“The closeout of XB-1’s wings marks a significant milestone for the major structural assembly,” says Boom’s Head of XB-1 Production, Mike Jagemann. “It’s significant because of the finality of the event—once you close them out, you cannot go back and open it like you could a bolted structure. After we install a few more parts, such as the leading edges, the wing will be complete and moving on to structural testing.”

Since November, cross-departmental teams have worked together to establish best practices, draw on one another’s expertise, and document every step of the closeout process. Departments including Flight Controls, Hydraulics, Avionics, and Structures, as well as Boom’s two test pilots and the crew chief, offered insights and guidance as the build out of the wings progressed. Following the successful installation of XB-1’s seven wing spars and two aileron trays in January, dress rehearsals for the closeout got underway.

The closeout process is relatively simple, yet requires the highest level of precision possible. During the preparation phase, the team:

Installed the upper wing skin into its holding fixture

Bonded all spars and ribs into the upper skins — also known as the substructure

Installed flight control brackets and pulleys

Installed wire harnesses and instrumentation

On closeout day, the team ran concurrent safety checks to ensure the proper installation of hardware such as temperature gauges inside the wings, and that all cable bundles ran correctly through each wing. The team also inspected flight control pulleys and cables, which are routed through the wings to the systems bay, as well as the aileron trays on the outboard portion of each wing. (Ailerons are the hinged part of each wing that control roll or maneuvers, and are controlled by the pilot via wire pulleys that run through the wings.) A final bond line inspection and FOD (Foreign Object Debris) check also ensured that any and all foreign objects were removed before close out.

With the wings ready for final closeout, the operation got underway. The team dedicated the day to: