Is the A330neo engine Rolls Royce’s first carbon fan model?

The Airbus A330neo program has come a long way since our 29th of December article  “A330neo prospect gains traction.” With the Farnborough Air Show days away, we understand there are now Airbus internal job postings for engineers to join the program. The speculation then reduces to “when” the program will be announced, not “if.” Another would be what improvements are foreseen for the Boeing 787-derived engines that may power the neo.

Rolls Royce reportedly gains exclusivity

Reuters recently reported that Rolls Royce might get an exclusive engine deal for the A330neo. There are many reasons Airbus might give Rolls Royce or General Electric exclusivity on an engine for the A330neo, especially if Airbus sees the likely sales of the updated aircraft to stay below 500 units. The reasons can range from how much of the $2B estimated program cost the engine manufacturer would pay to what efficiency improvements they would undertake on top of what is already on the way for their 787 engines. There is every reason to believe the GEnx-1B can match the fuel consumption performance of a further developed Trent T1000-TEN. We understand Rolls Royce will leverage developments from the A350 TXWB engines but GE can just as easily leverage developments from the LEAP program.

T1000 ALPS demonstratorThe picture shows the Rolls Royce Trent 1000 carbon fibre fan demonstrator engine from the companies ALPS (Advanced Low Pressure System) program.  Is this also the looks of the Rolls Royce A330neo engine?

If the reason for Airbus giving Rolls Royce exclusivity would be technical, we think it might rather be that Rolls Royce have finally realized a long standing potential in the Trent’s engines weight domain. The more efficient 787-derived A330neo engines are a full tonne heavier per engine then the engines they replace. As an A330-300 classic and its competitor, the 787-9, have similar empty weights, the heavier engines will set a A330neo back with a further 2.5-3 tonnes, knock-on effects included. This extra weight will be felt on the  2,000-3,000nm missions these aircraft often fly where the engines improved fuel consumption will be less noticeable. Any weight that can be saved in an A330neo engine will therefore be of utmost importance to Airbus.

The lighter Tri-shaft

Contrary to what one assumes, a triple-shaft turbofan is principally lighter than a two-shaft architecture, everything else being equal. This comes from the fact that a two-shaft engine couples the low pressure compressor, the Booster, to the rotational speed of the fan. The fan is spun so that the outer third of the fan blades have supersonic speeds, the middle part transonic and the inner part subsonic. As the booster comes directly after the subsonic inner part of the fan and shares its rotational speed, it also works with subsonic blade speeds. The result is very low pressure gains per stage, about +10%, compared with +30-40% per stage for an optimal spinning compressor like the ones in GEnx high pressure compressor. This results in more stages for a given pressure ratio and to not lose even more efficiency, the booster diameter is kept as large as possible, thereby rendering all discs and frames heavier then the comparable tri-shaft compressor part. In the equal scale cut-through of the GEnx-1B and Trent 1000, it can be seen that the GEnx’s low pressure compressor diameter is essentially double that of the Trent’s low pressure compressor, the IPC.

GEnx vs T1000 cut-through

This then repeats on the turbine side. The turbine section of the GEnx is longer and has a larger diameter than the T1000.

General Electric have mitigated any weight disadvantage their chosen architecture would have by going to a CFRP fan already in 1995 with the GE90. Rolls Royce tried a carbon fiber fan for the RB211 (Hyfil fan) but changed to the heavier Ti fan due to Hyfil toughness problems. The end result is that today’s 787 engines both weighs around 6.1 tonnes but Rolls Royce should be able to lower that to 5.9 tonnes should it decide to use the CFRP fan and fan case from its ALPS program.

Design and production system

Rolls Royce have always maintained that the hollow Ti fans it produces can be made thinner and therefore more aerodynamically efficient than CFRP fans and that the weight disadvantage is minimal. After a decade of research RR now claims it has a CFRP fan blade design and production system that can compete with Ti blades. The end result of this development is the ALPS demonstrator engines that now run on the Derby test beds and which will fly on its 747 test aircraft this fall. RR also perfected a 3D woven carbon fiber production system which uses resin infusion, which was done together with GKN in the CTAL joint venture where Rolls Royce has now bought out GKN.

With both design and production being ready for prime time, we see no reason to wait until 2020 for the Advance engine to use this technology. An A330neo could use it to equal advantage in the 2017-2018 time frame.

By Leeham Co EU

27 Comments on “Is the A330neo engine Rolls Royce’s first carbon fan model?

  1. A pressure ration of 2 for an axial compressor seems to high for me. A 1.8 pressure ration for the first stage seems reasonable, then decreasing with every stage.

  2. From Wikis GEnx-1B entry:

    – High pressure compressor based on GE90-94B, with 23:1 pressure ratio and only 10 stages

    Makes for more gain per stage then 2 in my book…, this is for Top of Climb of course, not cruise.

