Update – Boeing 7J7

Powered by ultra high bypass (UHB) engines, the 7J7 will also have vastly improved fuel efficiency. Reduced maintenance costs, through simplified design and application of the new technologies will contribute further to the economical operation of the aircraft, claims Boeing. Overall, the 7J7’s direct operating cost (including fuel, maintenance and ownership) is expected to be lower than that of any competing airliner.

Developmental progress is aimed at projecting 1992 as the time period for introducing an all new aircraft of this size. Currently, the dominant 150-seat aircraft is the 727-200, with more than 1,200 still in service. Many of these will approach their time for replacement by the beginning of the next decade, but only if the price, operating economics and marketing advantages of alternative aircraft are compelling enough.

To assure affordability, Boeing is reassessing the entire process needed to design and build a new aircraft. The goal is to introduce more efficient methods, both at Boeing and at the vast number of programme participants and subcontractors.

Boeing will share investment risk on the 7J7 programme through international participation. The company has reached agreements with several overseas aerospace industries. A memorandum of understanding (MOU) was signed providing the Japan Aircraft Development Corporation (JADC) with a 25% partnership or equity share in the 7J7 programme. JADC is the coordinating agency for Fuji Heavy Industries, Mitsubishi Heavy Industries and Kawasaki Heavy Industries. Together they will participate in all phases of the 7J7 programme, including design, development and production.

In addition, Short Brothers of Northern Ireland, Saab-Scania of Sweden and our own Hawker de Havilland signed MOUs in 1986 to become programme associates, enabling each of them to participate in the development and production of part of the aircraft on a non-equity basis.

Boeing’s timetable calls for discussing final specifications for the new aircraft with prospective customers during late 1987. Boeing would then proceed with detailed engineering, production and certification flight testing once a go-ahead decision is made.

Currently, development work is proceeding at Boeing and key suppliers in the following areas:

Propulsion

The 7J7 will be powered by two ultra high bypass engines Several versions are under development at major suppliers. These engines have very large diameter fans with variable pitch blades. They can move a larger volume of air for a given amount of fuel compared to the latest high bypass turbofans, offering the potential of a 20% reduction in specific fuel consumption and up to a 45% reduction compared to low bypass engines. Noise levels will meet the current US and ICAO standards.

The version of the ultra bypass concept that is the baseline powerplant for the 7J7 is General Electric’s ‘unducted fan’ engine or UDF. It features two counter-rotating fans external to the nacelle. The fans, about 11½ feet (3. 5m) in diameter, are powered directly by a counter-rotating jet turbine. The blades of each fan are distinctively swept back and slightly spiral-shaped.

On August 20, 1986, GE and Boeing began flight testing a proof-of-concept version of the UDF. It marked the first time that an ultra high bypass powerplant took to the air. For the test programme, the UDF replaced one of the conventional engines on a Boeing 727. The 727 flight test concluded in early 1987 though an improved version of the engine continues flight development through this year aboard an MD-80. The performance had met design expectations and firmly established the UDF as the leader in this advanced propulsion technology. On the 7J7, the UDF engines would be mounted on the aft fuselage.

Structures

Where it is cost-effective to do so, lightweight structural materials will be used on the 7J7 to enhance efficiency. Two very promising types are an aluminium-lithium alloy and a range of advanced composites. Developments underway at Boeing and aluminium suppliers now point to weight savings of about 8% in those areas where aluminium-lithium would be used compared to regular alloys on today’s jetliners.

Composites such as graphite/epoxy are already in service on the secondary structures of Boeing’s current twinjets. Weight savings of up to 25% have been demonstrated. For the 7J7, the primary structure is being targeted, including the tail section and floor structure.

Conventional thermoset composites as well as newer thermoplastic types are also under study. Thermoplastic composites offer particular advantages because they can be formed to shape without separate parts and without need of fasteners, thus reducing fabrication and assembly costs.

Aerodynamics

Another gain in efficiency for the 1992 aircraft stems from advanced aerodynamics. A new wing design will allow a longer span with less sweep, for improved lift and less drag. Performance will be further enhanced by vertical winglets on the wing lips, which effectively increase the span with only a minimal impact on the overall dimension. Aerodynamic shaping of the aft fuselage in the vicinity of the engines will result in smoother airflow for reduced drag.

During the aircraft’s development phase, new computer simulation techniques have permitted the analysis of large amounts of aerodynamic data prior to wind-tunnel testing. Researchers can then devote costly wind-tunnel time to the acquisition of data not available through prior analysis. This greatly refines the analysis process, reduces development costs and helps produce a more efficient design.

Flight Deck

The 7J7’s flight deck will be equipped with new flat-panel displays to provide pilots with flight and performance information. These thin, multi-colour units take up far less space, require less power, save weight and have far greater reliability compared to today’s cathode ray tube displays. They allow more flexibility in flight deck design and will not require the heavy, complex air conditioning apparatus needed to cool equipment on current aircraft.

