As the 737 Max 9 begins stability and control testing, Boeing’s engineers are working to finalise a critical detail in the configuration of a proposed larger variant aimed at forming a two-pronged attack on the Airbus A321neo, which is currently dominating the market for large narrowbodies.
The 737 Max 9 opened a series of initial airworthiness tests four days after achieving its first flight on a breezy Seattle morning on 13 April. After validating flutter prediction models, the prototype aircraft will enter a long series of performance evaluations, including a round of runway tests on the non-public runway at Edwards AFB, California, says Capt Christine Walsh, Boeing’s deputy chief test pilot.
Within weeks, a second flight-test vehicle, equipped with a full interior, will roll off the assembly line, and Boeing then hopes to take the largest member of the re-engined 737 Max family on an international marketing tour this summer, with potential stops at air shows in Paris and Moscow lined up in June and July, says Keith Leverkuhn, Boeing’s vice-president and general manger of the 737 programme.
A dose of publicity might help the 188-seat-class single-aisle address the A321neo’s nearly six-to-one advantage in firm orders to date. According to Flight Fleets Analyzer, Airbus has taken firm commitments for 1,325 A321neos, versus only 231 for the 737 Max 9, with United Airlines’ deal for 100 of the type accounting for 43% of the total orderbook. The A321neo was launched with a roughly 10-month lead on the 737 Max 9, and is scheduled to enter service in May.
Boeing has chosen to release sales data only at the family level for the 737 Max and the 777X, departing from a practice of breaking out firm order totals by variant on previous commercial models. The company’s shift in disclosure policy reflects a new degree of flexibility selected by some customers to convert to smaller or larger variants closer to the date of first delivery, says Randy Tinseth, Boeing vice-president of marketing. In the end, Boeing expects 20-25% of all 737 Max family deliveries to involve aircraft larger than the 162-seat-class 737 Max 8, Tinseth says.
However, the 737 Max 9 would need a historic wave of order conversions to achieve that standard alone. Of Boeing’s 3,703 firm orders through March, only 6.24% are assigned to the Max 9 - nearly 700 short of achieving the upper-range of Tinseth’s forecast demand.
That disparity helps explain why Boeing now intends - assuming customers are supportive - to launch the 737 Max 10 with a further 1.62m (5.51ft) stretch, adding two more rows of seats.
Last summer, Boeing replaced the original design of the 737 Max 7 with a similar stretch. Instead of replacing the 737 Max 9 with the larger 737 Max 10X, Boeing intends to offer both aircraft against the still-larger A321neo.
Boeing’s strategy depends on solving one engineering challenge posed by the 43.8m-long 737 Max 10X. Being already equips the 737 Max 8 and Max 9 with collapsible canisters on the aft fuselage to prevent damage from a tail-strike on take-off and landing. To give 737 Max 10X crews acceptable clearance, Boeing has to do something to effectively lengthen the main landing gear and increase the angle of the nose in pitch.
“We’re going to need that gear [redesign] for the performance that we believe we’re going to get out of the Max 10, but I’m confident in the solution set,” Leverkuhn says.
As of mid-February, the 737 Max 10X engineering team was studying several options for altering the main landing gear. Those studies have coalesced into a single solution that adds a 777-300ER-style semi-levered gear to the Max 10X, Leverkuhn says.
“I think we’re really zero-ing in on one now. it’s really about the upper portion of the gear as it integrates into the actuator and can we do some clever folding using a link mechanism at the top and then an additional shock struck that we can fit inside the same forging,” he says.
Leverkuhn acknowledges the kinematics of the gear’s moving pieces are “tricky”, but the major engineering effort is focused on developing a reliable mechanism. The 777-300ER and the 787-10 also are designed with semi-levered main landing gears, but are not exposed to the relatively frequent landings of a medium-haul narrowbody aircraft.
“The functionality is going to be fine. I really want to make it maintainable,” Leverkuhn says. “I just want to make sure it’s tailored to meet all the same criteria we’ve been talking about - performance, maintainability, reliability - because it still has to be as maintainable and reliable as the gear we’ve got on the [737]NG.”
Ahead of a 737 Max 10X launch decision, Boeing has scheduled several months of testing to verify how the semi-levered gear will perform in service. A drop test will first confirm that the new structure will fit inside the existing wheel, Leverkuhn says. A new test rig will also evaluate the reliability and maintainability of the gear under simulated operational conditions, he adds. The trials should be complete in time for Boeing to pass through a scheduled firm configuration milestone by the end of year.
If Boeing launches the 737 Max 10X, the first aircraft would enter service in 2020, or three years after the operational debut of the 737 Max 8 with a Malaysia-based Lion Air subsidiary next month. By then, it would become the fifth of at least six potential models of the 737 Max to enter service, with the Boeing Business Jet version of the 737 Max 7 scheduled to arrive in 2022.
In the meantime, Boeing plans to usher the first 737 Max 9 into service early next year, followed by the 737 Max 200 and 737 Max 7 in 2019.
Boeing has released design drawings for the 737 Max 7 to the supply chain and parts are already flowing into the production system, says Michael Teal, Boeing vice-president and chief project engineer for the 737.
Source: Cirium Dashboard
