The aft face of Frame #4 soon after its removal from the rollover frames. While several corrosion spots were evident, further inspection was required before making any decisions regarding its future airworthiness potential. Note, the lighter colored strips reveal where the roll over extrusion attaches. (image via Pioneer Aero Ltd.)
The aft face of Frame #4 soon after its removal from the rollover frames. While several corrosion spots were evident, further inspection was required before making any decisions regarding its future airworthiness potential. Note, the lighter colored strips reveal where the roll over extrusion attaches. (image via Pioneer Aero Ltd.)

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.

Following bead-blasting, the corrosion damage to the upper section of Fuselage Frame #4 was found to be beyond airworthy repair and thus a new example needed to be made. The original component is seen here (aft face on view) sitting above the wooden forming block which will be used to fabricate its replacement. Note, the raised areas along the top edge of the forming block; this will prevent the aluminum from being folded over in that area. (image via Pioneer Aero Ltd.)
Following bead-blasting, the corrosion damage to the upper section of Fuselage Frame #4 was found to be beyond airworthy repair and thus a new example needed to be made. The original component is seen here (aft face on view) sitting above the wooden forming block which will be used to fabricate its replacement. Note, the raised areas along the top edge of the forming block; this will prevent the aluminum from being folded over in that area. (image via Pioneer Aero Ltd.)

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).

The original upper section of Fuselage Frame #4 sitting above the aluminum blank which will be formed into its replacement. The notches cut into the blank’s top edge will allow the various heights required to be replicated; the outer flange will be shaped first. (image via Pioneer Aero Ltd.)
The original upper section of Fuselage Frame #4 sitting above the aluminum blank which will be formed into its replacement. The notches cut into the blank’s top edge will allow the various heights required to be replicated; the outer flange will be shaped first. (image via Pioneer Aero Ltd.)
The newly-fabricated upper section of Fuselage Frame #4 following the completion of its manufacture is seen here sitting atop the forming block used to shape it. The next step will involve heat treating the metal, after which it will be sprayed with primer paint. (image via Pioneer Aero Ltd.)
The newly-fabricated upper section of Fuselage Frame #4 following the completion of its manufacture is seen here sitting atop the forming block used to shape it. The next step will involve heat treating the metal, after which it will be sprayed with primer paint. (image via Pioneer Aero Ltd.)