Rolls Royce looking ahead...

Yesterday Rolls Royce surprised the aero engine world at a briefing about it's strategic roadmap by looking ten and more years ahead and revealing, what the company plans as their next steps in engine development.

In the 2020 timeframe we could see a further evolution of the Trent 3-spool engine family for now called "Advance" (I am sure the name will change once it should evolve from being a technology project and becomes a real program). This engine should deliver an SFC that is 5% better than the Trent XWB. As aspire aviation pointed out, the GE9X for the B777X should be about 5% better than the Trent XWB, so it is clear who is the "enemy" here.
The time frame and the SFC goal puts this engine concept  in the position to be a good candidate to power the A380neo, if the project goes ahead. But Airbus could also ask for a version with more thrust than the roughly 70klbf needed for a re-engined A380 to power a A350-1100 and then have a formidable competitor to the Boeing B777-9.
A first test engine based on the Trent XWB, but with a new core with a higher OPR - up to 60 and thus being on the same level as the GE9X - should run as early as next year.

The second engine does not necessarily build on the Trent 3-spool architecture as it - potentially - could use a gear as we currently have on the PW1000G family from Pratt&Whitney. Of course also a 3-spool GTF is possible, but I doubt that makes real sense, so I would guess it would have 2 spools. This engine should then be another 5% better than the "Advance" engine.
This engine concept should not only target the widebody market but also future narrowbodies. In the light of recent discussions about a possible B757 replacement and a successor to the B737MAX family with an EIS around 2025 this is an interesting move of course. After selling their stake in the IAE to P&W, both companies announced  a partnership for future narrowbody programs. This partnership was later canceled. But for any future narrowbody we should expect a choice of two engines, not three. And CFM seems to be the frontrunner in any case (unless the LEAP engines will fail completely, what I doubt), so either RR or P&W would be out of the game. So is this move aimed at P&W begging for a new try of the partnership? Who knows...
Anyway, the above SFC comparisons are true for widebody engines in the GE9X class - for narrowbody engines we have to scale the SFC values, as for example the tip clearances are not scaling with the physical smaller components of the engines. Relative clearances are larger and so are aerodynamic and parasitic losses. Therefore all engine components have lower efficiency levels. And as the core components (high pressure compressor and turbine) get smaller and smaller with increasing bypass ratio (BPR) and overall pressure ratio (OPR) for a given thrust, it gets harder and harder to maintain a decent efficiency level. Also surge capability of the compressor might not be easy to control. In the end, to achieve an OPR of 70(!) for this engine I predict this will only be achievable with a radial compressor stage at the back and of the compressor. And at temperatures that will be reached at such a high OPR this wheel has  to be out of a material that can only be found in turbines today. Maybe CMC? Then good luck producing such a complex piece out of that material? The other possibility would be to have an intercooler between the low and high pressure compressors. But that would add weight and complexity, counterproductive for a narrowbody engine. This is why I see that concept better suited for a long range application, where (engine) weight does not have such an immediate effect on fuel burn, The same argument could be, but must not be necessarily true for the envisioned variable pitch fan system. This idea goes back to the ADP concept from P&W from the 1980's. The variable pitch system has two great advantages versus non-pitch fans: there is no need for a thrust reverser (which save weight) and the whole nacelle can be shortened, also saving weight. On the other hand, the pitch system itself is complex and needs additional maintenance. As these maintenance cost are mainly cycle driven, I also see this technology better suited for long-range, low cycle operations.
But who knows what "white rabbits" Rolls Royce will pull out of their hat by then - it is a great company and I would not be surprised if they find ways to handle all these challenges.


  1. "Of course also a 3-spool GTF is possible, but I doubt that makes real sense..."

    Would you be able to explain simply why it doesn't make sense?


    1. A 3-spool GTF offers not really much benefit in terms of optimized component efficiencies versus a 2-spool GTF, but is mechanically more complex. For a narrowbody (physically smaller) engine the diameter of the inner shaft may also become to small transfer the torque.

    2. The transformative advantage from a reduction gear is linked to fansize. limitations on tipspeed for the front demand a large ( diameter, blades ) turbine section. The gearbox allows a faster turning smaller, less blades turbine. Independent spools on the other hand allow for a wider efficiency plateau in use.
      A 3 spool GTF would make sense efficiency wise. It may be too complex to reap the potential gain in use.

  2. I wrote a story to my group about the 30 years ago study by Hamilton Standard of the Q-FAN provide me a email and i will forward to you.