737 Max wingtips kept under wraps

Boeing is yet to settle on a wingtip configuration for the 737 Max despite having last week firmed up several key design attributes of its revamped narrowbody twinjet family.

Current 737s are offered with Aviation Partners Boeing (APB)-supplied blended winglets, while the US Navy's 737-based P-8 features 777-style raked wingtips. Boeing's 737 Max chief project engineer and deputy programme manager Michael Teal says the manufacturer is "testing a possible revision to the wing tips on the Max" in the wind tunnel to "see if this new technology could further benefit the airplane".

Boeing says it will continue with aerodynamic, engine and airframe trade studies to optimise the design of the 737 Max by mid-2013.

© Boeing The US Navy's 737-based P-8 uses 777-style raked wingtips, while current artist impressions of the Max show blended winglets

Patrick LaMoria, chief commercial officer at APB, a Washington-based joint venture that is 45%-owned by Boeing, says there is no guarantee the company will select APB blended winglets for the CFM International Leap-1B-powered 737 Max, set for entry into service in 2017 with launch customer Southwest Airlines.

"We have a lot of long-lead future-oriented plans in place in hopes of working with Boeing for many years to come," says LaMoria. "But Max is still an open question."

Boeing confirms it has decided to adopt a 20.3cm (8in) nose gear extension for the 737 Max, in addition to controlling the new twinjet's spoilers using fly-by-wire. The longer nosegear is needed to accommodate the larger diameter of the Leap-1B engine, provisionally specified with a 1.74m-wide fan, although the precise dimensions could change before the design is frozen in the fourth quarter.

By using the maximum extension in the trade study, Boeing potentially opens the door to slightly increasing the diameter of the turbofan.

Meanwhile, the new Leap-1B engine will be integrated into the wing in a design similar to the 787, the company adds. All flight controls will remain mechanically-driven except for the spoilers, Boeing says. The 737 Max also will adopt an electronic bleed air system, designed to reduce fuel burn without adopting the 787's bleedless architecture.

Boeing also is extending the 737's tail cone and thickening the section above the elevator for the re-engined variant.