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Aerospace composites — the story so far
Aerospace composites - the story so far The aerospace industry has used composites ever since they were developed. But the materials kiled to achieve the heights forecast for them in the early 1980s. George Marsh looks at the historical use of composites in aircraft and points the way ahead. The history of man-made composites in aircraft goes back at least 50 years, though most has happened within the 40-years during which Reinforced Plastics has been published. The frost signiticant application of a reinforced plastic in aircraft structure was, according to the Society for the Advancement of Materials and Process Engineering (SAMPE), an aft fuselage skin of glassfibre sandwich on a Vultee BT-15 trainer in the USA in 1945. This, as we shall see, could be debatable. In a sense, composites are as old as the history of flight itself. The ‘wood, string and dope’ era saw the process of building aircraft from spruce as the framework, covered with fabric whose fibres were tensioned and stabilized in a matrix of fast-drying paint (dope), developed to a
Reinforced Plastics September
1996
high pitch of perfection. Later, Howard Hughes’ Spruce Goose and, in UK, the all-wooden World War 2 Mosquito designed by DeHavilland in a sandwich of birch ply over end-grain balsa, marked the pinnacle of wooden aircraft construction.
FIGURE 1: While Boeing and the other major airframers were prudently qualifying structuresfor control surfaces. Beech was flying its all carbon composite Starship business turboprop.
q A A
After the War came a period during which, while constructors turned, amid trials and tribulations (witness the DH Comet disasters), to producing aeroplanes in metal, some suppliers were flirting with early man-made composites. Generally the approach was low-tech. Short-strand glassfibre material was laid-up manually. Similar technology was to become popular for aircraft components requiring compound curves and good surface finish, such as trim panels and aerodynamic fairings. Earlier, manufacturers had in-
0034~3617/96/$15.00 Copyright01996, Published by Elsevier Science Ltd. All rights reserved.
Aerospace
traduced other composite materials that were basically resin:stiffened fabric. Micarta was used by Dowty for its propellers before 1920 and in the US Hartzell used a mixture of fabric and phenolic resin, called Hartzite, for propellers it made during the 1940s. Both these manufacturers later became leaders in the use of fibre reinforced plastics for today’s advanced propellers.
composites
-
the story so far
composites year.
every
The frost commercially successful composite light aircraft was probably the WA52, built in France by Wassmer Aviation, a constructor having experience of composite sailplanes. This was a two-seater with a 150 hp engine and a new low-drag wing.
The major bigleague planemakers were more cautious. This is FIGURE2: Many sub contractors sought to build a specialism in composite aerospace probably because, components. Westland Aerospace produces carbon flap vanes for the MD 11 hijet. in an industry where safety must Also before come first, qualification can be a Historically, manufacturers of World War 2, Aero Reseach Ltd long and arduous process; it may small sport and lesiure aircraft have (ARL) at Duxford, Cambridge, UK, take lo-20 years for any major new led the way in applying the new had produced a composite commaterial to become accepted into materials. The first glass reinforced prising flax linen roving held in a aerospace. When world leader Boeplastic (GRP) sailplane, the German synthetic urea formaldehyde (pheing began to use glassfibre compoFS-24 Phoenix, was proposed in nolic) resin. Wartime construction site on its commercial aircraft 1951 and finally flew in 1957. Balsa of a Spitfrre fuselage in this materiin the mid-1960s it first concenwood stiffened with outer layers of al, Gordon Aerolite, ahead of a trated on secondary structure, paper and glue had been the frost threatened aluminium shortage, items such as wing-body fairings, suggestion for reducing weight, but was probably the first composite and later flight control surfaces research showed that fibres of glass primary aerostructure. Ironically (flaps, ailerons, etc.) Incursions into in polyester resin would be better. ARL had wanted to use glass primary wing and fuselage strucSince that venture, German manustrands, but no glass manufacturer tures came much later and across facturers have supplied over would supply them for fear of being the industry these