"Corrugated" Skin For Lower Drag
Texas A&M University researcher Dimitris Lagoudas and his colleagues claim that by creating an undulating skin they have been able to demonstrate reductions in skin friction drag of up to 50 percent. To maximize efficiency, the skin must be able to adapt to very subtle changes (micrometers in height) at different speeds, adopting active wrinkle patters in a skin that "shifts to the shape of an ideal surface wave," according to NewScientist.com. The complexity of controlling an actively morphing skin controlled by electric fields that match the wavelengths necessary to reduce drag currently poses significant challenges, and would be especially difficult to adapt to aircraft. But the researchers claim that even a fixed corrugated skin design would reduce drag and could be tailored to be most effective during specific phases of flight -- cruise, for example. With some tweaking, the same fixed skin could also be designed to increase drag while the aircraft is in landing configuration.
The research team says the idea is not entirely original -- dolphins have been wrinkling their skin to reduce drag for perhaps as long as there have been dolphins. One scientific approach designed to mimic the behavior involves using an electrical field to manipulate "piezoceramic legs" under the skin, bending the skin upwards by as much as 30 micrometers where applied. Corrugations generated by that technique have resulted in increased surface flow velocities, and it is those that researchers have translated into skin friction drag reductions of as much as 50 percent.