A switch from composite to titanium inner wall of the thrust reversers on the Boeing 737 Max has allowed designers to increase the fan diameter in the airplane’s CFM Leap-1B turbofans without a proportional increase in the size of the nacelle. The relatively minimal growth of the nacelle means Boeing could keep its original plans for coping with the small amount of ground clearance margin available while optimizing thrust levels, explained 737 Max program vice president and general manager Keith Leverkuhn.
“We tailored the engine to the wing, and we tailored the engine to the thrust that we need to be able to deliver the combination of fuel burn and range,” said Leverkuhn, who took over as Max program head from Bob Feldman some two months ago, when Feldman moved to the 777X program.
Another recent advance involved what Leverkuhn described as a “sculpting” of the engine inlet to maximize laminar flow. Those and other refinements allowed Boeing to raise the target range of the 737 Max 8 some 500 nm beyond that of the 737-800, to 3,620 nm, while also meeting ICAO Chapter 4 noise requirements. It also now expects the fuel burn advantage to reach 13 percent. Previous estimates placed the benefit at 11 percent. “And I would say there is pressure for even more as we learn more and more about the engine and more about the airplane,” said Leverkuhn.
Although titanium weighs somewhat more than the composite material typically used for the inner wall, the need for insulation blankets to protect the composite from the heat generated means the traditional combination weighs more, explained Leverkuhn. The titanium option will also result in less maintenance, he added, particularly given the increased heat exposure that will result from bringing the inner wall closer to the engine to minimize the size of the nacelle.
“A titanium inner wall is unique in the industry,” said Leverkuhn. “However, we’ve had some experience with it in military applications, so we’ve taken some lessons learned from them and brought that technology forward on the Max.”
Now scheduled to reach firm configuration in July, the program has already passed through the mid-point of its so-called long-lead releases as part of the detailed design process, added Leverkuhn. In short, although the program is still relatively early in the development process, all evidence presented by Boeing appears now to indicate a clear path toward certification and entry into service as planned, in the fourth quarter of 2017.
“We’ve got a mini iron-bird…so we already know pretty well how the systems interactions are working on the airplane,” said Leverkuhn. “The trick on this program, in addition to delivering the customers the fuel burn that they absolutely need, [is that] we’ve got to weave this thing into a production system that’s going to be at a high rate. So it’s not only about proving the technology, it’s about proving the production capability.”
The job of overseeing the integration of the Max into the current 737NG line falls on 737 program vice president and general manager Beverly Wyse, who, during a pre-Paris briefing at Boeing’s Renton 737 assembly site, near Seattle, talked of a “strategic application of automation” as the company attempts to execute a virtually complete production transition to the Max by the end of 2019.
A prime example of such automation will appear in the 737 wing-assembly facility in Renton. There, plans for the next several years call for the deployment of a continuously moving vertical-panel assembly line that will “drill and fill” upper and lower wing skins to create an entire wing panel. “One of the key benefits we’ll get from this is the number of crane moves will be reduced when we go to this continuous flow assembly,” said Wyse. It will also reduce the amount of hand-drilling required, she added, and–perhaps most important–reduce the so-called footprint needed for panel assembly by about 50 percent, raising production capacity to 60 wing sets per month.
Still, Wyse espouses a measured approach to introducing new technology into the production system while the Max comes on line. “We’re going to try to separate that risk, and make sure that technology is proven out ahead of time,” she said. “We’re going to be very methodical and disciplined. That has been the strength of this program; it’s why we have been able to introduce these production rates so well and we’re going to use those same techniques when we bring the Max on line.”
Boeing’s next rate break, due next year, would see production rise from 38 to 42 per month. However, the company hasn’t shared any plan for increasing rates beyond 42 per month by the time the Max enters production in 2017. Quite apart from upsetting the status quo in terms of supply and demand balance, Boeing would rather not concern itself with placing further strain on its supply chain while it attempts to maintain quality standards and meet delivery promises during the transition to the Max.
Patterned after the production system devised by Toyota, the 737 line over the past 10 years has managed to decrease flow times from 22 days to 11 days, and plans call for removing a day of flow “nearly every year,” said Wyse. “What happens when we reduce that flow is that it transitions into capacity, and it’s a big reason we’ve been able to go from 14 a month 10 years ago to 42 a month next year in effectively the same space.”
Over the past two years, she added, the 737 team has delivered on-time–to the exact day–at a rate of 95 percent, even while it executed rate breaks and product improvement changes. At the same time, findings of defects by customers has declined by 45 percent, said Wyse. Of course, Boeing would like to at least maintain that level of performance when it starts building the Max.
Plans for the Max center around building what would become a third line in building 4-82 in the Renton complex, where four flight-test airplanes would occupy space directly next to Line 1. Both Line 1 and Line 2–located in the 4-81 facility–now hold enough capacity to each build 21 airplanes per month. Next to Line 2, nine systems installation positions will feed both lines, said Wyse, enabling them each to maintain their 21-per-month rate.
Wyse explained that creating a third line on which to build the first four aircraft will allow mechanics to install sensors and other flight test equipment without disrupting the flow of the two main lines. It will also allow Boeing to train its teams for the integration of the new components on the Max. Once those airplanes get built, said Wyse, training will immediately begin on the two main lines as the company introduces the Max onto them.
“These transformations will not only allow us to ensure on-time delivery performance of the Max, but it will also provide us the capacity in the final assembly area if we should need additional production rate increases,” she noted.