are still the 12 000 gliders and motor gliders associated with a failure! exception rather than the rule. to customers around the globe. In the USA 3M, well known for A dentist built the first compoA particular niche where comits tape products, had begun to site light aircraft in the United posite materials have made a conreinforce tape with Bbres in the States, in the late 1950s but the tribution right from the early 1960s 1940s. Later, aircraft constructors American Eagle remained a one-off. has been floors. Composite flooring tried to strengthen the adhesive (The dentist, Bert Rutan, was later materials, such as Fibrelam, a sandbonds between alloy panels on to produce the glassfibre Voyager wich of fibre reinforced plastic metal aircraft by adding glass fibres two-seater, which in 1987 caught (FRP) skins over honeycomb core, to the bonding resin. These early the public’s imagination by flying proved able to withstand abuse innovations showed that designers round the world non-stop without from passengers’ stiletto heels to appreciated the reinforcing potenrefuelling.) Rutan’s canard designs aggressive chemicals in galley and tial of continuous fibres disposed in remain a favourite with the strong toilet areas and have proved an appropriate direction. Such American home-build movement, more durable than aluminium moves pointed the way to the which nowadays completes many floors in service. emergence of true aerospace compersonal aircraft in glass and other posites in the 1950s. Improvements in materials
Reinforced Plastics September 1996
Aerospace
composites
-
the story so far
suppliers focused strongly on aerospace, calculating that added value, rather than sheer material volume, would yield useful margins. Companies moved more closely alongside aircraft prime and subcontractors, keen to help new applications over their development and qualification hurdles and into service.
FIGURE3: Some of the most intensive use of advanced composite materials has been seen in combat aircraft. The British Aerospace/McDonnell Douglas advanced Harrier has a carbon fibre composite main wing torque box and large CFRPslottedflaps and ailerons.
made composites more attractive for aerospace and accelerated their use. Epoxies superseded polyester resins. The use of pre-pregs, rovings of continuous isotropic fibres pre-impregnated with resin as a manageable cloth, facilitated the lay-up process and enabled constructors more readily to concentrate strength and stiffness where they were required. In the UK, the Royal Aircraft Establishment (RAE) at Farntook an early lead in borough developing carbon fibre reinforced composite (CFRP) during the late 1950s. This was to become an industry standard. The katerials Laboratory at the Wright Patterson Air Force Base, Ohio, USA, for instance, introduced carbon composites into fins for F-14, F-15 and F-l 6 fighters in 1974 - two years after introducing boron-epoxy composites into similar components. Only these materials clearly surpassed aluminium in the combination of strength, stiffness and other properties required for high-performance combat aircraft.
Reinforced Plastics September 1996
Carbon composite is now used extensively in the world’s current generation of combat aircraft. The use of advanced engineered FRP composites for aerostructures in the early 1970s marked the start of an increasingly hectic period which was to peak in the early 1990s. It was as though the genie had been let out of the bottle. New or improved materials, processes and applications were announced seemingly every week. Materials
As the main thrust, in the drive to tolerance of higher service temperatures epoxy resins were joined by phenolics, bismaleimides (by 1989) metallic composites, ceramics and ultimately carbon (as a matrix). Other resins, such as urethanes and cynate resins, were promoted too. Glass fibres were joined by boron, graphite and carbon from the early 196Os, aramid (DuPont’s Kevlar remains the best known) from the late 1970s ceramics such as silicon carbide, and metallics. New laminates, such as ARALL and GLARE pioneered in the Netherlands, combined the advantages of both composite and metal plies. Composites, it seemed, had brought ‘designer materials’ to aerospace. Again the smaller airframe manufacturers proved to be the bolder trail blazers. While Boeing and others were trialling composite control surfaces, US-based Avtek Corp was designing its all-compo-
FIGURE4: When the European ATR consortium rolled out its AZ? 42, it was one of the earliest regional/commuter aircraft to have significant composite content.
