Rolls-Royce Pearl 15
The launch of the Global 5500 and Global 6500 was the biggest story at EBACE 2018. But the Rolls-Royce Pearl engine which powers the aircraft did not get as much coverage. Expect to see it at other aircraft launches soon.
IN MARCH 2017 Rolls-Royce organised a press trip to its facility in Dahlewitz, south of Berlin, in Germany. The slides had been checked, the speakers were ready, and the refreshments ordered. But the day before the tour there was a sudden panic when they realised that the aviation journalists would be taken straight past the core of a brand-new and totally secret engine programme.
Although the engine had already been selected by Bombardier in 2012, had its first ground run in 2015 – and been type tested in 2016 – Rolls-Royce and Bombardier did not want to announce it for at least another year.
The team quickly established that there was no way that it could be moved and there was no other route available. “We discussed covering it up with a sheet, but thought that would be more obvious, so in the end we hid it in full sight,” says one RollsRoyce executive. “Everyone walked straight past and no one noticed.”
Bombardier and Rolls-Royce repeated this exercise a few months later when the engine flew for the first time. In fact, by the end of 2017, the Pearl 15 had completed numerous flight tests and received its engine certificate. It was announced six months later, when a Pearl 15 powered Global 6500 was unveiled at EBACE in Geneva. The day before it had flown over from Wichita.
The Pearl 15 is an easy engine to hide, because it fits the same nacelles as the Rolls-Royce BR710A2-20 which powers the Global 6000. It is a much more powerful, and at the same time more efficient, engine with some significant differences on the inside. It delivers up to 9% more thrust than the BR710, burns 7% less fuel while NOx emissions have improved by another 20%, is two decibels quieter and enables the aircraft to fly faster. If you understand how a jet engine works, please excuse some of the next nine paragraphs. For those that do not, here goes.
A modern aircraft engine does four things: Suck, squeeze, bang, and blow. And because of thermodynamics, generally the hotter an engine is, the more efficient it is. The fan (the part of the engine that you can see) sucks air. Some of this goes straight into the compressor, while some bypasses this and goes straight out of the back. The amount of air that bypasses is divided by the amount that passes through the core to get the bypass ratio.
Air that goes into the engine is then compressed (squeezed) by a series of spinning rotors and stationary stators that compress the air. The Pearl does this over 10 stages (this is why it called a 10-stage compressor). Six of these stages use blisks. Blisks are single components made up of blades and a rotor disk – rather than attaching blades to a disk. As well as reducing the number of components in the engine and weight, blisks are more efficient.
By the time the air leaves the compressor it is 24 times more compressed than when it entered. This is a record pressure ratio in business aviation and a 50% increase compared to the BR710. It is also very hot. It then enters the core where it is mixed with jet fuel and ignited (bang). Rolls-Royce says that the core uses: “advanced materials to achieve higher temperatures and record-level pressure ratios.” The engine manufacturer says that it is using advanced nickel alloys and specialist ceramic coatings in the core.
The combustion chamber (where the bang happens) is tiled with ceramic coatings. This allows the temperature to be as high as possible – making it most efficient.
The hot gasses leaving the core then turn a brand new, two stage high-pressure turbine. This was specially developed for the Pearl engine. The gasses passing through this turbine provide energy to turn the blades of the high-pressure compressor. Rolls-Royce says that the high-pressure turbine has enhanced aerodynamics and blade cooling. It also uses a fully modulated case-cooling system – so cooler air passing through the engine is used to lower the temperature of the core’s walls.
The company says that this is more efficient and reduces fuel consumption. The engine is criss-crossed by a network of holes that cool components – this allows metal components to keep operating at temperatures greater than their melting point.
Like all engine manufacturers, Rolls-Royce will not reveal exact formulas, but the new engine relies on new alloys and ceramics. These are lighter and often rely on additive manufacturing (similar to 3D printing)
The gases then enter the three-stage low-pressure turbine. The low-pressure turbine uses new high-temperature materials so can operate at higher temperatures than the BR710 – giving the engine higher power and thrust. As well as not melting, the materials used in the low-pressure turbine are also lighter than traditional ones. Rolls-Royce has also developed new seals and segments allowing the engine to operate at higher pressures and temperatures than the BR700 engine family.
Thrust is provided by both the air coming from the turbine and the air passing around the engine (the blow), driven by the fan. The Pearl engine has a bypass ratio of 4.8:1 so 4.8 kilogrammes of air is pulled through the engine for every 1 kilogram going through the core. High bypass engines are more efficient. The BR710, which beside others powers the Global 5000 and 6000 and shares the same footprint, has a bypass ratio of 4.2:1.
Rolls-Royce has a tradition of naming engine programmes after rivers – such as the Trent, Tay, Derwent and Welland. With the Pearl it has gone more international and been very canny with its marketing. As both the US (Texas) and China have Pearl rivers it is appealing to two big markets.
When Gulfstream chose Pratt & Whitney engines for the G500 and G600 and Dassault and Textron went with Sncema Silvercrest, there was some of talk of Rolls-Royce losing market-share. Rolls-Royce kept silent and developed the brand-new Pearl engine. Today everybody knows that the manufacturer is good at keeping secrets – even if it hides them in plain sight.