EADS reveals developments in aerospace energy harvesting

The aim of the project is to reduce maintenance costs, which account for up to 22% of an aircraft's overall expenses per flight hour. Sensors can inform a plane's operator about the vehicle's condition ('health monitoring'. The system helps to save money, as the maintenance engineers only need to take action when there really is a fault, not on suspicion or at regular intervals. However, the savings effect can only work if the sensors' installation and operation are not too costly in themselves. "A wireless sensor network that supplies itself with energy on location is a good solution to collecting maintenance relevant data at a low cost," said PhD student Dominik Samson from EADS Innovation Works, a member of the project team led by Prof Dr Thomas Becker and Martin Kluge. "Saving energy is not our primary goal. What we want to achieve is energy autonomy. We will save money by making systems independent of central electricity sources." The energy harvesting team investigated a system to convert heat flow into electrical power with the aid of a thermoelectric generator. "This technology is particularly suitable, as major temperature differences occur in and around the aircraft," explained Samson. "There is the difference between the ambient air, with temperatures ranging from about -20 to -50°C and the passenger cabin with a temperature of about 20°C, for example. Then there are also the strong temperature fluctuations on the outer skin after takeoff or during landing." Samson noted that an artificial temperature difference could be created anywhere on an aircraft's outer skin. This was done by connecting one side of a thermoelectric generator to a heat storage facility, while the other side was connected to the outer skin and cooled down more quickly. The difference in temperature generated an electric current. The researchers used water as a heat storage medium, as it could store heat for a particularly long period of time. Small hemispheres filled with water were adhered to the inside of the aircraft wall, forming the most noticeable part of a 'health monitoring' sensor node. A power management system was needed to transform the generated voltage into a value suitable for the sensor. The system developed by the researchers for experimental purposes has now been tested in a climate chamber. The result was that, given an energy consumption of several milliwatts at the sensor node, the amount of energy produced and stored during the flight is sufficient to reliably operate the sensor node. It is also enough for long haul flights, as the 'health monitoring' sensors do not need to be active all the time and the sensor nodes are consumption-optimised. By comparison, a typical LED consumes 20 to 50milliwatts. According to Samson, the next step will be to test the technology in flight. A different team from EADS Innovation Works is currently investigating ways of using the heat of an aircraft engine's exhaust jet. An analogous technique is also being intensively examined in the automotive industry. "Energy harvesting could conceivably be applied to other sectors, too," says Samson. "Industrial machines and domestic appliances are just two examples. Energy harvesting can give machines of all kinds an artificial nervous system."