Itoero Posted November 21, 2018 Posted November 21, 2018 Researchers from MIT have flown a plane powered by an ‘ion drive’ for the first time. The drive uses high powered electrodes to ionise and accelerate air particles, creating an ‘ionic wind’. This wind drove a 5m wide craft across a sports hall. Unlike the ion drives which have powered space craft for decades, this new drive uses air as its accelerant. The researchers say it could power silent drones.
swansont Posted November 21, 2018 Posted November 21, 2018 It looks like they launch with a catapult of some sort. How far does it fly without the ion wind? Because it's not obvious that it's gliding any further than unpowered flight.
Externet Posted November 21, 2018 Posted November 21, 2018 Is it correct to name it "solid state" flight/propulsion as by time stamp ~3:00 ?
Itoero Posted November 21, 2018 Author Posted November 21, 2018 27 minutes ago, swansont said: It looks like they launch with a catapult of some sort. How far does it fly without the ion wind? Because it's not obvious that it's gliding any further than unpowered flight. It accelerates due to ion drive. But you need to believe it works….perhaps they use a hidden propellersystem. And only launching a plane with ion drive isn't that special now I think about it.
Externet Posted November 22, 2018 Posted November 22, 2018 What if these spinning arms were instead, propeller blades for that airplane ? Would it work better ?
tinkerer Posted November 22, 2018 Posted November 22, 2018 (edited) Is this really any different? https://youtu.be/APUDHFUKYrA Crookes radiometer, invented in 1873. Over the years, there have been many attempts to explain how a Crookes radiometer works: Crookes incorrectly suggested that the force was due to the pressure of light.[5] This theory was originally supported by James Clerk Maxwell, who had predicted this force. This explanation is still often seen in leaflets packaged with the device. The first experiment to test this theory was done by Arthur Schuster in 1876, who observed that there was a force on the glass bulb of the Crookes radiometer that was in the opposite direction to the rotation of the vanes. This showed that the force turning the vanes was generated inside the radiometer. If light pressure were the cause of the rotation, then the better the vacuum in the bulb, the less air resistance to movement, and the faster the vanes should spin. In 1901, with a better vacuum pump, Pyotr Lebedev showed that in fact, the radiometer only works when there is low-pressure gas in the bulb, and the vanes stay motionless in a hard vacuum.[6] Finally, if light pressure were the motive force, the radiometer would spin in the opposite direction, as the photons on the shiny side being reflected would deposit more momentum than on the black side where the photons are absorbed. This results from conservation of momentum - the momentum of the reflected photon exiting on the light side must be matched by a reaction on the vane that reflected it. The actual pressure exerted by light is far too small to move these vanes but can be measured with devices such as the Nichols radiometer. Another incorrect theory was that the heat on the dark side was causing the material to outgas, which pushed the radiometer around. This was effectively disproved by both Schuster's[7] and Lebedev's experiments.[6] A partial explanation is that gas molecules hitting the warmer side of the vane will pick up some of the heat, bouncing off the vane with increased speed. Giving the molecule this extra boost effectively means that a minute pressure is exerted on the vane. The imbalance of this effect between the warmer black side and the cooler silver side means the net pressure on the vane is equivalent to a push on the black side and as a result the vanes spin round with the black side trailing. The problem with this idea is that while the faster moving molecules produce more force, they also do a better job of stopping other molecules from reaching the vane, so the net force on the vane should be the same. The greater temperature causes a decrease in local density which results in the same force on both sides. Years after this explanation was dismissed, Albert Einstein showed that the two pressures do not cancel out exactly at the edges of the vanes because of the temperature difference there.[citation needed] The force predicted by Einstein would be enough to move the vanes, but not fast enough.[citation needed] The final piece of the puzzle, thermal transpiration, was theorized by Osborne Reynolds[8] in an unpublished paper that was refereed by Maxwell, who then published his paper which contained a critique of the mathematics in Reynolds's unpublished paper.[9] Maxwell died that year and the Royal Society refused to publish Reynolds's critique of Maxwell's rebuttal to Reynolds's unpublished paper, as it was felt that this would be an inappropriate argument when one of the people involved had already died.[3] Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge Edited November 22, 2018 by tinkerer
Externet Posted November 22, 2018 Posted November 22, 2018 35 minutes ago, tinkerer said: Is this really any different? The airplane works on 'electric wind' from ion emission. The radiometer is onto something else.
tinkerer Posted November 23, 2018 Posted November 23, 2018 On 11/21/2018 at 7:09 PM, Externet said: The airplane works on 'electric wind' from ion emission. The radiometer is onto something else. Yes, of course I was being rather facetious. I recall seeing a large Crooke's in the Museum of Science and Industry in Chicago as a kid, and was fascinated by it. Forgot about it all these years (strangely, one of those unusual things I failed to try building), then the OP brought back the memory.
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