Big twin

Boeing is developing new Triple Sevens with its 777X programme. Mark Broadbent looks at the features of the new variants

COMMERCIAL BOEING 777X

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The 777-9 will be the largest twin-jet airliner ever built and it will be 10ft (3m) longer than the 777-300ER; four extra fuselage frames give it the extra length compared to the current-production model.
All photos Boeing

Four years after its formal launch in November 2013, the Boeing 777X programme is gathering pace. Basic engineering is approaching completion, the supply chain is gearing up, qualification testing is in progress and building work on the first aircraft is under way.

Terry Beezhold, 777X Vice-President and Chief Project Engineer, told AIR International: “This is an exciting phase. After several years developing and reducing risk for the flight test programme now we’re in the build phase.”

Boeing is developing two new Triple Sevens in the 777X programme, the 777-9 and 777- 8. The company hopes these aircraft will continue the popularity well into the future of what has been the most successful widebody twin-jet airliner ever built. At the time of writing, just short of 1,800 Triple Sevens had been sold, with more than 1,500 of those delivered.

The 777-9 is being developed first. It is scheduled to fly in the first quarter of 2019 and, Beezhold revealed, enter service early in 2020 after flight testing and certification. The 777-8 will follow around 18 months later.

With these milestones looming ever larger, now is a good time to look at the new variants in more depth – and the 777s have many notable features.

Largest twin-jet

Size will make the 777-9 stand out. The aircraft will be 251ft 9in (76.7m) in length, making it 10ft (3m) longer than the 777- 300ER; four extra fuselage frames give it the extra length compared to the currentproduction model.

It will be the longest airliner ever built by Boeing, slightly longer than the 250ft 2in-long (76.2m) 747-8 and 13ft 2in (4m) longer than the 72.7m-long (238ft 7in) Airbus A380. Such is the new Triple Seven’s length that it will be only 23ft 8in (7.2m) shorter than the sole Antonov An-225 Myria, the world’s largest aircraft, which is 84m (275ft 7in) long. In flight the 777-9’s wingspan will be 235ft 5in (71.7m) – not as wide as the A380’s 79.7m (261ft 8in) wingspan and some way down on the An- 225’s huge 88.4m (290ft), but wider than the 777-300ER’s 212ft 9in (64.8m).

The 777-9 is the first twin-engine airliner designed to carry more than 400 passengers. According to Boeing’s latest provisional Aircraft Characteristics for Airport Planning document released earlier in 2017, the jet will have capacity for 414 seats in a standard two class seat layout, up from the 777-300ER’s 396 two-class. Scalloped frames, which have widened the cabin by 2 inches (50mm) on either side of the fuselage compared to the 777-300ER, will allow for ten-abreast seating in a typical 3-4-3 seat layout.

For the major network airlines that form the customer base for widebody aircraft, the 777- 9’s greater seat capacity provides the potential to carry more of the travellers they prize the most: those flying in lucrative premium classes.

There’s more revenue-raising potential compared to earlier 777s, thanks to greater lower-deck cargo volume. With an 8,131ft3 (230.2m3) lower-deck cargo hold, compared to 7,120ft3 (201.6m3) on the 777-300ER, the 777-9 will be able to carry 48 LD3s (26 in the forward hold and 22 in the rear hold) if the optional rear cargo door is selected, up from 44 LD3s on the 777-300ER.

According to the Aircraft Characteristics for Airport Planning document, the 777-9’s basic maximum take-off weight (MTOW) will be 775,000lb (351,534kg), the same as the 777-300ER.

All these statistics and performance figures look set to cement the 777’s position as the largest twin-jet airliner: it truly will be a big twin.

Range and efficiencies

At 229ft (70m) long the second new 777X variant, the 777-8, will be nearly 23ft (7m) shorter than the 777-9. It will have fewer seats than its sister aircraft (365 passengers, two classes), and although the figures have yet to be disclosed, the shortened fuselage inevitably means less underfloor cargo capacity.

However, the 777-8’s leading feature will be its range. It will be able to fly 8,690 nautical miles (16,090km), which Boeing says opens new route development possibilities for airlines. Range maps for the variant show the aircraft will be capable of flying ultra-longhaul city pairs such as London Heathrow– Perth and New York JFK–Auckland non-stop, assuming a 365-passenger, two-class layout.

