Airplane structures are designed with extreme attention in weight. The first aircraft had two wings of light wooden frames with fabric cloths, which are held by wires and beams. In the 1920s, metal began to be used for the structure of aircraft.
The metal wing is a box structure with skins consisting of:
· the top and bottom,
· Spars (front and back formed by I-beam)
· Ribs (internal structural parts running fore and aft in the wing)
· Stringers (in-out stiffeners)
The box structure can experience both tension and compression during turbulence air flow. Metal wings dramatically reduced the aerodynamic resistance that the aircraft managed to fly twice as fast with the same engine.
Then Air craft structures are made with carbon fibre epoxy composites. Carbon Fire epoxy are strong stiff and light weight material. They are formed by combining a supporting fiber and with resin matrix system such as epoxy. These combined composites are being a replacement for heavy metal wing. The major advantage is they can be assembled into larger not riveting structures. Strong molecular bonds of carbon-carbon chain give the fibers high strength to withstand forces. Polymer fibers such as polyacrylonitrile produce carbon fibers. Then carbon fibers are heated upto 1000 ° C with high tension is causing the formation to 2-dimensional carbon-carbon crystals when hydrogen is extracted.
Cost is the main barrier to the use of carbon composite fibers in aircraft. The autoclave method is more expensive due to the cost of capital equipment and the energy required for heating and pressure at 60 psi. Autoclave treatments cost £ 70.00 each and the curing of the oven used for CL2 was priced at £ 10.00 to reflect these differences in conditions.
Another element of cost is molds. These are usually made from Invar or other material with a very low thermal expansion coefficient in order that the curing process does not introduce size or shape differences.
The third major cost component is layup, which refers to the formation of uncured composite materials on the mold.
The fourth cost is reprocessing and repair. The composite components are made in layers and a significant failure in the separation or internal separation of the layers due to gas bubbles or insufficient connection. The parts and subassemblies at this stage are extremely rigid. If they do not fit properly, it is not possible to use the connectors to pull them together.
In the co-curing method, the uncured parts are placed on the surface on a carefully constructed mold, compressed together with a vacuum bag and placed in a large pressure vessel called autoclave. Then they are subjected to high pressure and high temperature while epoxy cures. In the welding process, the performed and pre-hardened parts are glued together with epoxide and the glued joints are cured with the use of the vacuum bag and the autoclave method.
Air craft wing structures are made to accurate shape and size. Then they will be tacked together to get the final product we want to achieve. There is greater saving in this process if the products are accurate. the holes of the aircraft must be substantially just opposite each other or else the fastener cannot fill the hole. Thousands of parts are made, and they are assembled by placing them in the correct place and fit drill holes with seals. Finally, fasteners are installed. If the holes are not accurate then the problem is harder to find and fix. This has been the biggest problem for many company. Answer for this problem is on its way. If this problem is solved the production cost will be low and making the components will be easy. This would lead us into Type 1 aircraft assembly.
Recent years the world has seen the advancement of design innovation at Aircraft wings. The transformation of airwings started since the Wright brother’s first plane. The use of composites has brought improvements in aerodynamic performances, weight reduction and efficiency on fuel saving. Composites brought 4%-5% fuel burn improvement and 4790 tonnes of CO2 per plane per year. In recent years there is increased investment in composites research and development. Over the past four years Broughton has invested over 400 million in production of air wings,
The investments do not provide an attractive rate of return for estimated investments.
Aeroplanes consists of a 40% weight distribution for the wing and 45% for fuselage. The manufacturing cost for these two large structures is about same range. Skin, Frames, Stringers are the main section that are manufactured using composites. The advance composite parts wave the path to reach the economical goal. And, to reduce the cost of manufacturing process as compared to aluminium fuselage. Before the designing process starts some mechanical elements must be taken to consideration:
· Forces produced by wings, empennage and landing gear.
· Inertia forces of components, loads and equipment
· Mass of Fuselage
· Air forces that run over the surface of the fuselage
· Pressure difference
The biggest that can we come across is the force which can create bending stress around fuselage structure.
Primary Structure- Passenger Area: This structure contains of two side shell and floor structure with circular skin which is twice the radius compared to the shell.
Secondary Structure- Cargo Department: The cargo compartment area is built with cargo platform
Obtaining cost-efficiency developed the concept of manufacturing shell. Greater fire resistance is critical in choosing the material. And, special attention is given for cost.
Manufacturing Process: – THE SINGLE LINE INJECTION (SLI)
This method is used in manufacturing primary structures. Specially shaped stainless-steel plates were used for the stiff parts that represent the aerodynamic surface. The detector layer consisted of a single layer of CFRP fabric and was placed directly on attached tooling. This manufacturing process will give best surface finish. synthetic fibers such as Aramid or Zylon is an option in order to attain higher resistance. The foam was used as a production aid. This allow a very easy setting of the shells. Considering the stiffness requirements, the strings were formed by wrapping the closed pore PMI foam with dry carbon fiber tubes and bands. They were placed next to each other The foam is mechanically processed with heat. The skin is placed on the wrapped tubes. The warp-knitted fabric is used. In order to obtain constant bending in the whole area, different thickness skin must be achieved by applying thinner foam cores. An aluminium tool was used to show contours. Vacuum-assisted resin infusion process was used to manufacture cargo components.