Carbon-fibre planes

IF YOU want to know why carbon-fibre planes such as the boeing 787 are still on the tarmac, it's worth rewinding to the 1950s.

That's when the UK's chances of dominating the post-war aviation market were dashed by fatal in-flight failures of the de havelland comet, the first airliner to sport a pressurised aluminium fuselage. Metal fatigue induced by repeated pressurisation cycles created cracks that started around the plane's window frames. "Although much was known about metal fatigue, not enough was known about it by anyone, anywhere," lamented Geoffrey de Havilland in his autobiography.

Such are the risks of switching from well-understood materials to novel ones. Now aviation is on the verge of just such a switch - to lightweight "composite" materials. It has been a turbulent journey. In June, for example, boeing found problems with the composite joint where the 787's wing meets the fuselage, requiring the addition of metal reinforcements.

On 14 August, the day the UK government offered Airbus a £340 million loan to help it develop a carbon-fibre rival to the 787, it also emerged that Boeing had found weaknesses in the form of wrinkles in the tubular "barrel" sections that make up the fuselage. In a patent (US 2009/0202767) filed the day before, Boeing proposed a way to prevent such "uncontrolled wrinkle formation".

Clearly, composites are a work in progress. The trouble, says aviation engineer Philip Irving at Cranfield University in the UK, is that computer simulations often differ from reality. "Computer models are good at calculating composite displacement and stress levels, but they are not yet good at accurately predicting when they will fail," he says.

But thanks to the Comet's legacy of exhaustive fail-safe testing, he says, stringent real-world tests are mandatory, ensuring plane designers' simulations are correct. And that should ensure that when composite planes finally get off the ground, they will be safe to fly in.