As with previous widebody aircraft families, including the older Triple Seven variants, the 777-9 and 777-8 are designed to be complementary. Beezhold said: “The 777-9 gives you large capacity and then the 777-8 gives you range. [The 777X has] got the range if you need range, or if you don’t it has tremendous flexibility in terms of high-altitude airports and hot-weather performance.”

Boeing says both 777X variants will be able to fly hot and high sectors (for example, Madrid–Mexico City), long and hot (such as Los Angeles–Dubai), long and high-payload (such as Sydney–Sao Paulo) and ultra-long haul (for instance, New York JFK–Singapore).

It should be added here that although the 777-9 is not optimised for ultra-long range like the 777-8, it will hardly be short legged; its 7,525 nautical miles (13,940km) capability means it will be able to fly London–Los Angeles or New York JFK–Hong Kong, assuming a 414-passenger, two-class layout and a 775,000lb (351,534kg) MTOW.

The 777Xs will bring performance improvements on earlier Triple Sevens. The 777-9’s capacity and range is an increase from the 777-300ER’s 396 seats and two classes and 7,370 nautical miles (13,650km) range, and the 777-8’s capabilities are up from the 317 seats and 8,555 nautical miles (19,840km) range of the current-production 777-200LR, previously the longest-range 777.

In efficiency terms, Boeing claims the 777X variants will be 20% more fuel efficient per seat than the 777-300ER. The company claims that compared to the Airbus A350- 1000, the principal competition to the new Triple Sevens in the high-capacity long-range market for twin-jet airliners, the 777Xs will be 12% more fuel efficient per seat, 10% cheaper to operate and generate 12% less carbon dioxide emissions.

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At 105ft (32m) long, the spar is the largest single-piece composite part ever developed for an airliner.

Beezhold said Boeing’s opinion is there’s no other aircraft in the part of the market where the 777-9 sits and said the company sees the A350-1000 as: “actually a more direct competitor to the 777-8, although our view is that we have a much more capable airplane in the 777-8.”

Expect the verbal barbs between Europe and North America to continue as the A350- 1000 starts entering service and the 777X becomes a reality.

Wing

The 777X’s GE Aviation GE9X turbofan engines (see p56-59) are the largest commercial aero engines ever built. They will play a major part in the new Triple Sevens achieving their promised performance. However, the engines are only part of the equation. The 777X’s wings have a major role, too.

The variants’ wings feature extensive use of carbon fibre reinforced plastic composites, with the panels, skins, stringers and the entire spar all made from the material. At 105ft (32m) long, the spar is the largest single-piece composite part ever developed for an airliner.

As with any composite materials in an airframe, the composite wing is designed to eliminate the typical features of a traditional metallic structure, such as fasteners, joints and overlaps, which creates a weight saving and a performance benefit.

The composite panels, skins, stringers and spar are produced at Boeing’s Everett factory, the home of the 777, in the new Composite Wing Centre (see pp.52-55) adjacent to the 777’s final assembly line. The Boeing Fabrication facility in St Louis, Missouri, produces other composite wing components, including the leading and trailing edges.

Folding mechanism

Another important feature of the 777X variants’ wings, which will also provide a key visual difference from earlier models, is something never seen before on a commercial airliner: folding wingtips. Boeing wanted a wide wingspan for the 777X, as per the company’s overall approach to widebody aircraft wing design, which is to maximise aspect ratio to create superior lift-to-drag characteristics.

Wide wingspans impose limitations, however. International Civil Aviation Organization regulations governing safety separations between aircraft and ground objects at airports for taxiway and gate compatibility classify aircraft into different design codes. Aircraft with wingspans greater than 52m (170ft 6in) but less than 65m (213ft 2in) are classified in Code E and aircraft with wingspans between 65m and 80m (262ft 4in), such as the 747-8 and A380, are categorised separately as Code F.

The full 235ft 5in wingspan would put the 777Xs into Code F rather than Code E, where the current-production models sit with their 212ft 9in wingspans. The new variants would therefore be precluded from using the same gates, as airports would potentially be required to make infrastructure changes to accept 777Xs.

