The last few decades have seen a steady rise in the amount of ‘composite’ materials used in the airframe of aircraft. These have added strength but lowered the overall weight of the aircraft. The use of composites in one new aircraft has generated a weight saving of 20% over traditional aluminium alloys.

A composite material typically consists of relatively strong, stiff fibres in a tough resin matrix. The fibres are set into resin to form sheets which are laid on top of each other, bonded and then heated in a large oven, or “autoclave”.

The main materials used in aerospace composite structures are carbon- and glass-fibre reinforced plastic. They have several advantages over traditional aluminium alloys. As carbon composites are, in general, only 60% of the density of aluminium, they provide a much better strength-to-weight ratio than metals: sometimes by as much as 20%. They can also be formed into more complex shapes than their metallic counterparts, reducing the number of fuselage parts and the need for fasteners and joints.

Specially made for the task

The increasing use of composite structures in aircraft is only part of the story. Design engineers now have very detailed data on the different forces and loads on each millimetre of the aircraft’s structure. With the availability of new light aluminium alloys, metal-composite materials and different types of composites, the modern aircraft can be built with materials which precisely match the task they have to perform on the aircraft.

For example, the kind of material required to resist bird strike impact, in the aircraft nose, is unlikely to be the same material used in the wing, which will have incorporate highly elastic properties to take into account the lift forces on the wing during turbulence and take-off.