When is a flying carpet not a flying carpet?

When it’s a land-based hovercraft, of course!

Princeton PhD student Noah Jafferis had originally planned to carry out his study project on the technology of printing electronic circuits. However, he changed his mind after reading a 2007 paper on the “Settling and Swimming of Flexible Fluid-Lubricated Foils” that, in the words of its authors, allowed them to ” partly answer the long-standing question in cartoon physics—can carpets fly?”

Jafferis built on the ideas in this paper to build a four-inch wide transparent plastic sheet that moves in the air. It’s powered by electrical current waves pushing air back across the undersurface of the sheet, propelling the sheet at around a centimeter per second.

As the BBC notes, Jafferis’s own paper places “flying” in quotation marks because the device has to be kept low enough to trap air between it and the ground: in reality it’s far closer to a hovercraft than something that’s going to be up in the clouds.

While the concept was simple enough, the real work has been figuring out exactly how the sheet will flex. Extensive measurements from sensors has allowed Jafferis to calculate exactly what currents are needed.

There’s no prospect of this carrying humans as that would require the device to be around 50 meters wide according to Jafferis. However, the lack of moving parts means it could have practical uses in environments where dirt or dust would normally cause problems — including even on the surface of Mars.

For now, though, the next step is to work on replacing the tiny batteries in the device with solar equipment that would not only allow it to move faster, perhaps up to a meter per second, but also run uninterrupted for a far longer time.


One Response to When is a flying carpet not a flying carpet?

  1. Just to clarify, the current work is about demonstrating a propulsive force
    produced by traveling waves in a thin plastic sheet, not lift as of yet. To
    achieve lift, the sheet has to be untethered to allow it reach faster speeds
    (while still being only a few mm above the ground).
    We performed such measurements in two setups – one with the sheet suspended
    using an air table, and the other with the sheet hanging from elastic threads.
    The propulsion only works when the sheet is suspended ~1-2mm above the ground, as expected from theory.

    The BBC also did not include the description of the videos, that I had given them:

    The first video is demonstrating the propulsion caused by the traveling wave.
    The sheet is supported on a cushion of air from the air table, ~1mm above it,
    and is connected to conductive threads to supply power. When the sheet is off,
    its equilibrium position is near the center of the air
    table, and it does not move significantly. When the sheet is on, in this case
    with a traveling wave propagating to the left, it is propelled in the opposite
    direction (to the right in this case). The video shows the sheet turning on and
    off in several cycles, and it thus moves back and forth. Because the frequency
    of vibration is 100Hz, the actual wave shape can not be seen; rather the sheet
    seems to "shimmer" when on.

    In the second video, the vibration is only a few Hz, to allow viewing of the
    actual traveling wave vibration. But frequencies this low are not sufficient to
    propel the sheet. In addition, the sheet is suspended from elastic threads in
    this case (~1cm above the ground, so no propulsion would be observed even at
    higher frequencies). Also, the second video is not displaying properly here, presumably due to skipped frames, so it does not look like a traveling wave. The BBC version is better.

    Several other errors in the bbc article:

    It is not really like a hovercraft, which pushes air down to create lift – our device pushes air backwards to propel itself forward.

    The sentences "He abandoned what would have been a fashionable project printing electronic circuits with nano-inks for one that seemed to have more in common with 1001 Nights than 21st-Century engineering. Prof James Sturm, who leads Mr Jafferis' research group, conceded that at times the project seemed foolhardy." were completely made up by the BBC.

    The sheet would actually only need to be 50 feet on each side to carry the weight of a person, not 50 meters.

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