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Boeing 777X with carbon fiber wings

Some of the newest aerocomposites manufacturing technologies are being deployed in the manufacture of the wings for the Boeing 777X. The wingspan of the plane is 235 ft (72m) and the wings are being fabricated with autoclave-cured carbon fiber prepreg at a Boeing facility in Everett, Wash., U.S. The plane is expected to enter service in 2020. Source | Boeing

In 2019, the global commercial aerospace industry was shaped and dominated by the grounding of the Boeing 737 MAX, which was precipitated by the crash of two 737 MAX aircraft, one in late 2018 and the other in early 2019. The cause of the crashes, which killed more than 300 people, was an automated flight control system Boeing developed specifically for the 737 MAX. Boeing has committed significant resources to correcting the automated flight control system. As of mid-December 2019, longer-than-expected re-certification has led to a suspension of 737 MAX production beginning in January 2020.

The grounding of the plane has had significant ripple effects throughout the aerospace industry supply chain, with some consequence to the composites industry as well. In particular, Boeing has had on the drawing board for some time the New Midsize Aircraft (NMA), a twin-engine, twin-aisle, mid-range plane that would fit between the 737 and the 787 in terms of size and range and would serve a segment that used to be occupied by the discontinued 757. Initial speculation said Boeing would announce the NMA at the 2019 Paris Air Show, with entry into service around 2025. However, the 737 MAX grounding apparently has not allowed the company to devote significant resources to a new program launch, plus Boeing experienced problems with the engine on the 777X and delayed first flight of this craft (with all-composite wings) to early 2020. All of this added up to no NMA announcement in Paris. 

Airbus A321XLR extended range passenger plane

The Airbus A321XLR, introduced at the Paris Air Show in 2019, is the latest — and possibly last — variant of the A320 lineup. It is designed to offer long-distance travel options in a single-aisle architecture. Source | Airbus.

The NMA program is also complicated by Airbus, which announced at the 2019 Paris Air Show the A321XLR, an extended version of the single-aisle A320. It will seat 240 people and have a range of 4700 nautical miles. This makes the A321XLR competitive with the NMA, for which Boeing is contemplating two versions: One that seats 225 with a 5,000-nautical-mile range and another that seats 275 with a 4,500-nautical-mile range. If Boeing announces the NMA soon after the 737 MAX returns to service, and assuming both of these things happen by mid-2020, then prospective customers would have a choice of two aircraft that offer similar passenger and range options, with comparable efficiency, with one a single-aisle and the other a double-aisle configuration. 

The NMA is significant because it represents the next all-new aircraft program on the horizon, and, like the Boeing 787 and 777X, and the Airbus A350, it is expected to feature major structures fabricated with carbon fiber composites. In addition, beyond the NMA, just over the horizon, are expected single-aisle replacements for the Boeing 737 and the Airbus A320. Both of these aircraft are ripe for conversion to carbon fiber composites and would represent a major leap forward in composites manufacturing throughput — Boeing and Airbus both anticipate single-aisle replacement build rates of 100 shipsets per month. These programs could, if announced in the next couple of years, enter service in the 2028-2030 window.

The 737 MAX grounding, however, has thrown some uncertainty into this timeline. That is, Boeing could decide that a 737 replacement should be accelerated, and launch its development sooner than planned. Such a decision could, consequently, prompt Airbus to move up its A320 replacement, which is likely that company’s next all-new aircraft. In short, as long as the 737 MAX is grounded, there is much uncertainty in the commercial aerospace supply chain in general, and the aerocomposites supply chain in particular.

Setting aside the issue of which aircraft programs might be announced when, there are substantive and unanswered questions surrounding the NMA and single-aisle replacements. The overarching question is if and where composites will be used on these planes. For the twin-aisle NMA, use of composites is almost certain, particularly given the supply chain and manufacturing processes in place for the 787, 777X and the A350. Also important is the fact that the air carriers themselves prefer the durability and ease of maintenance of composite structures compared to traditional aluminum structures — this fact in and of itself might be enough to compel continued use of composite materials in large aerostructures, regardless of size or configuration.

