FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1990
1990 - 0035.PDF
bulk resins and dry, low-strength fibres at a cost below one-third that of prepreg material. The dry fibres are then sewn together in the desired orientation, with the majority of fibres lying in the direction in which strength is needed and the remainder "knitting" to gether the fibres to provide strength in other directions. "It's like a gigantic carpet maker," says Klotzshe. Panels and stiffeners are sewn seperately then stitched together, still dry, and placed in a self-heating tool into which the resin is injected. The completed part is therefore formed and cured in a single operation. Douglas uses modified industrial sewing machines to produce a basic nine-ply stack of 0°, 90° and ±45° dry fibres with about 95% of fibres in the strength direction and 5% hold ing the stack together. The stacks are then stitched together dry. This avoids the fibre damage encountered on early attempts to stitch together prepreg plies, says Klotzshe. There is still some fibre damage, but the reduction in ultimate load is small compared with the increase in damage tolerance dry stitching provides, he argues. Douglas has already produced sizeable panels for tests which have shown strength after damage to equal that of high-strength, toughened composites. "We have increased damage tolerance 100%, which allows us to take more weight out, so that composites become cost-competitive with metals," says Klotzshe. GREATER SAVINGS The weight saving possible with damage- tolerant composite primary structures has been increased from 20% to 30% using a process which requires less manual labour and less-expensive tooling and manufactur ing, he claims. A specification will be issued soon for a multi-needle machine specially designed to meet Douglas' manufacturing needs. As part of NASA's five-year Advanced Composite Transport programme, Douglas will scale up its resin transfer moulding process in an effort to demonstrate that acceptable composite parts can be made at a cost equal to or less than metal, says Klotzshe. The company will make generic MD-80-size wing-root and fuselage-barrel sections. Douglas aims, by the mid-1990s, to build a new regional airliner based on its existing MD-87, but with a new DC-9-30-size all-composite wing built using the process, he reveals. All-composite fuselage technology will be developed in parallel, but will take longer to reach fruition, says Klotzshe, which could be good news for metals suppliers who see their share of airframe materials being eroded despite the advent of lightweight aluminium- lithium alloy. Low-density aluminium-lithium is still re garded with suspicion by many of its poten tial users. Typical of attitudes is the recent comment by Boeing Commercial Airplanes' Automation of layup, cutting, kitting and drilling director of advanced technology—new aero plane development, Peter Sutcliffe: "That [Al- Li's] reduced density is almost entirely offset by its reduced properties and increased cost." McDonnell Douglas Helicopters' Logan ac knowledges that Al-Li is attractive, but says that the industry's ability to supply the material is "questionable". Douglas Aircraft's Klotzshe' notes that Al-Li can be substituted directly for conventional aluminium alloys, for an immediate 8%-10% weight saving without any additional manufacturing cost, but believes the material's high cost limits its appeal. Airbus is more enthusiastic, and plans to use some 2t of Al-Li in its A340 airliner from the first aircraft, the weight saving growing from some 200kg to 1,100kg if allpotential applications materialise (Al-Li content will then match the use of composites in the aircraft). Initially Al-Li will be used for secondary structures such as wing leading- edge D-nose skins, brackets, seals and pas senger seat rails. Further applications will be tested on Airbus' A330/A340 full-scale fatigue-test air frame and include some fuselage and lower- wing skin panels, stringers, doors and wing- tip fences. Airbus will also test Arallglass, a fatigue-resistant, damage-tolerant, multi layer laminate of aluminium alloy and glass- fibre-reinforced plastic. Potential uses in clude cabin roof skin panels and as a replacement for titanium crack-stoppers, lap joints and doublers. With typical aggression, Airbus is also looking at the application of high-strength metal-matrix composites, including fibre-re inforced casting of complex structures and ill reduce composites' cost premium the replacement of steel with fibre-reinforced aluminium for items such as engine pylon ribs and landing-gear components. Where the cost-benefit equation is biased in favour of high performance, metals fare better, and aluminium-lithium is expected largely to replace conventional alloys in the next generation of combat aircraft. Both EFA and the Dassault Rafale D will make substan tial use of Al-Li for components such as wing leading-edge flaps, where the superplastic forming of complex shapes plays a key role in reducing manufacturing costs. BIGGER ISSUES Only McDonnell Douglas Helicopters' Andy Logan argues that, overall, composites are cheaper than metals: "Total cost includes fabrication, parts holding and handling. It's a much larger issue than just material cost, and cost is lower for composites than metals." Logan also argues that the biggest impact of automation is independent of the material choice: "The all-digital design database allows you to get design information from drawing board to shop floor—'art to part'— quickly. We can feed large numerical-control machines directly, and kit parts rapidly." More costly or not, the desirability of lightweight composites is such that any re maining cost barriers will be breached sootier, rather than later. With aerospace accounting for two-thirds of the carbonfibre consumption in Europe and the USA, the impetus to meet the industry's continuing demands for higher performance and lower cost will drive developments that will see composites accounting for a greater and greater proportion of aircraft structures. Q EI ir.HT INTERNATIONAL 3-9 January 1990 53
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
