Anyone with a passion for order would throw up their hands in horror at the hundreds of cables apparently hanging in chaos out of Rolls-Royce Deutschland´s newest engine. But the specialists in Dahlewitz know precisely which line belongs to each of the approximately 1,800 measurement points on this, the first example of the BR725. FLUG REVUE recently visited Dahlewitz shortly before the first full engine test of the latest member of the BR700 family which took place on 28 April.
The BR725 powers the Gulfstream G650, which is destined to become the business jet with the highest speed and longest range (see page 32 of FLUG REVUE 6/2008). This means that it has to achieve more power than the BR710, but with approximately the same weight. Thus, the take-off thrust is 4.6 percent higher, at 71.55kN. But this extra thrust is not at the expense of the environment, as the specific fuel consumption and hence the carbon dioxide emissions will be a full four percent lower than on the BR710. The amount by which it clears the CAEP VI limits will be 21 percent better on nitrogen emissions and as much as 72 percent on smoke emissions. Noise emissions will be four decibels lower. At the same time, the time between overhauls will be extended by 3,000 hours to 10,000 operating hours.
This is no easy task for the engineers, but to meet the challenge they have harnessed the technology spectrum of the entire Rolls-Royce Group. “Naturally it possesses elements which are derived from the BR710 and BR715, but it also incorporates elements from the Trent family,” explains Dr. Rainer Hoenig, Project Director BR725 and Future Programmes at Rolls-Royce Deutschland.
The aerodynamic design of the fan comes from the Trent 800. It possesses 24 titanium blades and its diameter has increased by about 10cm to 1.27m. The blades are curved, as on their bigger sisters on the Boeing 777. “The BR725 is the first real example of a swept fan on a corporate engine,” says Dr. Hoenig. For the first time in the BR700 series the fan outlet guide vanes are constructed from composite materials in order to save weight. However, the larger fan has required the low-pressure turbine to be extended from two to three stages.
For the first time in the BR series, the improved high-pressure compressor contains blisks, i.e. blades and discs fabricated in a single piece, in the second to sixth stages. The designers have also optimised the turbine, which is based on the BR715. “This means that we can actively change the clearances in flight to increase efficiency still further. This is the first time we have used this Active Clearance Control System in an engine of this size,” explains the engineer. “It is already integrated into the bigger Trent engines.” The combustor is based on the one from the BR715. On the other hand, the digital engine control (FADEC) is completely new and comes from the Trent 1000 on the Boeing 787.
Preliminary discussions with Gulfstream on the subject of the new powerplant took place back at the end of 2004. Development work then commenced in 2006. The plan is to build five development engines altogether and to achieve certification in June 2009. “This means that the programme has to advance at a high speed, in fact this is one of the shortest development programme ever undertaken at Rolls-Royce,” says Dr. Hoenig. The start of 2012 has been named as the official in-service date. Due to the expected considerable sales success of the G650, a somewhat earlier date is also conceivable.
The programme manager sees a promising future ahead for his product. “The good thing about the BR725 is not just that it is continuing the success story but that it is also opening up an additional market. We are working on the assumption that the G650 will by no means be the only application.” Accordingly, the engine has built-in growth potential.
On the other hand, development of the RB282 for the new Dassault Super Midsize Jet is not yet so advanced because of its later entry into service date. Serial production of the engine is to be carried out in a new facility in Virginia, USA, while the first test engines will be built in Bristol. But we can be sure that the engine will incorporate some design features developed in Dahlewitz.
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