Lubrication-free and maintenance-free bearing technology in wing model for flow measurements

Within the framework of the DFG Collaborative Research Centre 401 "Flow Influence and Flow-Structure Interaction on Aerofoils", measurements of the vorticity wake of aerofoils are carried out at the Institute of Aeronautics and Astronautics at RWTH Aachen University. A so-called reference wing (half-span 675mm, solid construction, material: X42Cr13) serves as the measurement object. This half-wing model was to be modified as part of research work. The aim was to investigate the vorticity wake of an aerofoil with the help of this new application in the in-house water circulation channel and in the drag channel of the DST in Duisburg. If successful, the use of this system in practice would offer economic and safety-related advantages for civil aviation. One focus of the design was the development of a transmission gearbox. The bearing of this assembly had to be particularly suitable for use in the water circulation channel without showing signs of corrosion. However, there were a number of other requirements for the bearings. They had to be as small as possible to minimise the impact on the flow, function maintenance-free over a long period of time (no corrosion, insensitive to dust and dirt), be as clearance and vibration-free as possible, generate only a moderate amount of heat and be cost-effective.

Following theoretical methods, tests with various transmission gears and iglidur ® polymer bearings were carried out over the course of the one-year project in order to determine the most suitable solution for the task. A toothed belt drive in combination with plain bearings was selected. The system is driven by a shaft-hollow shaft combination, which is connected to the model in the wing root by a generously dimensioned plain bearing (floating bearing) and in the wing tip by shell-shaped plain bearings (fixed bearing). In addition to the toothed belt pulleys, there are two discs on the shaft that are supported axially against the plain bearings, which in turn are secured against axial slippage by the tensioning plate located between the belts. The tensioning plate is also intended to maintain the blade stability and apply the pretension of the timing belt. By using plastic plain bearings, it was possible to keep the production costs of the customised product low. The plain bearing fulfils the requirements for low clearance, low vibration and moderate heat generation. Organic materials are also non-corrosive.