the forming block and its backing plate. He then beat the outer edges over the form, periodically removing the part to shrink the edges so it would fit the forming block correctly. Hedley then worked similarly on the inner flange, albeit using a stretching tool periodically instead of a shrinker. Great care had to be taken with this step, especially when forming the tightest curve, to ensure that the aluminum sheet did not crack. After Martin Hedley completed shaping the part, he sent it off for heat treating to bring it up to the correct temper (consistent with 2024-T3).

Wooden forming blocks with the aluminum blank for replicating Fuselage Frame #4 sandwiched between them just prior to beginning the shaping process. The flange side is facing the camera. Note the four steel pins, two on either side of the frame. These are press-fitted into jig holes drilled through both the blocks and the aluminum sheet to ensure that all three remain aligned in the same relative position to one another while the aluminum sheet is worked on.(image via Pioneer Aero Ltd.)
The replacement upper section of Fuselage Frame #4 during the shaping process. The outer and upper flanges having already been formed, while work on the inner flange has just begun. The c-clamps hold the forming block against the backing block, with the aluminum sheet sandwiched tightly between them to prevent unwanted movement when the aluminum flanges are hammered into shape. (image via Pioneer Aero Ltd.)
A closeup showing the inner flange of Fuselage Frame #4 being shaped around its tightest corner. The aluminum blank has just been beaten with a mallet against the forming block up until this point however, when creating such tight bends, the aluminum sheet needs stretching periodically to prevent it from cracking. This requires removing the partially formed frame from the blocks so the appropriate area can be stretched. Various techniques and tools can be used to do this, but in this case Martin Hedley used a hammer and a steel stake to gently work the metal. Following stretching, the frame is returned to the forming block and beaten closer to the final shape. The process is repeated, as necessary, until the correct profile is achieved. (image via Pioneer Aero Ltd.)
The replacement upper section of Fuselage Frame #4 towards the end of being shaped. The inner flange has just been finished. Visible through the opening in the forming block is an array of hammers, mallets, steel stakes, dollies and other tools which have been used to form the flanges. The original frame is visible on the workbench behind these tools. (image via Pioneer Aero Ltd.)
