FLUG REVUE October 2005: Trent for A380 and 787

October 2005

TRENTS FOR A380 AND 787

By Patrick Hoeveler

Every airline's nightmare is having to find alternative flights for 555 passengers or to put them up in hotel accommodation. Hopefully for them this scenario will never occur with the Airbus A380. Reliability is the key here. This applies to the Rolls-Royce Trent 900 and the Engine Alliance GP7200 as well. In developing their product, the engineers from Derby have concentrated heavily on this subject at the request of the launch customer, Singapore Airlines (SIA). For this customer, the requirement for high reliability was even more important than performance and fuel consumption. “We have done more in this area than ever before,” confirmed Robert Savidge, Chief Engineer Trent 900, in an interview with FLUG REVUE. As a result, the engines are currently undergoing hour upon hour of scrutiny on the test rigs, so that by the time the A380 enters into service, which on the current schedule is planned for the third quarter of 2006, the Trent 900 fleet should have completed up to 22,000 simulated flight cycles. To achieve this figure, one of the new megaliners would have to fly once a day for about 15 years. As of the end of August, all the Trent 900's had between them already completed 10,000 cycles.

Trent

Here Rolls-Royce has not just set itself a tough target, but its suppliers are threatened with tougher contractual penalties than on other programmes, should their components fail to achieve the required reliability values. However, according to Savidge, apart from a problem with excessive oil consumption with extended idle time, which was solved by modified seal and bearing arrangements, everything so far appears to be going to plan. “The first flight of the A380 went off without any issue on the engine. The Trent 900 has met the specifications right out of the box.” MSN001's engines correspond to an early build standard, so one would normally expect its fuel consumption to be inferior to that of production machines. “By contrast, we achieved between 0.5 and 1 percent better specific fuel consumption than guaranteed,” Savidge is pleased to report. The differences compared with the early prototypes lie in detailed design modifications which mostly result from practical experience in flying operation, such as the layout of harness clippings and pipes. How many of those units will be built for customers this year is not clear, due to the delay in the aircraft programme. “At the moment we are in the middle of a big planning debate with Airbus as to when they will need the engines. We don't want to build any engines and then have to stockpile them.”

No upgrades are planned as yet. However, Savidge can well imagine that in three to four years' time technology from the Trent 1000 could flow into the A380 powerplant, especially as regards the diagnostic systems. After all, the Trent 900 already possesses the QUICK system, which monitors performance data and vibration, and passes this information on to the operations centre in Derby in real-time, from where it is then forwarded to the customers. However, this does not mean that the maintenance intervals will be extended. Rather, it is a case of avoiding unforeseen problems during flying operations.

These diagnostic systems will very likely be quite different on the Trent 1000 - which also Northwest Airlines recently ordered for its Boeing 787 - since, according to Gary Cutts, assistant chief engineer Trent 1000, they are “very much beyond those on the Trent 900”. The Dreamliner powerplant will have twice as many sensors recording performance data for the individual modules. “This will mean that we can see what is going on mechanically in the engine.” Some of the measurements are taken once per revolution of the relevant component.

The distinctive feature of the latest member of the Trent family is the taking of power from the shaft of the intermediate pressure compressor to meet the aircraft's power requirements. “The IP power offtake is the core of the Trent 1000,” Cutts explains. Put in simple terms, its advantage is that “the more power you take off the IP compressor, the further the working line gets away from the surge margin”. Here the interaction between high and intermediate compressors plays an important role. Due to the power offtake the intermediate compressor runs slower and builds up less pressure. Therefore its working line falls. Since engines usually are designed to a fixed core pressure ratio, the HP compressor has to run faster to achieve this overall rate. Because of this its working line moves further away from the surge margin.

Due to the fact that the overall idle thrust level orientates itself on the HPC surge margin (of which there is more now in the HPC), the designers could reduce the level of thrust in idle. This results in a lower fuel consumption, up to six percent at decent during short haul flights. “That is one of the benefits of the three-shaft design,” says Cutts. The power itself taken off in the conventional way, via shafts and transmissions. The one special feature is that when the engine is started up, both compressors have to be linked to each other, as the high pressure compressor has to be started up. This requires a coupling which is active for only about 30 seconds. Here the engineers decided on a more traditional wet clutch instead of the newer fluid coupling.

Another new feature is the fan. “The fan is by some margin the most efficient one we have ever seen. It corresponds to the second generation of fan on the Trent 900.” It rotates about ten percent slower than the fan on the A380 powerplant and possesses 20 rather than 24 swept fan blades made of titanium. Thanks to improved 3D computer programs, the engineers have been able to reduce the hub-tip ratio. “With this 2.84 metre diameter design we achieve an airflow equivalent to that of a conventional fan with a diameter of 2.88 metres for no weight increase.”

Altogether the planners expect to use seven engines in the development programme plus one additional unit for testing on the in-house flying testbed, a Boeing 747 that was purchased recently. The first parts, such as discs and blades for intermediate and high pressure compressors and the first fan casing are already in Derby. Final assembly is expected to commence in November. The target first run date is February 2006. Meanwhile discussions continue with Airbus as regards possibly using a Rolls-Royce engine on the A350. “It will be very similar to the Trent 1000, but not a simple derivative. Everything will be tailored to the particular application,” says Cutts. As the Airbus aircraft operates with bleed air, the engine will need more airflow in the core, but may possibly retain the present fan diameter. It will have a different starter system and different externals. Currently there are bets placed in Derby on what exactly the engine will be called…

From page 74 of FLUG REVUE 10/2005

Last updated 14 September 2005

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