Henry Petroski. American Scientist. Volume 83, Issue 6. November 1995.
In April 1994, what has been called “the last all-new, long-range transport of the 20th century” was unveiled in Everett, Washington, about 25 miles north of downtown Seattle at the Boeing wide-body airplane factory. The ceremonies marking the official debut of the Boeing 777 were attended by a select group of approximately 100,000 invited guests, including employees and executives from component suppliers and customer airlines in addition to government officials. Although the Everett factory is by volume the largest building in the world and, with its recent expansion to 280 million cubic feet, will allow for a monthly production run of seven 777s under its roof, even its space was not adequate to accommodate all the guests at one time. They were scheduled in shifts of about 7,000 each between 6 a.m. and 9 p.m. to view the multimedia ceremonies orchestrated by Dick Clark Corporate Productions.
With as many as 28,000 visitors on site at any given time, and with the expected arrival and departure of approximately 48,000 cars throughout the long day, the logistics of keeping everything on schedule were not unlike the problems faced by a large theme park and could not be left to chance. Computer flow simulations, in which people were assumed to walk at the rate of 3.5 feet per second, were used to plan the event. Boeing’s own Methods Engineering group employed software like that used to move and track parts about the factory. The real-life audience was assembled first in a hangar in which they listened to a speech by a top Boeing executive, after which they were ushered into the rollout hangar. There they were treated to a multimedia show that highlighted the history of the aircraft and emphasized the concept of teamwork. After the show the screens were raised, revealing the first 777 bathed in color, the crowd was motioned forward by light wand-wielding guides in jumpsuits, inviting the audience to “kick the tires.”
The use of computer simulation in planning the 777 unveiling must have appeared to many at Boeing to be a natural extension of the design of the plane itself. As with any large engineering project, a conceptual design was worked out first, in the late 1980s, showing the overall size of the proposed plane and its general configuration, including seating options and cabin layout. Even such important details as wingspan were not yet fixed at this stage. However, the objectives of the new 777 series were clear: to develop an aircraft that would be economical to manufacture and operate and that would provide a suitable replacement for fleets of aging wide-body jet aircraft such as the DC-10, the L-1011 and older Boeing 747s. Not incidentally, the 777 would also compete for the same passenger capacity and flight-range business as the then-recently announced A-330 of Airbus Industrie, the heavily government-subsidized consortium of British, French, German and Spanish aircraft companies.
Computer-Aided Design
Although its origins can be traced back to the mid-1980s, when Boeing was considering a new prop-fan-powered airplane then designated the 7J7, the detailed design of the 777 can be said to have begun in earnest in the fall of 1990. It was then that Boeing and United Airlines executives signed a one-page, handwritten agreement for 34 of the new airplanes, with an option for another 34. That airline and eventually other customers (including All Nippon Airways, British Airways and Japan Airlines) would have input into how the plane ultimately would be designed. Rather than the 48 months traditionally allowed for the development of a new commercial aircraft, almost five years were allowed for the 777. This extra time was scheduled in part because the design was to proceed in a new technological environment, for the intent of Boeing was to integrate computer-based engineering design, analysis, testing and manufacturing throughout the project, thus eliminating the need for conventional drafting services. Such a totally new design system had itself to be designed before the aircraft. Thus, in April 1991, a second one-page agreement was signed by Boeing, IBM and the French-owned software developer, Dassault Systemes. Each of the documents ended with the commitment, “User friendly and everything works.”
According to early reports, the 777 has proved to be remarkably user-friendly, and just about everything does work. This is attributed largely to the fact that the detailed design and development was completely computer-based. The Computer Aided three-dimensional Interactive Application (CATLA) of Dessault Systemes, used previously to design French Mirage fighter aircraft, is known today as the leading computer-aided design (CAD) software. CATIA, running on IBM workstations and mainframes, supplemented with much Boeing-developed CAD and computer-aided engineering (CAE) software, made it possible to eliminate drawings and physical mockups throughout the development process, thus making the 777 the first completely “paperless” major commercial transport design. This was not done without some innovations in computer engineering, however, and in Boeing’s Washington facilities alone an unprecedented 2,200 workstations and eight of IBM’s largest mainframes had to be linked. Suppliers and manufacturers of systems and components for the 777 were actually spread throughout the world, including Japan, where the Japan Aerospace Consortium (comprising Mitsubishi, Kawasaki and Fuji Heavy Industries) was responsible for 20 percent of the airframe design and construction. To serve these participants, dedicated trans-Pacific high-capacity data cable was laid by Boeing, with a secondary satellite link for backup. Thus everyone involved in the design, development and manufacturing endeavor had ready access to all design data. At the peak of the project, the system served some 7,000 workstations spread across 17 time zones.
