Airlines satisfied with 787 engines despite efficiency miss

By: Stephen Trimble published in flightglobal.com, Nov 17 2014

If one of today’s market fashions becomes permanent, the Boeing 787 could be the last commercial widebody aircraft that offers buyers a choice of engines from competing suppliers – in this case the GE Aviation GEnx-1B or the Rolls-Royce Trent 1000.

This increasingly rare engine competition has delivered two propulsion systems with reliability levels well above the average at the aircraft level.

At the same time, it has so far failed to produce a turbofan engine designed by either competitor that meets Boeing’s original promise of a 10% reduction in specific fuel consumption.

Additionally, competitive pressures have not provided airline customers with immunity from brief operational crises with both engines, in one case an operational restriction that still continues.

Both engines boast despatch reliability levels above 99%, the benchmark Boeing is still seeking to claim for the aircraft as a whole.

“The engines are operating flawlessly,” says Zemene Nega, vice-president of maintenance, repair and overhaul for Ethiopian Airlines, a GEnx-1B customer.

It has not always been so. In July 2012, All Nippon Airways, a Trent 1000 customer, grounded five 787-8s after Boeing informed it of a potential problem in the gearbox. Crown gears had corroded faster than expected in endurance tests on the ground, causing damage to the engine. R-R traced the problem to a manufacturing process change by gearbox supplier Hamilton Sundstrand. It was corrected within weeks.

The GEnx-1B became the focus of the next engine crisis. A decision by GE Aviation to adopt a new lead-free coating on the fan mid-shaft backfired with explosive results. The coating caused the component to corrode faster in humid climates. In late July 2012, a GEnx-1B on board a newly assembled Air India 787-8 sustained a contained failure. GE reverted to a previous lead-based coating, and the problem disappeared.

Rolls-Royce‘s next move is to deliver the Trent 1000-TEN upgrade in mid-2016

Rolls-Royce

A longer-term problem for GE Aviation is a relatively new phenomenon called ice-crystal icing. Liquid water is not present above about 22,000ft, so airframe icing is never a concern at cruise altitudes for a turbofan-powered widebody aircraft.

However, meteorologists have recently discovered the presence of ice crystals at even higher altitudes, especially in tropic latitudes. In massive storm concentrations stretching 100km (62mi) across, convection forces can carry ice crystals the size of a grain of flour to cruising altitudes above 30,000ft. The crystals bounce off an aircraft’s skin, but can be ingested into an engine. It is believed that crystals land on a warm blade and begin to melt, which attracts other crystals to stick to the blade. Eventually, enough ice develops on the blade to cause damage downstream when it sheds.

The phenomenon is particularly acute on the GEnx engine. On its predecessor, the CF6, the ice build-up would most often shed as the aircraft descended. The GEnx experiences the ice shedding problem at cruise altitude, leading to in-flight engine shutdowns. As a result, the US Federal Aviation Administration issued an airworthiness directive last year requiring airlines to steer 787s at least 50mi wide of major storm concentrations.

For some airlines, the restriction is an annoyance but not a network issue. Japan Air Lines, however, has pulled the 787 off three routes originating in Tokyo: Bangkok, Delhi and Singapore.

By contrast, the Trent 1000 engine faces no such operational restriction, says R-R project director Gary Moore. Fortuitously, the three-spool architecture of the Trent engine family happens to be less prone to ice crystal build-up inside the core. The intermediate compressor section, which is absent in the GEnx design, rotates at a higher speed, making it more difficult for dangerous quantities of ice to build up on the blades.

“We don’t have this problem,” Moore says. “It is just a very clear difference in the two engines.”

Another clear difference between the engines is the order split. So far, 787 customers have chosen the GEnx-1B over the Trent 1000 by a nearly two-to-one margin, with 17% of the order backlog still unspecified.

R-R places a couple of caveats on the GEnx-1B’s strong start. First, not all airline decisions have been the result of a competition. When given the chance to compete, the Trent 1000 has claimed nearly half of the orders, Moore says. Moreover, the Trent 1000 is starting to gain some momentum. In the last 19 engine selections, the Trent 1000 has won orders 11 times, he says.

