Boeing engineers appear to have kept themselves busy refining the design of the 737 Max since the company announced its intention to re-engine the ubiquitous 737NG with CFM Leap-1B turbofans. Apparently, the laws of physics have challenged Boeing’s ambition to minimize airframe and systems changes, judging by the extent to which it now expects to refine the design to achieve the fuel burn and performance targets it set for itself when it launched the Max last August.

Changes to the design announced just last week include aerodynamic improvements to the aft body section, on which designers have extended the tail cone and thickened the section above the elevator to improve the steadiness of airflow. Boeing expects the modifications to eliminate the need for vortex generators on the tail and result in less drag.    

As expected, in an effort to maintain about the same engine ground clearance of the NG, Boeing plans to use a new engine pylon and strut, along with an eight-inch nose-gear extension and a change to the nose-gear door design. Meanwhile, designers have integrated the engines with the wing to produce aerodynamic lines similar to those seen on the Boeing 787.

A change to the flight control system involves a switch from mechanical to fly-by-wire spoilers to save weight, while an electronic, rather than pneumatic, bleed-air system allows for increased “optimization” of the cabin pressurization and ice protection systems, resulting in better fuel burn.

Of course, Boeing will also need to strengthen the main landing gear, wing and fuselage to accommodate the increase in loads due to the larger engines, which have a fan diameter of 68 inches. Boeing also continues to conduct wind tunnel testing on a possible revision to the wing tips. The company said it will continue to conduct aerodynamic, engine and airplane trade studies as the design team endeavors to finish its work by mid-2013.

“Any new technology incorporated into the Max design must offer substantial benefit to our customers with minimal risk for the team to pursue it,” said Michael Teal, chief project engineer and deputy program manager. “On the 737 Max we are following our disciplined development process and continue to work on an airplane configuration that will provide the most value for our customers.”

Boeing promises the Max will deliver a 10- to 12-percent fuel-burn improvement over today’s 737 and a 7-percent per-seat operating cost advantage over the Airbus A320neo.