Boeing’s solution? Eleven foot-long (3.3m) wingtips that extend and retract. On the ground, with these outboard sections in an upright position, the 777X will have the same 212ft 9in wingspan as the current models to maintain Code E compatibility. Using a dedicated control panel on the flight deck the crew will be able to unfold the tips prior to departure to the full span for flight. Beezhold said: “When we were looking at the wing design, where the optimum span would be to provide the highest efficiency, we did look at putting winglets on, but the right answer was to go with this longer span wing and then put on the folding wingtip to maintain airport compatibility. We wanted to maintain Code E classification.”

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Although not optimised for ultra-long range like the 777-8, the 777-9’s 7,525 nautical miles (13,940km) capability means it will be able to fly London–Los Angeles or New York JFK–Hong Kong.

Beezhold said reliability was key to the folding wingtip’s viability. He insisted: “We have come up with a very simple yet robust mechanism to control the wing fold.”

The system works, he explained, through mechanical actuation. Redundancy from the 777X’s integrated drive train is used to power a motor. This motor drives a rotating actuator that raises and lowers the wingtips when commanded by the flight deck control panel.

Pins lock the tips when they are raised and lowered to the desired position. The entire subsystem is self-contained in the wing loft area. German company Liebherr Aerospace is supplying the wing fold, drawing from its experience designing hydraulic actuation systems for primary flight controls. The fold mechanism will be integrated into the wingtip assembly by Boeing at the St Louis factory, which is fabricating the wingtip as part of its 777X work package.

The composite wing and its folding tips are not the only airframe differences between the 777X variants and earlier models. To optimise for drag and ensure there are no steps and gaps in the structure that create inefficiencies, there are completely redesigned fuselage fairings, a new wing-to-fuselage fairing and a new empennage.

Beezhold also highlighted the GE9X engine nacelles as an important aerodynamic achievement. Although GE designs the powerplant, Boeing is responsible for the nacelle, the thrust reverser and the inlet.

Beezhold said natural laminar flow was used to ensure optimal efficiency for these parts. He added having a single-source engine supplier in the form of GE was beneficial: “You can have multiple engine off erings, but we partnered GE so we could go in with them and optimise the way that engine is integrated into the wing to really maximise the total efficiency, versus having to make compromises for different engine types.”

Aerodynamic efficiencies

Another influence on wing efficiency is loading. Aircraft manufacturers have become increasingly interested in designing ways to optimise wing profile in flight to account for changing loads and ensure airflow around the wing is kept as efficient as possible. On the 777X there is a variable camber trailing edge and a vertical gust suppression system. Variable camber adapts the position of the wing and the gust suppression system deploys the flaps, ailerons and spoilers to move the loading of gusts around the wing to give a more aerodynamically efficient wing shape.

Beezhold explained these systems work because accelerometers mounted on the wing measure vertical and lateral separation of the gusts over the wing. These sensors automatically send electronic signals to the actuators, which then make tiny adjustments to the flight controls to distribute the loading evenly across the wing to ensure optimal airflow and minimal drag.

The combination of the wingspan and the various aerodynamic efficiencies all working together gives, Beezhold said, “the highest lift over drag efficiency aircraft ever developed”.

Link to the 787

The 777X’s use of composites in the wing and of variable camber and gust suppression technologies highlights a link between the 787 and the new Triple Sevens, but the crossover between the families goes much further.

Control laws from the Dreamliner’s flight control system (FCS), including angle of bank protection and an automatic roll and yaw asymmetry compensation system that applies rudder if engine power is lost, have been integrated into the 777X FCS.

Beezhold continued: “For the 777X we’ve adapted the 787 Common Core System [CCS] to provide a much more advanced and capable platform for hosted functions that share a common set of computing resources.”

The CCS is effectively the central nervous system of the aircraft, hosting avionics and utilities functions. On the current production 777s the CCS is a basic computing platform. The 777X’s CCS, supplied by GE Aviation, is like the 787 CCS designed to eliminate the boxes and wiring that housed and supplied computing power aboard. GE Aviation says it provides a weight saving of hundreds of pounds on earlier 777s.

The 777X CCS is also designed to share common components with the 787 CCS. Its open system architecture means developers are only required to test and certify functions that have been altered and operators can scale the system depending on their needs; both are designed to minimise costs.