Aerospace
composites
-
composite. In the late 1980s Airbus researched a carbon libre fuselage and wing, intended to save 35% in weight over metal.
site Avtek 400 business turboprop canard, which frost flew in September 1984. This aircraft broke new ground in being designed to use Kevlar and Nomex core as the basic airframe materials. Some 18 months later, Beech flew its all-composite Starship business aircraft. Beech engineers reckoned that, despite the extra cost of the Starship’s graphite-epoxy/ aramid fibre honeycomb sandwich material, the reduced parts count would compensate during manufacture. The 8-10 place fuselage weighed just 4 18 kg and the wing was 35% lighter than that of a comparable metal structure.
the story so far
FIGURE5: Even the largest autoclaves are insufficient to cook the whole wing or fuselage of a major passenger jet.
Glassfibre still had its adherents. Claudius Dornier stayed with this traditional boatbuilding medium for his Seastar amphibian, which frost flew in 1987. The low pressure cure technique used in its construction contrasted strongly with the high-pressure autoclave process Beech used for its Starship. But it was the technology applied by Beech which was becoming the industry norm.
entering service in 1982, and the advanced 737 in 1986 all had advanced composite rudders, ailerons and elevators. The 767 rudder, for instance, had a 10.7 m long graphite spar, a Nomex core and carbon skin. Composite control surfaces, fairings and nacelles saved almost 680 kg in the 767 design. McDonnell Douglas, too, had significant content on its DC10 successor, the MD1 1.
The oil crisis of the early 1970s powerfully concentrated minds on reducing weight and saving energy. NASA in the US set out to examine the advantages of carbon and aramid in more heavily loaded structures. The Aircraft Energy Efficiency (ACEE) programme saw Boeing build various carbon composite spoilers, elevators and horizontal stabilisers for Boeing 727 and 737 aircraft during the early 1980s. The Boeing 757 and 767,
Europe was not lagging. Air-bus Industrie used glass FRP in the radome and various panels and fairings on its A300 in the mid1970s. Increasing contributions from both carbon fibre and aramid items have saved weight in successive Airbus products, culminating in its latest A330 and A340 widebodies which have significant composite content, including some primary structure. All Airbus fins, for example, are now of advanced
British Aerospace has been involved with carbon composite since the 1960s when RAE first developed the material. Demonstration programmes included a Jaguar wing and engine bay door, and the Tornado’s aileron. BAe subsequently designed the CFRP wing for Sweden’s Saab Gripen fighter and now contributes advanced composite structures for the latest European combat aircraft, Eurofighter 2000.
The latest generation of smaller, regional aircraft also benefit from the new materials. The Saab 2000, Dornier 328 and ATR Series all have significant composite content in nacelles, control surfaces, propellers and interiors. Europe’s ATR produced the only carbon fibre wing on a commercial aircraft for its ATR 72, and Dornier fitted the first all-composite pressure bulkhead to its 328. In helicopters composites have lightened airframes and the development of new-generation rotors having aerodynamic profiles impossible to produce in metal have improved rotor performance by about a third. The end of the 1980s was a boom time and pundits spoke of a third age of aerospace materials in which composites would take over from metals. As it turned out, this spirit of heady optimism was misplaced. At the begining of the 1990s the industry was hit by the double
Reinforced Plastics September 1996
Aerospace
composites
-
the story so far
blow of the most suitably fibre reinsevere airline reforced, can be cession ever thermoformed, removing the need known, and an unfor cumbersome expected outautoclaving techbreak of peace nology. Thermostarting at the plastic compoBerlin Wall. The nents flying on ensuing mayhem aircraft since the saw many players early 1970s have depart, shaking shown promise, their heads, for but much more greener pastures needs to be or the bankruptcy known about this court; others ralittle qualified tionalizing, downtechnology before sizing and conaerostructures can centrating on FIGURE6: Airframers would like to sidestep cumbersome autoclave technology if they be moulded like their core busicould. Westland Helicopters tried this polyetber-ether ketone (PEEK) thermoplastic polythene housenesses. For the air- composite on its West&d 30 helicopter during the 1980s. hold goods. framers and their Manufacturing major suppliers it The high strength-to-weight costs must be reduced. The modest was a case of heads down, with benefit of composites