Boeing 787 Dreamliner - Mark Wagner [60]
But these projects remained nebulous, and 2000 saw the focus shift to Airbus, which was studying a potential 250-seat, medium-range “shrink” version of the A330, variously dubbed the A330-100 and the A306. The new aircraft would have required a 55,000-to-60,000-pound-thrust range, which, although significantly below the Boeing study thrust sizes, was enough to pump new life back into the CF6-80G2, which was outlined with a hybrid titanium fan.
However, the Airbus performance targets were extremely aggressive, and GE began to be pushed inexorably in the direction of a new centerline design. It was a tough decision for GE to turn its back on the long-serving CF6, as well as the considerable investments in future growth studies such as the -80G2. But the company had the massive benefit of the GE90 and its new core at its disposal, and was determined to use this as the springboard for a whole new family. This was particularly so since GE’s momentous 1997 “U-turn” decision not to write off the GE90 and pursue further growth to support the 777.
The GE90 was a solid foundation for new growth because it used a raft of technology derived from a long series of successful GE and NASA research programs. These included the 9:1 bypass ratio; a wide-chord, composite fan blade that evolved from the GE36 unducted fan (UDF) program; low-noise and low-weight composite nacelle technology from the quiet, clean, short-cycle, energy-efficient (QCSEE) program; and a rugged dual-dome, low-emissions combustor design from the efficient, clean combustor (ECCP) program.
Rolls-Royce’s Trent 1000 built on many features developed for the Trent 900 for the Airbus A380, including a swept fan and contrarotation. While the A380 high and low/intermediate pressure systems rotated in the opposite direction, it was the intermediate spool that counterrotated in the 787 engine. Here Trent 900s are mounted on the right wing of a Qantas A380 flying down the California coastline in 2008. Guy Norris
One of the most critical efforts, however, was the joint NASA/GE “E3” (energy-efficient engine) program, which proved the design benefits of a ten-stage high-pressure compressor (HPC) with radically advanced aerodynamics. The E3 spawned the advanced 23:1 pressure-ratio HPC at the heart of the GE90 and formed the basis for a whole new set of derivative cores, including a nine-stage HPC for the higher-thrust GE90-115B and the Engine Alliance GP7200.
In November 2001, GE revealed that its GEN X concept would be based on a scaled-down compressor from the GE90-115B, by then in initial tests. Admitting it was “very early days,” GE90 Advanced Program General Manager Mike Benzakein said the GEN X would be more integrated with the airframe than previous engines.
“On GEN X we are looking at a thrust requirement of around 90,000 pounds, assuming a Mach 0.98 cruise speed and a capacity of 250 passengers. This means we’re looking at around an 80 percent scale of the GE90 core in terms of flow scale,” he said. GE “always expected” Boeing to favor an all-new engine for the Sonic Cruiser over simpler derivatives of 777 engines such as the baseline GE90, and GEN X satisfied this requirement, he added.
The GEN X concept study rested on the evolved nine-stage HPC tested in the eighth of a series of GE90 test cores. Previous tests included the fourth core, which focused on three-dimensional (3-D) aerodynamic improvements, while the fifth was used to test a nine-stage configuration. The sixth core, tested as part of GE90-115B development, further refined this configuration, while core seven, which ran in late 2002, formed the basis for a 72 percent scaled version for the GP7200.
The Sonic Cruiser engine contest moved up a notch when detailed analysis revealed that simple derivatives of existing 777 engines would not work. The call for an all-new engine set manufacturers on the path to what would become the world’s most efficient turbofans. Mark Wagner
A big part