Bjorn’s Corner: Turbofan developments in 2017

By Bjorn Fehrm

January 06, 2017, ©. Leeham Co: Before we finish of our series on airliner turbofan technology, let’s spend this Corner on what will happen on the airliner engine front during 2017.

While there is no totally new engine that comes into the market during 2017 there are a number of new variants of existing engine families that will be introduced.

Figure 1. GasTurb principal representation of a three shaft turbofan like our reference Rolls-Royce Trent XWB. Source: GasTurb.


If we start with the engines for regional/single aisle aircraft and then climb the thrust scale, we will cover the engines in climbing thrust class.

Pratt & Whitney Geared Turbofan (PW GTF)

The largest Pratt & Whitney GTF engine (the one with 81-inch fan) entered service during 2016 on the Airbus A320neo in the PW1127G variant. For Airbus engines, the numbers 27 stands for Max Sea Level Static Thrust, 27,000lbf in this case. During 2017, the highest thrust version PW1133G will enter service on the A321neo at a 33,100lbf thrust rating. The PW1431G variant of the 81-inch engine should enter flight test on the IRKUT MC-21 during 2017.

The smaller 73-inch fan variant entered service on the Bombardier CS100 and CS300 during 2016 and is also in flight test as PW1919G on the Embraer E190-E2. The 56-inch fan variant is conducting flight tests during 2017 as PW1217G on the MRJ90. Service entry is planned for 2018 for the engine.

The 73 and 86 inch versions use AlLi-based fan blades, whereas the 56-inch uses normal Ti fan blades. The AlLi fan blades are of a new design which combine AlLi blade covers with an Al foam core. The use of aluminum for the fan blades has been made possible by the low RPM that the fan has. This is possible as all variants use a 3:1 gearbox between the fan and the low spool of the engine.

This increases the efficiency of the low spool booster, compressor and turbine, as the blade speeds can be increased, despite running the fan at a lower RPM than is normal for this engine class. We will cover the implications of using a gearbox when designing a Turbofan in a subsequent corner.


The CFM LEAP-1B engine has to be seen as a new engine compared to the LEAP-1A. The technologies are the same between the variants but there are no common parts (other than perhaps the engine computer, the FADEC). The 1B is a custom design for the needs of the Boeing 737 Max series.

The LEAP-1B in its 1B26 variant will enter service on the Boeing 737 MAX 8 during Q2. The 1B26 designation should tell you that the engine is a 26,000lbf variant. Well it’s not. The 26 stand for 26,000lbf defined under the “Boeing Equivalent Thrust (BET)” principle, a more clever way to define engines than the normal Static Max Thrust at Sea Level definition.

Boeing rightly focuses on the thrust at M0.25 (which includes the forward speed thrust lapse, i.e., loss of thrust) which is where the single engine max thrust is critical to fly the aircraft at a minimum of 2.4% climb angle with one engine inoperative (the V2 safety speed region). This thrust (~20,700lbf in this case) is then jacked up with a constant 1.255 to get to BET. The Static Thrust at Sea Level is slightly higher than the BET rating for high bypass ratio engines, good to know when comparing engines between Boeing and other aircraft manufacturers.

The LEAP-1B contains the same technology advancements as the LEAP-1A that entered service during 2016 on the Airbus A320neo. Highlights are a resin infusion Carbon Fiber Reinforced Plastic (CFRP) fan and fan case, a 21:1 highest compression high pressure compressor and the first airline application of Ceramic Matrix Composite (CMC) static parts in the high pressure turbine shroud (the static shroud around the tips of the turbine rotor blades). The advantage of CMC is that the cooling air flow can be reduced for the shroud area.

The later stages of the low spool turbine also have Titanium Aluminide (TiAl) blades, but that was introduced on the GE GEnx-1 before the LEAP. Their advantage is lower weight than the normal nickel alloy blades used in this part of the engine.

The larger LEAP-1A entered service during 2016 on the A320neo in the 1A26 variant (which has a 26,600 static thrust rating). The highest thrust 1A32 variant will enter service on A321neo during 2017 at a 32,200lbf thrust rating. The technology used in the LEAP-1A is the same as for the 1B.