and the production runs of aerospace heavy cost cutting, to survive. manufacturability of ideal aerody(compared with automotive and namic profiles are undisputable, A more critical and realistic other sectors) stubbornly resist but Boeing’s ‘slow ahead, causpirit emerged. As user experience the economic application of autotiously’ policy has evidently been grew, field reports were suggesting mation to present labour-intensive the right one. Composites now that composites were not the holy hand lay-up of pre-pregs, but some have to win their way onto an grail. Strength after impact of CFRP progress is being made and, where aircraft with economic benefits was suspect; microcracking caused components such as shafts and which are clear, demonstrable and by repeated thermal cycling in the rotor blades can be wound, filabeyond doubt. harsh aerospace environment alment winding is a readily autolowed subsequent ingress of moistThe aerospace industry needs, mated process. Improved high ure to degrade the strength of stiff above all, a number of well qualified quality resins which cure at room composites like carbon; while aramaterial standards backed by a temperature will facilitate some mid and glass were notably weabody of user experience. Glass fibre aerospace fabrication and may kened by moisture uptake. Repairs is here to stay, aramid has its place make field repairs easier. Now that in the field could be a problem, and carbon composite has become ways have been found of increasing expensive removal of a damaged a standard, especially for fins, horfibre volume fraction, low-pressure component to take it to an oven for izontal stabilizers, control surfaces, technologies like resin transfer curing proving unpopular with parts of nacelles and portions of moulding are likely to be more wings. Progress into the largest maintenance chiefs. widely adopted for components of primary structures may be slow modest size. Over the last year or so, airlines until the need for high-temperahave started to make money again Those wilder early projections ture, high-pressure technology is and, in defence the realization that of an industry sector seduced by its overcome; even the largest of threats still exist, albeit in a more own hype in the 1980s may never today’s massive and energy-intendiverse and unpredicatable form, materialize. That third age of aerosive autoclaves is rarely big enough has tempered the enthusiasm with space materials may not be a taketo cook a whole fuselage or wing which budgets were once being over situation, but one in which for a major passenger airliner. cut. (Moreover, concepts such as composites, over time, take their place as part of the mix of enan-mobility, in theory, place a preThermoplastics, such as polyetherimide (PEI) and polyethergineered materials which will make mium on composite weight saving). ether ketone (PEEK), hold out up the advanced airliner or combat But the pace will inevitably be hope of such as revolution. These, aircraft of the future. more sober. n
Reinforced Plastics September 1996
Reinforced Plastics September
1996
high pitch of perfection. Later, Howard Hughes’ Spruce Goose and, in UK, the all-wooden World War 2 Mosquito designed by DeHavilland in a sandwich of birch ply over end-grain balsa, marked the pinnacle of wooden aircraft construction.
FIGURE 1: While Boeing and the other major airframers were prudently qualifying structuresfor control surfaces. Beech was flying its all carbon composite Starship business turboprop.
q A A
After the War came a period during which, while constructors turned, amid trials and tribulations (witness the DH Comet disasters), to producing aeroplanes in metal, some suppliers were flirting with early man-made composites. Generally the approach was low-tech. Short-strand glassfibre material was laid-up manually. Similar technology was to become popular for aircraft components requiring compound curves and good surface finish, such as trim panels and aerodynamic fairings. Earlier, manufacturers had in-
0034~3617/96/$15.00 Copyright01996, Published by Elsevier Science Ltd. All rights reserved.
Aerospace
traduced other composite materials that were basically resin:stiffened fabric. Micarta was used by Dowty for its propellers before 1920 and in the US Hartzell used a mixture of fabric and phenolic resin, called Hartzite, for propellers it made during the 1940s. Both these manufacturers later became leaders in the use of fibre reinforced plastics for today’s advanced propellers.
composites
-
the story so far
composites year.
every
The frost commercially successful composite light aircraft was probably the WA52, built in France by Wassmer Aviation, a constructor having experience of composite sailplanes. This was a two-seater with a 150 hp engine and a new low-drag wing.
