Refurbish or Replace?
Pioneer Aero had to remove numerous small parts in order to separate the SBD's fuselage into its major subassemblies. While some members of the restoration team are focused on the larger assemblies, others have begun assessing the smaller items, refurbishing what is rebuildable and remanufacturing what is not.
There is an old adage in aircraft restoration which seems to prove true all too frequently: "If it ain't bent it's corroded, and if it ain't corroded, it's bent." Even so, it is often possible to save and refurbish damaged components, as the Pioneer team has demonstrated time and again on this project. The SBD's wing leading edges have proved a particular challenge, however, as the above image intimates...
When our Dauntless ditched into Lake Michigan in January, 1944, the dive bomber's forward fuselage and wing leading edge took a pummeling as they struck the water. Indeed, the crash essentially crushed the wing's leading edge flat against the main spar in places. A couple of months ago, the restoration team carefully stripped back this structure on the wing's center section (see image above) as part of their preparations for separating the fuselage. More recently, they began disassembling this crumpled mass of metal to assess what remained, and began replicating the parts which proved beyond salvage.
Wing Leading Edge Structure:
The SBD's center section wing leading edge structure comprises many different subassemblies, as revealed in the image above from page 50 in the A-24 illustrated parts manual. The elements labeled #23 and #24 in the drawing are of particular interest in this update. These components are officially described as "Web Assembly - Center Section Wing Nose", with the left hand example having part number 5062769, while the right is 5062769-1. While these numbers may seem innocuous to many, Douglas Aircraft employed a useful logic in their parts numbering protocol, which is worth examining further.
The Douglas Aircraft Company Part Numbering System:
To keep track of where everything goes, each of the many thousands of parts involved in the manufacture of an aircraft requires its own unique identifier - typically a number.
Different manufacturers each had their own methodology for part number assignment, but the Douglas Aircraft Company came up with a particularly effective one. While they too labeled each subassembly with a seemingly random number, Douglas reused this number as the basis for identifying the individual parts comprising that component, simply adding a hyphenated numerical suffix (e.g. "-23") to differentiate them from each other.
Furthermore, since aircraft are usually symmetrical, they have numerous, near-identical parts which are essentially mirror images of each other - oriented in either a right- or left-handed configuration. To simplify the process for the factory workers, parts with a righthand orientation had an odd-numbered suffix, while those on the left were even-numbered. This made it much easier for them to be certain they were working with the correct parts when fabricating a given subassembly.
Drawing Information Block - An Explanation:
The above image is a close up of the Information Block from the earlier drawing for Douglas part #5062769, the web assembly for the SBD center section’s wing leading edge. While this image is fuzzy, and perhaps a little confusing to those who aren’t used to reading manufacturing drawings, there are essentially four important areas of information depicted here.
- The block at the lower right delineates what the drawing describes, along with the names of the people who created and/or updated the drawing, as well as the dates of each release.
- The block at the lower left delineates the “change notices” in this version of the drawing, what they involved, who signed off on them, and when.
- In between these blocks at the bottom of the image, is another identifying the next assembly associated with the component this drawing describes, and the particular aircraft variant it involves.
- Perhaps the most important information, however, is featured in the “bill of materials” table at the top right. Reading from the left, the first two columns identify the part number suffix; odd numbers being for the right-handed components and the even for the left. The third column describes how many of that given part are needed. Adjacent to these three columns is information describing the material these parts are made from. This particular assembly primarily comprises parts made from either aluminum sheet stock or extruded aluminum. For the extruded parts, the bill of materials essentially identifies which extrusion profile to use, its length, material and temper state. However, for the parts made from sheet metal, there are a series of squares identifying the length and width of the material blank to start forming the part from, the thickness, alloy and tempered state of this material before manufacture commences, and then the material specifications the part must conform to following its completion.
Web Assembly - Center Section Wing Nose:
Douglas Part Number 5062769 essentially serves as a secondary spar, connecting ribs between the main spar and leading edge, while stiffening the structure over the wheel bays. As typical for its era, this component consists of a flat, sheet metal assembly (the web) with stiffeners (spar caps) running down its lateral extremities. Understandably, given how comprehensively the water impact crushed this area of the aircraft, very little of the original structure was salvageable, but what remained has served as a useful template (complemented by original factory drawings) for the remanufacture of replacement parts.
The following images describe some of the work underway to rebuild the web assembly. We have included closeup views of the earlier manufacturing drawing for Part Number 5062769, highlighting where each of these different components fit in the overall subassembly. Hopefully this provides a clearer idea of the work which the restoration team is undertaking, and how much effort is involved!
Assembling the Web:
With parts for the secondary spar either refurbished or remanufactured, it was time to begin putting it all together.
Leading Edge Ribs:
The remanufacture of all the leading edge ribs for the wing center section is also underway now. Using Douglas Aircraft's ordinate table drawing, which tabulates the coordinates defining the outer profile for each rib, the team cut out an appropriately sized forming block to shape a sheet metal blank into a new rib. Once fully formed, the rib is ready for heat treating to significantly increase the material's tensile strength and hardness.
Skin Assembly - Center Section Wing Nose:
Douglas Part Numbers 5090535-2 and 5090535-3 form the skins for the leading edge in the SBD's wing center section; Pioneer Aero has begun forming these key parts in recent days. Using the manufacturing drawing below (amongst others) the restoration team was able to create a jig-like cradle defining the cross-sectional profile for these skins. Using a combination of a rolling machine and an English Wheel, the engineers shaped a section of sheetmetal so that it conformed to the cutouts in the jig, a tool which they amusingly refer to as 'dinosaur bones', for obvious reasons. Once the team has completed and assembled the internal structure for the wing leading edge, they will rework and trim the skin section so that it lines up perfectly on top.