“Passive controls” of airflow over aircraft wings focus on airflow boundary layer effects, with benefits of drag reduction, lift to drag ratio enhancement, wing stall delay, better post-stall behavior and performance, reduced stalling at steep attack angles, shorter take off and landing distances and overall flight control performance, increased aircraft operating range, higher operating altitudes, improved roll rates, less take-off noise, reduced engine emissions, reduced separation distances and improved ground crew safety during take-off and landing operations due to wake vortex turbulence reduction, increased aircraft cruise velocities, and greater fuel efficiency during level flight duration.
This proposal contemplates periodic structures which could be deposited on existing aircraft wings as coatings that are laid down as “riblets” using injet-like computer controlled technology. Such periodic coatings would serve to form “hydrophobic” or water-repellent functions. It could also serve the dual function of reducing aerodynamic drag, even in the absence of any water, ice, dirt, or insect remains that might reduce drag from those factors, due to the air flow boundary layer effects of such “inkjet” deposited “riblets” oriented parallel to airflow along the leading edge and over the upper surface of the aircraft wing. The material so deposited would be very durable, over many years, and would be completely adhesive to aviation aluminum alloys.
Testing adhesion and durability under high airflow conditions would be simple, setting up an “inkjet” scale model on a small sample of the aircraft alloy in “bench-scale” tests The test sample can be subjected to wind tunnel experiments and microscopic evaluation, (electron microscope evaluation), and multiple standard surface profilometric measurements over many hours of wind tunnel testing. Alternatively, test squares could be riveted to existing (legacy) aircraft wings and flown under real world conditions, exposed to high altitude flight, very high air velocities and changes in humidity, sunlight exposure, insect impacts, etc., for a number of years of measurement for durability testing and surface morphology and structural stability.
Nature offers lessons in aerodynamics and hydrodynamics, in moth wings, shark skin, surfaces of lotus (lilypad) leaves, and desert beetles, with microstructures that aid fluid flow or repel water. “Biomimicry” refers to studying nature for inspiring design element principles - structures known to improve flight or swimming performance, as in hawk wings and shark skin riblets, or water repelling properties on lily pads and the cuticle of some beetles. Similar structures can be reverse-engineered as modern composite coatings on aluminum alloys, for improving performance and energy efficiency of aircraft. This proposal contemplates using “inkjet”-like technology to deposit onto the leading edge and upper wing surfaces of existing (legacy) aircraft, highly regular or periodic “riblet-like” structures of deposited coatings to offer water, ice, and debris-repellent properties in addition to passive airflow control to reduce aerodynamic drag. This approach could be classified as a kind of “biomimicry”, with modern materials such as polyimide or expoxy polymers, with a regularity or periodicity on the order of microns to millimeters for the riblets themselves.
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