Structural concept of ECHO - Hybrid bonding and laminar joints

Abstract

The Clean Sky 2 project ECHO focuses on integrating a hybrid laminar flow control (HLFC) system on a horizontal stabilizer for a long-range aircraft. HLFC extracts a portion of the boundary layer to stabilize the flow, reducing drag on the airfoil. The transition from laminar to turbulent flow must be retarded on the airfoil far behind the leading edge. For this reason, the horizontal stabilizer box has tight tolerances and a minimum number of gaps and steps. A common approach to reduce the gap dimensions is filler, but this process is time consuming and exact geometry cannot be guaranteed due to the high thermal expansion of the filler. In this new concept, a preformed steel foil is used to cover the studs in the gap between the leading edge and the box. The foil is bonded to the titanium leading edge after the leading edge is assembled. This ensures both accessibility of the fasteners in case of maintenance and compliance with aerodynamic requirements.