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ENGINE GIANTS

Civil turbofans are becoming larger and more powerful, as engine manufacturers dash into dimensions that almost were inconceivable not that long ago. The latest generation of products from General Electric, Pratt & Whitney and Rolls-Royce produce up to 512kN (115,000lb) of thrust. To put this in perspective, the engine that powered the DH Comet, the first Jetliner, delivered just 22kN (4,950lb). Thanks to the latest technologies, engineers are coaxing more and more thrust out of the powerplants.

Thus, for example, the fan diameter is increasing steadily. The largest fan around today can be found on the most powerful civil engine in the world, General Electric's GE90-115B (512kN ). With a diameter of 3.25m, a Boeing 737 cabin would almost fit inside it. Yet, there are good reasons for these gigantic dimensions. The bigger the fan, the higher the bypass ratio and hence the more power is generated, as GE engineer Klaus Huber explains. "The capture area of the fan is significantly larger. That means we can pump in enormous air masses, up to 1,400kg per second."

Another decision the Cincinnati design engineers have made on their new flagship for the Boeing 777-300ER is to apply swept wide-chord fan blades. These special blades achieve a higher air flow and, according to GE, produce up to 8.9kN/2,000lb more power but with reduced fuel consumption. The most powerful version of the GE90 also has a four-stage booster instead of the three stages found in the 94B version, plus a dual annular combustor (DACT2) for more effective combustion through higher airflow.

In the high-pressure turbine improvements have been achieved by using 3D aerodynamic design. Through accurate calculations and simulations with computers it is possible for the individual elements to be precisely tailored to the airflows involved. This means that fewer blades are needed. The first test run is scheduled for the end of this year. Flight testing on GE's 747 is planned for the spring of 2002. In September 2003 the engine will then enter service with Air France.

Naturally GE is in discussions with Boeing regarding new applications such as the Sonic Cruiser. According to Klaus Huber, this will entail a new engine although it will no doubt build on the technology of the GE90. With regard to the 747LR, possible plans depend on Boeing's performance requirements. However, these have not yet been defined.

The new technologies employed in the GE90-115B are also used on the GP7000 engine produced by the Engine Alliance of General Electric and Pratt & Whitney. Thus 3D aero technology is being used on every aspect of design of the engine for the ultra-large Airbus A380. The engine core comprising of a nine-stage high-pressure compressor (HPC) and a two-stage high-pressure turbine (HPT), the annular combustion chamber and the FADEC control system are all to be produced by GE. HPC and HPT correspond to the components used in the GE90 but on a smaller scale. Pratt & Whitney is contributing the five-stage low-pressure compressor and the six-stage low-pressure turbine from the PW4000. In addition P&W is building the fan with swept wide-chord blades, whose overall diameter is 2.95 m.

The joint product will initially be offered in two versions. The GP7270, with a performance rating of 311kN (70,000lb), will power the passenger version of the A380 and should be flying with Air France by the end of 2006. The GP7277 for the A380F freighter, with 342kN (77,000lb) of thrust, is even more powerful. However, the certification rating will be at 362kN (81,500lb) to allow for possible growth.

Huber is confident of further orders in addition to the only order so far from Air France, despite the delay in Lufthansa's decision. "We continue to be optimistic on FedEx and are working hard on Lufthansa and Emirates." The marketing strategists who compete with the rival Trent 900 from Rolls-Royce, also have their eye on Atlas Air and Qatar.

At present the EU Commission studying whether to launch an investigation of the #250 million financial support received by RR from the British government to fund development of the latest version of the Trent. The competition views this assistance as trade-distorting and an illegal practice. All the same, the UK engine manufacturer has already won four customers for its A380 powerplant, ILFC, Singapore Airlines, Qantas and Virgin Atlantic.

Rolls-Royce attributes its success to its philosophy of family development. "We are building on a familiar design to ensure the reliability of the product for our customer," says Robert Nuttall, Head of Marketing. The improvements have evolved as part of a gradual process. "Between the Trent 700 and 900 lie almost 10 years. Therefore there is hardly any comunality between the two engines."

All versions of the Trent incorporate the three-shaft system already demonstrated on the RB211, with an additional intermediate pressure unit. According to Nuttall, this design allows the engine to be shorter and have fewer stages. Thus, for example, there are no booster stages necessary. Moreover, the three shafts allow the components to rotate in their optimal speed ranges. By contrast, the competition in the USA prefers only two shafts which, it is argued, makes the engine simpler and more robust.

Like the Engine Alliance, Rolls-Royce has also decided on swept wide-chord fan blades in the Trent 900. These, according to Nuttall, direct the supersonic shockwave from the blades into the engine. "That makes the engine more effective, lighter and also more resistant to foreign object damage." However, this is not the only change that has been made to the fan. "A higher bypass ratio increases effectiveness and reduces noise because the fan is turning more slowly." For this reason the fan diameter has been raised to 2.95 m. The Trent 900 thus has a bypass ratio of 8:1. 3D aero design has been used as well. As an already proven component the enlarged Trent 500 combustor comes into play.

This engine shows the progressive development of the UK company. While the fan is essentially similar to the fan on the Trent 700 for the A330, the engineers have used 3D technology in the intermediate and high-pressure areas. The compressor blades now have small ribs which improve the airflow individually for each stage. Another novelty is a tiled combustor which has a more effective combustion process and therefore reduces emissions.

Airbus chose the Trent 500 as the exclusive powerplant for the A340-500 (Trent 553 with 236kN, 53,000lb thrust) and the A340-600 (Trent 556 with 249kN, 56,000lb thrust) longhaul airliners. However, the engine is certificated at a rating of 267kN (60,000lb). According to Nuttall, there is no difference between the two variants. "The data plug in the aircraft determines what rating is needed." The first flight of the Trent 500 took place on 23 April of this year on the A340-600. It is scheduled to enter service with Virgin Atlantic as early as July 2002.

In the meantime the British engine builders have been in discussion with Airbus's arch-rival Boeing regarding two new applications. According to information supplied by RR, the Trent 600, with between 65,000 and 70,000lb of thrust, will possess slightly less thrust than the Trent 900. The precise figures will depend on the performance specification which has yet to be issued by Seattle. Rolls-Royce is also working closely with Boeing on the Sonic Cruiser. According to Nuttall, the engine will have a lower bypass ratio and build on the technology used in the Trent, although it will not be an existing version of the Trent.

Improvements are also under way among the large engines produced by the three companies that are already in service . Thus, for example, the CF6-80E1A3, the latest and, with 320kN (72,000lb), the most powerful variant of the proven CF6 family from General Electric, is currently being flight tested. According to GE, moreover, the engineers are considering an even more powerful version with up to 75,000lb of thrust. This engine could then be fitted with swept fan blades. A chevron nozzle which would reduce noise emissions by up to 3DB is also under investigation.

Pratt & Whitney is sticking with its PW4000 family, more than 2,400 of which are in service today. In the fierce three-way competition on the engine market, the company just has the edge over Rolls-Royce and GE on the A330, whereas the Europeans are in the lead on the 777. But how the market will develop following the recent atrocities in the USA is anybody's guess. Before the terrorist attacks Rolls-Royce was predicting that between 2001 and 2020 there would be a requirement for 9,400 engines in the 45,000-65,000lb thrust class, and 13,484 units above 65,000lb. "It is still too early for detailed estimates", confirms Robert Nuttall. But if the recession in air traffic should continue, the engine makers will not escape unscathed.

From page 94 of FLUG REVUE 11/2001