A drawing from the SBD/A-24 Illustrated Parts Manual showing the structure which forms the upper fuselage structure for the Dauntless. The upper lefthand longeron, referred to as a stiffener assembly in the manual, is identified by lines #5 and 6. It has an identical, but opposite companion, of course, on the other side of the airframe.
A drawing from the SBD/A-24 Illustrated Parts Manual showing the structure which forms the upper fuselage structure for the Dauntless. The upper lefthand longeron, referred to as a stiffener assembly in the manual, is identified by lines #5 and 6. It has an identical, but opposite companion, of course, on the other side of the airframe.

Overview:

Pioneer Aero’s William Lowen has been working on the upper longerons for the SBD’s fuselage. Running horizontally from the engine mounting bolts through Fuselage Frame #11 as the above image shows, these complex, sturdy components form a significant aspect of the airframe’s structural integrity. Sadly, B-22’s original upper longerons were ruined beyond airworthy repair in the wartime crash (not to mention the subsequent corrosion damage), however they did include a number of potentially reusable ancillary parts.

The original, upper righthand longeron is seen here sitting behind its replacement, which came with the project. Note the significant level of corrosion to the original component, as well as the twist in the forward section at image right. Such damage rendered the original longeron beyond airworthy repair. For reference, the rib still attached to the original longeron’s upper face supports the windscreen bow. (image via Pioneer Aero Ltd.)
The original, upper righthand longeron is seen here sitting behind its replacement, which came with the project. Note the significant level of corrosion to the original component, as well as the twist in the forward section at image right. Such damage rendered the original longeron beyond airworthy repair. For reference, the rib still attached to the original longeron’s upper face supports the windscreen bow. (image via Pioneer Aero Ltd.)

Salvaging Parts:

To determine what he could salvage, Lowen stripped B-22’s original longerons down into their component parts, bead-blasting away the corrosion, dirt and old paint so he could inspect and evaluate the condition of each piece individually. He was able to refurbish several parts to airworthy condition, but also made headway refabricating replacements for items too far gone to reuse.

A closeup showing the forward end of B-22’s upper righthand longeron. The small rib supports the exterior skin, while the larger, partially visible rib supports the windscreen frame. Note the twist to the structure near its terminus at the steel engine mount bracket; this damage resulted from B-22’s wartime accident. (image via Pioneer Aero Ltd.)

An even closer look at the damage to B-22’s upper righthand longeron near the engine mount bracket. While it isn’t easy to spot in this image, impact damage from the SBD’s wartime ditching accident twisted the longeron down slightly. Deep-seated corrosion damage is quite evident, however. (image via Pioneer Aero Ltd.)

A closeup view of the upper righthand longeron from roughly where the forward bulkhead to the rear cockpit lies. The rusted fitting forms part of the latch which holds the rear canopy closed. Intergranular corrosion has taken root around that latch, due in part to the galvanic reaction between steel and aluminum. (image via Pioneer Aero Ltd.)

Machining a new channel for the canopy latch mechanism which attaches to the longeron. The original component, sitting on the milling machine table beside the vise, suffers from intergranular corrosion damage which rendered it beyond salvage. (image via Pioneer Aero Ltd.)

A closeup near the aft end of the upper lefthand longeron. The rib is located at the aft end of the rear cockpit. It holds the skin which forms the rear curve of the cockpit opening. (image via Pioneer Aero Ltd.)

A view of the bottom side of the upper, lefthand longeron in the area around the rear cockpit. Note the heavy corrosion on view. (image via Pioneer Aero Ltd.)

The rib (and its replacement) seen here attach to the upper righthand longeron at the aft end of the rear cockpit. Irredeemable corrosion damage to the original part is clearly evident here. (image via Pioneer Aero Ltd.)

This set of ribs attaches to the top side of the upper longerons at the aft end of the rear cockpit, one on either side. They hold the skin which forms the rear curve of the cockpit opening. The closest example to the camera is a restored original from the left side of the airframe, while the other is a newly-manufactured replacement for the righthand side. (image via Pioneer Aero Ltd.)

