09 October 2012
09 October 2012
A Lehigh engineer and computer scientist have completed a carbon fibre wing designed for an unmanned aircraft that may never land, powered by the wind and the sun.
The long road toward building a self-powered, gliding aircraft that can remain in the air indefinitely has reached a new milestone. The first, uniquely designed carbon fibre wing has emerged from Lehigh's Composites Lab. The 6.5 m (21.3 ft) wing was made in a single moulding process, complete with wing planks, spar caps to fortify the wings, six internal webs to carry shear loads and a trailing edge ready to accommodate wing flaps.
The wing has been designed for an unmanned aircraft designed to fly at high altitude and generate power from the jet stream and the sun. The long-term goal of the project, led by Lehigh engineer Joachim Grenestedt and computer scientist John Spletzer, is perpetual flight.
The engineer explains, to keep an autonomous aircraft aloft for years at a time requires not just a source of power in the sky—in this case solar and wind—but a very unique aircraft. It needs to have very low drag and long slender wings, as on manned gliders, but it also needs to be able to fly very fast. The wings must be very stiff to avoid flutter and divergence (two phenomena of flight which become very important at high speeds) and very strong to be able to perform hard, high-speed turns. The present wing was designed to not fail before the aircraft sees 20 G in the turns.
Mechanical Engineer Joachim Grenestedt and computer scientist John Spletzer say they have met the challenge, with a carbon fibre wing built as a single piece. No nuts and bolts. No glue joints. No weak points. No trimming or fitting of parts. No complex alignment jigs. The entire wing is made from thin layers of carbon fibres (0.6mm thick) configured into complex geometric shapes and placed layer by layer in moulds digitally designed and machined at Lehigh. The resulting wing has stronger-than-steel performance.
The researchers use carbon fibre reinforced epoxy, similar to the material Grenestedt used to build the Numerette, the largest craft yet constructed with a composite sandwich hull. The advanced material makes the wing very strong, stiff but still flexible, and extremely light. Steel is too heavy. Aluminium sheets wouldn’t work, since the material’s surface imperfections don’t allow for the geometrically perfect airfoil shape needed for long term flight. While carbon fibre is expensive, so little is used it becomes cost effective.
Grenestedt and a team of students fabricated the prototype this month and are now testing whether it stands up to extreme forces. If successful, the final craft could alter the way we launch satellite communications, monitor weather and conduct surveillance. The multi-year project is funded by the National Science Foundation and Lehigh University.