Overview:

Over the past six months, Pioneer Aero’s engineers have made significant progress restoring elements of the SBD’s lower forward fuselage which are integral to the dive bomber’s Wing Center Section. This includes the stringers, joiner strips, mounting angles, skins and wing-to-fuselage fairings. This article will bring that effort into focus, picking up from where we left off in Update No.93.

Screenshot

For Reference:

The above image from the A-24/SBD Illustrated Parts Manual will be familiar to regular readers of this blog, as we have used it in several previous articles, such as Restoration Update No.100, which covered the rebuild of the SBD's lower rear fuselage. The image labels all of the SBD's different lower fuselage skin panels via a 'callout number' in black ink. These callout numbers, when cross-referenced to the previous page in the Illustrated Parts Manual, assigns each skin panel a unique Douglas Aircraft part number beginning with the root "5063493" followed by a dash number to identify the specific component. To simplify the process of identifying each skin panel by its Manufacturer's part number, we have amended the image so that it pairs the call out numbers in the original document with their associated dash number (written in blue). This will, hopefully, make it easier for readers to interpret what they are seeing since Pioneer Aero's engineers typically refer to any given skin by these same dash numbers. For instance, the callout numbers 01 and 02 represent skin panels with part numbers 5063493-6 and -7 respectively, so we will refer to these components simply as Skin #6 and Skin #7.

As noted on the illustration, SBD fuselage skin panels with even 'dash numbers' are situated on the lefthand side of the airframe (other than a handful straddling the belly) whilst those with odd numbers fit on the righthand side.

Trial-Fitting Skins, Stringers and Fairings:

Earlier this year, Pioneer's Rod Hansen temporarily reattached both original and newly-made fuselage skin panels and wing root fairings to the SBD's Wing Center Section assembly in its jig. This allowed him to line up and trial-fit newly-made and refurbished original stringers running between the lower Fuselage Frames on each side of the airframe. Gradually, he began substituting new skins for old, where necessary, and trial-fitting some of the small rib assemblies used to cinch down the wing root fairings as well. As implied earlier, some of the latter were refurbished originals, the restoration of which we covered more than two years ago in Update No.33.

Lefthand Side:

The following images in this section will describe the process of trial-fitting the skins, stringers and wing root fairings to the lefthand side of the SBD's Wing Center Section in its jig. A subsequent section will cover the same process for the righthand side of the airframe.

An exterior lefthand view of the SBD’s lower forward fuselage during the process of trial-fitting skins, stringers and mounting angles to the Wing Center Section in its jig. A replacement fuselage skin #6 (bare aluminum) is seen just above the wing surface, with original, non-airworthy skins #80 (fore) and #12 (aft) having been fitted above it to help align both the skin joins and the stringers attached to their interior surfaces. Note the small curved ‘riblet’ mounted at the aft end of skin #6 where the latter attaches to Fuselage Frame #4. This is part of the interior structure for riveting on the wing root fairings. (image via Pioneer Aero, Ltd.)
An exterior lefthand view of the SBD’s lower forward fuselage during the process of trial-fitting skins, stringers and mounting angles to the Wing Center Section in its jig. A replacement fuselage skin #6 (bare aluminum) is seen just above the wing surface, with original, non-airworthy skins #80 (fore) and #12 (aft) having been fitted above it to help align both the skin joins and the stringers attached to their interior surfaces. Note the small curved ‘riblet’ mounted at the aft end of skin #6 where the latter attaches to Fuselage Frame #4. This is part of the interior structure for riveting on the wing root fairings. (image via Pioneer Aero, Ltd.)

An interior view featuring roughly the same section of fuselage depicted in the previous image. Replacement fuselage skin #6, still bare aluminum, is visible just above the wing surface, whilst original (albeit non-airworthy) skins #80 and #12 still bear their wartime paint. The latter skins are temporarily fitted to allow Pioneer’s engineers to align the stringers and skin joins. Several stringers are visible running along the skin sections, with the unpainted examples being newly-made replacements and the painted ones being refurbished originals. For reference, Fuselage Frames #2 through #4 are visible, with #4 closest to the top of the image. (image via Pioneer Aero, Ltd.)

Another interior view of the lefthand side of the fuselage (this time slightly further aft than the previous shot) showing the replacement stringers and skins in the process of being trial-fitted and drilled off against the non-airworthy original skin. For reference, Fuselage Frames #4 through #6 are visible, the latter being at the top of the image. Each of these frames is original to B-22, although only Fuselage Frame #4 is in restored, airworthy condition. The other two are for alignment purposes only, and will eventually be replaced with newly-made examples. (image via Pioneer Aero, Ltd.)