The storage requirements of the CATIA system, the largest installation ever, reached as high as 3.5 terabytes. If stored on high-density 3.5-inch disks each holding 1.44 megabytes, that amount of data would require almost two-and-a-half million disks, which would constitute a stack of floppies almost five miles high. With the computer network, all engineers working on the project could access all the data electronically, but only those authorized to change it could do so. As many as 238 teams, some as large as 40 members, were working on the project at a single time. In a conventional mode this would be expected to lead to numerous potential interferences among hardware systems–to be caught by building physical mockups–and to necessitate costly design changes and revised drawings, which traditionally were a major determinant of final cost. One senior draftsman on the 777 project remembered in the past “waiting days to get someone else’s drawing, getting a copy made and slipping it under mine to trace their part.” In the case of the 777, he could do the same task electronically in a matter of hours.
Such advantages saved in excess of 50 percent of the change orders and reworking typical of a project of the m’s magnitude and complexity, but for competitive reasons Boeing is not willing to say how much in excess. With more than 130,000 unique engineered parts and, when rivets and other fasteners are counted, with more than 3 million individual parts going into each plane, having things fit right the first time is a manufacturer’s dream. Some early physical mockups of m subsystems intended to check the reliability of the CATIA installation showed that physical models would not be needed. The computer-based design proved to be so effective that expected glitches, such as mismatches of parts, interference of lines and ducts, and inaccessibility for manufacture and maintenance, were virtually eliminated. In fact, it is said that the parts of the m fit better the first time than those of any earlier commercial airliner. Components of the 20.33-foot-diameter fuselage structure, for example, matched within 0.023 inch vertically and 0.011 inch horizontally, which is less than one in ten thousand.
Hidden Fly-by-Wire
For all of its departure from traditional commercial jet transport engineering, the 777 is still an evolutionary design in the successful Boeing product family, and the company is eager to maintain that impression. Boeing is quick to remind media commentators who call the plane the “triple-seven” or “seven cubed” that its name is more properly pronounced “seven-seventy-seven” or “seven-seven-seven,” in line with the names of its predecessors. As if designed to assert the pedigree of the plane, the 777 cockpit appears to be a cross between that of a 747-400 and a 767, with perhaps only the replacement of cathode-ray tubes with flat-panel, full-color liquid-crystal displays suggesting the innovations behind the instruments and controls.
The 777 is Boeing’s first fully “fly-by-wire” commercial airliner, which means that the controls in the cockpit are connected electronically through intermediary computers by wires to the systems they operate, and not physically by levers, pulleys, steel cables and hydraulic lines, incidentally saving hundreds of pounds of airplane weight. Although Boeing had had prior experience with the fly-by-wire principle on some engine controls, on the 747-400 high-lift system and on the 767 spoiler system, the company was charting new territory in giving over to software and electronics the primary flight controls of the 777. (In the concept stage of the 777, a “fly-by-light” system was even contemplated, but in the end fiber-optic cables were used for less crucial systems such as digital data transmission to the individually controlled entertainment screens that will be located at each passenger seat.) In the 777, the use of a two-way digital data bus patented by Boeing enables a single pair of twisted wires, rather than a series of separate one-way wire connections, to serve as the communication link among airplane controls, actuation systems and on-board computes. In anticipation of accelerating the regulatory approval of the fly-by-wire system of the 777, Boeing installed it on a 757 transport, which served as a “flying testbed.”
Fly-by-wire and computer control go together in late 20th century aircraft, of course, and a central and gargantuan problem in developing the 777 was writing the software for the digital flight-control system. According to Jim McWha, the chief engineer in charge of the task, it is not so much the software per se but the seemingly endless requirements, the calls for ever-increasing complexity, and the last-minute changes that are presented to the software developers that make the task so difficult. Even with highly reliable software, however, computer control is only as good as the integrity of the wiring carrying the digital commands and feedback. Experiences of past “common-mode” failures–such as that involved in the 1989 crash of a DC-10 in Sioux City, Iowa, caused when an explosion destroyed all three redundant hydraulic control lines that had been grouped together near the tail section–led to the routing of different wires of the flight-control system in the 777 through different parts of the plane.
