Making two halves whole: Fuselage bonding advances XB-1 build

A transformation took place in the Boom hangar in early March with the bonding of XB-1’s left-hand skin into the fuselage. Also known as the left-hand fuselage closeout, the operation covered three-quarters of the fuselage profile. It was the single largest bonding event for Boom’s demonstrator aircraft, representing a higher risk to the build schedule and rollout. With an aircraft bonding operation of this magnitude, even a minor error could trigger setbacks. But when it came to bonding day, the team’s ability to plan and adapt paved the way for success, making it a seamless experience.

The sheer size of the bond was a challenge in itself. For this operation, the team had to cover a massive area — about 10,000 square inches. That’s roughly the size of two queen beds. Compared to previous XB-1 bonds, which were a quarter to a third of the size, the left-hand skin represented a momentous task.

Every bonding event has a maximum eight-hour time limit. There are no exceptions because the specialized adhesive hardens within a defined window. If the team encounters unexpected delays during application, the adhesive will harden too quickly and ultimately, won’t make a good bond.

The mission-critical aspect of the operation wasn’t lost on the team. Damage from this particular bonding operation could trigger a time-consuming correction, setting back the XB-1 build by weeks if not months. If the operation failed, there were no good alternatives for pulling the fuselage skin off and starting again.

Drawing upon their extensive expertise, the team’s advanced planning mitigated much of the risk. During previous bonding events, the team determined ways to streamline each step, constantly refining and improving processes. Planning, which began during XB-1’s design phase, had resulted in continuous refinements that accelerated how quickly the small and dedicated team executed each step.

Due to the sheer size of the left-hand fuselage — 46-feet — the operation demanded a highly-synchronized effort. The bond encompassed 10,000 square inches and required 140 adhesive kits — each taking six minutes to mix. It would take 840 minutes to mix all the kits, almost as long as three major league baseball games. But by using several mixers in tandem, the team produced the kits precisely when needed for application and drastically reduced the total time required.

After mixing began, the team worked at a fixed, steady pace to cover three-quarters of the fuselage area with the adhesive. Following a “map” established during the planning phase, the team moved rapidly along the fuselage. Once application was complete, they applied about 9,000 pounds of force (equivalent to the weight of three small cars) to close the bond and adhere parts together. The team squeezed the parts together using pulleys — similar to how an anaconda squeezes its prey.

It ran like clockwork. The total run time of the bonding operation was 13 hours, including mixing adhesive and curing the fuselage in the in-house oven. The final step was verification. The team “cracked” the shell, removed it and ran a series of checks and tap tests to verify the bond’s success.

“XB-1 is the eighth new design aircraft I’ve built in my career and of all bonding operations, this was the most demanding — and the most intense,” recalls David Rawley, Boom Supersonic Manufacturing Engineer. “Our team rallied behind the effort to refine and revise procedures and methods so we could accomplish much more in a limited time window, and still maintain quality and safety. The Boom team, through continuous improvement, made it possible.”

The successful operation set the final shape of the aircraft — a long, sleek supersonic “canoe” that’s currently resting in a “cradle” in the hangar. It also confirmed that aerodynamics (measurements) aligned with design and that subsequent aspects of the build can move forward exactly as planned.

With XB-1 in its cradle, Boom is moving ever closer to first flight — and the return of supersonic commercial flight to the skies.