An investigation of glider winch launch accidents utilizing multipoint aerodynamics models in flight simulation

Santel, Christoph; Gäb, Andreas (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2010)
Diploma Thesis

Aachen, Techn. Hochsch., Diplomarbeit, 2010

Abstract

The presented thesis investigated the mechanisms leading to accidents during the winch launch of gliders. Initially, data from the accident database of the German Federal Bureau of Aircraft Accident Investigation was studied. Critical phases of the launch were identied along with the associated probabilities and risks of accidents. From this data requirements to an aerodynamics model suitable for accident reconstruction were formulated. An instationary multipoint aerodynamics approach, based on blade element theory, met these demands. A "prescribed wake" model was then coupled with this multipoint aerodynamics approach to determine the induced velocities at all surfaces. The developed models were then validated and checked for plausibility with flight test data from a Schweizer SGS 1-36 sailplane. For the purpose of describing the relations between pilot and aircraft behavior as well as launch safety, a flight envelope limiting airspeed and pitch attitude was proposed. It was shown that the aircraft's radius of gyration along its pitch axis influences the path taken through the flight envelope. As a consequence, motorglider conversions of existing sailplane designs operate closer to the upper pitch boundary of the flight envelope. With this knowledge a generic 18 m class motorglider model was then implemented in the developed aerodynamics model and exposed to a hypothetical accident scenario. Here it was shown that under the presented circumstances the risk of a pilot-provoked stall of the horizontal stabilizer exists. Depending on the severity of the stall, a catastrophic accident might result.