In an era of concern about global warming, the economic crisis and concerns about the depletion of global oil reserves, the issue of reducing fuel consumption in transport has come to the fore. Especially in the aviation sector, using as little fuel as possible – combined with protecting the environment – is an issue of paramount importance, to the solution of which the SARISTU (Smart Intelligent Aircraft Structures) programme, inspired by bird wings, aims to contribute.
Birds are able to change the position of the feathers on their wings depending on the airflow, but aircraft wings are made of rigid materials. For landing purposes (and to reduce speed in general), special “flaps” are extended at the tips of the wings, but these are also rigid. The SARISTU project aims to change this: “The flaps should be able to adapt to the airflow and thus improve the aerodynamics of the aircraft,” says Martin Schuler, a researcher at the Fraunhofer Instıtute for Electronıc Nano Systems ENAS. In this context, a mechanism has been developed that changes the shape of the flap, depending on the airflow. The extent of the change, which takes place in flight, is determined by special algorithms, created by ENAS in collaboration with researchers from CIRA (the Italian Aerospace Research Center) and the University of Naples.
The mechanism that allows the flap to change shape can only work if it is made of a flexible material. Researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM have addressed this problem. “We developed a ‘skin’ with alternating rigid and soft ‘zones’,” says Andreas Löhring of Fraunhofer IFAM.
The mechanism is located under the soft zones, which are also the ones that “see” the greatest stretch. The particularly innovative feature is the material used, as the flexible points are made of a special elastomeric foam, thus maintaining their elasticity even in extreme temperature conditions (from -55 to 80 degrees Celsius). Four 90-centimeter prototypes are already in the testing stage, while this technology was demonstrated at the ILA Berlin Air Show.
However, the desired reduction in kerosene consumption (of the order of 6%) will not be achieved in this way alone: researchers at Fraunhofer IFAM are also working on a second project, focusing on the wingtip. In particular, they have developed a “lobe” that forms part of the wingtip and changes shape during flight to keep air resistance as low as possible. Since any gap between this and the fixed wing would negate any positive effect, the researchers developed an elastic connecting element.
“This work covers everything from chemical composition to processing and manufacturing technology,” says Lerring. As in the aforementioned flap case, this part maintains its elasticity in temperatures from -55 to 80 degrees Celsius and does not face any problems at high wind speeds.
