Estado del arte de los sistemas de bombeo fotovoltaicos

Late in 1996, Airbus started its final materials selection for the A3XX, which was carried out in a very systematic way. A detailed risk assessment performed by Heidenwolf identified the risks associated with the application of Glare, by plotting a graph of the level of severity (the criticality) against the probability of occurrence. Elements that had to be taken into consideration were, amongst others: manufacturing costs, weight savings, design criteria, material properties and manufacturing processes. Associated risks that ended up in the top right-hand corner of the graph were unacceptable. All risks needed to be reduced to acceptable levels, in the green zone in the graph. An important factor in this selection process was that, as was shown in the first chapter, Glare fitted neatly into the history of metal bonding.

Airbus had already used metal bonding in the past on its first A300 aircraft, and although they had encountered severe problems in the beginning because of corrosion along the bond line, better pretreatment had fixed the problem. In 20 years of service, no problems were encountered.

The limited in-service experience of Arall and Glare was more of an issue:

the Fokker F-27 tank cover made of Arall was the longest experience (>12 years), slightly longer than an Arall reinforcement of the Fokker 100 emergency door cut-out (>12 years), followed by the C-17 aft cargo door (>9 years), Rob Fredell’s C-5A bonded Glare repairs (>5 years) and Soerjanto’s Fokker F-28 cargo bay repair (>5 years). The decision to apply Glare on the

A3XX was taken in steps. Acceptance of the material was therefore also achieved in steps, and at every milestone there were sceptics who wanted to kill the material. Glare survived the feasibility phase that ran up to 1995 (material properties and potential applications), and also the concept phase of the A3XX running from 1997 to 1999 and ending in a Critical Design Review held on the of November 1999. The review was successful for Glare, although serious problems had been encountered with Glare in Delft in March 1999: shear properties, residual strength, off-axis strength and blunt notch strength appeared to be relatively low. The application of Glare in the A380 appeared to lead to the type of problems that had not surfaced before in studies on Glare for smaller aircraft like the A330. There were times in Delft in which we lost our belief that the material would be successful. After the Critical Design Review, some risks were still too high in the graph and a risk mitigation phase was introduced to limit them. The design phase started including Glare in 2000, but it was never decided with absolute certainty that Glare would really be used. Nonetheless the outcome of deliberations was positive every time and thus the material stayed on the A3XX all the way to the end.

In the summer of 2000, Jens Hinrichsen had to skip his holidays to study the implications of the first design computer calculations for the design in Glare. Dr. Schneider decided to reduce the risks further by reducing the area where Glare would be applied from the whole top section to two sections in front of and aft of the wing of the A380. This is still a very large area because of the sheer size of the A380, comparable to the complete area of the fuselage of an A320, and will lead to a weight reduction of 500 kg. Even so, some people still have reservations about the material. In July 2000, severe doubts were expressed within EADS concerning one of the properties of Glare that was reduced under higher temperatures. It was in the middle of the holiday season and several people, including Gunnink, had to rush back to Delft. It took a special meeting with Dr. Schneider and the EADS specialists in Delft to address these worries. Finally, the contracts on Glare between EADS and Fokker Aerostructures were signed in May 2001.

This again created a lot of stress but this time especially for the Fokker employees, because the first Glare production panels must be delivered in September 2002. A new Glare production plant is currently under construction in Papendrecht.

Such construction activity indicated that the future for Glare remains positive. There is good cause to keep Glare on the A380, for the weight problems in the design have still not been completely solved at the time of writing. Even in 2001 there is a chance that more Glare will need to be applied. Perhaps further testing will lead to such a decision. Recently, material has been delivered for the full-scale fatigue test on a fuselage segment – the Megaliner barrel test – led in Hamburg by the former Delft PhD-student Tjerk de Vries.

Beginning

While most of the faculties in Delft are shrinking, the success of Glare, and of other projects, in combination with a clear philosophy led to a further growth of the Aerospace Faculty. In March 1999, the green light was given for a new building to be built for the staff and the institutes on material and production. In this building the Fibre Metal Laminates Centre of Competence (FMLC) will also be located. The FMLC is an independently operating foundation founded by Delft University, NLR and Fokker Aerostructures. It aims at further technological and business development for new applications and new variants of the fibre-metal laminates. The NIVR’s new head, Ben Droste, played a vital role in realising this new institute. Jürgen Thomas and Jens Hinrichsen were prominently present at its opening on the 16^th of May 2001, and both of them delivered speeches.

Hinrichsen stressed the importance of openness about this new technology to boost its further use. Companies that want to protect their knowledge will slow down new applications of the material, which will in the end be counterproductive. But Hinrichsen also had a sobering thought to offer his audience. He stressed that we have not yet passed the finish line with Glare, but are only halfway. The material has been applied, but the technology is still far from fully optimised and is not widely used. Even the advantages in terms of safety and reduced fuel burn still have to be proven in reality. This was just the first step in a new direction. It is, maybe, appropriate to quote Winston Churchill, who declared after the battle of El-Alamein: “This is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.”

roles and the intentions of the various actors, and I did not analyse in detail what type of knowledge was gathered in our lab or how exactly it was applied.

