Karen Walker/ATLANTA
A TYPICAL light aircraft's shape most likely to come to mind is almost cruciform - a squarish wing across a squarish fuselage. Now think of a modern yacht and its smooth, curvaceous, outline. While the former is usually made of riveted metal, the latter is formed from glassfibre-reinforced plastic. A revolution is taking place in general-aviation (GA) manufacturing, which could literally, change the shape of personal aircraft.
The use of composite materials in aircraft is not new. Manufacturers of military, commercial airliners and, increasingly, business aircraft make widespread use of composites, but factory-produced plastic aircraft are still a rarity in the GA world.
The benefits of using composites in aerospace manufacturing are known to most of the industry. Proponents cite how much easier it is to obtain smooth, more aerodynamic shapes with composites, and point to the robustness of the materials, their resistance to corrosion and their lightness.
Introducing composites to GA manufacturers has not been an easy task, however. The prime reason for this is best summed up in a familiar phrase: the GA industry is about cost, cost and cost. Even with the recent and welcome indications that the industry is about to enter a long-awaited revival, no-one would deny that cost will be the all-important factor in deciding whether the public will once again buy personal aircraft in their thousands.
Despite all their advantages, composites are still regarded as expensive materials to purchase, tool up for, and work with. That additional cost can be justified in a fighter or airliner, especially when weight savings and lower maintenance costs are considered. It is much more difficult to pass down the same extra charges to an individual buyer of a light aircraft - who might well decide that, a yacht is better value for money.
COMPOSITE INITIATIVE
Composite-airframe light aircraft are being made and sold, however. Diamond, based in London, Ontario, will have built 140 all-composite DA20 Katana two-seat trainers by the end of 1995. It plans to produce 200 units in 1996, with a second production line being started during the second quarter. The company recently gained an order from Spartan School of Aeronautics for 42 Katanas, to replace Cessna 150s. Spartan, based in Tulsa, Oklahoma, cites the new technology evident in the Katana as the main reason for its decision.
The second prototype of another composite construction aircraft, the Cirrus SR20, is scheduled to be flown this month. Cirrus Design, based in Duluth, Minnesota, expects to receive US Federal Aviation Administration certification in time for production to begin in 1997, and is firmly committed to manufacturing all-composite light aircraft.
Other companies are following more traditional routes and staying with aluminum. When Cessna confirmed in mid-1995 that it was back in the business of building single-engine piston-powered aircraft, no one expected plastic 172s, 182s and 206s to begin rolling off the production line. Cessna has sound reasons for staying with the familiar, and its new aircraft will essentially remain true to the all-metal design tradition of the 1960s, although they will incorporate numerous refinements and upgrades in the cockpit.
Some industry newcomers also are choosing the traditional route. Zenith, of Mexico, Missouri, gained FAA certification for its all-metal two-seat CH 2000 earlier this year and has orders from customers in Asia, Europe and North America. The company boasts that the CH 2000 takes "...yesterday's tried and proven general-aviation technology [and blends it with] today's modern design and manufacturing technology". Zenith believes that it is this formula which will make new GA aircraft readily available at the right price.
How to best use new methods of manufacturing technology is part of the work being conducted under the US Advanced General Aviation Transportation Experiment (AGATE) programme. The purpose of the AGATE, which combines the resources of NASA, the FAA and US industry, is to evolve technologies, which will point the way to a modern type of GA aircraft which appeals to a new mass market. Key factors in an AGATE aircraft include comfort, safety, ease of use and affordability. The AGATE programme, is divided into eight study areas, called work packages, and among those is integrated design and manufacturing. Companies such as Raytheon, Cirrus, Cessna, Lancair and Mooney are working with scientists and engineers at NASA Langley within this work package.
DEVELOPMENT AND VALIDATION
The focus of the package is to develop and validate manufacturing methods which will reduce airframe and propeller costs and weights. The ultimate goal is to reduce costs by between 25% and 40%. In terms of materials and manufacturing techniques, Huey Carden, a senior researcher at NASA Langley, says that the majority of research is focusing on composites because there are not enough funds to look at both traditional and new materials comprehensively, and it is the composites area which GA companies most need to study.
"We are trying to focus on those methods that would allow large pieces of structure to be made in one shot, or at least with a reduced parts count, while still giving quality. Getting the hands-on man-hours out of the process is very important when you are trying to keep costs down," says Carden. As part of the study, researchers are looking to the boat industry and its capacity to manufacture entire glassfibre-reinforced plastic hulls in one piece, using moulds. The boat-manufacturing industry, however, is not constrained by weight or airworthiness regulations: the challenge lies in how to adapt some of those techniques to the stringent requirements of small-aircraft manufacture.
The all-important issue of cost also largely rules out the use of complex composites, such as carbonfibre-reinforced plastic, despite their lighter weights and additional strengths. The AGATE programme focuses on simple composites, such as glassfibre-reinforced plastic, but is seeking new, more efficient, ways of using them. Manufacturing methods being studied and which have the potential for reducing cost and time in composite manufacture, include resin-transfer moulding, resin-film infusion and compression moulding.
According to Carden, the advantages of composites over metal cannot be ignored. "Composites have strength-to-weight ratios that are better than metals, and they are less susceptible to the fatigue problems that have traditionally been a factor with metals," he says. What the AGATE programme has to discover is how to adapt them to the requirements of small aircraft, how to make it easy for manufacturers to get composite aircraft certificated, and how to make composite manufacture less "hands-on" and, therefore, cheaper.