R-R’s next move is to deliver the Trent 1000-TEN upgrade in mid-2016. GE has acknowledged that the GEnx-1B misses, by 1-2%, Boeing’s original specification for reducing specific fuel consumption. The Trent 1000-TEN – packed with technological improvements inherited from the Trent XWB – is still aimed at achieving the 787’s original fuel-burn target.

“We’re targeting the original spec that was put upon the airplane,” Moore says. “You don’t spend this level of investment to think we’re not going to get there. We’re going to get there.”

GEnx misses fuel burn spec on 787, but on upgrade path

By: STEPHEN TRIMBLE, published in flightglobal.com, Sep 23, 2014

One month before Boeing returned the 787-8 to flight in May 2013 after an 18-week grounding caused by battery fires, GE Aviation quietly certificated the third major production version of the GEnx-1B, inching one of the two propulsion options for the Dreamliner closer to the promised fuel efficiency targets.

Similar to the rival Rolls-Royce Trent 1000 engine, the original Block 4 version of the GEnx-1B entered service with Air India in early 2012 several percentage points below the specification. The Block 4 standard also featured an under-performing low-pressure turbine (LPT) section that would require a redesign.

As of early September, GE had delivered 246 GEnx-1B engines, including the last 150 built to the performance improvement package (PIP) II standard. That number includes the first GEnx-1B-powered 787-9 delivered to United Airlines on 4 September, the last major certification campaign until the arrival of the 787-10 in four years.

With tens of thousands of hours and now two applications in service, GE now understands exactly how close the PIP II standard came to meeting Boeing’s specification – and it is not as close as was once widely expected.

“We’re probably off the original ‘spec’ by perhaps a little more than 1% but less than 2%,” says John How, business operations leader of the GEnx product line for GE Aviation.

Boeing

Importantly, the upgraded engines delivered after Block 4 was phased out of the production system meet contractual guarantees for airlines, How says.

“What matters to the airline customer is what they were sold by Boeing and what they were guaranteed,” How says.

Even the latest GEnx PIP-II engine installed on the United 787-9 delivered earlier this month, however, falls short of Boeing’s original promise to airlines. Judging by GE’s lead over R-R in the787 order backlog, the performance of the Trent engine has not been enough to usurp the GEnx.

The Trent and GEnx performance shortfalls were apparent well before either version was delivered to a customer. A leaked Airbus dossier on the 787 in 2008 included the prediction that both engines would miss the specification by 2-3%. As the original Trent 1000 and Block 4 entered service, the 3% shortfall became the baseline estimate used by both companies.

GE and R-R then designed a series of performance upgrades to reclaim the specification target. R-R has already rolled out Package B and C standards, with the final 1000-TEN configuration scheduled to appear in 2016.

GE, meanwhile, followed the Block 4 standard with the PIP 1 design, which included a revised LPT. GE had introduced lightweight titanium-aluminide blades in the LPT section of the GEnx engine, believing it could reduce the blade count significantly and lower the weight of the engine compared with the preceding GE90.

That estimate proved to be too aggressive by about 30% of the LPT blades that would ultimately be required to manage the airflow. The PIP 1 programme corrected the error with a more robust LPT blade count.

GE advertised that the PIP I would reclaim 1.4-1.6 percentage points of the 3% performance shortfall from the specification. A second upgrade – the PIP II design – was supposed to push the performance to nearly match Boeing’s original fuel burn target. With the LPT improved by the PIP 1 programme, GE now focused on improving the high-pressure compressor section in the PIP II design.

In previous statements, GE had indicated the PIP II configuration was coming within 1% of the specification target for fuel burn efficiency. That estimate proved illusory, however. GE has now recalculated the actual performance results, with the new figures showing the Block 4 missed the specification by 4-5%. With the PIP II standard, fuel burn efficiency improves by 3 percentage points, but remains 1-2% shy of the specification.