The type of knowledge that was obtained during the development can be loosely grouped into four categories: material data and behaviour, modelling, manufacturing aspects, and application and design oriented research (including work on the F-27, C-17, and A3XX). The first two types each had their own independent development by way of Master’s thesis projects and dissertations, while the third and fourth types were strongly linked. Application oriented research, for example, for the F-27 wing panel and the A3XX, appeared to be essential to guide the first three types of basic investigations. Basic material development is impossible without an application in mind. For the first type (material data and behaviour) fatigue, damage tolerance, and durability were key issues and the results were

always compared with competing materials: aluminium alloys and composites. For the modelling work, the PhD-studies were essential since a Master’s thesis does not usually allow enough time to cover a material property by fully modelling its behaviour (e.g. fatigue, buckling, impact, strength of joints). Two full-scale tests, i.e. the F-27 wing panel for Arall and the A330/340 fuselage section (‘barrel’) for Glare, were crucial to show that the results of the small-scale lab tests remained valid for realistic structures.

However, the relationship between lab tests and real life remains problematic. Durability, for example, remained a difficult issue throughout the development, since it is impossible to simulate realistic aircraft use in a lab.

In-service experience, no matter how limited it was, therefore played an important role in the argument for the application of Glare on the A3XX.

Another ongoing problem was the economic aspect of the material. Per kilogram, Arall and Glare were seven to ten times more expensive than aluminium. Whether this was balanced by the reduced fuel burn and cheaper manufacturing of products could only recently be fully resolved, because investigation into these matters required the support of an aircraft industry and an aircraft to apply the material on. The use of splices to increase the maximum size of the material and going directly to the layup in a curved mould were both necessary to reduce the manufacturing cost level to that of aluminium, as required.

In hindsight it is striking that at the beginning of the development of Arall, the actors chose to manufacture semi-finished products, i.e. sheet material, and not products, especially because product orientation is customary for the use of bonding processes in aircraft industry. This applies to metallic as well as to composite structures. Delft’s decision to involve material producers (AKZO, ALCOA and 3M) in the development, instead of the aircraft manufacturer Fokker, may have played a role in this choice. If so, the fact that this decision was taken shortly after Delft and Fokker had quarrelled was no coincidence. The step toward the manufacture of products in a curved mould, including splices and reinforcements, occurred relatively late in the development – in fact when it became apparent that the materia l cost of Glare sheets would remain prohibitively high for commercial application.

From the history of Arall and Glare, it became clear that the scientific process itself was not central to the success of the material, although the university in Delft was the pivotal point in the development. Instead of science, engineering inventiveness, overview and flexibility were vital.

The introduction of a new material affects many engineering disciplines: manufacturing, design, aeroelasticity, maintenance, damage tolerance, and so on. As Van Riessen¹ pointed out, the strength and weakness of modern technology is that products are split up and covered by many specialists by way of a separation of the different functions of the artefact. This makes it extremely difficult to introduce a new technology, because a large organisation like an aircraft manufacturer has to achieve interaction and the combined effort of many different specialists and departments. Delft ‘beat’ ALCOA’s Technical Center in the contest of Arall versus Glare and convinced specialists in Airbus, not by scientific rigour but by inventiveness, engineering overview and flexibility. The development of Glare was driven by engineering as the interrelation of different material properties combined in a design. The strength of Delft engineers like Roebroeks, Vogelesang and Gunnink was their generalist’s perspective on problems in contrast with the often narrow specialists’ views in companies like ALCOA and Airbus.

As Van Lente and Mulder stated, expectation plays a key role for scientific and technological development.² A strong belief in the eventual possibilities of fibre-metal laminates like Arall, and later Glare, was crucial for the people concerned to continue the battle over the years, and also to overcome obstacles. The outcome was not certain until the very end of our story. The success of this new technology depended not so much on its intrinsic technical opportunities, as on belief and on the power of persuasion of the researchers and engineers that were involved. It was not the technology itself that laid down the direction of the development, but the continuous interaction between the researchers in Delft and their environment, their ‘customers’.

Expectation plays such a significant role because, as Vincenti rightfully states, “growth of knowledge in engineering can be described in terms of the blind-variation and selective-retention model put forth by Donald Campbell.”³ Technological development takes place through variation s of

1 H. van Riessen, Filosofie en techniek. Kampen, 1949.

2 H. van Lente and K. Mulder, ‘The Dynamics of Expectations in Scientific and Technological Development’, Scientia Yugoslavica, Vol. 15, (issue 3-4). The contents are also given in a Dutch report: Philip Vergragt, Karel Mulder, Arie Rip en Harro van Lente, 1990, De matrijs van verwachtingen, ingevuld voor de polymeren Tenax en Twaron. Den Haag: NOTA werkdocument no. 12.

3 W.G. Vincenti, What Engineers Know and Why They Know It - Analytical Studies from Aeronautical History. The John Hopkins University Press, 1990, p.241.