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gle skin radomes and sandwich radomes [7].

Glass Reinforced Plastic is widely used in aircraft for ducting. Apart from the protective ducting for electrical cable, most ducting is employed in air-conditioning system. Several considerations for their acceptance are given below [7].

Excellent resistance to vibration compared with the fatigue prone thin metal ducts.

Ease of fabrication into many unusual shapes.

The advantage of weight over any metal ducting.

The nose sections and general fairings of several gliders are made of GRP [7]. The outstanding fatigue performance of composites is used to good effect with propeller designs. Complex aerodynamic shapes are more effortlessly manufactured with composites. This provides design flexibility. Composites are used in jet engines mainly in cooler regions. With the introduction of carbon/polyamide, the early complications associated with turbine blades have been largely overcome. The helicopter rotor blade design was made flexible with the availability of composites. The rotation of the blade causes the change in pitch and will eventually results in very high levels of fatigue loading. Composite main rotor blades that utilizes unidirectional CRFP in the spar design have virtually unlimited life [9].

The structure that attaches the blades and the main body of the aircraft is known as the conventional rotor hubs. These are very complex units which have a variety of bearings, seals and lubricators to allow blade movement while guaranteeing proper load transfer. Innovative design using elastomeric composite materials with high levels of elastic deformation have resulted in concepts which are eventually bearing less. The benefits are manifold including reduced maintenance and drag, reduced part count, lower weight and improved damage tolerance and life time. The centrifugal load from the elastomeric bearing is carried by a hub plate which is also a composite [9].

Space application provides more possibility than aircraft industry in terms of advanced use of new materials. Launch condition regulates the mechanical design requirements for satellite components. Loading will be 7g in the axial direction with 1g in the lateral direction, for conventional rocket launch. For space shuttle launch the loading is more uniform with approximately 5g in both directions. GRP is use in places where thermal insulation is important. Carbon fibre systems are more often associated with space applications. Fairings, manipulator arms, antenna reflectors, solar array panels and optical platforms and benches are all examples of CFRP space structures [9].

2.4.2 Rail Transport

The increased practice of plastics came as a result of the development of high speed, lightweight rolling stock and the need for fast commuter transport. The most vital reason for the use of plastic is that, with high speeds and rapid accelerations, the weight of the railway vehicles becomes critical. In UK, British Railways use GRP rod stock coated with butyl rubber as under bridge, tunnel and section insulators on the 25kv overhead power system. In 1954 the utilization of and awareness of GRP on the part of British Railways began with the production of canopy ends for diesel rail cars. As a result the production cost reduced [7].

Using a sandwich structure consisting of outer skins of polyester glass fi