Paul Marks, chief technology correspondent
(Image: Airbus / H. Gousse)
The frigid temperatures of an aircraft's skin could be harnessed to help keep it safely airborne, say engineers at Cardiff University in the UK. They reckon the temperature difference between the fuel in a plane's tanks, and that of the surface of the wing, can generate enough electricity to power a network of sensors that will give pilots early warnings of critical stress fractures.
Peppering a whole fuselage, wing and tail with sensors has not been possible until now, because the electrical power has not been available to drive them. Sucking the necessary juice out of a plane's generators would burn more fuel at a time when CO2 emissions in aviation are being closely watched. "Providing power for a full coverage structural health monitoring system is the problem," Carol Featherston of the Cardiff team told New Scientist
at last month's Farnborough International Airshow. "But we think it can be done from ambient sources like temperature gradients and vibrations
The need for such systems became clear in January, when European aircraft maker Airbus revealed that cracks had been found
in the brackets that secure the wing skin in place on its 800-seat jumbo jet, the A380. The problem, the company's chief executive later admitted, was that they had used new composite materials in the aircraft whose properties they did not grasp.
"We thought we understood the properties of the materials and the interface between carbon fibre and metal and found out the wrong way we didn't know everything," said Airbus CEO Tom Enders
in late May.
Fixing the wing problems in the 74 A380s currently in service has cost Airbus $222 million
in the first six months of the year alone. So it's little surprise,
perhaps, that both Boeing (maker of the carbon fibre 787) and Airbus are
among those funding the team's research - which would allow cracks to be
found long before regular inspections are due.
The work exploits the thermoelectric effect
in which the temperature difference across a thin film of a material
generates an electric current. When a plane takes off, the cold airflow
over the wing during the climb renders it 40 degrees Celsius colder than
the mass of fuel inside the wing. In test rigs, Cardiff has shown that such
a gradient in a thermoelectric film between the wing and fuel tank can
generate adequate electricity to charge a bank of batteries that powers the
full-coverage sensor network - especially when supplemented by devices
that harvest power from vibration.
cruise part of the flight, when the temperature of the wing skin and
fuel evens out, current stops flowing - but the charged battery carries
on running the sensors. During descent, a reverse temperature gradient
charges the sensor batteries again.
and colleagues believe they are well on their way to developing a
system which can sense airplane deterioration without boosting CO2
emissions - and which will boost safety by allowing damage severity and
the useful remaining life of planes to be assessed.