Project HighPerFlex (High Performance Flexible Aircraft)

Abb. 1: A340 half-model for fluid-structure coupled computations

Abb. 2: Comparison of airfoil geometries with and without mini-TEDs

Normally transonic aircraft are designed for one specific flight condition. The wing geometry is optimised for this condition, and only small improvements (of less than one percent) would be achieved by any further optimisation. However if such an aircraft operates outside its design envelope, the performance is suboptimal. Likewise, unexpected events in flight (like emergency descent or gusts) can cause the aircraft structure to become overloaded.

To alleviate these problems, aircraft designers attempt to control the load distribution over the wing by using adaptive wing elements. Investigations in the project AWIATOR showed that the use of mini-TEDS (small flaps with a length of approximately 2% of the chord length) can improve the lift and, in some flight conditions, also reduce the drag (Figure 1). Additionally, these small and swiftly-deployable elements can achieve relatively large load redistributions. These mini-TEDs also cause a twisting moment on the wing. In AWIATOR, the simplified modelling ignored the drag increases due to the additional trim required and due to the aeroelastic deformation of the wing when mini-TEDs are deployed. The inclusion of these additional variables, and a comparison of the load-redistribution effects of mini-TEDs and the flaps of the high-lift system are the basis for the work package LAWIA.

HighPerFlex is an example of the new methods by which wing-elements for new aircraft will be designed, in that fluid-dynamic and structural computations are coupled for a complete, trimmed aircraft. Aeroelastic computations with the DLR-TAU code and an A340 beam-model should give a better estimate of the flight behaviour, especially in the case where additional elements are added to the wing trailing edge (Figure 2). The aircraft elasticity is increasingly important as the flight speed and aircraft size increase, and as increasingly light-weight elements and designs are used in aircraft.