The major bigleague planemakers were more cautious. This is FIGURE2: Many sub contractors sought to build a specialism in composite aerospace probably because, components. Westland Aerospace produces carbon flap vanes for the MD 11 hijet. in an industry where safety must Also before come first, qualification can be a Historically, manufacturers of World War 2, Aero Reseach Ltd long and arduous process; it may small sport and lesiure aircraft have (ARL) at Duxford, Cambridge, UK, take lo-20 years for any major new led the way in applying the new had produced a composite commaterial to become accepted into materials. The first glass reinforced prising flax linen roving held in a aerospace. When world leader Boeplastic (GRP) sailplane, the German synthetic urea formaldehyde (pheing began to use glassfibre compoFS-24 Phoenix, was proposed in nolic) resin. Wartime construction site on its commercial aircraft 1951 and finally flew in 1957. Balsa of a Spitfrre fuselage in this materiin the mid-1960s it first concenwood stiffened with outer layers of al, Gordon Aerolite, ahead of a trated on secondary structure, paper and glue had been the frost threatened aluminium shortage, items such as wing-body fairings, suggestion for reducing weight, but was probably the first composite and later flight control surfaces research showed that fibres of glass primary aerostructure. Ironically (flaps, ailerons, etc.) Incursions into in polyester resin would be better. ARL had wanted to use glass primary wing and fuselage strucSince that venture, German manustrands, but no glass manufacturer tures came much later and across facturers have supplied over would supply them for fear of being the industry these are still the 12 000 gliders and motor gliders associated with a failure! exception rather than the rule. to customers around the globe. In the USA 3M, well known for A dentist built the first compoA particular niche where comits tape products, had begun to site light aircraft in the United posite materials have made a conreinforce tape with Bbres in the States, in the late 1950s but the tribution right from the early 1960s 1940s. Later, aircraft constructors American Eagle remained a one-off. has been floors. Composite flooring tried to strengthen the adhesive (The dentist, Bert Rutan, was later materials, such as Fibrelam, a sandbonds between alloy panels on to produce the glassfibre Voyager wich of fibre reinforced plastic metal aircraft by adding glass fibres two-seater, which in 1987 caught (FRP) skins over honeycomb core, to the bonding resin. These early the public’s imagination by flying proved able to withstand abuse innovations showed that designers round the world non-stop without from passengers’ stiletto heels to appreciated the reinforcing potenrefuelling.) Rutan’s canard designs aggressive chemicals in galley and tial of continuous fibres disposed in remain a favourite with the strong toilet areas and have proved an appropriate direction. Such American home-build movement, more durable than aluminium moves pointed the way to the which nowadays completes many floors in service. emergence of true aerospace compersonal aircraft in glass and other posites in the 1950s. Improvements in materials
Reinforced Plastics September 1996
Aerospace
composites
-
the story so far
suppliers focused strongly on aerospace, calculating that added value, rather than sheer material volume, would yield useful margins. Companies moved more closely alongside aircraft prime and subcontractors, keen to help new applications over their development and qualification hurdles and into service.
FIGURE3: Some of the most intensive use of advanced composite materials has been seen in combat aircraft. The British Aerospace/McDonnell Douglas advanced Harrier has a carbon fibre composite main wing torque box and large CFRPslottedflaps and ailerons.
made composites more attractive for aerospace and accelerated their use. Epoxies superseded polyester resins. The use of pre-pregs, rovings of continuous isotropic fibres pre-impregnated with resin as a manageable cloth, facilitated the lay-up process and enabled constructors more readily to concentrate strength and stiffness where they were required. In the UK, the Royal Aircraft Establishment (RAE) at Farntook an early lead in borough developing carbon fibre reinforced composite (CFRP) during the late 1950s. This was to become an industry standard. The katerials Laboratory at the Wright Patterson Air Force Base, Ohio, USA, for instance, introduced carbon composites into fins for F-14, F-15 and F-l 6 fighters in 1974 - two years after introducing boron-epoxy composites into similar components. Only these materials clearly surpassed aluminium in the combination of strength, stiffness and other properties required for high-performance combat aircraft.