Beezhold added: ‘[The 777X’s CCS has] a lot more growth capability as we look ahead to the demands on systems like flight management where there’s a huge amount of data.”

Another similarity between the new Triple Sevens and the 787 is the flight deck. Boeing’s CGIs show the 777X’s flight deck will look much more like a 787’s than a 777’s. Like the Dreamliner, large-format LCD screens will be supplied by Rockwell Collins.

Hybrid approach

Besides the link to the 787, there will also be extensive commonality with currentproduction Triple Sevens; a quite deliberate approach by Boeing.

Beazhold acknowledged: “The 777 is very reliable, so one thing we wanted to ensure we did was to carry over the systems that are operating really well.”

Among the key commonalities with the current models will be the fuselage barrels, which will be made from conventional aluminium like the current 777s, rather than composites like the Dreamliner’s. Power for key systems such as the auxiliary power unit, hydraulics, wing anti-ice protection and cabin environment control systems will be drawn from a conventional pneumatic architecture using high-pressure bleed air diverted from the engines, rather than the electrical power architecture used on the 787.

INTEGRATION AND RELIABILITY TESTING

Boeing regards maturity testing as especially important for the 777X. This is perhaps unsurprising, given the bad publicity caused by the development delays that afficted its last new widebody airliner, the 787. One comment from Terry Beezhold to AIR International indicated the experience has left its mark on the company. He said: “One of the things we’ve done on this programme to drive maturity into all of the systems much earlier than what we’ve done historically is to drive all the qualification testing to completion much earlier.”

Mid-to-late 2018 is the company’s milestone for completing qualification testing. Beezhold said: “That means we have completed the full hardware and full environmental aspects/conditions, we’ve done all the systems testing, we’ve done all the EMI [electronic magnetic interference] testing. We do that across all of our suppliers so they’re all responsible both to design and to qualification testing of their equipment.

“Something we’ve also done to ensure the hardware is really robust and reliable is we’ve asked our suppliers, especially on new equipment, to do something we call reliability enhancement testing. They build their initial prototype of the hardware and then they’ll put it through a preliminary qualification test and test it above the vibration levels to look for the weak link of the hardware. Then they’ll make design changes to make it more robust so it can withstand higher levels than what we’d normally qualify.”

Beezhold said the process is designed to build a high level of reliability and robustness into the 777X’s design which, in his words, “ultimately then goes through to qualification testing, usually with ease, and ‘hardens’ the design before we actually go through to full testing. We do that so we’re not [catching issues] at an aircraft level while we’re doing flight testing. That dramatically reduces the risk of having to make changes late in the programme and gives a nice, mature aircraft during flight test.”

The 777Xs’ power generation system, supplied by UTC Aerospace, will comprise two 150kVA integrated drive generators, an auxiliary generator, three generator control units and a bus power control unit, which the company says will provide 25% more power than the system on current production 777s.

There will be lots of features which will be familiar to pilots, with those similar flight control laws mentioned earlier and Rockwell Collins avionics (used on current and legacy 777s). Boeing has also sought to position control switches in the same places. For instance, Beezhold said: “The overhead P5 panel is very similar to the 777 to minimise any kind of difference training. We wanted to make sure the crew interface [is] maintained to make sure that memory motion that flight crews have is unchanged.”

All this commonality is by design to minimise key operational costs, such as spares management and pilot training. The intention is the new 777s will have a common type rating with all three 787 variants.

This is not to say, however, that the 777-9 and 777-8 will not have their own novelties.

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A folding wingtip mechanism will extend the 777Xs’ wings to their full 235ft 5in (71.7m) span for flight, the mechanism folding upwards to narrow the aircraft’s wings for ground operations and ensure taxiway and gate compatibility.

Although the flight deck will have the familiar Rockwell Collins multifunction displays, interfaces, checklists and dual head-up displays, one big difference with older 777s is the five large-format LCD screens, as opposed to the current generation’s six smaller screens.

These displays will feature resistive technology that, by requiring a firm rather than a light touch to operate the display, is designed to avoid unintentional interaction. The displays will also have bracing features for operation during turbulence and the lower display will be multitouch, meaning both pilots can simultaneously interact with the display.

