Improving the Aerodynamic Efficiency of High Lift Devices by a Stiffness Oriented Re-design with Tailored Laminates

Starting point of this work was the question, to what extent it is possible and reasonable to improve the high lift behavior of thin and long fowler flaps by improving their deformation behavior with a stiffness optimized design. Due to undesired large deviations of the flaps elastic line from the elastic line of the wing there is a significant lift reduction during take off and landing. This lift reduction is caused by an uneven gap between wing and extended flap. The gap is necessary to accelerate the airflow and prevent it from separating from the upper side of the flap. Furthermore, the trailing edge of the flap is simultaneously the trailing edge of the wing during cruise flight. Due to the elasticity of the material there is an upward bending of this trailing edge, leading to an increased aerodynamic drag in cruise flight.

Therefore, the goal of this work was the stiffness oriented re-design of such a flap under consideration of necessary strength criteria. The Airbus A340-300 was chosen as an example because of the known quality and quantity of the deviations and the possibility to quantify the gained improvements. Due to the large flap span of more than 10 meters the outboard fowler flap is bedded on three flap tracks. In the course of the necessary redesign a reduction of this number of tracks from three to two was investigated, too. The decrease of the track number reduces aerodynamic drag, complexity and costs. The following paper describes, how the re-design was done by fast and parametric analytical means as well as by using a detailed three dimensional finite element model.