GE

GE officials emphasise that the performance will continue to improve as the new upgrades enter the fleet. They point to the record of the GE90-115B, the engine that powers the 777-300ER. That engine also entered service slightly below Boeing’s specification for fuel burn. Ten years later, it is now running more than 3% above the specification, according to GE’s numbers.

Despite the shortfall, there is no “PIP-3” version being proposed for the GEnx-1B. Instead, GE will introduce improvements gradually leveraging engine development programmes launched after the GEnx was unveiled in 2003 with a then-state-of-the-art 45:1 compression ratio. GE is currently testing a compressor section for the GE9X that will power the 777X with a 61:1 compression ratio.

Key enabling technologies, such as ceramic matrix composites, have already been tested in the core of a GEnx engine, as part of GE’s campaign to mature the technologies for the CFM InternationalLeap engine and the GE9X.

As GE works to improve the GEnx-1B’s fuel performance, the company is also looking at adding more thrust capability. The engine is already able to produce 78,000lb thrust (111kN) at sea level, a power reserve well beyond the needs of the 787-8 and 787-9. It is expected, however, to allow the 787-10 to take off with a full payload at high-altitude runways or in very hot weather. The standard rating for the 787-10 is 76,000lb thrust, with a 2,000lb thrust margin for “high-hot” conditions.

GE is now studying an even more powerful version of the GEnx, which would raise maximum thrust at sea level to 80,000lb. Although Boeing has not publicly discussed a requirement for such an engine -– perhaps to power a high-gross-weight version of the 787-10 – GE is preparing “in case the airplane needs increased thrust”, How says.

An increase in thrust often involves a wider inlet diameter, as more airflow is needed to produce more power efficiently. But there are ways to avoid a wider engine exterior. The PIP-II configuration, in fact, includes a 12.7mm (0.5in) wider flow path, without changing the exterior diameter.

“Thrust increase always involves more airflow,” How says. “As to whether or not we would need to increase the diameter of the fan, that’s not really decided.”

More efficiency and more power are not the only items on the list of improvements for the GEnx-1B engine.

Boeing and GE are close to clearing one of the most bothersome operational restrictions for certain operators, such as Japan Air Lines. The GEnx-1B has proved susceptible to a phenomenon unique to tropical clients called ice crystal ingestion. In tropical latitudes, small ice crystals can form at high altitudes, potentially causing damage to the engines. The GEnx-1B is currently restricted from flying within 50nm (93km) of weather in which ice crystals are able to form. As a result, JAL has replaced 787s with 777s on two routes to Vietnam and India.

“We think by the end of October Boeing will be able to issue a revision to that flight restriction, increasing the altitude limit significantly,” How says.

The solution to the problem requires no changes to the turbo machinery. Instead, GE has reprogrammed the software controlling the variable bleed valves located in front of the compressor section. These valves are normally opened on take-off or landing, siphoning potentially damaging objects sucked in by the fan into the bypass flow. The reprogramming allows these valves to open when conditions suggest ice crystals are forming on the blades.

Morris explains how GE came to embrace 3D printing

By: STEPHEN TRIMBLE, published in flightglobal.com, Sep 24, 2014

GE Aviation has spent decades building a reputation as a materials trailblazer in the engines business.

The Cincinnati-based engine maker has consistently turned to new and sometimes exotic materials to solve engineering problems. As modern engines have driven up bypass and compression ratios to become more fuel efficient, GE has introduced carbonfibre fan blades to reduce the weight of wider fans and integrated titanium aluminide turbine blades and ceramic matrix composite (CMC) turbine shrouds to survive in higher temperatures.

Despite this reliable track record, industry peers still seemed caught off guard and unguardedly sceptical about GE’s sudden and deep plunge into the emerging world of additive manufacturing. Like the widespread introduction of composite materials in the 1990s, additive manufacturing inserts both new materials and a new production process far removed from industrial age practices like forging and casting.

The speed and scale of GE’s embrace of 3D printed parts seems unprecedented. It took the industry decades of experimentation before allowing composite materials to be used in load-bearing structures, starting with the rudder of the Airbus A310 and increasing gradually over the next four decades.

