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Composite-titanium hybrid aircraft wing structure with tiny holes enables laminar flow to reduce drag

Laminar flow wing designs outperform conventional designs in terms of the lift-to-drag ratio of aircraft wings – a measure of aerodynamic efficiency. Aircraft designers can move closer towards optimal performance thanks to laminar flow designs where an adhered thin titanium layer with tiny holes helps stabilise airflow and further minimises drag.

Transport and Mobility
Industrial Technologies

Laminar flow is the holy grail of wing design, because it reduces drag and helps aircraft engineers lower the environmental impact of aviation. In this condition, the air contacting the wing behaves as if it were a sandwich of many parallel layers – each adjacent layer slides past the other like playing cards. Sustaining laminar flow over the entire surface of a wing or tail is difficult. The slightest manufacturing flaw, a sharp edge or even a bird strike in the aircraft's skin are enough to interrupt the smooth flow and increase drag. The air starts to swirl violently in a tangle of tiny eddies that ultimately increase drag and reduces efficiency.

Novel composite wing designs for more efficient flight

“The future of sustainable air travel relies on turning to new and more efficient aircraft that burn less fuel. Improvements in wing design have the potential to improve efficiency and lower pollution. Hybrid laminar flow control technology, which changes the air pressure at the leading edge of the wing, can largely improve the aerodynamic efficiency and cut drag on the wing,” notes Wouter van den Brink, coordinator of the EU-funded TICOAJO project. Hybrid laminar flow control technology is a technique whereby part of the turbulent airflow around an aircraft is drawn in through microperforations in its skin. These tiny holes continuously remove the boundary layer in which turbulence develops, and create a more stable aerodynamic flow. The TICOAJO project made significant headway in hybrid laminar flow control technology by investigating the connection between the thin sheet of titanium entirely perforated with a myriad of microscopic holes and part of the composite aircraft wing. “Perforated titanium surfaces are thin metal plates which cover the leading edge of the wing and contain tiny holes (around 0.1 mm in diameter) that change the airflow over the wing,” explains van den Brink.

Creating a strong bond between dissimilar materials

The project tested how well different adhesive formulations maintain their strength when bonding the composite material and the titanium, to prevent the two materials from separating during the flight. “What happens when a bird hits the wing, or what will the wing structure look like after 20 years of flight?” questions van den Brink. Researchers sought to address these challenges by conducting static, dynamic and fatigue analyses on the newly developed laminar flow wing demonstrator panel. Besides testing proper adhesive formulations and techniques, the project team also applied advanced pre-treatment techniques in their demonstrator. Grit blasting, a surface treatment process to modify the surface properties, whereby abrasive particles are fired through a nozzle using compressed air, is one such technique. Another is an ultraviolet ozone cleaning process that is highly effective in removing a variety of contaminants from surfaces. The project is keeping many of the details under wraps, but according to the project coordinator, the novel combinations of adhesive and pre-treatment solutions outperform the state of the art.

Keywords

TICOAJO, aircraft wings, composite, drag, adhesive, tiny holes, hybrid laminar flow control, surface treatment, grit blasting, microperforations, airflow

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