Aviation composite engineering for structural airframe parts

Citation

(1999), "Aviation composite engineering for structural airframe parts", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 6. https://doi.org/10.1108/aeat.1999.12771fab.002

Aviation composite engineering for structural airframe parts

Keywords Dunlop, Composites, Ice buildup, Protection, Aerospace industry

Dunlop is a specialist in electro-thermal ice protection systems for aircraft, supplying manufacturers both in Europe and North America. As a result of its experience in ice protection, the company has also built up specific expertise in the production of high quality structural resin/fibre composites to meet demanding dimensional and service requirements.

Modern ice protection systems for aircraft are the culmination of a long process of development over the years since 1948. This process began with rubber heater mats bonded on to metal components supplied by the aircraft manufacturer. Today, Dunlop Ice Protection and Composites is a separate business unit within the Coventry headquarters of Dunlop Aviation, designing and manufacturing structural composite parts for many aerospace applications in addition to ice protection systems.

The aircraft industry is turning more and more to advanced composites for their combination of weight saving and high performance - characteristics which are of particular importance where components are subject to extreme conditions and mechanical stress. As experience grows and designers become more familiar with the possibilities of composites, they find a growing number of applications with more demanding performance requirements.

Dunlop Ice Protection and Composites is able to deploy the full range of technical disciplines required to meet the most complex and demanding applications -- materials technology, computer-aided design and manufacture, computational fluid dynamics, stress and thermal analysis.

Manufacturing facilities in the Coventry plant are equally advanced. Dunlop Ice Protection and Composites has a fully-equipped clean room and digitally-controlled autoclave to ensure structural integrity of the composite moulding (Plate 1). The largest autoclave has the capacity to handle parts up to 4m x 3m x 2m high.

Plate 1 Loading a helicopter engine intake moulding in Dunlop Aviation's 10m3

Male or female moulds in metal or composite materials are used, depending on finish requirements and other parameters. They are produced by specialist contractors to Dunlop design requirements and are generally of multi-segment construction to facilitate removal of the finished moulding. A number of special features are incorporated to reduce the need for ancillary jigs and fixtures during post-finishing operations.

Engine intakes for helicopters exemplify the particular strengths of Dunlop Ice Protection and Composites. These are three-dimensional parts which incorporate undercuts and compound curved surfaces to meet aerodynamic requirements. They also incorporate heater elements designed to prevent ice build-up during flight, while using the minimum of power.

Extremely tight tolerances are vital, both for consistent heating and in order to achieve the accuracy required in such a complex component. The heating elements, also produced at the Coventry factory, are integrated within the laminate at various stages to provide the required heating pattern.

Intakes for the EH 101 Anglo-Italian helicopter are manufactured by Dunlop Ice Protection and Composites using a high temperature epoxy resin hybrid reinforcement system with a nonmetallic honeycomb. They are moulded by conventional hand lay-up techniques followed by autoclave curing and incorporate a number of features which are unique to Dunlop.

One such feature is the resin's hardener/filler system, which has been developed from commercially available materials to produce high temperature operational properties. Dunlop Ice Protection and Composites manufactures the resin-impregnated fabric (pre-preg) in-house using a special solventless process. This capability facilitates complete control of resin formulation, pre-preg manufacture and storage management.

Fire resistance is another important issue in all aircraft design. Dunlop has the capability to use ceramic fibres in the lay-up to provide a fire barrier which can be as effective as titanium. This technique was employed in the case of the engine intakes of the Sikorsky S-92 civil helicopter, where the company combined ceramic fibres with a carbon pre-preg. The finished laminate incorporates additional reinforcing layers of woven fabric, built up to achieve specific operational requirements.

Dunlop has also developed special techniques to overcome the inherent handling and machining difficulties of some of the reinforcement materials. Finally, the units are finished with a special erosion-resistant paint coating to provide environmental protection in the extreme conditions in which helicopters operate.

Details available from Dunlop Aviation. Tel: +44 (0) 1203 666655; Fax: +44 (0) 1203 662294.