Laminar Interface Concept for a HLFC Horizontal Tailplane Leading Edge, Design and Manufacturing Approach

With the aim of reducing fuel consumption and CO2 emissions, the CS2 HLFC on HTP project
is investigating the replacement of a conventional leading edge on the horizontal tailplane of an
Airbus A350 with a leading edge equipped with an active HLFC system. By extracting the
boundary layer through a perforated titanium outer skin, the laminar flow is stabilised and thus
the aerodynamic drag is reduced. In order to prevent laminar-turbulent transition of the
boundary layer behind the suction area at the leading edge, tight tolerances for gaps and steps
must be maintained at the interface to the HTP box.
With state-of-the-art technology, gaps between the components are closed with a filling
compound. This is a time-consuming process and compliance with the exact geometry is not
guaranteed due to the strong thermal expansion of the filler. Also, the bolt heads of the structural
connection can disturb the laminar flow.
A design concept is presented for the attachment of the leading edge to the HTP box, covering
the bolts and the gap between the leading edge and the skin of the HTP box with a pre-curved
steel foil, which is bonded onto the titanium leading edge skin after the leading edge has been
assembled. This ensures both the accessibility of the fastening elements in the case of a
necessary replacement if damage has occurred, as well as complying with the aerodynamic
requirements.