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.
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.
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.
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.
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.
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.