Reinforced Plastics September 1996
Carbon composite is now used extensively in the world’s current generation of combat aircraft. The use of advanced engineered FRP composites for aerostructures in the early 1970s marked the start of an increasingly hectic period which was to peak in the early 1990s. It was as though the genie had been let out of the bottle. New or improved materials, processes and applications were announced seemingly every week. Materials
As the main thrust, in the drive to tolerance of higher service temperatures epoxy resins were joined by phenolics, bismaleimides (by 1989) metallic composites, ceramics and ultimately carbon (as a matrix). Other resins, such as urethanes and cynate resins, were promoted too. Glass fibres were joined by boron, graphite and carbon from the early 196Os, aramid (DuPont’s Kevlar remains the best known) from the late 1970s ceramics such as silicon carbide, and metallics. New laminates, such as ARALL and GLARE pioneered in the Netherlands, combined the advantages of both composite and metal plies. Composites, it seemed, had brought ‘designer materials’ to aerospace. Again the smaller airframe manufacturers proved to be the bolder trail blazers. While Boeing and others were trialling composite control surfaces, US-based Avtek Corp was designing its all-compo-
FIGURE4: When the European ATR consortium rolled out its AZ? 42, it was one of the earliest regional/commuter aircraft to have significant composite content.
Aerospace
composites
-
composite. In the late 1980s Airbus researched a carbon libre fuselage and wing, intended to save 35% in weight over metal.
site Avtek 400 business turboprop canard, which frost flew in September 1984. This aircraft broke new ground in being designed to use Kevlar and Nomex core as the basic airframe materials. Some 18 months later, Beech flew its all-composite Starship business aircraft. Beech engineers reckoned that, despite the extra cost of the Starship’s graphite-epoxy/ aramid fibre honeycomb sandwich material, the reduced parts count would compensate during manufacture. The 8-10 place fuselage weighed just 4 18 kg and the wing was 35% lighter than that of a comparable metal structure.
the story so far
FIGURE5: Even the largest autoclaves are insufficient to cook the whole wing or fuselage of a major passenger jet.
Glassfibre still had its adherents. Claudius Dornier stayed with this traditional boatbuilding medium for his Seastar amphibian, which frost flew in 1987. The low pressure cure technique used in its construction contrasted strongly with the high-pressure autoclave process Beech used for its Starship. But it was the technology applied by Beech which was becoming the industry norm.
entering service in 1982, and the advanced 737 in 1986 all had advanced composite rudders, ailerons and elevators. The 767 rudder, for instance, had a 10.7 m long graphite spar, a Nomex core and carbon skin. Composite control surfaces, fairings and nacelles saved almost 680 kg in the 767 design. McDonnell Douglas, too, had significant content on its DC10 successor, the MD1 1.
The oil crisis of the early 1970s powerfully concentrated minds on reducing weight and saving energy. NASA in the US set out to examine the advantages of carbon and aramid in more heavily loaded structures. The Aircraft Energy Efficiency (ACEE) programme saw Boeing build various carbon composite spoilers, elevators and horizontal stabilisers for Boeing 727 and 737 aircraft during the early 1980s. The Boeing 757 and 767,
Europe was not lagging. Air-bus Industrie used glass FRP in the radome and various panels and fairings on its A300 in the mid1970s. Increasing contributions from both carbon fibre and aramid items have saved weight in successive Airbus products, culminating in its latest A330 and A340 widebodies which have significant composite content, including some primary structure. All Airbus fins, for example, are now of advanced
British Aerospace has been involved with carbon composite since the 1960s when RAE first developed the material. Demonstration programmes included a Jaguar wing and engine bay door, and the Tornado’s aileron. BAe subsequently designed the CFRP wing for Sweden’s Saab Gripen fighter and now contributes advanced composite structures for the latest European combat aircraft, Eurofighter 2000.
