Structural concept of ECHO - Hybrid bonding and laminar joints

Th Clean Sky 2 project ECHO focus on the integration of an hybrid laminar flow control (HLFC) system on an horizontal stabilizer for a long range aircraft. HLFC extracts a part of the boundary layer in order to stabilize the flow and thus reduce the drag on the airfoil. The transition from laminar to turbulent flow has to be delayed on the airfoil far behind the leading edge. Therfore, the the horizontal stabiliser box has tight tolerances and a minimal amount of gaps and steps. A common approach to reduce gaps are fillers, but this process is time consuming and an exact geometry cannot guaranteed due to strong thermal expansion of the filler. This new design concept uses a pre-curved steel foil to cover the bolts at the gap between leading edge and box. The sheet is bonded on the titanium leading edge after leading edge has been assembled. This ensures both the accessibility of the fastening elements in the case of maintenance, as well as complying with the aerodynamic requirements.