MAX vs. A321XLR - AW&ST

 

Could A Rewinged, Reengined 737 MAX Compete With The A321XLR?

Guy Norris March 25, 2021

Credit: Boeing

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Can a rewinged, reengined and longer Boeing 737 MAX be a viable competitor to the hot-selling Airbus A321XLR??

Aviation Week Senior Editor and Western U.S. Bureau Chief Guy Norris responds:

In a word, no. Here’s why: The baseline 737 configuration has proved to be remarkably resilient for a 55-year-old design with 13 major derivatives and more than 10,500 deliveries and counting since 1967.

Conceived initially for short-haul routes, the aircraft was designed with engines mounted directly beneath the wings rather than underslung on a 707-style pylon. This enabled a shorter, inward-retracting landing gear and placed the fuselage lower to the ground—making ground-servicing access easier at regional airports, most of which at the time lacked skybridges and other elements of the new jet-age infrastructure.

Boeing could not have imagined in the 1960s that the short, stocky gear arrangement would one day prove to be a limit to its growth, and over the decades, the company has worked within the same basic center wing structure to adapt the 737 to heavier weights, larger engines and longer fuselages.

The process began with the launch of the reengined CFM56-powered 737 Classic in the 1980s. The nose gear was lengthened 6 in. and the main gear strengthened, while the new, bigger engines were cantilevered up and forward of the wing to maintain ground clearance.

The launch of the 737 Next Generation in the 1990s saw a major redesign of the wing that widened the main landing gear track by almost 2 ft. The gear itself received few dimensional changes, although tire size increased, and the nose-gear wheel well was extended forward by 3 in. to accommodate fuselage growth. The baseline gear arrangement was again slightly modified for the MAX in the 2010s, and despite the increased size of the CFM Leap 1B engine, the design minimized the required change to a mere 8-in. extension to the nose-gear leg.

But more fundamental changes were unavoidable when Boeing wanted to challenge the Airbus A321neo by stretching the 737 beyond the 737-9’s length of 138 ft. 4 in. Boeing’s big challenge was how to extend the fuselage 66 in. for the 230-seat 737-10 while maintaining aft body clearance on rotation—all without altering the geometry of the wheel well.

After ruling out a costly center wingbox or side-of-body redesign, Boeing looked at several gear options before settling on a new design combining a semi-levered, trailing-link extension with a shrink link. The former feature moves the rotation point aft, while the latter compresses the 9.5-in.-taller gear leg on retraction, allowing it to fit into the same volume as the standard MAX main-gear wheel well.

Ingenious though the new gear design is, the size and position of the wheel well mean that further fuselage extensions are impractical without a major wing redesign. The cost of this—added to the associated revisions of the fuselage structure, systems and wing to accept an even larger engine—make this an unattractive option against the relative benefits of an all-new uncompromised design.

After performing beyond all expectations as a wellspring of derivatives, the 737 likely will have run its course after the -10—hence Boeing’s pursuit of new options to counter the Airbus A321XLR.