A switch from composite to titanium for the inner walls of the thrust reversers on the Boeing 737 Max has allowed designers to increase the fan diameter in the airplane’s CFM International 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 for Bob Feldman some two months ago, when Feldman moved to the 777X.
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, as well as meet Chapter 14 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 resulting from drawing 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 bring 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 remains still relatively early in the development process, all evidence presented by Boeing appears to indicate a clear path toward certification and entry into service as planned, in the fourth quarter of 2017.