The latest generation of smaller, regional aircraft also benefit from the new materials. The Saab 2000, Dornier 328 and ATR Series all have significant composite content in nacelles, control surfaces, propellers and interiors. Europe’s ATR produced the only carbon fibre wing on a commercial aircraft for its ATR 72, and Dornier fitted the first all-composite pressure bulkhead to its 328. In helicopters composites have lightened airframes and the development of new-generation rotors having aerodynamic profiles impossible to produce in metal have improved rotor performance by about a third. The end of the 1980s was a boom time and pundits spoke of a third age of aerospace materials in which composites would take over from metals. As it turned out, this spirit of heady optimism was misplaced. At the begining of the 1990s the industry was hit by the double
Reinforced Plastics September 1996
Aerospace
composites
-
the story so far
blow of the most suitably fibre reinsevere airline reforced, can be cession ever thermoformed, removing the need known, and an unfor cumbersome expected outautoclaving techbreak of peace nology. Thermostarting at the plastic compoBerlin Wall. The nents flying on ensuing mayhem aircraft since the saw many players early 1970s have depart, shaking shown promise, their heads, for but much more greener pastures needs to be or the bankruptcy known about this court; others ralittle qualified tionalizing, downtechnology before sizing and conaerostructures can centrating on FIGURE6: Airframers would like to sidestep cumbersome autoclave technology if they be moulded like their core busicould. Westland Helicopters tried this polyetber-ether ketone (PEEK) thermoplastic polythene housenesses. For the air- composite on its West&d 30 helicopter during the 1980s. hold goods. framers and their Manufacturing major suppliers it The high strength-to-weight costs must be reduced. The modest was a case of heads down, with benefit of composites and the production runs of aerospace heavy cost cutting, to survive. manufacturability of ideal aerody(compared with automotive and namic profiles are undisputable, A more critical and realistic other sectors) stubbornly resist but Boeing’s ‘slow ahead, causpirit emerged. As user experience the economic application of autotiously’ policy has evidently been grew, field reports were suggesting mation to present labour-intensive the right one. Composites now that composites were not the holy hand lay-up of pre-pregs, but some have to win their way onto an grail. Strength after impact of CFRP progress is being made and, where aircraft with economic benefits was suspect; microcracking caused components such as shafts and which are clear, demonstrable and by repeated thermal cycling in the rotor blades can be wound, filabeyond doubt. harsh aerospace environment alment winding is a readily autolowed subsequent ingress of moistThe aerospace industry needs, mated process. Improved high ure to degrade the strength of stiff above all, a number of well qualified quality resins which cure at room composites like carbon; while aramaterial standards backed by a temperature will facilitate some mid and glass were notably weabody of user experience. Glass fibre aerospace fabrication and may kened by moisture uptake. Repairs is here to stay, aramid has its place make field repairs easier. Now that in the field could be a problem, and carbon composite has become ways have been found of increasing expensive removal of a damaged a standard, especially for fins, horfibre volume fraction, low-pressure component to take it to an oven for izontal stabilizers, control surfaces, technologies like resin transfer curing proving unpopular with parts of nacelles and portions of moulding are likely to be more wings. Progress into the largest maintenance chiefs. widely adopted for components of primary structures may be slow modest size. Over the last year or so, airlines until the need for high-temperahave started to make money again Those wilder early projections ture, high-pressure technology is and, in defence the realization that of an industry sector seduced by its overcome; even the largest of threats still exist, albeit in a more own hype in the 1980s may never today’s massive and energy-intendiverse and unpredicatable form, materialize. That third age of aerosive autoclaves is rarely big enough has tempered the enthusiasm with space materials may not be a taketo cook a whole fuselage or wing which budgets were once being over situation, but one in which for a major passenger airliner. cut. (Moreover, concepts such as composites, over time, take their place as part of the mix of enan-mobility, in theory, place a preThermoplastics, such as polyetherimide (PEI) and polyethergineered materials which will make mium on composite weight saving). ether ketone (PEEK), hold out up the advanced airliner or combat But the pace will inevitably be hope of such as revolution. These, aircraft of the future. more sober. n
Reinforced Plastics September 1996