ow do you combine two recognized industry benchmark flight-deck designs into an even safer hybrid while including novel features and margins for growth for the air traffic environment of the 2030s and beyond?H
That is the challenge facingas it carves out the basic flight-deck design for the , using a former 787 development cab at the company’s Integrated Aircraft Systems Laboratory near Boeing Field, Seattle. The plan is to integrate the best features of the two twinjet cockpits to maximize commonality for easier transition to the 777X. Boeing has already opted for the larger displays of the 787, making the development cab from this recent program the obvious jumping off point.
The early flight deck and associated flight control law work are driven by three main goals, says 777X chief pilot Mike Carriker. “You have to use the capital invested in 777 and 787 pilots, and that translates into a desire for a common type rating. We also want this airplane to fly amazingly well at cruise and we want to get it into the gate,” he adds, referring to the decision to adopt folding wingtips as part of the baseline configuration. Flight-deck and systems design will continue through to firm configuration in 2015. Following detailed design, production of the first 777-9X will begin in 2017 with first flight late in 2018.
Carriker, who helped lead the 787 andflight-deck development, says the key question over the 777X and its links to the current 777-300ER and 787 revolves around “what are we going to bring from each? It has a mother and a father and there is a hybrid offspring. So we are saying ‘this is really good on 777 and we know about it, and this is really good on 787 and we know about that too.’”
The least surprising decision, so far, is the move to a 787-style large display format. The 787 is equipped with five 12 in. X 9-in. displays with 546 sq. in. of display space, or double that of the current 777. The jury is still out regarding head-up displays (HUD). These are not currently offered on the 777 but are standard on the 787, and Carriker is unapologetic in his support of them for the 777X. “I am an unadulterated HUD cripple. I love them because you are looking out of the airplane,” he admits.
Like the airframe, which will combine the composite wing design of the 787 with the baseline metallic fuselage of today’s 777, the 777X flight control laws will be a combination of those twinjets. Key targets include ensuring top performance by maximizing the structural benefits of the flexible wing and, despite the added length and wing span, guaranteeing handling characteristics identical to the current 777. Boeing aims to make flying characteristics and the flight decks so common between the 787 and 777X that a pilot can transition from one to the other with just five days of “differences” training.
Like the 787, but unlike the 777, the 777X fly-by-wire flight control system (FCS) will operate in all three axes (pitch, roll and yaw). “Pitch control law is identical between the 777 and 787, but roll control will include changes,” says Carriker, who adds that the roll control law in the 777X will be a derivative of the 787. The 777 was Boeing’s first fly-by-wire airliner and employs a flight control law called C*u (pronounced Cee star u), which governs longitudinal stability via speed control rather than pitch stability. For the 787, Boeing added a P-Beta (P-aerodynamic term for roll rate, β-sideslip angle) control law, which coordinates lateral and directional control, and opposes disturbances caused by thrust asymmetry and other factors. The control wheel commands roll rate, while pedals command sideslip angle; the aileron and rudder trim are automatic.
Although Boeing was able to flight test the 787 control laws in a modified 777-200ER during the control verification/risk-reduction effort in 2006, Carriker does not anticipate a repeat for the 777X. Because “most of the load-alleviation systems are in the wing, we will transplant a little of the same sort of experience between the airplanes on how to build a composite wing and how to alleviate the structural loads. That comes from lessons learned on theand -9. The -10 will also be done by the time the 777X flies and we will take all that data. The 787-10 is a really long airplane so that will help with our analysis,” he adds.
As with the 787, in which the fly-by-wire system contributed to making the overall design lighter, the 777X FCS is also crucial to Boeing’s plans for improving the aircraft’s performance. The control system will help reduce the structural weight of the outboard section of each 114-ft.-long wing by shifting lift distribution further inboard. Boeing reduced the weight of the 787 wing box by nearly 4,000 lb. by using maneuver load alleviation systems to decrease structural loads.
The design team also is defining how crews will control the wing-fold mechanism that will raise the outer 11 ft. of each wing tip to allow the 777X to park in existing 777 gates. The device, which will reduce overall wing span from 233 ft., 5 in. extended to 212 ft., 9 in. folded, has been scrutinized since early 2013, “when we realized it was new and novel,” says Carriker. Boeing first developed an optional wing-fold concept for the baseline 777-200 in the 1990s, but it was never adopted. The 777X fold system, which is now part of the baseline design, is simpler to actuate and lighter, according to the company. It is “designed to not fail in flight and never come off, similar to a flap,” Carriker adds.
The original design was configured with all-manual modes for folding and extending-and-folding, but the approved design includes a mix of automatic and manual modes. Although it is “easy to define how to fold the wingtips (automatically) after landing,” Carriker says the logic for an automatic extension system before takeoff is more challenging because of the unpredictable hazards that may appear on taxiways and ramps.
Crews will be presented with “lots of cautions, warnings and advisories” about whether the wingtips are extended or folded. The prime rule will be the tips should be extended “when the nose gear crosses the hold short line” as the aircraft enters the runway for takeoff,” he adds.