Assuming that carbon fiber composites use in large aerostructures will continue, the next question is what type of materials those will be. The incumbent material and process (M&P) combination is autoclave-cured carbon fiber/epoxy prepreg, laid down for the most part via automated tape laying (ATL), automated fiber placement (AFP) or by hand. However, the M&P combinations qualified for the 787 and the A350 in particular are relatively old, having been developed in the early 2000s.

Still, the fact that these M&Ps are qualified gives them a leg up against newer M&Ps, which are still being developed and qualified. And for the NMA, for which Boeing likely does not want to develop significant and new M&Ps, the incumbent technology likely wins out. Further, the build rate of the NMA is likely to be similar to the build rate of the 787 (12/month) and the A350 (10/month); thus there is less pressure by Boeing to develop and qualify faster-cycling M&P technologies.

All of these assumptions, however, go out the window with the single-aisle replacements that will follow the NMA. Boeing’s and Airbus’s current single-aisle aircraft, the 737 and the A320, are the aerospace industry’s best and most profitable sellers. Manufacture of composite parts and structures for these planes at the anticipated rate of 100/month is not feasible using current autoclave cure technology. Because of this, the new single-aisle planes in development will almost certainly employ out-of-autoclave (OOA) materials and processes that deliver dramatically shorter part cycle times.

This has thrust to the fore several OOA technologies that are almost certain to be deployed extensively in next-generation aircraft. These technologies include thermoplastic composites, resin infusion and resin transfer molding (RTM). Boeing and Airbus each are pursuing these technologies through a variety of research and development programs designed to bring maturity to a technology readiness level (TRL) that allows commercial deployment by 2025 at the latest.

Airbus, for its part, is pursuing a variety of solutions through multi-company, high-profile programs. Most notable is the Wing of Tomorrow Programme, being led by GKN Aerospace (Shirley, Solihull, U.K.), with the National Composites Centre (NCC, Bristol, U.K.), Northrop Grumman (Clearfield, Utah, U.K.), Spirit AeroSystems (Wichita, Kan., U.S.) and Solvay Composite Materials (Alpharetta, Ga., U.S.). This program is assessing use of RTM to fabricate wing skins, wing spars, ribs and wing box. GKN announced at the 2019 Paris Air Show that it had produced demonstrator parts for Wing of Tomorrow, followed in October by the news that it had delivered a demonstrator tool

Richard Oldfield, CEO of the NCC, told CompositesWorld in March 2019 that the Wing of Tomorrow’s goal is to develop a very high-rate commercial aircraft wing structure manufacturing process that is, in nearly every measurable way, an order of magnitude better than current wing manufacturing technology. This means better automation, fewer parts, better parts integration, faster cycle time, faster NDI and faster assembly. Testing of a full wing is expected to begin in 2021.

Bombardier Belfast A220 wing.

Airbus A220 wing being assembled at the Bombardier Belfast facility in Northern Ireland. The wing is fabricated via resin infusion, but consolidated in an autoclave to acheive desired porosity. Spirit AeroSystems announced in October 2019 that it is acquiring Bombardier’s Belfast operations. Source | Bombardier

Infusion of wing structures is not novel. Two commercial aircraft already use the process: The Airbus A220 and the Irkut MC-21, both single-aisle aircraft. The A220 was developed by Bombardier as the CSeries and then sold to Airbus in 2018. Its infused wings are still fabricated by Bombardier at its Belfast, Northern Ireland, facility, which Bombardier put up for sale in 2019 (Spirit AeroSystems announced in October 2019 that is acquiring Bombardier’s Belfast operations). The Irkut MC-21 is being manufactured by United Aircraft Corp. (Moscow, Russia) for the Russian market. Its wings are fabricated by AeroComposit (Moscow) using a Solvay Composite Materials single-component resin system. What the A220 and the MC-21 prove is that infusion is feasible for commercial aircraft, but the rate on both of these planes is relatively low. The technology must now be matured for a high-rate environment.

