Indian American scientist at Harvard, Lakshminarayanan Mahadevan, and other scientists — Mederic Argentina of the University of Nice, and Jan Skotheim of the Rockefeller University in New York have invented the magical flying carpet of Alladdin in Arabian Nights based on the aerodynamics of a flexible, rippling sheet moving through a fluid.
The scientists are confident to make one that will stay aloft in air, propelled by actively powered undulations much as a marine ray swims through water. If it becomes a reality, our future generations would be flying on carpets in air.
The drawback is that it cannot take humans aboard. To stay afloat in air the sheet requires to be typically about 10 cm long, 0.1 mm thick, and vibrate at about 10 Hz with an amplitude of about 0.25 mm. Making a heavier carpet ‘fly’ is not impossible, but it would require a powerful engine to drive vibrations that the researchers say “our computations and scaling laws suggest it will remain in the magical, mystical and virtual realm.”
The magic carpet is possible if we can create uplift as the ripples push against the viscous fluid. If the sheet is close to a horizontal surface, like a piece of foil settling down onto the floor, then such movements can create a high pressure in the gap between the sheet and the floor, says Mahadevan. “As waves propagate along the flexible foil, they generate a fluid flow that leads to a pressure that lifts the foil, roughly balancing its weight”, he writes.
Ripples can also drive the foil forward if the waves propagate from one edge causing the foil to tilt slightly and permanently and then move in one direction. Fluid is then squeezed from this end to the other, causing the sheet to progress like a submarine ray, explains Mahadevan.
To generate a big thrust and speed, the carpet has to undulate in big ripples, comparable to the carpet’s total size. This makes for a very bumpy ride. But a smooth ride is possible if you can generate a lot of small ripples, he says. “But you’ll be slower.” He says speed always is bumpy in other transportation modes as well.
Commenting on the innovation, physicist Tom Witten at the University of Chicago says the result is not very surprising, but “the main interest is that someone would think to pose this problem.”
“In air, it should be possible to make moving sheets – a kind of micro hovercraft – with very light materials, or with very powerful engines”, says Mahadevan.
Mahadevan has developed the new concept while working on unusual effects on our daily tryst with physics. His previous study on the ‘Cheerios effect’ helped him moot the new idea that floating rings stick together through surface tension.