When the design was announced, Rockwell Collins Commercial Systems’ Executive Vice-President and Chief Operating Officer Kent Statler said: “Touchscreens are everywhere in our lives. A touch-controlled flight deck environment makes it easier for pilots to manage information and do their jobs, and speeds up the process to complete tasks.”

From an operator’s perspective, the flight deck is a good case study of the line Boeing has tried to walk with the 777X, taking the familiar and the proven and adding new elements.

Beezhold summed up the approach: “The 777X is really a hybrid of the best of the [current] 777, the best of the 787 and some new technologies that don’t feature on either of those models. It’s about adapting to keep the commonality, but accounting for any differences.”

Cabin

Passengers will notice differences in the cabin of the 777-9 and 777-8 compared to earlier Triple Sevens, however. In this area, the Dreamliner has again left its mark on the new aircraft.

Beazhold said: “When we set out to develop the 787 there was a lot of focus on the cabin experience and how we bring the joy back into flying. All the things that were introduced on the 787, the lower cabin altitude, the larger windows, the air purification, the ride quality, work together to provide a much better experience.”

The result is the 777Xs will also have a larger window to let more natural light into the cabin (Beazhold said: “We shifted the window belt upwards so everybody whether you’re at the window or at the aisle, has a better view.”) and LED lighting to create a brighter, lighter atmosphere.

The cabin altitude will also be at what Beezhold called similar levels to the 787’s. Boeing has yet to confirm that altitude publicly, but on the Dreamliner the cabin is pressurised to an altitude of 6,000ft (1,828m).

Boeing explains the 787’s lower altitude was achieved by a higher level of pressurisation, which the manufacturer stresses was made possible because the composites in the fuselage off er better fatigue resistance.

As noted earlier, however, the 777Xs’ fuselages will not be composite, so how is the 787-style cabin altitude possible?

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High-speed wind tunnel testing for the 777X was carried out in the Boeing Transonic Wind Tunnel in Seattle. Data from the high-speed tests helped with configuration development by validating computational fluid dynamics predictions and support preliminary loads cycle development.
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With an 8,131ft3 (230.2m3) lower-deck cargo hold, compared to 7,120ft3 (201.6m3) on the 777- 300ER, the 777-9 will be able to carry 48 LD-3s (26 in the forward hold and 22 in the rear hold).
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A developmental 777X flight deck. The five large-format display screens will mean the flight deck will look like a 787’s, although Boeing says similar flight control laws, Rockwell Collins avionics and positioning control switches in the same places as current-generation aircraft will maximise commonality.

Beezhold said although the 777X has an aluminium fuselage: “We understand the margins. We were able to introduce the lower cabin altitude with some minor changes to the airframe. We were able to increase the cabin humidity levels.”

Milestones

These are important times for the 777X. Beezhold said: “This whole past year has been focused on getting all the engineering completed. That’ll pretty much wrap up towards the end of the year, wrapping up the payloads and systems installations that typically are the last things to be released.” At the time of writing, AIR International’s interview engineering was 85% complete.

The supply chain, meanwhile, is ramping up. Beezhold continued: “They’re well into production, the fuselage [barrels] are being produced in Japan and all our systems suppliers are meeting their hardware and software [targets]. They’re sending that back to us to build up our integration labs at Boeing Field where we begin our integration testing.”

In September, the wing spars for the first static test airframe entered the Composite Wing Centre. Right behind those spars, the parts for the first flight test aircraft were being prepared.

Beezhold said: “The critical path at this point [is ensuring] the engineering is all completed [on] the long lead-time things, like the wing [and] some of the major system components. The critical path towards next year is when we start building the first flight test aircraft and we start installing all the systems and put power on the aircraft.”

With the 777-9 and 777-8 joining the Boeing widebody family portfolio alongside the three Dreamliner variants, the 787-8, 787-9 and the new 787-10, the American company will have five twin-engine widebody aircraft of different size, payload and range configurations.

Beezhold said: “It’s about the flexibility of a family. You think about the common type rating between the 787 family and the 777X family: your flight crews can move across five aircraft. That really gives you a great capability if you’re a 787/777X customer; you can serve any mission, any capacity. We’re pretty excited about that.”

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Touchscreen flight deck displays will feature resistive technology that, by requiring a firm rather than a light touch to operate the display, is designed to avoid unintentional interaction.