Thermoplastic composites, for their part, are being targeted toward fuselage structures. This is important because for many years it was unknown if composite materials made sense for use in the fuselage of a single-aisle aircraft, primarily because fuselage skin thickness on a single-aisle is thinner than that on a twin-aisle aircraft. That thinner skin, using incumbent composite materials and processes, makes composites cost- and weight-prohibitive. The challenge, then, is to develop a composites M&P combination for the fuselage that provides relatively thin and affordable skin thickness.

In Europe, this effort is being funneled through the Clean Sky 2 Next Generation Multifunctional Fuselage Demonstration (MFFD) project. As the name implies, the program aims to increase integration of fuselage, systems, cargo and cabin elements, in the process minimizing the use of fasteners. Use of thermoplastics would allow this via welding. One of the most active companies in the development of thermoplastic aerostructures is GKN/Fokker (Hoogeveen, Netherlands), which at JEC World 2019 in Paris exhibited a thermoplastic fuselage panel fabricated for Gulfstream. It features an interconnected, welded grid structure that exemplifies the multifunctionalism envisioned by Clean Sky’s MFFD. The Fokker structure represents a small step of many to come in the maturation of this technology for potential use in a single-aisle commercial aircraft.

GKN/Fokker thermoplastic fuselage panel for Gulfstream jet

This thermoplastic fuselage panel, on display at the GKN/Fokker stand at JEC World 2019, features the company’s grid-stiffened architecture and is a precursor to large and more complex thermoplastic structures to come. Source | CW

Beyond the fuselage, thermoplastic composites are already making significant inroads with aircraft already in service. Boeing in particular is in the midst of a concerted effort to convert smaller structural parts (brackets, clips, fasteners) from thermoset to thermoplastic composites. Thermoplastics specialists like ATC Manufacturing (Post Falls, Idaho, U.S.), which specializes in continuous compress molding, are leading this conversion effort.

Activity is also significant on the raw materials side of thermoplastics. Resin manufacturer Victrex Plc (Cleveleys, U.K.) made waves in the composites industry with the introduction of PAEK AE 250, a line of carbon fiber tapes and laminates prepregged with its low-melt polyaryletherketone (PAEK) resin. PAEK offers a melt temperature of just 305°C — compared to 350° for polyetheretherketone (PEEK), a mainstay in thermoplastic aerocomposites. This is important because reduced melt temperature speeds the heating/cooling cycle and allows for fast cycle times. It also enables overmolding of PEEK functionality (ribs, attachment clips) onto PAEK laminates. See this CW story for more on thermoplastic material types.

Anticipating increased demand for thermoplastics in aerocomposites, Solvay Composite Materials announced in September 2019 that it is expanding production capacity at its Anaheim, Calif., U.S. facility. The plant makes unidirectional (UD) carbon fiber tapes prepregged with PEEK, PEKK or PAEK resins. The expansion, combined with ongoing process optimization efforts, will increase capacity at the facility fourfold since 2016. 

Also on the fuselage front, but back in the thermoset realm, Spirit AeroSystems introduced at the Paris Air Show 2019 its newly developed Advanced Structures Technology and Revolutionary Architecture (ASTRA) fuselage panel for a single-aisle aircraft. It’s autoclave cured using a new fuselage design Spirit developed called “sheet stringer technology.” The company says ASTRA offers cost savings of 30% compared to incumbent architectures and production approaches and can meet a rate of 60 shipsets/month. Further, physical testing showed that ASTRA met all of the strength and stiffness requirements of a single-aisle aircraft.