Even as most aerospace companies still limit 3D printers to rapid prototyping shops and one-off plastic components, GE is opening a 9,290m2 (100,000ft2) factory in Alabama to produce a key component in every CFM International Leap engine, with annual production of up to 40,000 pieces a year. The same factory and another facility recently erected in Italy also could produce an even more numerous part on the GE9X, GE’s highly prized power source for the Boeing 777X family.

GE

Most aerospace industry officials agree that additive manufacturing will be revolutionary, but not for at least 20 years. GE is revolutionising its manufacturing system now, with billions of orders at stake on every Boeing 737, Comac C919 and CFM-powered Airbus A320 in the backlog.

Although it appeared that GE emerged as the industry’s lonely champion of additive manufacturing overnight, the real story unfolded over several decades, with a starring role played by an industrial neighbour in Cincinnati with no background in the aerospace manufacturing business.

Greg Morris comes from a Cincinnati family that presided over a large steel distribution company since the mid-19th century. The family business was sold, however, in the early 1990s, leaving Morris with plenty of capital and nothing to do.

Over the next 20 years, the company he founded with two others – Morris Technologies – would help transform additive manufacturing from a niche technique to make one-off prototypes into a mainstream production system for some of the world’s most advanced aircraft engines.

Morris Technologies began in 1994 with the acquisition of a 3D Systems SLA-250, the first 3D laser printer on the market. The system was advanced for its time, but still limited to building fragile materials.

“At that point the resins were okay but they not robust at all,” Morris says. “In fact, you could drop it from here to the table and it would likely break.”

Despite the limitations, such early 3D printers transformed rapid prototyping operations. For the first time, an engineer with a 3D computer-aided design (CAD) drawing could make parts from scratch within hours, without the need to order raw materials, invest in new tooling and tie up machinists.

Moving from rapid prototyping into mainstream production would take nearly a decade of further development. Even as 3D printers became more powerful and the resins more robust, such systems were still comparatively unsophisticated compared to mainstream production tools like computer numerical control machines.

Not only would such a system have to precisely manufacture thousands of parts with close tolerances reliably and affordably, the machines would also need to monitor themselves, alerting operators of anything unexpected. Ideally, the machine would sense small fluctuations in the power supply to the laser, or perhaps minute changes in atmospheric pressure inside the printing chamber.

Obtaining machines with such potential became possible about a decade ago, but only with significant alterations. On a visit in 2003 to a UK facility of a key client – Cincinnati-based Proctor & Gamble – Morris discovered the direct metal laser sintering machine made by Munich-based EOS.

At the time, Morris Technologies was still a start-up company with a broad range of clients spanning GE’s rapid prototyping shop, medical devices and consumer products. Buying the EOS machine, however, was still a big risk. Their intention was to acquire the machine and modify it substantially to suit a more sophisticated clientele, and thereby void the warranty and the guarantee for EOS support on the machine.

“We went over to Germany, we researched it and then we took the plunge,” Morris recalls.

That decision would set in motion a path to make highly sophisticated direct parts using exotic metals, such as the cobalt-chromium discs at the base of an engine fuel nozzle, where tiny perforations and channels blend kerosene and highly compressed air in a precisely calibrated mixture before it is ignited in the combustion chamber.

By 2005, Morris Technologies had upgraded the direct laser sintering machine from a carbon dioxide-based laser to a fibre-optic laser. The more powerful laser allowed the company to start working with more exotic metals, including cobalt-chromium, Inconel 718, Inconel 626 and various titanium and aluminium alloys.

Other modifications focused on controlling the environment inside the printing chamber. Consumers can buy 3D printers with a guarantee of 10,000 oxygen parts per million inside the printing chamber. The best manufacturing machines available on the market offer better quality, limiting oxygen to 2,000 parts per million. The Morris Technologies machines are rated to maintain an atmosphere of 50 parts per million.

Other manufactures are using 3D printed parts as support structures in engines, such as brackets. It is also commonly used for serpentine-like ventilation ducts in aircraft. Some industry officials, such as Pratt & Whitney vice-president of technology and environment Alan Epstein, have challenged the “hype” over additive manufacturing techniques, arguing that the technology will not be ready for widespread application for another 20 years.