This composite image resulting from the photographic merger of the two previous shots offers a more comprehensive view of the overall work underway on this side of the fuselage. Please note that while the lower fuselage frames appear distorted, this is an optical illusion, an artifact resulting from the merging process.
This composite image resulting from the photographic merger of the two previous shots offers a more comprehensive view of the overall work underway on this side of the fuselage. Please note that while the lower fuselage frames appear distorted, this is an optical illusion, an artifact resulting from the merging process.
Another view of the SBD’s lefthand forward fuselage, now pictured with a replacement Skin #80 in the process of being refabricated. We can see the new aluminum sheet (at left) during its trial-fitting with the rivet holes being drilled off against the stringers behind it. Interestingly, in the available SBD manufacturer’s drawings, this skin panel is referred to as 'dash #4', which might initially seem confusing until one realizes that the drawing was for very early SBD variants. Subsequent examples used an updated design for this part, which is why it gained a new, and seemingly way-out-of-sequence dash number (#80). This is one of the many issues which workshops have to deal with when rebuilding 80 year old aircraft. Thankfully, Pioneer had the original skin #80 on hand from which to make a replacement for the updated part. (image via Pioneer Aero Ltd.)
Another view of the SBD’s lefthand forward fuselage, now pictured with a replacement Skin #80 in the process of being refabricated. We can see the new aluminum sheet (at left) during its trial-fitting with the rivet holes being drilled off against the stringers behind it. Interestingly, in the available SBD manufacturer’s drawings, this skin panel is referred to as 'dash #4', which might initially seem confusing until one realizes that the drawing was for very early SBD variants. Subsequent examples used an updated design for this part, which is why it gained a new, and seemingly way-out-of-sequence dash number (#80). This is one of the many issues which workshops have to deal with when rebuilding 80 year old aircraft. Thankfully, Pioneer had the original skin #80 on hand from which to make a replacement for the updated part. (image via Pioneer Aero Ltd.)

A view just a short distance back along the fuselage from the previous image showing a replacement wing root fairing (skin #48) in the process of being trial-fitted. It has been clecoed to the underlying wing center section skins and to the refurbished original, primer-painted wing root fairing immediately to its aft (skin #14). The line of holes along its upper edge had been plotted and transferred (drilled off) against Skin #6 beneath it. (image via Pioneer Aero Ltd.)

Moving aft from the previous image, we see an original, primer-painted wing root fairing (skin #14) from B-22 in the process of being trial-fitted. Rod Hansen has clecoed it to the SBD’s Wing Center Section skins and another wing root fairing (skin #48) and the underlying wing root ribs (not seen). Note the repair along the aft lower edge of skin #14. We described this repair two years ago in Update #33. (image via Pioneer Aero Ltd.)

An expanded view of the structure featured in the previous three images showing the wing root fairings and replacement fuselage skins undergoing trial-fitting. Note that the B-22’s original skin #12 is being used to help precisely locate the replacement skins. (image via Pioneer Aero Ltd.)
An expanded view of the structure featured in the previous three images showing the wing root fairings and replacement fuselage skins undergoing trial-fitting. Note that the B-22’s original skin #12 is being used to help precisely locate the replacement skins. (image via Pioneer Aero Ltd.)

The SBD's righthand lower forward fuselage interior is seen here with skin #80 in the fabrication process of. The holes in Stringer #7 (to the left of the fuselage join) between Fuselage Frames #1 (at bottom) and #3 (at top) are partially done. Some of the holes in Fuselage Frame #1 still required marking and drilling out at the point this image was captured. (image via Pioneer Aero Ltd.)

A view just slightly further aft to the previous image, showing the non-airworthy original skin #12 from B-22 being used to align and trial-fit the stringers and an original, primer-painted wing root fairing (skin #14). The lighter area around the ovular access hole on skin #12 shows where its doubler is located. Rivet holes from this skin will be transferred onto the replacement stringers and frames. (image via Pioneer Aero Ltd.)

Access Hole Doublers:

Skins #12 and #13 each have a maintenance access hole just aft of where the foremost edges attach to Fuselage Frame #3. To add additional strength to the hole opening, the SBD’s designers riveted on an extra section of sheet aluminum to the interior face of the skin around it, essentially doubling the skin thickness in that localized area. While it might seem like a more elegant solution would have involved Douglas simply choosing a thicker gauge aluminum for the entire skin section, that would have added unnecessary weight to the Dauntless; perhaps no more than a few ounces in this case, but repeating such compromises over an entire airframe can end up reducing both payload and combat radius capacities — not something any aircraft designer is willing to contemplate. Sadly for B-22, the ‘doubler plates’ for both Skins #12 and #13 were corroded beyond airworthy reuse. Pioneer Aero’s engineers therefore had to refabricate them, an effort which also required the manufacture of a forming block to add a radius around the opening. This radius provided additional rigidity to the part, but also made it easier for maintenance personnel to reach through the hole without snagging themselves on a sharp edge as they drew their hands back.