Spirit AeroSystems: Advanced Structures Technologies and Revolutionary Architecture (ASTRA)

Close-up of Spirit AeroSystems’ all-composite ASTRA fuselage panel, on display at the 2019 Paris Air Show. The panel features a novel architecture that Spirit says will allow it to meet strength, cost and rate targets for a next-generation single-aisle aircraft. Source | CW

Similar to Spirit, although on a smaller scale, was MTorres (Torres de Elorz, Navarra, Spain), which exhibited at the Paris Air Show a rib-stiffened “grid/skin structure,” manufactured via resin infusion of dry carbon fibers. The idea came from Stephen Tsai, composites veteran and professor of aeronautics and astronautics, emeritus at Stanford University, who designed the ribs in a lattice structure, with each rib a fixed width and height, and spacing between ribs also fixed. The rib architecture uses carbon fiber tapes placed continuously, by MTorres AFP equipment, in one direction (A), and discontinuously in the intersecting direction (B). Then, for the next layer, tapes are placed discontinuously in the A direction and continuously in the B direction. This pattern would continue until the rib’s desired thickness is reached. In this way, each rib joint would always be crossed by a continuous tape. Once the ribs are built in the tool, a skin is laid over it via automated AFP/ATL and the entire structure is co-cured.

Use of resin transfer molding, infusion, thermoplastics and additive manufacturing in next-generation commercial aerospace structures is explored in greater detail in a special issue published in July 2019 by CompositesWorld. Click here to access Next-Generation Aerospace: Advanced Materials and Processes.

MTorres grid/skin structure for aircraft fuselage design

This shows the rib intersection on the MTorres/Steve Tsai “grid/skin structure” developed for next-generation aircraft fuselage. The ribs are built with alternating layers of continuous and discontinuous carbon fiber tapes. Source | CW

The carbon fiber supply chain, meanwhile, has been busy positioning new and existing fibers for next-generation aerospace applications. Toray (Tokyo, Japan), the world’s largest carbon fiber manufacturer, introduced in 2017 its T1100/3960 prepreg, which offers excellent strength and stiffness properties. T110/3960 has been qualified by Spirit AeroSystems. Hexcel (Stamford, Conn., U.S.), for its part, has introduced HexTow HM50, a high-modulus and high-tensile strength carbon fiber. Teijin (Tokyo, Japan), announced in January 2019 that its Tenax carbon fiber and carbon fiber thermoplastic unidirectional pre-impregnated tape (Tenax TPUD) have been qualified by Boeing and registered in its qualified products list. Finally, Hyosung (Seoul, South Korea), in late 2018, introduced a new intermediate modulus, high-strength carbon fiber for the aerospace market, and in June 2019 signed a memorandum of understanding with Saudi Aramco (Dhahran, Saudi Arabia) for the building of a joint carbon fiber manufacturing facility.

All of this activity, positioning and jockeying of the aerospace supply chain anticipates substantial growth in the commercial air travel market over the next 20 years. Boeing, in June 2019, issued its Commercial Market Outlook 2019-2038. In it, the company estimates that the world will need, over the next two decades, 32,420 single-aisle aircraft, 8,340 twin-aisle aircraft, 2,240 regional jets and 1,040 freighters. Airbus issued its own Global Market Forecast 2019-2038. It divides aircraft into small, medium and large categories, but reaches a conclusion similar to Boeing’s. Airbus anticipates need for 29,724 new small aircraft, 5,373 new medium aircraft and 4,116 new large aircraft, with freight units comprising 855 planes total in the medium and large categories. 

Boom Aerospace Overture concept

Boom Aerospace is developing the all-composite Overture supersonic passenger aircraft, which is designed to travel up to Mach 2.2 at an altitude of 60,000 ft. Source | Boom Aerospace