    • Uhm, no.

      With 10 stages, PR of 23 and an average pressure increase of pi, we get:

      pi^10 = 23
      pi = 10^((log23)/10) = 1.368273

      But as OV points out, in practice the PR per stage varies quite a lot.

      • Thanks guys, the pressure gain percentage has been adjusted.

        @mneja, thanks but it can also be expressed as:

        PR = Stage gain ^ Stages

        and therefore:

        Stage gain = PR^(1/Stages)

        Gives the same result with a simpler formula. Example:

        A typical booster like the GEnx-1B gains you over 4 stages a PR of 1.5 ie you have:

        Stage gain = 1.5^0.25

        which gives you 11% per stage on average.

        • Ah… you can obviously express it like that. Must have been low on sugar…

  3. Nice post! Interesting to see some engine stuff once in a while.

    Speaking of weight savings, I’d expect a carbon fan case to save a good amount of weight. As will a composite fan (especially in the disk).

    RR can also introduce more rows of VGV’s in their compressors. I think they on the T1000 only have one (HPC 1st stage). Would perhaps allow them a shorter HPC, due to better off-design characteristics? This has been a GE strong point in compressor design historically.

    • composite fan:
      Doesn’t GE gain significant weight savings from reduced blade out containment requirements on/in the fan? ( probably by way of having proved that CFRP fanblades don’t come off in one intact piece )
      i.e weightsavings not only from lighter blades but also reduced containment.

      • They somehow convinced the FAA that with CFRP the most likely failure mode is one-third or halfway of the blade span (can’t remember which right now), rather than at the blade root, like for metallic blades. This gives significantly lower weight of the impacting mass on the fan case, which can hence be made lighter than would otherwise be the case (pun intended…). In my understanding this is a large part of the weight savings with CFRP fan blades (although the blades are a little lighter too, which also has knock-on effect on fan case thickness).

        • You can compare carbon fibers with a steel cable: very strong for tension but extremly bad for pressure.
          Unlike a solid titanium blade you can design weak points within the blades so that they easilier disintegrate on impact.

  4. The cabin of the A330-300 is 92 inches longer, accommodating not even 3 rows of 8 seats (ignoring the tapering) but is 1 seat narrower throughout. So the 787-9 is quite a bit larger. But the A330-300 already weighs more, 274.5K lbs empty vs 259.5K lbs of the 787-9. Adding 5K lbs for the new engines, a smaller A330-300 weighs 20K lbs more than a larger 787-9. Plus the 787 has newer and better wing and aerodynamics. How is it possible that the A330 will come anywhere near the 787-9 in operating economics? If I were Boeing I would just relax.

  5. Will the actual engine have those funky blue blades? Or is that just the demonstrator. It’d be really cool.

    • I’d love to see the final product having the cool blue blades too. But unfortunately, I think I remember reading somewhere that the blades will be black for the actual versions. Maybe this is just for the test version.

      • FWIW, a new company (http://www.hypetex.com/) is just bringing coloured CF to market, whereas CF in the past required painting. Does anyone know what the surface finish is on GE CF parts? Maybe there is weight to be saved there.

  6. Boeing is somewhat worried about the A330 Neo and stated that they “will react if the 330 Neo is launched”. It is possible that Airbus has few surprise tricks/enhancements ready to go that no one knows about. Lets hope so as it would make things far more interesting.

    • Going by the rolling AstroTurfing and Fudding attacks we see on anything Airbus
      Boeing is majorly worried 😉

  7. Does anyone know whether decoupling the neo fuselage timeline from the neo engine timeline is possible, technically? What I’m thinking is for Airbus to start manufacturing everything down to the end of the pylons to neo standard as soon as possible but, for the first 2-3 years, fitting these aircraft with decent low mileage 2nd hand engines. With airframes being scrapped earlier and most of the value at that time in the engines, surely there should be some availability of engines with 2-4 years resonably efficient years left that RR/GE & Airbus could work out a deal on with customers.

    Then simply swap them for the neo engines when they become available. Would allow RR to go for the full step change engine at the end of the decade, or GE to deliver further improvements compared with 787 tech.

    • For the A320 aero improvements where decoupled from engine upgrade.
      Some cabin changes seem to follow the engines.

  8. Will an A330neo get the A350XWB’s blended winglet?

    As they’ve adopted the moniker “sharklet” for their A320neo blended winglet why haven’t they named the A350XWB’s something like, “Orcalet,” akin to Keiko’s curved dorsal fin?

    Orcalet is a fine sounding name for a blended winglet as is Sharklet.

    • Probably for the same reason Boeing would never use the “Nightmareliner” moniker for referring to the 787 😉

  9. Pingback: Airbus A330-800 and -900neo, first analysis part 2: engines and maintenance costs | Leeham News and Comment

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