Overview:
As most readers will know, the Douglas SBD Dauntless featured two forward-firing machine guns mounted in the nose right behind the engine. To make sure the shell casings and separated ammunition links fell away cleanly from the airframe when the machine guns fired, Douglas designed a pair of chutes which directed the detritus through the lower fuselage. The chutes for the spent casings also had to pass through the wing's leading edge, one on either side of the aircraft. Last October, we covered the work which Pioneer Aero's engineers completed to create the openings for these chutes in the righthand inboard leading edge. More recently, they were able to perform the same treatment on the lefthand inboard leading edge, as the following text and images describe.
A closeup of the lefthand inboard leading edge for the SBD’s Wing Center Section. As is visible here, Martin Hedley has carefully inked in the locations for the cutout and where the rivets will hold the doubler to the skin. The spent ammunition casing chute will be able to pass through the upper skin within the inner-most rectangle once the interior sheet metal is cut away. (image via Pioneer Aero Ltd.)
A similar image to the previous one, only this time showing where the cutout and doubler will go on the lower side of the leading edge structure. (image via Pioneer Aero Ltd.)
Placing these holes accurately is no mean feat, considering the complex curves involved, and that the holes on both the upper and lower sides of the wing leading edge must align perfectly for the chute to pass between them at the correct angle. As a result, Pioneer's Chief Engineer Martin Hedley took on this task. Using manufacturing drawings and parts from both a donor airframe and B-22 itself as a reference, he carefully marked out in ink where the cuts needed to go on the outer skin for the lefthand inboard leading edge. He then rolled out a small sheet of aluminum with an English Wheel, so that it matched the skin contours in the desired region precisely. This piece of sheet metal would eventually serve as a skin doubler, to bolster strength around the chute openings. With the skin doubler formed, Hedley then drilled the rivet holes needed to affix the doubler to the skin and cut away the aluminum where the chute had to pass through the skin. The final steps involved trimming the outer edges of the skin doubler and de-burring the edges and rivet holes. Following primer painting, the doubler will be riveted onto the leading edge structure, rendering the subassembly ready for reattaching to the Wing Center Section when the time comes.
The leading edge skin and doubler section after the appropriate holes have been cut through each part to permit the passage of the spent ammunition casing chute, and after the rivet holes have been drilled for mating the two components together. This is the topside view. (image via Pioneer Aero Ltd.)
An image showing the skin doubler after Martin Hedley has shaped the aluminum sheet to perfectly match the lefthand inboard leading edge skin contour where the spent ammunition casing chute is set to pass through the structure. This is the topside view. (image via Pioneer Aero Ltd.)
An image showing the skin doubler after Martin Hedley has shaped the aluminum sheet to perfectly match the lefthand inboard leading edge skin contour where the spent ammunition casing chute is set to pass through the structure. This is the bottom-side view. (image via Pioneer Aero Ltd.)
A topside view of the doubler after it has been trimmed to fit the spent ammunition casing port. (image via Pioneer Aero Ltd.)
A bottom-side view of the doubler after it has been trimmed to fit the spent ammunition casing port. (image via Pioneer Aero Ltd.)