Occupying a small corner of the global commercial air travel market are supersonic aircraft, which have not been in service since the Concorde was retired in 2003. There are several firms now pursuing new supersonic aircraft, and one of the most prominent is Boom Aerospace (Englewood, Colo., U.S.), which is developing the composites-intensive Overture. Boom CEO and founder Blake Scholl, at the Paris Air Show, said that Boom is nearing completion of the XB-1, a subscale prototype of the Overture that is expected to be rolled out by the end of 2019 and test flown sometime in 2020. Overture will have a maximum speed of Mach 2.2, a cruising altitude of 60,000 feet (19,354 meters) and will take passengers (55-75) from Sydney to Los Angeles in just 7 hours, or Washington D.C. to London in just 3.5 hours. Scholl stated that ticket cost on Overture is expected to be competitive, on a seat-per-mile basis, with current airline pricing. Scholl also said that Overture is expected to use a technology called Prometheus Fuels, which converts atmosphere carbon into gasoline or, in Boom’s case, jet fuel, using electricity sourced from renewable resources. In this way, he said, the plane will provide zero net carbon supersonic flight.

2019 also saw a small but growing aerospace segment begin to take shape. It’s most broadly called urban air mobility (UAM) and includes a variety of small craft (4-10 passengers) designed to move people in intra and inter-city environments. Aircraft range varies, depending on the size of the craft and its propulsion system, but the goal is to be able to move a few people from one point to another within a major urban area, or from one urban area to another. Uber, which is working on its own eVTOL, requires a range of 60 miles on a charge. Regardless of the range requirements, composites use in eVTOLs is a must, particularly given the dependence on battery power. Because of this, several eVTOL developers (and there are more than 150) are investing heavily in composites engineering talent. The challenge is that the eVTOL market will likely have certification standards as stringent as the commercial aerospace market, but also will require much higher manufacturing volumes that step toward those in automotive. This is driving increased interest in automation and efficiency in composites fabrication processes to drive down cost, boost quality and meet rate. The high level of activity in this market not withstanding, there is still much to be done before eVTOLs begin commercial service. Certification, airspace management, safety standards, take-off/landing locations, and more are yet to be worked out. Commercial service of the first eVTOLs likely will not begin until 2024-2025.

Eviation Alice at 2019 Paris Air Show

The Eviation Alice is an all-composite, all-electric, 9-passenger aircraft with a range of 1,000 km at 240 knots. Eviation hopes to certify it by early 2021. Source | CW

Another craft within the UAM sector that is set to consume composite materials (for the same reason) is the all-electric commercial airplane. An example of this, introduced at the Paris Air Show 2019, is the Alice, an all-electric, all-composite aircraft developed by Eviation (Kadima-Tzoran, Israel). Alice is a nine-seat regional transport aircraft that has a range of 650 miles/1,000 kilometers at a cruising speed of 240 knots. The plane features one primary pusher propeller at the tail and two additional pusher propellers at the wing tips. The company expects the plane, which has a list price of $4 million, will be certified in late 2020 or early 2021.

The advent of Eviation’s Alice portends an emerging future for commercial air transport — that of all-electric regional transport. Although the Alice seats only nine passengers, it’s not difficult to imagine the technology behind it evolving to allow a larger craft that can carry more people and fly further — similar to today’s regional jets. As if to prove the point, Boeing and engine-maker Safran announced in September 2019 a joint investment in Electric Power Systems (EPS, Hyde Park, Utah, U.S.), which manufactures electric and hybrid-electric energy storage systems. These would be applied to aircraft propulsion. EPS is the second advanced battery solutions company to join the Boeing HorizonX Ventures investment portfolio, following an investment in Cuberg (Emeryville, Calif., U.S.), a lithium metal battery technology company, in 2018. Safran Ventures also recently invested in OXIS Energy (Abingdon, U.K.), a leader in lithium-sulfur cell technology for high energy density battery systems.


Rendering of the Airbus E-Fan X hybrid-electric demonstrator. One of its engines will be powered by a 2-MW electric motor, supplemented by a generator. Source | Airbus

Airbus, for its part, is developing the E-Fan X, a hybrid-electric aircraft demonstrator. In the test aircraft, one of the four jet engines will be replaced by a 2-megawatt electric motor. The electric propulsion unit is powered by a power-generation system and battery. When high power is required—at take-off, for example—the generator and battery supply energy together. The E-Fan X is expected to make its first flight in 2021.