In contrast to the fly-by-wire system introduced in the Airbus A-320, which incorporated into a novel cockpit design sidestick controllers and throttles that remained stationary when engine power was adjusted by the computer, the Boeing system has retained a conventional cockpit design with a yoke before the pilot that moves with the autopilot commands and throttles that move with adjustments made by the autothrottle system. Tactile feedback, such as the three pounds of force that builds up in the control column for every 10 knots of airspeed change, makes it less likely that the pilot will fall asleep at the stick while the computer is accelerating or decelerating the plane. The reduced crew of only two (the flight engineer is not needed in the computerized cockpit) is seen not so much as flying the aircraft as interfacing with it, by programming in and checking flight information via keyboards and computer displays. (One version of a joke among flight-control software designers has fly-by-wire airplane cockpits evolving from (1) requiring a pair of human copilots to (2) requiring a single pilot and a dog, with the dog barking when the pilot nods off, to (3) requiring a dog and a pilot, the dog there to keep the pilot from touching the controls and the pilot there only to feed the dog and to make announcements to the passengers.)
Pilot Friendly
Pilots flying the 777, with or without a hungry companion, have been finding the plane to have the same “feel” as its predecessors. Designed with the aid of computational fluid-mechanics techniques to fly at an energy-efficient Mach 0.83, flight tests proved the 777 actually to operate smoothly at Mach 0.84. The plane has been found to be very easy to land because its wings, as large as those of a 747 but closer to the ground, experience a strong “ground effect.” Taxiing the 777 is a new experience for pilots, however, because the nose wheel is 12 feet behind the pilot’s seat. But the two main landing gears with six wheels each (to distribute the weight in order to maintain acceptable runway loadings) appear to present no unusual characteristics to the cockpit. An option not yet elected by any 777 purchasers is a feature suggested by American Airlines, namely wings that fold, like those on carrier-based aircraft, in order to minimize objections to using the new plane in airports with tight clearances on taxiways and at gates designed for smaller planes.
The first ms have been fitted with two Pratt & Whitney turbofan engines rated at approximately 77,000 pounds of thrust each to move the aircraft’s half-million-pound takeoff mass. (Other engine options include General Electric and Rolls-Royce models.) Early pilot experience with the Pratt & Whitney engines, with a fan diameter alone in excess of 9 feet, is that the great amount of rotary inertia contained in such massive rotating structures makes for smooth speed changes and easy taxiing under low power. The engines have been under development since 1990 and, like the 777 itself, represent evolutionary rather than revolutionary change from earlier Pratt & Whitney products, thus building on a data base of experience on the order of 10 million hours of operation. Extensive flight testing, confirming a predicted shutdown rate for the new engines of approximately 1 in 100,000 flying hours, was expected to help gain unprecedented early extended-range twin-engine operations certification for the 777 to fly routes that take it up to three hours from the nearest possible landing point. This, in effect, meant that the 777 could begin commercial transatlantic service without the customary two-year test period during which previous new airplane models had to remain within an hour of a major airport.
In early June, a United Airlines flight from London Heathrow to Washington Dulles International Airport inaugurated commercial 777 service. Few passengers on that flight or subsequent transcontinental ones are likely to realize or care that 9 per cent by weight of the new plane is made of composite materials, including a tougher and easier to fabricate and repair carbon epoxy material, that 9 percent of the plane is made of titanium, or that the selection of programs on their personal video screens, soon to be accompanied by handsets that will double as credit-card telephones and keyboards for playing video games, is brought to them via fiber-optic cable. However, virtually all travelers, even in economy class, are likely to appreciate the general roominess of the cabin, greater-than-normal legroom and overhead storage bins that provide increased headroom.
Although Boeing has not revealed the exact cost of the entire 777 research, design and development program, it is believed to have taken an investment of approximately $4 billion to reach the rollout stage. This would make it among the world’s largest engineering projects funded by a corporation. However, United Airlines’ initial order, for a record $22 billion, and subsequent additional orders have augured well for the financial success of the new airplane. Market projections have been that in excess of $800 billion will be spent on about 12,000 new commercial aircraft of all kinds through the year 2010, and Boeing expects to capture a very profitable share of that business with the 777.
Early versions of the Boeing 777 will carry about 300 passengers on flights ranging up to about 4,600 nautical miles. A later stretch version will carry up to 370 passengers, with future plans calling for 777s with a range approaching 9,000 nautical miles. Boeing and European partners of its main competitor, Airbus Industries, had been looking ahead to the planes they will develop for the 21st century, and they identified an extended-range, 800-seat super-jumbo jet. Since the investment was considered too much for any single company, Boeing and the Airbus partners were exploring an unprecedented cooperative endeavor, but as of mid-year the idea had been shelved because the projected market demand did not appear to justify the projected $20 billion development cost. As new and larger commercial aircraft are built in the 21st century, however, their designs will necessarily rely heavily on experience gained on the 777.