Structures
As far as structures are concerned, the manufacturers are going to try to get away from the traditional methods of working with metal. There was first the move from riveting to bonding, followed by the transfer from mechanical to chemical milling. The next move, which has already begun and which is going to increase, is towards composite materials. Their intensive use should produce a reduction in the empty weight of an aircraft of about 20 per cent. Each part made of composite material is 20 to 30 per cent lighter than the same part made in metal.
Several types of business aircraft already incorporate various parts made of Kevlar, glass, carbon or other fibre composite materials. This is especially true for the Canadair Challenger, and development managers of this Canadian company told INTERAVIA that while Kevlar would continue to be used for the manufacture of secondary structures, increasing attention was going to be paid in the future to the possibilities offered by carbon fibre materials, which can be used to produce components subjects to high stresses and which are still made of metal today. There will be a resultant simplification of the manufacturing process and, as a result, a reduction in cost. This is a point of view, which is currently developing a wing box to be tested on the Falcon 10 as part of a research program into the application of carbon fibres. This program is being carried out jointly with Aerospatiale. In spite of a number of difficulties, which have recently arisen in the program, the two French manufacturers have decided to persevere as they are convinced that they will make definite progress in the medium term.
Another project which should not be omitted is the Lear Pan, which is successfully continuing its test flights. Manufactured almost completely from composite materials based on carbon fibre Kevlar, this aircraft has a planned minimum service of 15.000 hours and typifies one of the objectives of the whole industry, which is waiting for the results of its certification program with some interest, and in particular, the solution of the problem of residual strength after damage.
Another problem which arises in the production of aircraft using parts made of carbon fibre is testing, not of the material itself but of the finished part. Unlike metal components, it is not sufficient to use statistical methods of checking. It is necessary, to carry out a quality check on every part. In addition, the manufacturers will have to develop methods of checking the whole production process, step-by-step1, before they can really launch large-scale composite production of primary structures.
Aerodynamics
Innovation in aerodynamics is likely to produce the greatest changes in the external appearance of future light and business aircraft. In the course of the past few years, winglets have gained considerable ground2, and this tendency will probably continue; likewise we may see the appearance of new canard foreplanes and other aerodynamic devices, as well as the development of new aerofoil sections or wing shapes. In this connection, one of the preoccupations3 of the design departments is to develop a transonic wing with drag at least 20 per cent lower than current wings, within the next five or six years. Several thicknesses and cambers are being examined and, from the first wind tunnel tests, it seems that the move is towards thicker sections than those used at present (relative thickness exceeding4 15 per cent at the root) as well as towards wings with high aspect ratios (more than 10) and increased sweep (35 per cent and more).
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Canards are the subject of some controversy with some designers maintaining that they represent an ideal aerodynamic solution while others remain more sceptical and feel that this still needs to be proved. NASA, which is currently carrying out tests and performance measurements with a modified Varieze aircraft, has already established that the foreplane appears to be a potentially useful device (improving safety by eliminating nearly all risk of stalling and going into a spin).
The only limitation is that, in the case of aircraft with a high maximum weight, to keep the centre of gravity in the correct position, the installation of a foreplane requires a reduction in the dimensions of the wings. As a result, the capacity of the wings to carry fuel is reduced appreciably5.
As for the so-called active techniques used in aerodynamics, such as control of the boundary layer or the various methods of over-wing blowing, some manufacturers believe in these very strongly, and it is certainly not likely that NASA is going to, contradict them, bearing in mind that the agency has launched a research project for a four-jet business aircraft with over-wing blowing.
4000
Notes:
1. step-by-step
2. to gain ground (.) ()
3. preoccupation
4. to exceed
5. appreciably considerably, greatly
UNIT 16