The LEAP-1C, which is identical to the 1A except for the mounting principle to the pylon (fan case and turbine case mount instead of core mount for the A320 series), is ready for flight test on the COMAC 919. Let’s see if COMAC gets as far as flight tests this year for the C919.

Rolls-Royce Trent 1000/7000

The Trent 1000-TEN started flight testing on a 787-9 during 2016. The highest thrust variant (78,900 lbf) will start flight testing on the Boeing 787-10 during 2017, as will the lower thrust Trent 7000 variant for the Airbus A330neo. The Trent 7000 is a Trent 1000-TEN with an added outlet for customer bleed and a simplified auxiliary gearbox.

Service entry for the 787-10 is planned for early 2018. Service entry for the A330neo should have been 4Q2017 but is now scheduled for 1Q2018.

GE GEnx-1

The highest thrust GEnx-1B76 variant will start flight testing on the Boeing 787-10 during 2017. The engine was first with introducing a CFRP fan case and TiAl based blades for the last stages of the low pressure turbine.

Rolls-Royce Trent XWB

The 97klbf variant of Trent XWB for the Airbus A350-1000 will enter service with Qatar Airways during 2017. It’s currently in flight test on the A350-1000 test aircraft. The 97klbf version has a completely redesigned high pressure turbine section which uses non-shrouded blades for the first time on a Trent engine.

The main reason for changing to non-shrouded blades (which forces active casing clearance control) is the complexity of cooling shrouded blades at the very high temperatures of the 97k versions high pressure turbine (around 2000K).


The gigantic GE9X (it has a fan diameter of 134 inch) started ground testing during 2016. Flight tests are planned for 2017 and certification for 2018. The GE-owned Boeing 747-400 test bed had to be specifically adapted to carry the much larger GE9X than the GE90-115.

The engine introduces CMC technology in more hot static parts than the LEAP (combustor liners, turbine first nozzle and shrouds). It has an advanced 27:1 highest compression high spool compressor. Thrust rating is nominally 105,000lbf for the 777-8 and -9, but there is reserve to also power a future 777-10 variant.

31 Comments on “Bjorn’s Corner: Turbofan developments in 2017

  1. Dear Bjorn,
    thanks for the overview. I wounder if you heart anything of the Trent 7000 status? All I could found out anything but that they started ground testing late 2015 and flight testing was planned for later 2016. However, it looks like they didn’t fly yet?!? Is the engine the cause of the delay?

    • Perhaps the Trent 7000 doesn’t need to be flight tested separately (on RR’s 747), since it’s essentially a bleed-air-version of the Trent 1000-TEN.

        • Thanks, but I’ve read that article. The point is that if separate flight testing of the Trent-7000 on RR’s own 747 would be required — and a corresponding (time-consuming) extensive flight-testing analysis — then you’d probably have a pretty long delay of the first flight of the A330-900.

          • It may look indeed as if RR is not planning to undertake a separate flight test programme for the Trent- 7000.

            Rolls-Royce is gearing up to support Airbus and Boeing flight-test campaigns in the coming months as two new variants make their first flights powered by Trent engines.

            Meanwhile, the first A330-900, which is the larger of the two A330neo variants, was moved from the paint shop in Toulouse on 23 December, without engines (below). Airbus says that the re-engined variant is to fly “in the spring”.

      • I believe that’s correct. The delays with the 787-10 variant gave Rolls more time to work on the 1000-TEN hence the temptation to grant more time to the 7000 also.

    • Rolls-Royce had a delay in the Trent 1000-TEN program that spilled over to the Trent 7000 (a changed seal in the compressor did not perform to expectation, so RR went back to the present seal). If this is the major cause for the slip into 2018 for A330neo EIS we don’t know. The “late 2017” was an aggressive plan by Airbus and we talk about a delay of a couple of months.

  2. The shroudless HPT of the Trent XWB-97 has been borrowed from the EJ200. Apparently EJ200s with 3000 hours are running without any degradation in performance. Not sure about the 2000K though. Seems high! 1700-1800K is more likely. RR engines have typically run colder than GE engines. The Trent XWB-97 changes that!

  3. Its time to get the latest and greatest from GE’s tool box on the genx on the 787..cmc’s …latest tial blades …
    If they want to maintain they marketshare lead..
    The trent 1000-TEN should be a def.improvement in efficiency

    • GE was missed out on the GENX, but they are doing what RR is doing and that is a significant revision of it.