But Morris argues that the naysayers simply have not been working on the technology as long or made the same investments in improving the commercially available machines.

“It’s very expensive. It takes millions of dollars to develop your material curves,” Morris says. “We have probably a much better understanding of the technology and the material characteristics than others who have either gone down that road or haven’t been playing with the technology as long as we have.”

In 2012, GE acquired Morris Technologies shortly after revealing that each of the 19 fuel nozzles inside each Leap engine would be manufactured with a cobalt-chrome tip.

The design of a fuel nozzle made by the Morris Technologies machines presented challenges. Engineers assessed a “debit” on the low- and high-cycle fatigue properties of the original part, a characteristic caused by using laser sintering to produce it, rather than a casting.

“What our engineers and designers did is they designed around that debit, and that’s the beauty of what you can do with this technology,” Morris says. “Instead of letting a debit… cause a roadblock they simply designed around it.”

If GE’s strategy works, this is only the beginning. Additive manufacturing opens doors to more than just new designs and new materials, Morris says. It also allows GE’s engineers to design something like a turbine blade very differently, with several layers of material optimised for their location on the blade. Right now, a turbine blade is made with a single material, even though blending different materials could be more effective.

“What if in a high-pressure turbine blade instead of it being one material I can vary my materials in the future, and I can use one material here, blend in the next material and at the tip I get an abrasion resistant material,” Morris says. “That’s coming. That’s work that GE is on the leading edge of understanding fundamentally how to do.”

GE9X engine for the 777X to feature fewer, thinner composite fan blades

Published in compositesworld.com, September 2, 2014

 

GE Aviation (Evendale, Ohio, USA) reported on Aug. 26 that its GE9X engine for the Boeing 777X aircraft will feature fewer and thinner composite fan blades than any GE widebody engine in service. To do this, GE is designing a new composite fan blade using next-generation carbon fiber composite material.

GE Aviation says the new material incorporates a higher stiffness carbon fiber and a new epoxy resin. The leading edge material will also be modified from titanium to a steel alloy to further enhance the blade’s strength. GE Aviation declined to reveal type of carbon fiber that will be used, the type of epoxy that will be used, nor who the material suppliers would be.

“It has been a decade since GE designed a new composite fan blade for the GEnx engine,” says Bill Millhaem, general manager of the GE90/GE9X engine programs. “Carbon fiber composite material has advanced in those 10 years, and the advancements enable GE engineers to design a thinner GE9X blade, which is just as strong as our current composite fan blades. Fewer, thinner blades will enhance the airflow and make for a lighter, more efficient fan that will help with the GE9X engine’s overall performance and fuel burn.”

Last year, GE engineers received positive results from material testing on full-sized GEnx blades. Testing of the new material continues this quarter in preparation for next year’s testing on the new GE9X blade design.

The GE9X fan blades are the fourth-generation composite fan blade design, built on the success of the GE90-94B, GE90-115B and GEnx engines. GE engineers continue to work the final design of the GE9X fan blade that will incorporate improved aerodynamics.

GE will spend $300 million in 2014 on technology maturation testing for the new GE9X engine. Tests include the Universal Propulsion Simulator (UPS) fan performance tests as well as testing of ceramic matrix composite components in a GEnx engine.

The GE9X engine will be in the 100,000-lb thrust class. Key features include a 133-inch diameter composite fan case and 16 composite fan blades; a next-generation 27:1 pressure ratio 11-stage high pressure compressor; a third-generation TAPS (twin annular pre-swirl) combustor for greater efficiency and low emissions; and ceramic matrix composite (CMC) material in the combustor and turbine. Almost 700 GE9X engines have been ordered by customers since it was launched on the Boeing 777X aircraft last year.

The first full core test is scheduled for 2015. The first engine will test in 2016 with flight testing on GE’s flying testbed anticipated in 2017. Engine certification is scheduled for 2018.

IHI Corporation, Snecma and Techspace Aero (Safran) and MTU Aero Engines AG are participants in the GE9X engine program.