Numeric simulation of glider winch launches
Gäb, Andreas; Santel, Christoph
Aachen : Publikationsserver d. RWTH Aachen Univ. (2010)
In: XXX. OSTIV Congress, 28. Juli - 4. August 2010, Szeged, Hungary
A numeric simulation tool for simulating the winch launch of gliders has been realized and employed for a number of analyses. It comprises models of aircraft, pilot, winch, winch operator, cable, atmosphere and terrain. Results are in agreement with pilots' experience. The simulation framework is implemented in Matlab/Simulink. It is based on an existing flight dynamics simulation used e.g. to assess the application of actuators in sailplanes. Configuration has been kept fairly generic to allow modeling of different aircraft, winches, cables and conditions. A GUI allows easy change of parameters. The cable may be modeled either as a simple secant between winch and aircraft, where force variations along the cable are neglected. The alternative is a FEM representation with the cable separated into massless cylinder elements connecting mass points. This allows including aerodynamic forces acting on the cylinders and gravity acting on the mass points. The cylinders may also be assigned spring and damping constants to model elasticity effects. Finally, they also interact with the terrain. For the winch, an automotive drive train model was employed. The rotating parts act as a flywheel whose acceleration is determined by power input from the engine and power drain from the cable. Ground interaction is modeled for a set of discrete contact points including wheels, exposed structure elements like skids or wingtips and the cable elements. Each contact point has spring and damping constants to model the force normal to the terrain. Forces in the contact plane are calculated via friction coefficients. The humans in the loop are approximated by simple control elements, namely PID controllers. The winch operator controls the cable force at the winch using engine throttle. The glider pilot model is divided into three submodels controlling elevator, aileron and rudder. The elevator channel is responsible for airspeed, while bank angle (and thus heading rate) is controlled by aileron deflection. The objective of the rudder channel finally is to minimize the angle of sideslip. All pilot controller gains are scheduled by dynamic pressure. Human factors are included in terms of reaction time and neuromuscular delay. Analyses were carried out varying different simulation parameters like cable type, cable force, hook position, pilot behavior and wind influence. Results will be presented in the paper.