Paris Air Show

GEnx orders may swell here

 - December 13, 2006, 12:32 PM

Orders for as many as 250 new General Electric (GE) GEnx engines are expected here at the Paris Air Show this week as the Boeing 787 program gathers pace after last year’s hesitant start. Announcements will come as Boeing prepares for the launch of the stretched 747 Advanced (for which it predicts a market for up to 300), and Airbus launches its A350 variant of the A330–both programs representing applications of the new engine. Airbus expects to announce here commitments for at least 100 examples of the A350, for which Rolls-Royce is likely to be a competing engine supplier.

Boeing had hoped to have firm orders for the 787 covering at least 200 aircraft by the end of last year, but only in recent weeks have some deals finally fallen into place. At the beginning of June, “orders and commitments” covered 266 aircraft and 21 customers, including Ethiopian Airlines, which has become the first to exercise 787 purchase rights or options.

Customer selections set to be announced this week, including Korean Air and possibly Air Canada, may introduce balance to the currently somewhat one-sided 787 engine orderbook. So far, the Rolls-Royce Trent 1000 has accounted for 52 aircraft ordered by major carriers All Nippon Airways and Air New Zealand, while GE has only a memorandum of understanding for just six machines from UK charter operator First Choice, which has options on a further six. Other outstanding engine decisions include those by Japan Air Lines, which has only recently opened an engine-selection competition; Air India (a previous GE customer);  and Ethiopian Airlines.

The U.S. engine maker will go “full steam ahead” with the 55,000- to 72,000 pound-thrust GEnx after agreeing a detailed powerplant specification with Boeing. Late last month, GEnx program manager Tom Brisken told Aviation International News that the two companies were within 30 days of final agreement. “Open” items included installation configuration and details of nacelle and thrust-reverser fit.

Based on the architecture of the much larger GE90, the GEnx is a successor to the CF6 series. Its characteristics include composites front fan-case and fan blades for improved durability and weight reduction, and a “next-generation“ combustor for efficient pre-ignition fuel mixing, which is aimed at generating lower nitrous-oxide emissions levels. GE claims composites save as much as 800 pounds weight per aircraft. Later this year and in 2006, GE will run full-scale case and blade tests to evaluate the GEnx fan configuration.

Four months after freezing the design, GE is well into production of the initial GEnx, according to Brisken. “We already have got the titanium casting finished for the fan hub frame. The high-pressure compressor disk forgings are complete, and turbine nozzle airfoil castings have been poured.” Both items will be machined by October “ahead of instrumentation,” explained Brisken. GE plans to run the first engine next March and will build seven production-standard units that will be used for certification, which is expected by July 2007.

Rolls-Royce has completed detail design of the 63,000- to 70,000-pound-thrust Trent 1000 engine, which is due to run on February 14, 2006. Development is well under way, with the fan case forging having been completed earlier this year. All components for the engine must be in the parts store by November when assembly of initial engines begins, said managing director (airline) Charles Cuddington.

Rather than composites, Rolls is using a lightweight forged titanium fan case. The 112-inch-diameter fan comprises 20 wide-chord, hollow-titanium swept blades. The company has concluded that nickel alloys offer the best heat-capacity characteristics for compressor blades, with performance tied to high-quality surface finish and close-tolerance leading-edge profiles. Cuddington sees the nickel alloy compressor blades as a good example of emerging Rolls-Royce technology with potential application on other engines.

By using a smaller “spinner” in front of the Trent 1000 fan, Rolls has been able to enhance the engine’s bypass ratio because the lower hub-to-tip-diameter ratio improves the flow area. Following previous experience, the UK manufacturer has introduced core de-icing, although this is not required: “It is an issue we have identified, particularly with operations in freezing fog,” said Cuddington.

To save weight and improve maintainability and simplicity, Rolls uses a single- (rather than double-) skin tiled combustor and single-piece titanium intercase casting. Forced-air cooling has been introduced for intermediate-pressure spool blades, which are subject to generally higher temperatures (unrelated to the local power-generator drive for the aircraft’s more-electric architecture).

The Trent 1000, which also was a candidate engine for the 747 Advanced, is to be offered on the Airbus A350 under commercial arrangements likely to be announced here this week. This model will reintroduce bleed air, which is not required on the 787. Variants with more than 75,000 pounds thrust will be offered, to provide sufficient power for a higher gross weight, longer-range variant of the new airliner (possibly dubbed A350-1000) that could compete against the Boeing 777-200ER.

P&W declined to offer an engine for the 787, since “the numbers were just too hard,” president Louis Chenevert said.