A Passive Tip Blow-Out System for Yaw Control of a Sailplane: Preliminary Results

Abstract

The potential yaw moment generation of a wing-internal-flow system to counteract the adverse yaw of high-performance gliders was explored.  In contrast to existing approaches (e.g. application of spoilers), the yaw moment of the system increases when the drag (in terms of friction) of the system is minimized. The biggest moment would be achieved when friction and pressure losses are assumed to be zero.  When spoilers are applied, the yaw moment increases with the drag and will be small when drag is minimized. Following this argument, the system can be interpreted as non-drag based in terms of maximization of the moment which means minimization of the drag.  However, the performance of the system mainly depends on the losses caused by friction-drag and pressure-losses of the tube installations as inlet, elbows, etc.  These losses are theoretically predicted and validated with measured results.  The flow system is driven by the stagnation pressure only.  To validate the moment-prediction theory, a tube system was tested in an in-house free-stream wind tunnel.  The predicted values and the results achieved by the measurements agree well with each other.  Moreover, it was shown that for actual geometrical parameters of a sailplane, the yaw moment produced by the internal-flow system and the adverse yaw have similar magnitudes.  The adverse yaw was estimated, assuming the yaw is mainly based on the induced drag of the ailerons, using a lifting-line Multhopp method.  Additional necessary drag-calculations are identified which are expected to strengthen the proposed system.