Boeing eyes further payload increases and weight cuts as 747-8 engine upgrade debuts
With more upgrades in the pipeline, is optimistic that its battle to boost the performance and long-term future of the has turned the corner with entry into service of the upgraded version of the aircraft's -2B engine.
The first aircraft to be powered with the performance improvement package (PIP) version of the GEnx-2B67 is a747-8F freighter delivered Dec. 18 from Boeing's site in Everett, Wash. The upgrade forms the core of a broader set of aerodynamic and structural improvements that have been introduced since the freighter and passenger versions of the aircraft first entered service in 2011 and 2012, respectively, and was launched after pre-delivery flight tests revealed a fuel-burn performance shortfall in excess of 2%.
“Together with the other improvements made since entry into service on the 747-8F at the end of 2011, the engine PIP bundles 1.8 percent with another 1.7 percent for a total of 3.5 percent [fuel burn],” says 747-8 chief project engineer Bruce Dickinson. The GEnx-2B67 PIP incorporates an all-new low-pressure turbine, as well as compressor, combustor and turbine improvements derived from the second batch of upgrades (PIP II) devised for the GEnx-1B engine on the 787. GE provisionally expected a 1.6% fuel-burn improvement but, based on positive test data, increased this to 1.8%.
Flight tests of the PIP were conducted with RC021, a 747-8 passenger model previously allocated for -8 Intercontinental launch customer. Testing also included a block change software upgrade (FMC Block 3.0) to the flight management computer (FMC) and related work to enable activation of the 3,300-gal. tail fuel tank, which only the passenger model has. Both features are expected to be certified shortly and remain on schedule for activation by year-end and early 2014, respectively. The FMC update provides “a number of capabilities that include 'quiet climb,' [required navigational performance] and optimum step climb,” says Dickinson. The added capability will enable crews to take greater advantage of favorable tail winds and gain other routing bonuses that should save more fuel. However, Boeing is not booking any of the potential performance benefits, as these savings are difficult to quantify from operator to operator, he adds.
The tail tank was deactivated before the first aircraft entered service, when analysis indicated that it could induce flutter under certain fuel-load conditions. The additional volume has now been cleared for use and will provide 300-400 nm more range, says Boeing.
Boeing is also releasing more details of the aerodynamic modifications that have been introduced since entry into service. Drooped ailerons, which improve span loading across the wing, were tested on the -8 passenger version and gleaned a fuel-burn improvement of “four-tenths of one percent,” says Dickinson. “That was after everything was locked down on the -8F, so we went back and applied the same droop as a retrofit to the freighter,” he adds. Changes to the rigging alignment of the rudder have also been made to reduce cruise drag. “There were minor thermal effects at cruise, and we realized we could rig the aircraft so that once it was cold-soaked, the rudder could be optimized,” he says. “It was really as simple as going through extensive reviews of the data and understanding where the rudder is under sustained cold-soak conditions. We can set the rudder rig in manufacturing so that it is now optimized for cruise.”
Performance enhancements have also been introduced through a 12,000-lb. increase in maximum takeoff weight (MTOW) to 987,000 lb. with a concurrent reduction in operating empty weight of almost 8,000 lb. The MTOW increase was enabled through detailed analysis of the results from the flight-loads survey conducted during flight tests. The weight reduction target is 10,000 lb. by 2016, of which 7,900 lb. has already been identified.
“We continue on that journey to 10,000 pounds,” says Dickinson. “We definitely see opportunities to do that, and we are continuing to study ways of getting there. It's not all engineering design change. We are also going after it from all angles, including getting into detailed discussions with suppliers on reducing the weight of fasteners to the amount of corrosion compounds to use, and what is just enough. It all adds up.”
In the longer term, Boeing's product development studies continue to address other upgrades under the collective title Project Ozark. “We're in the middle of all those product development studies about the best ways for improvements, and there's a host of them,” says Dickinson. These range from additional weight and drag reduction, including lower-drag wing-body fuselage fairings to “get even more MTOW from the structure we already have,” he adds. Much of this is focused on a deeper analysis of the flight-loads survey. “We looked at that loads data extensively and knew we could increase to 12,000 pounds without any changes, and now we're looking at it through the microscope and seeing what else is possible. We're going after what we could do, but in a way which would take only minimal changes,” he says.
Independently of the PIP introduction, Boeing and GE also continue work to mitigate core-icing, which has impacted operators of GE-poweredand 747-8s. Updated engine control software will open variable bleed valve (VBV) doors to eject ice crystals before they enter the core. “We did test the functionality of the software on RC021, but that was for the simple operability questions for VBV operations. GE is prime on that, and we are going through the validation plan for what will be done on that software,” he adds.
The debut of the engine upgrade coincides with long-awaited signs of a slow recovery in the air cargo market, which accounts for most 747-8 demand. “We're quite optimistic because people take notice of improvements like this bump in performance. When you take the PIP, tail fuel and FMC improvements and combine them with everything else we've done to get a 3.5 percent improvement in efficiency, then it starts to get a lot of notice in the marketplace,” Dickinson says. “As far as the freighter goes, we are equally optimistic. The freighter market has been quite difficult, but we're expecting that to return in the near term.”