Flight deck functions will be even more integrated than in the latest of today’s jetliners. As a result, much of the information previously displayed on numerous instruments will be consolidated into just a few of the new flat panel displays. Greater integration will also enhance aircraft handling and flight management capabilities for better control during changing weather conditions and improved overall flight efficiency.

Data Systems

Boeing has developed a new high speed, two-way digital data communications system for the 7J7 called Digital Autonomous Terminal Access Communications (DATAC). DATAC enables aircraft instruments, actuation systems and computers to communicate with one another through a common wire path instead of through individual wire connections. The path, or data bus, consists of a twisted pair of wires.

Six of these simple wire pathways will be installed in the 7J7 and each will be linked to dozens of transmitting/receiving points via non-contacting inductive connectors. For redundancy, many of these points will be coupled to more than one pathway.

DATAC needs no central controller to distribute data among the various electronic boxes. The key is a specially designed very large-scale integrated circuit chip, one for each device linked to the DATAC system. The chip controls the output of data generated by its associated device, such as a wing flap actuator. The chip is also able to recognise and accept data that the device needs from other sources connected to the data bus, including the flight deck.

Benefits of DATAC include the elimination of 75 kilometres of wire and 114 kilograms of plug-type connectors compared with current technology. This helps simplify both the manufacture and maintenance of the aircraft while also reducing weight. In addition, DATAC and the new inductive connectors make it easier to add new devices and systems to the aircraft as they become available.

DATAC’s impact goes even further. It’s at the heart of new fly-by-wire control systems planned for the aircraft and it integrates data collection for an Onboard Maintenance System (OMS). The OMS will enable maintenance crews to rapidly isolate any fault or malfunction through a video display terminal on the aircraft, or through a ground based video terminal that can receive maintenance data during the aircraft’s flight. In either case, the terminal will use text and graphics to describe the problem, show its location and explain how to correct it. There will be no need to search through printed manuals. The result: faster repairs and less chance of schedule interruptions.

Flight Control Systems

On current aircraft, directional control is transmitted mechanically from the flight deck to control surface actuators via a heavy, complex system of steel cables and pulleys. For the 7J7, by contrast, the pilot’s commands will be transmitted as electrical signals through wires to the actuators.

The ‘fly-by-wire’ concept (already being used on the Airbus A320) achieves considerable weight reduction and design simplification. Both primary and backup flight control systems will utilize this technology, with the DATAC databases providing the means of signal transmission. This will be the first total fly-bywire system in commercial service.

Fibre optic signalling will be used in the engine control system. Commands in the form of light pulses will pass through glass cables running from the engines through the struts to an interface with the DATAC system. Fibre optics were chosen for this application as a reliability enhancement since they are unaffected by lightning or other electromagnetic interference.

Cabin Design

A unique set of cabin simulators helped Boeing evaluate relative advantages of single and twin-aisle cross-sections. The simulators had moveable sidewalls and expandable seats to assess passenger reaction to different widths of cabins, seats and aisles in both single and twin-aisle arrangements. More than 2,500 frequent flyers and airline officials were surveyed in the simulators before the twin-aisle decision was reached.

The two-aisle design offers advantages for both passengers and airlines. Passengers will appreciate the roominess and ease of inflight mobility. The wide cabin will also afford ample space for large stowage bins, located above not only the outboard seats but the centre seats as well. Boarding and deplaning will be faster than in single aisle aircraft, reducing airline turnaround times for increased flight frequencies.

The interior of the 7J7 will be designed to offer maximum flexibility in adjusting to changing market demand levels – seasonal, day of week and sector by sector. Airlines will be able to quickly reconfigure combinations of galleys, lavatories, seats and class dividers. Any combination of four distinct seating alternatives can be offered: seven-abreast economy, six-abreast full fare and five or four-abreast first class.

Passenger entertainment will be available through flat-panel TV screens on seat backs (refer our Paris Air Show report, this issue), which may also serve as a means of communicating with the cabin crew. A connectorless signal transmitter will eliminate the maintenance-prone plugs used in today’s entertainment systems and greatly increases flexibility in repositioning seats.

Twin-aisle comfort and efficiency together with cabin flexibility – will be definite revenue enhancing features for 7J7 operators. The aircraft’s low operating costs attributable to advanced technologies will further contribute to profitability. These advantages claim Boeing, will give operators a competitive edge, even in the face of future market uncertainties.

Affordability

While development work is proceeding in major areas of technology, Boeing is undertaking a concerted effort to reduce costs. Design/build teams have been established with responsibility for attaining cost goals on each of the 7J7’s major aircraft segments. Computer-aided design and manufacturing capabilities are being expanded, improving accuracy and greatly reducing the possibility of costly changes once production has begun.

At the factory level, digitally programmed machining and assembly equipment will further contribute to cost efficiencies. The new technologies themselves will help cut costs through reduced numbers of parts and simpler designs.

Boeing hope now to formally launch the project by the end of this year for a first flight in 1990/91 and airline service by 1992.