The original access hole doublers for Skins #12 & #13 were too damaged for airworthy repair, so needed replacing. Pioneer Aero machined the forming tool shown here from MDF to help refabricate these parts. (image via Pioneer Aero Ltd.)
The original access hole doublers for Skins #12 & #13 were too damaged for airworthy repair, so needed replacing. Pioneer Aero machined the forming tool shown here from MDF to help refabricate these parts. (image via Pioneer Aero Ltd.)

The replacement doubler for Skin #13 (righthand side) is seen here sitting in position on the forming block after its completion. Note the handwritten words in the part’s upper lefthand corner. “R/H” is shorthand for righthand side, while “5045057” is the doubler’s specific part number, and the word "cooked" refers to the part having been heat treated, with the date identifying when that process took place. (image via Pioneer Aero Ltd.)

From top to bottom, we see the remanufactured access hole doublers for Skins #12 & #13 respectively. Note that the interior side is visible for the top example, whilst the opposite is true for the lower unit. (image via Pioneer Aero Ltd.)

Here we see the replacement righthand doubler for Skin #13 being offered up to the original, non-airworthy B-22 component, which is clamped temporarily in place for trial-fitting associated stringers. (image via Pioneer Aero Ltd.)
Here we see the replacement righthand doubler for Skin #13 being offered up to the original, non-airworthy B-22 component, which is clamped temporarily in place for trial-fitting associated stringers. (image via Pioneer Aero Ltd.)

Righthand Side:

The following images in this section describe the process of trial-fitting skins, stringers and wing root fairings to the righthand side of the SBD's Wing Center Section, sitting in its jig.

An interior view of the SBD’s lower forward fuselage in the process of being restored while attached to the aircraft’s Wing Center Section. The bare aluminum of the replacement Skin #7 is visible just above the wing’s surface leading forwards from Fuselage Frame #4 in the lower third of the image; Fuselage Frame #6 is visible at the top of the image (both frames are restored original components from B-22). Note that the replacement stringers are in the process of being positioned against the fuselage frames. (image via Pioneer Aero, Ltd.)
An interior view of the SBD’s lower forward fuselage in the process of being restored while attached to the aircraft’s Wing Center Section. The bare aluminum of the replacement Skin #7 is visible just above the wing’s surface leading forwards from Fuselage Frame #4 in the lower third of the image; Fuselage Frame #6 is visible at the top of the image (both frames are restored original components from B-22). Note that the replacement stringers are in the process of being positioned against the fuselage frames. (image via Pioneer Aero, Ltd.)

A similar perspective of the righthand lower fuselage interior, but from further forwards in the airframe. Replacement Skin #7 is visible just above the wing surface, running from Fuselage Frame #1, at the bottom of the image, past Fuselage Frame #3 nearer the top. Note the two painted sections of stringer (on row #7) forward of Fuselage Frame #3 are original, restored parts from B-22 whilst the unpainted stringers are newly-manufactured replacements. (image via Pioneer Aero, Ltd.)

An exterior view of the lower forward fuselage structure shown in the previous image. (image via Pioneer Aero, Ltd.)

A later view of work progressing on the SBD’s lower righthand forward fuselage, this time showing the trial-fitting (at top) of an original, restored wing root fairing (Skin #15) from B-22 to the airframe. It has been clecoed to Wing Center Section skins and underlying wing root ribs as well as another wing fairing (Skin #49) just ahead of it and towards the lower part of the photograph. (image via Pioneer Aero Ltd.)
A later view of work progressing on the SBD’s lower righthand forward fuselage, this time showing the trial-fitting (at top) of an original, restored wing root fairing (Skin #15) from B-22 to the airframe. It has been clecoed to Wing Center Section skins and underlying wing root ribs as well as another wing fairing (Skin #49) just ahead of it and towards the lower part of the photograph. (image via Pioneer Aero Ltd.)
A closeup of an original, fully-restored B-22 wing root fairing (Skin #49) during trial-fitting. It has been clecoed to the wing center section skins and to the wing fairing to its aft (Skin #15). The line of holes along its upper edge were about to be transferred to the refabricated, bare-metal fuselage Skin #7. Note the sheet metal section with the ovular opening just beside it - this is the non-airworthy, skin doubler described in the previous section of text in this article. (image via Pioneer Aero Ltd.)
A closeup of an original, fully-restored B-22 wing root fairing (Skin #49) during trial-fitting. It has been clecoed to the wing center section skins and to the wing fairing to its aft (Skin #15). The line of holes along its upper edge were about to be transferred to the refabricated, bare-metal fuselage Skin #7. Note the sheet metal section with the ovular opening just beside it - this is the non-airworthy, skin doubler described in the previous section of text in this article. (image via Pioneer Aero Ltd.)
An overall view of the wing fairings during their trial-fitting process on the lower righthand side of the SBD's fuselage. (image via Pioneer Aero, Ltd.)
An overall view of the wing fairings during their trial-fitting process on the lower righthand side of the SBD's fuselage. (image via Pioneer Aero, Ltd.)