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Aviation History
1990
1990 - 1887.PDF
The return on that investment is now at risk, with B-2 procurement to be almost halved from 132 to 75 aircraft and with the threat that Congress will mothball the entire programme after the 13 aircraft now under contract are built. Against this background the Air Force opened the gates of its B-2 final assembly plant at Palmdale, California, hopeful that the technology revealed — claimed to be in advance of any in the world — would be judged an asset worthy of preservation. Much of that technology still remains be hind closed doors, however, at the Northrop B-2 division's Pico Rivera, California, factory and at a network of subcontractors which includes Boeing and LTV (airframe). General Electric (engines) and Hughes Aircraft (radar). Pico Rivera was bought by Northrop in 1982 and the refurbished car plant now houses some 12,600 people and 400 com puter terminals. Here beats the heart of the B-2 programme, a computer database con taining every detail of the aircraft. The database, which Northrop describes as an "electronic product definition", influences all aspects of the B-2 programme —design, simulation, tooling, manufacture, testing and support. Northrop opted for electronic prod uct definition early in the B-2 development programme, which began in the late 1970s. Stealth required extremely precise control of a complex external shape and it was neces sary to design the aircraft from the outside in, the company says. Computer- integrated man ufacture was the solution. DIRECT FROM COMPUTER In the B-2 programme a mainframe com puter replaces paper drawings as the design release mechanism. The B-2 progresses directly from computer-aided engineering design through the database to computer- aided tooling design and on to numerical- control machines, production tools and finally to the aircraft. Stages eliminated in clude drawing prints, mockups, prototype tooling and, of course, prototype aircraft. It was important to build the first aircraft to production standard because early flight- test objectives include crucial evaluation of the B-2's low observability, for which shape is critically important. The precision of external shape (accurate to within 7mm wing- tip to wingtip, says Northrop) and its repeat ability were design drivers. The B-2 airframe is of largely composite construction, with some structures required to withstand temperatures exceeding 300°C. Others comprise complex laminates of com posites and metals which must be drilled in one operation. Surface conditioning of composite materials with special (presuma bly radar-absorbing) coatings is also an impor tant process. High-temperature materials in particular require special tooling, and the B-2 database short-circuits the normal sequence of going from design data to master pattern to tooling pattern to high-temperature pattern to pro duction tool, by going straight from design data to production tool. The B-2 product definition is, in effect, an electronic mockup allowing, for example, engineers to design wiring looms "on screen" then to "unwrap" the harnesses to determine the precise dimensions for manufacture and enabling connectors to be fitted before instal lation in the aircraft. Northrop reports a Total B-2 programme fabrication and assembly 5,000,000- £3,000,000- 2 2,000,000- 3 •§ 1,000,000- •§ 500,000- "" 300,000- 200,000- J»* 2 5 10 20 50 75 Aircraft unit no six-to-one reduction in first-time-fit errors, achieving a 97-99% fit for titanium tubing, up from an industry average as low as 60%. The effort required to create computer programs for numerical-control machine tools has been reduced by 40%, requiring only the addition of cutting speeds and material feed rates to the geometry already contained in the computer database. Computerised scheduling and control is used throughout the B-2 programme, with automated storage and retrieval of materials and components. Automated materials handling during composites manufacture, for example, reduces scrap rates below 4%, says the company. The computer database is directly involved in setting up tooling for B-2 assembly. Except for some large assemblies, Northrop has chosen to go direct from database to jig, virtually eliminating master tooling. A com puter-driven optical theodolite is used to align the jigs, reducing time taken to check their accuracy from weeks to hours. PROCESS AUTOMATION Automation of a large number of manufac turing processes is a key feature of the B-2 programme, and Northrop claims that the projected manufacturing hours per kilo gramme of aircraft weight are similar to those of the Boeing 757 commercial airliner. Exam ples abound: high-speed cutting of compos ite materials by ultrasonic knife, with simulta- Flight vehicle completion status EHnssna 5 IIJ 6 7 Aircraft number FLIGHT INTERNATIONAL 4 - 10 July 1990
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