Overview:
Pioneer Aero's chief engineer, Martin Hedley has been working hard on the restoration of upper fuselage frames for the Dauntless since completing the disassembly of the structure last September. Over the past few months, he has refurbished almost all of these components, although some required remanufacture when corrosion issues proved too severe to effect airworthy repairs. Recent articles have covered progress with upper Fuselage Frame #3 and upper Fuselage Frame #4, while this piece will discuss the work on Fuselage Frames #5 and #6.
Fuselage Frame #5:
Upper Fuselage Frame #5 showed signs of corrosion damage following its removal from the airframe, as the above image reveals (note the whitish-gray areas). After media blasting to remove dirt, old paint and any surface corrosion from the part, Martin Hedley inspected it carefully to determine the severity of these problems. He did indeed find minor corrosion pitting in a couple of places but, after consulting the SBD's Structural Repair Manual, he found a viable repair solution. Hedley first blended out the minor pitting and then manufactured doubler plates to rivet in over the affected areas and rebuild the frame's strength. This is precisely the same method which military maintenance teams used to mitigate combat damage on SBDs (and other aircraft types) during WWII.
A closeup of minor corrosion damage to the lefthand, aft corner of the upper section of Fuselage Frame #5. Fortunately, the SBD’s wartime Structural Repair Manual provided a repair solution for this issue; this involved blending away the corrosion and adding a doubler plate to the affected area, which boosted its overall strength to the appropriate level. (image via Pioneer Aero Ltd.)
A closeup of minor corrosion damage to the righthand, aft corner of the upper section of Fuselage Frame #5. The affected area proved repairable using the identical, approved technique described in the previous image. (image via Pioneer Aero Ltd.)
The upper section of Fuselage Frame #5 (aft face) shown here in its entirety just prior to primer painting. (image via Pioneer Aero Ltd.)
The upper section of Fuselage Frame #5 (forward face) shown here in its entirety just prior to primer painting. (image via Pioneer Aero Ltd.)
Riveting Frame #5 Repairs:
With the fuselage frame now fully prepared, and the doubler plates fabricated and drilled to fit, it was time to coat each part in primer paint. Hedley let the paint cure for a few days after which he riveted the doublers to the frame, using the same style of rivets applied to nearby structure. We have added a short video below showing Martin installing rivets into the left doubler plate on the aft face of the frame. This is how "one-man" riveting is done with the rivet gun in one hand and the dolly (bucking bar) in the other. It takes significant practice to ensure both tools stay perfectly positioned for the duration of the riveting action.
Fuselage Frame #6:
As with Fuselage Frame #5, media blasting and inspection of Fuselage Frame #6 revealed some minor, but repairable corrosion issues. Martin Hedley again used the SBD's Structural Repair Manual for guidance in determining a restoration strategy. This strategy was also affected by the fact that the frame sits at the front edge of the gunner's cockpit, making it quite visible. Hedley therefore chose to implement the repairs in as discrete a fashion as practical, which involved using countersunk rivets (for a flush finish) to fasten the repair doublers, placed on the frame's forward, non-visible side.
Frame #6 Repairs:
Hedley had to fabricate and install three different doubler plates. For each of these, he began by first determining an appropriate rivet pattern for installing each repair. He then created wooden forming blocks for fashioning each doubler plate, the latter being made from 'soft' 2024-T0 aluminum sheet. As the images below reveal, two sections of damaged aluminum had to actually be cut from the fuselage frame, with inserts created to replace the missing material. Hedley then drilled through the original frame and doubler at each of the repair locations. He then heat treated the replacement parts to bring them up to the required 2024-T3 temper condition. Each part was then coated in primer paint, left for a few days to cure, and finally riveted in place. A few additional parts were also riveted back onto the frame, including the upper mount for the gunner's instrument panel plus the handholds which the rear crew member uses to slide into the cockpit.
A closeup showing the damaged top right corner for the upper portion of Fuselage Frame #6 (aft face) alongside a newly-formed doubler section to strengthen it. The area of corrosion here is just below the rectangular opening. Martin Hedley has inked in the repair layout on the original part showing the cut lines, rivet lines and doubler edges. The rivet layout for the repair has already been drilled through the original frame and the doubler. Next the small area of damaged material will be cut away, with an insert fabricated to replace it. (image via Pioneer Aero Ltd.)
A reverse view of the upper section of Fuselage Frame #6 depicted in the previous image. The main area of corrosion here is seen just below the rectangular opening, while a second, smaller area is visible next to the inner flange. Note the latter area of corrosion is not deep enough to require its removal (unlike the other); the doubler will be sufficient to replace any lost strength. (image via Pioneer Aero Ltd.)
This image shows the process of removing the previously depicted damaged section of Fuselage Frame #6. Martin Hedley used an angle grinder to cut the straight edges and stitch-drilled the curves. The resulting rough edges were filed smooth to allow an insert to replace the excised material precisely. (image via Pioneer Aero Ltd.)
A closeup of the upper section of Fuselage Frame #6 showing the doubler plate for the structure’s top righthand corner resting in place, each of the rivet holes having been drilled through both parts. Care was taken to ensure that the doubler’s flanges matched the original frame perfectly so that neither piece is distorted following rivet installation. This doubler effectively repaired two areas of corrosion. Shaped from ‘soft’, 2024-T0 aluminum sheet, the part required heat-treating to bring it up to the correct tensile strength. (image via Pioneer Aero Ltd.)
A closeup of the upper section of Fuselage Frame #6 showing the doubler plate for the structure’s top lefthand corner resting in place, each of the rivet holes having been drilled through both parts. Care was taken to ensure that the doubler’s flanges matched the original frame perfectly so that neither piece is distorted following rivet installation. Shaped from ‘soft’, 2024-T0 aluminum sheet, the part required heat-treating to bring it up to the correct tensile strength. (image via Pioneer Aero Ltd.)
The original upper section of Fuselage Frame #6 (aft face) and the newly-manufactured repair doublers following primer painting. The parts were now ready for riveting together. (image via Pioneer Aero Ltd.)
A closeup showing one of the doublers for the upper section of Fuselage Frame #6 (aft face) being riveted into position. Countersunk rivets have been used here to both keep the surface flush and render its repair as discretely as possible. (image via Pioneer Aero Ltd.)
A reverse-side view of the doubler shown in the previous image following its installation. Note the cast bracket attached to the inner flange. This is one of the mounting points for the gunner’s instrument panel; it was riveted in place at the same time as the doubler (obviously). Note that the handholds which the rear gunner can use to position themselves in the cockpit have also been riveted on to the top side of Fuselage Frame #6. (image via Pioneer Aero Ltd.)
The original, upper section of Fuselage Frame #6 (forward face) following the completion of repairs. The hand holds and the instrument panel mount are also original B-22 components. One instrument panel mount remains to be sourced and installed, however. (image via Pioneer Aero Ltd.)
The upper section of Fuselage Frame #6 (aft face) following the completion of repairs. (image via Pioneer Aero Ltd.)
Trial Fitting:
To ensure that the repaired fuselage frames align properly, Pioneer's restoration team trial-fitted them into the purpose-built jig. The following image shows the process for Fuselage Frames #5 and #6. Note that Frame #5 also has some of the rollover structure attached to it as well; this will be covered in detail in a subsequent article.