      They are not taughting it as brand new, the GenX -1B76 is the same upgrade relationship for the 787-10 as the Trent 1000-10.

      • Interesting that RR are claiming nearly 79klb for the TEN while GE seem to be at 76klb. Are these figues comparable or are they measured differently, ie BET as opposed to static? If comparable then RR have their nose ahead in any EK order with the strongest engine on the 787-10 and only offering one the A350. I suspect that might tip things in Airbus’ direction as T-1000 was originally designed for 70klb and the consequences of pushing 79klb out of it should be more degradation than we will see with the XWB engines.

        Of course maybe EK aren’t in the market for new aircraft any more, but I think more likely they will be looking to open new thinner routes, that being the only expansion route open to them, as they seem to own most of the dense routes now!!

        • The GE figure is BET, its static SL rating is 78.5klbf, so it’s close to the Trent 1000-TEN. GEnx is also slightly lower in BPR so have less lapse at V2, the engines are most probably comparable in Take-Off performance. What can be more important is their kink temperature, i.e. to what temp they are flat rated at that thrust. Will be clear when we have a TCDS for both.

  4. A nice summary however it would be nice with a comparison on performance and price/EFH for different pax-routes. I.e. a A330-900 vs. 787-10 on a i.e. Paris-SFO or Paris -ORD route. Leading to an analysis of how much more Boeing can charge for the -10 than the A330-900 price for equal airline profit

  5. Which engine is the most efficient? Is there a relationship between efficiency and size? Like are bigger engines more efficient than smaller ones or is that not the case?

    • In general, for engines of the same vintage, the long range engines and therefore the larger ones are designed more for efficiency. The short range engines for regionals and single aisle aircraft are designed to withstand more cycles (take-off, landings) without requiring maintenance. This means running them cooler which lowers efficiency. The difference is not large, 3-6% but it’s there.

      Over time engines increase their efficiency with about 1% per year when they were designed (more advanced technology is available), so an engine which is a more recent design is as a rule more efficient than an older engine type.

  6. ” CFM LEAP-1B engine has to be seen as a new engine… with no common parts to other variants.”
    That surprises me, as it takes away the economic advantage of the larger installed base.
    The details given for the leaps compressor say 3 stage LP and 10 stage HP for all version. It would seem ridiculous to have completely different parts for the A and B versions. Its well known that the Boeing engine is constrained by its diameter and thus its BPR compared to its larger sisters. A smaller fan can reduce the number of LPT stages but there is some vague suggestion the LEAP-1B has a ‘smaller core’ to claw back a bigger BPR.

    Is there a link for a comparison ( outside the fan) of the A/B versions to back up the no common parts claim?

    • The first approach by CFM was to have the same core but Boeing asked for a 100% optimized engine and the 1B is a sub 30klbf engine and the 1A a 33k engine. So the core was adapted to the smaller massflows ie a 100% custom designed core and thereby engine. The exclusive delivery to 737 MAX could motivate a 100% custom design.

      • CFM56-5 and CFM56-7 have same cores, despite different cold sections.

        I thought the “fully optimized” ploy of the LEAP B was to mistify the perception Airbus puts on a bigger fanned LEAP for a reason.. godforbid sfc, noise?

  7. Dear Bjorn,
    I have a special engine question for a specialist like you.
    Iran Air is no coming back into business. Tehran Mehrabad is elevated 1200 m but Tehran has a colder climate than all airports of the big middle east three. What does challenge an engine more: 40 °C at sea level or 30 °C at 1200 m?

    • I checked it out with GasTurb simulating TO with a Trent XWB 84k engine. The case at 1200m is more demanding, the engine spins faster and might run into RPM limits (forces on rotors etc). I had T3 (end compressor temp) and T41 (High Turbine entry temp) as limits, but you have shaft RPM limits as well on an engine, question is just the exact RPM cut. The engine would deliver 2% more thrust (81k instead of 79klbf, you are over the 30°C sea level flat rate point for both cases) but it depends on what is set in the FADECs as limits, if its RPM limited before 81k then thrust wise it would be similar.

  8. Pingback: Bjorn's Corner: Aircraft engines in operation - Leeham News and Comment

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