These brackets hold an electrical box below the upper righthand longeron between Fuselage Frames #5 & #6. The tabs showing three rivet holes attach the bracket to the longeron’s outboard flange, allowing the (rust-stained) mounting faces to hold the electrical box vertically. (image via Pioneer Aero Ltd.)

The same brackets from the previous image after media blasting to remove old paint, minor surface corrosion and dirt. Close inspection proved these original parts to be in airworthy condition. (image via Pioneer Aero Ltd.)

The outboard face of the rib assembly which supports the right side of the windscreen bow. These ribs comprise of two main parts (forward and aft) and attach to the top side of the upper righthand longeron. The rough-edged piece of material stuck to the top right corner of the component is actually the remains of the neoprene seal which the cockpit canopy closes against. (image via Pioneer Aero Ltd.)

The opposite rib assembly to the one shown in the previous image. This one supports the left side of the windscreen bow and attaches to the top side of the upper lefthand longeron. (image via Pioneer Aero Ltd.)

The aft face of the lefthand windscreen support rib assembly shown in the previous image. (image via Pioneer Aero Ltd.)

These are the original aft components for the right and lefthand windscreen support rib assemblies. After media-blasting, both parts proved to be in airworthy condition. (image via Pioneer Aero Ltd.)

These are the original forward components to the left and righthand windscreen support rib assemblies. Unfortunately, media blasting revealed extensive corrosion (evident here) which rendered the parts beyond airworthy use. (image via Pioneer Aero Ltd.)

Trial Fitting:

Fortunately, a set of partially assembled, replacement longerons came with the project, so Lowen got to work on these. He first de-riveted the stiffeners and splices, then inspected all of the parts. To determine whether they would fit the fuselage properly, he lay them atop the temporarily assembled fuselage frames in the jig. It turned out that the outer faces of these longerons needed adjusting slightly so they matched the exterior fuselage contour, so Lowen began the process of rectifying this issue. With the parts properly formed, it seems likely that the longerons will undergo primer-painting and reassembly in short order.

A view of the replacement upper lefthand longeron (aft end towards camera) which came with the project. While the previous owner had fitted some rivets prior to the Museum’s acquisition, William Lowen removed them all so he could perform a complete inspection of each component prior to primer painting. (image via Pioneer Aero Ltd.)

This is the bottom side of the replacement upper lefthand longeron shown in the previous image (aft end towards camera), prior to the removal of the rivets holding ancillary parts to the main section. This image reveals just what a complex shape the part conforms to. It is fortunate that the Museum’s project came with a newly-manufactured set of these key components. (image via Pioneer Aero Ltd.)

A view of the replacement upper righthand longeron (forward end towards camera) which came with the project. Like the lefthand example, this component arrived partially reassembled and, as before, William Lowen de-riveted the attached pieces to allow a complete inspection of each part prior to primer-painting. (image via Pioneer Aero Ltd.)

The bottom side of the replacement upper righthand longeron and its component parts after disassembly. (image via Pioneer Aero Ltd.)

The replacement upper righthand longeron (forward section) is seen here temporarily positioned against the fuselage frames to ascertain whether its profile properly matches the adjacent structure (it required minor adjustments). The section of airframe visible in this image extends from Fuselage Frame #3 (closest to camera) out to Frame #6. Note that the original, damaged components from Fuselage Frame #4 are in use here to help position the longerons correctly while the team awaits the replacement frame (fabrication discussed in update #66) to return from heat treating. (image via Pioneer Aero Ltd.)

A similar view to the previous image showing the trial-fitting of the replacement upper longerons (forward sections) to the fuselage frames. The steel frame in the foreground is where Fuselage Frame #1 will sit. Note the large hole in the upper, outer corner of said steel frame; this is where one of the engine mount attachment bolts passes through. (image via Pioneer Aero Ltd.)