Since the beginning of this year, the Trent XWB-84 – the world’s most efficient large aero engine – has been providing exemplary service on the new Airbus A350 XWB airliner. However, the forthcoming larger version of the aircraft – the A350 XWB-1000 – will employ a different version of the Trent family.
The Trent XWB -97, as its designation suggests, is a 97,000lb thrust engine and is the more powerful sister engine of the -84. It is undergoing a rigorous test regime right now as it prepares for first flight later this year on an Airbus A380 flying test bed (FTB) and subsequent entry into service on the A350-1000 in 2017.
One man who has been intimately involved in the development of both the Trent XWB-84 and -97 is Simon Burr, most recently Director of Trent XWB Programmes and now COO for Civil Large Engines in Rolls-Royce.
Now the challenge is on for Simon to drive the -97 development to its successful conclusion.
And if you are thinking that this is just an upgraded version of the -84 and so does not require the same amount of development work, testing and proving, then think again. The -97 does of course have many attributes that are similar to its sister Trent, but it is also very different in some of the advanced technologies it employs to produce the extra thrust and optimum aircraft performance.
Cooling
According to Simon: “The Trent XWB-97 will be the highest thrust engine we have ever certified, the highest operating temperatures and the most advanced cooling systems we have ever designed in a civil engine. We are working at the leading edge of technology but that is what you do to produce the world’s most efficient engines.”
For the engine operators’ point of view there is deliberately very little visible difference, or indeed operating difference, between the -84 and -97.
However, look inside the -97 engine and the changes are notable. The front fan has the same number of blades and is the same diameter at 118 inches but it runs around six per cent faster. The engine core has been scaled up in size to cope with the consequential increased airflow into the compressor and, in this engine, the combustor and turbines run hotter than in the -84.
The high-pressure turbine gets additional technology too. “To get the performance and efficiency from this machine we need to grow the turbine temperature capability to a level higher than we have with any large aero engine in the past,” says Simon. “Maintaining thermal efficiency at those higher temperatures is critical, so we’ve invested in new materials and coatings for the high-pressure turbine blades, but also employed an intelligent cooling system that provides the right amount of cooling air to the blade throughout the flight cycle.
“You are always balancing durability against efficiency in designing aero engines but we have over 80 million hours of Trent experience behind us. This is a robust engine built on decades of 3-shaft engine design understanding.
The -97 development programme has also featured components produced by additive layer manufacturing (ALM, or sometimes commonly known as 3D printing). Rolls-Royce claimed a world record for the largest aero-engine component assembly ever manufactured in this way with a 1.5m diameter front bearing housing for the -97. The ring of ALM vanes form the inlet to the engine’s core and each vane has an intricate series of heating passages inside them that can be used by an anti-icing system to protect the engine during adverse weather conditions.
“We did it as a demonstration of our capability,” says Simon. “There are two real benefits to ALM,” he says. “The lead time in engine development is dramatically reduced and the design freedom it offers as opposed to conventional casting or machining, both could be significant.
“However, there are real considerations to be overcome. Once you have productionised a component via this method then you are committed, as it can only be made in this way. You also need to have enough machines that are fast enough for the production process. Lastly, you need a stable and adequate source of atomised metallic powder that you can trust. I think there is more work to be done on ALM but it is an enticing technology.”
So, although the ALM-produced front bearing housing will be in the development -97 engines, it won’t be in the initial production engines.
As of today, there are four engines running in the development programme for the -97. The first development engine conducted proving runs up until September of 2014. It provided a lot of useful data to the development team and that engine will now go on and do major tests such as ‘bird strike’.
A second engine is in Canada completing its cold weather and icing running. A third engine has been performing endurance work and has also been x-rayed on a test bed in Derby, UK. Dynamic x-rays show the behaviour of the components inside the engine as it operates, which can help prove the design theories by effectively giving the engineers ‘eyes-on’ the inside as the engine runs. The fourth engine in the development programme will be used for performance work.
All of this is in the build up to the fifth engine being employed on the Airbus A380 flying test bed(FTB).
Airbus is due to fly the first A350-1000 for the first time in 2016. Rolls-Royce is currently building the first flight engines for that event.
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