Boeing’s path for further development of the 737 series doesn’t necessarily include replacing the jet’s CFM56 engines, although that remains an option, according to John Hamilton, 737 chief project engineer. Meanwhile, 737 production continues at escalating rates, and Boeing is adding incremental aerodynamic improvements, as well as the new Sky Interior to keep the line fresh.
A 737-800 in the new United Airlines livery successfully completed its first test flight some two weeks ago, marking the start of an effort to certify a package of 737 performance improvements. Boeing has scheduled 43 flights through April 2011, by which time it plans to conduct 135 in-flight tests and 17 ground tests.
Although winglets and carbon brakes have improved fuel burn in the 737NG by about 5 percent, said Hamilton, there remained an opportunity for incremental improvements of another 2 percent. “This is a pretty efficient airplane,” he said, “and we’ve scrubbed it over the years to try to get drag out of the airplane to improve the fuel burn as much as we could.”
Boeing recently introduced the 26B2+ rating for the NG’s CFM56 engines to provide additional climb performance and improved payload capability. That option will enter service with a Chinese airline in the middle of next year.
Further changes include a more aerodynamically contoured anti-collision light on both the top and bottom of the fuselage and a re-contour of the ski jump fairing on the aft side of the wheel well. The ECS ram-air ducts will also see a change, employing the louvered-style doors used on the 777. The existing ducts, which deliver air to cool the air-conditioning packs, are open and create stagnated flow. Finally, changes under way on areas of the upper wing include a redesign of the trailing edge of the slats and the trailing edge of the spoilers “that cuts down on the bumps between the slat and the wing surface and reduces the drag,” Hamilton said.
Another wing change involves the way spoilers are rigged, to make sure they lie completely flush against the wing surface instead of causing a gap. Together, the changes account for a 2-percent fuel burn improvement, said Hamilton.
The first 737NG with Boeing’s latest performance improvement package flew to Boeing Field on November 4 for installation of new engines with a shortened nozzle. Technology changes in acoustic lining material allowed for a significant change to the engine nozzle, which designers had optimized for noise reduction. The new technology allowed designers to “optimize for fuel burn instead of noise,” delivering about four-tenths of a percent of fuel burn improvement.
Given the choice of more incremental improvements and re-engining, customers “like the incremental improvements,” said Hamilton. Consequently, Boeing might consider another performance improvement package, although extracting another few percentage points worth of performance will prove a challenge. “We think we can get something more out of this, but we haven’t been able to pin down a number yet,” he concluded.