For companies such as Cirrus, despite some of these unknowns, there is no argument: composites are the way to go - with conditions. Dale Klapmeier, executive vice-president at Cirrus, says: "What we are trying to do with the SR20 is not to use anything that in the past would be considered high-technology composites, because high-technology means high cost. Our aim is performance for the dollar, so we have been looking at how to get the best value out of composites. There are some spectacular qualities in these high-end composite materials, but they are not practical for the general-aviation industry. We have taken a new approach to it - taking really simple composites and then using them as extensively as possible."
The SR20 does make some limited use of complex composites, such as carbonfibre composites in some of the control surfaces because it is stiffer and lighter, but the majority of the SR20 is glassfibre-reinforced epoxy resin. "We are spending a lot of time and energy on tooling - getting the cost of tooling down - and also getting the number of aircraft parts down to a small number. That reduces cost and time. In general, this means that we are not choosing composites because they are lighter - the composite aircraft should not weigh any more, but it will not be lighter than an aluminum aircraft. It means that we can make a composite aircraft cheaper than an aluminum aircraft," says Klapmeier.
Cirrus says that designing in composites from the outset gives them another advantage - flexibility. Future modifications and upgrades to an aircraft design will be more easily incorporated when the aircraft is composite based. "We can handle different shapes more efficiently," says Klapmeier. "Every part of our fuselage is a continuous curve - there are no flat parts at all. That means the aerodynamics are very good."
Klapmeier acknowledges that some may be reluctant to purchase a composite aircraft because they perceive that repair and maintenance will be more complicated, but he says, this is an ill-founded perception. "We have to educate the public, because repair of composite pieces is actually extremely easy. First of all, glassfibre is more robust than aluminium and can take more damage. Secondly, you can repair a single damaged area up to 3in [75mm] very easily, whereas, for example, if you smack the leading edge [of a wing] of an aluminum aircraft, you will have to replace the entire leading edge," he says.
Klapmeier concedes that a well-built and properly maintained aircraft will enjoy a long life, whether it is of aluminum or composite construction, but he believes that composites are the way of the future. "I think that there is a movement towards composites for good reasons. Therefore, I do believe that, in the not too far distance, people flying around in aluminum aircraft will be flying in antiques. The new composite GA aircraft will take-over the industry," Klapmeier predicts.
COMPOSITE BENEFITS
Diamond echoes many of the views of Cirrus. It is imperative to get the tooling for composites right at the outset, but the investment in metal-stamping machinery required to build traditional aircraft is huge by comparison, says Diamond executive vice-president, Karl Pfister. "The benefits [of composites] are many, but they include a perfect surface, which is good for the performance of the aircraft, good anti-corrosion properties, high reliability and high crash- worthiness," he says.
Diamond holds maintenance classes for its customers so that they are familiar with composite-structure care and repair. The company warns that getting into the business of mass-producing composite light aircraft is not easy. "We are beginning to see a lot of companies interested in the idea, but I would say that 3% of the work [required] is good ideas. The rest of work is in bringing the aircraft to the line. People see our production set-up here and are amazed," says Pfister, who points out that, while the Katana is a new aircraft, Diamond's Austrian parent company, HOAC, has a history dating to the 1950s and its expertise with composites comes from many years of familiarity with this type of manufacture.
Sticking to what you do best, might also be the motto of Cessna as it relaunches its 172/182/206 production lines. The company finds itself competing in the 1990s with types of aircraft very different to those available in the 1970s. Still, Cessna is confident that it knows its aircraft, knows how to make them, and knows the customers.
"We have produced half of the general aircraft in the world," points out Cessna's senior vice-president of operations, Charles Johnson. "Our goal in the single-engine aircraft industry is to have the safest, most reliable, state-of-the-art aircraft that provides the best value for the customer." Cessna plans to open a 44,600m2 (480,000ft2) factory at Independence, Kansas, in July 1996 to produce the new aircraft. A production rate of 2,000 units a year by 1998 is forecast.
Johnson says that, when Cessna decided to return to small-aircraft production, it looked at the full spectrum of possibilities. "We still decided that, for that class of aircraft, our original design was still the right one for 1997 when you consider value, cost and passenger comfort. We are adding substantial upgrades in the cockpit and making improvements in areas such as ventilation and avionics, but the basic design remains the same because it works," he says.
Johnson points out that Cessna is familiar with composites and uses the materials in some of its other, larger, aircraft, such as the Citation X Mach 0.92 business jet, so it was able to make a value judgement of metal over plastic. "Our 20 years of experience with composites has shown us that they are generally more expensive. They are the right material in the right place, but are not the best answer every time."
Johnson contends that new-production 172/182/206s will be "conservative, but not archaic" because they will benefit from modern manufacturing processes and from the technology transfer in experience gained from "big-brother" aircraft such as the Citation X. "If I had to look into a crystal ball, then I would say that, somewhere in the future, all material media will probably be used in future general-aviation aircraft, but I think that is still some time off," he says.
Cessna says that it has received positive feedback from potential 172/182/206 customers who want the safe, durable, aircraft they know, with the planned improvements, and with which they feel comfortable about maintaining and repairing. "There is a very large demand for that type of aircraft. I don't think you can underestimate that because it's based on what we feel is still the best design in the marketplace today. We have no doubts about it - they are the best three aircraft when you add up speed, reliability, cost and safety."
It is evident at air shows such as Oshkosh that there are already two distinct types of GA aircraft - metal and plastic - and most in the industry would agree that there will be a crossover point, after which the balance will shift to more plastic than metal. Further confirmation is provided by the AGATE programme, which, because of its detailed look at composite manufacturing, will define the shape of future GA aircraft, especially in the USA. It seems probable that composites will ultimately be the way ahead for GA and that personal aircraft will look more and more like speedboats - the only question is how soon.
Source: Flight International
