The Boeing 777X has finally undertaken its first flight from Paine Field in Everett Washington and this delayed event will signal the start of a long-awaited the flight test campaign.
Rob Edgcumbe reports on the process to get the 777X programme this far, with pictures from Jake Welty and Rob Edgcumbe.
January 25, 2020 was the day that the Boeing 777X finally made its first flight. The attempt at flight that week itself suffered delays from the originally scheduled date which were emblematic of the larger problems that the programme has experienced getting to this point. Launched at the Dubai Air Show in 2013, the 777X takes the 777 family to a new generation and is intended to maintain Boeing’s strong position in the large twin segment. Previously controlled by the 777-300ER, the arrival of the A350 has put pressure on Boeing’s product line up. The 777X is supposed to reassert Boeing’s position in this segment.
The development of the 777X has been focused on two subtypes. The 777-9 is the larger of the two and the initial version. It has been the better seller of the two. The 777-8 is a shorter variant that is intended to provide longer range capability. This has not sold as well and, while Boeing asserts otherwise, there is plenty of talk in the industry as to whether this version will see the light of day. It has been put on a slower development path for the time being. If a freighter replacement for the 777F is required, the -8 would be the natural base.
While described as a variant of the 777 family, the 777X involves a significant redesign. The fuselage is lengthened and redesigned to provide larger windows and accommodate the lower cabin altitudes that were pioneered by the 787. The frames of the fuselage are reshaped to provide a wider interior cabin space. Metallic construction is retained in line with that of the original 777.
The wing, on the other hand, is a major redesign. It is a composite structure rather than the original metallic design on the 777. It has increased span to provide improved lift and drag characteristics to enhance efficiency. However, in order to ensure that the plane can still fit within the existing gates used by the 777 fleet, it is necessary to shorten the wing. Consequently, a folding wing tip is included and this is one of the defining features of the new type. This isn’t the first time that folding tips have been considered for the 777 family. The original design was configured to include a folding tip to allow the plane to fit in gates used by 767s. However, no customers took up the option and it was never developed at that time. Indeed, the space in the tip area which had not been included in fuel tankage because of the potential for the fold was ultimately freed up for the 777-200LR and 300ER to increase their fuel capacity.
For the 777X, the folding tip was considered a must have item and has been part of the design from the beginning. The controls for the fold are integrated into the aircraft systems such that folding and unfolding will take place without the risk of the aircraft taking off while folded or taxi in while still locked down. The wing tips seem to cause much consternation with observers, but the topic has been worked in great detail and I suspect it will not be a particular hurdle to certification. The repercussions from the 737 Max grounding are far more likely to have impacts on certification across the design than for this one element.
A new generation of engine has been designed by GE. The GE9X has the largest fan diameter of any engine but it is not the most powerful. While it has been tested to record breaking levels of thrust, it will be certificated to a thrust level below the GE90 on the 777-300ER. The improved aerodynamic efficiency combined with the improved specific fuel consumption of the new engine means that the aircraft potentially needs less fuel overall and, with the fuel burn associated with carrying the extra fuel itself gone, there is a further reduction in fuel needs. Consequently, you don’t need as much thrust. Even so, the thrust levels have grown a little during the development programme from what was proposed at launch.
The engine has been one of the delays to the programme. The first taxi trials commenced in mid 2019 – itself behind the original schedule. Then an issue was identified by GE with durability of the engine (exactly what was never publicly disclosed) and the need to resolve this pushed back the flight trials. The arrival of modified engines at the end of 2019 allowed the resumption of testing. Meanwhile, the structural test article suffered a failure slightly below the intended limit. Much speculation has resulted about this failure with little firm information coming from the company. If the failure was very close to that predicted, a simple resolution should be possible. If the area of the failure was well below its forecast limit (even if the overall limit was close) that might require a more detailed review of the design in that area. We cannot know at this point.
The taxi trials in mid 2019 exercised the plane to some extent but did not reach higher speeds. High speed taxi trials can require a flight clearance to be in place – just in case. Only with the modified engines in place and the flight clearances developed could the remaining taxi trials take place, and these were completed in January of 2020. First flight was scheduled for January 23rd but the weather forecast was not good, so it slipped to the 24th. Unfortunately, a strong southerly wind meant a tailwind for takeoff – first flights are routed to the north to minimize overflight of populated areas – and the winds were outside limits. The 25th was finally within limits and the flight took off. It headed to the area inland of the Cascade mountains for the initial handling checks before some photos around Mt Rainier and a landing at Boeing Field, the home of the flight test organization.
Now the main testing programme will get into high gear. The delays have resulted in several airframes already being complete. There are three more airframes for the flight test programme on the ramp at Everett and further production frames are now stored around the airfield awaiting completion. Certification is now likely to be in early 2021 with deliveries following on. Meanwhile, the middle eastern customers that drove the initial launch have been reducing their order quantities due to their own issues so Boeing will be working hard to backfill their production slots. Having an aircraft flying and producing real performance data can sometimes spur further orders so we shall watch and see whether new customers sign up soon.