Nov 292016
 

I’ve not devoted much cogitation to the EM drive, mostly because it just strikes me as bunk. There has recently been some renewed interest due to the appearance of a peer reviewed paper that seems to back up some of the claims… but when the thrust level for 100 watts is measured in *micro* newtons, I just can’t scrape up much interest. Especially when the guy behind the idea was claiming that it would be able to power flying cars (capable of VTOL) and space launch boosters, requiring an improvement in T/W on the order of ten to a hundred MILLION times. And, oh yeah, overturning the laws of thermodynamics. Whenever something claims to do that, I tend to tune out.

If the EM drive actually works (and it seems more likely that it works like a radiometer), then it’s kinda like everything else that has ever been touted as actual functioning magic. Yeah, sure, great, you can bend that spoon with your mind. But look at the effort required; using magic, you’re doing it the hard way.

Here is a good if lengthy explanation of why the EM drive most likely doesn’t work, and even if it did, why it sucks:

 Posted by at 2:45 am
  • thingytest 3

    Extraordinary claims require extraordinary proof
    Xkcd 955 (pertaining to the OPERA neutrino experiment) sums my feelings up nicely.
    https://xkcd.com/955/

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  • Bill H

    If it works it is a game changer. It doesn’t matter if the efficiency currently sucks – engineers will figure that out. You are looking at a lab experiment. The Wright flyer engine was 12 HP. 40 years later aircraft engines were over 2,000 HP – reliably.

    • Scottlowther

      Your comment seems to be a triumph of hope over skepticism, which is always a bad way to go when analyzing scientific issues.

      1) *If* it works, it’s violating the laws of physics as currently understood. Consequently, you *can’t* assume that performance will go up by a factor of several million. If it works by magic, the performance demonstrated – micronewtons per watt – might be all there is. Jamming a 220 volt power line up Harry Potters ass won’t necessarily make him a more powerful wizard.

      2) It *appears* that that trivial level of thrust, which is *barely* detectable, might well be explained largely and perhaps wholly via the same effect that spins a radiometer… one side is warmer than the other, and you’re generating a smidge of thrust form interaction with the thin atmosphere in the test chamber.

      • Paul451

        It *appears* that that trivial level of thrust, which is *barely* detectable, might well be explained largely and perhaps wholly via the same effect that spins a radiometer… one side is warmer than the other, and you’re generating a smidge of thrust form interaction with the thin atmosphere in the test chamber.

        It’s more likely that the heat produced by the high powered magnetron is either warping the torsion-pendulum or the frustum itself. The torsion-balance only measures angular changes, not actual linear force. Heat-twisting would be enough to register, and several amateurs have reported melting the HT plastic dielectric which is part of the set-up. These things run hot.

        Interestingly, the profile of the off-cycle is different in a vacuum than in air. After the power is switched off, the “force” fades more slowly. Which is what you’d expect from heat-warping effect. (Vacuum insulates, hence the warp cools more slowly than it did in air.)

      • publiusr

        Shh. Shelby is working on the giant frustrum
        https://www.youtube.com/watch?v=U-2PPmY3HLg

        So there wasn’t ever a rocket after all–it’s the Nazi bell I tells ya.
        https://www.nasa.gov/sites/default/files/thumbnails/image/img_5271.jpg

    • Paul451

      The Wright flyer engine was 12 HP. 40 years later aircraft engines were over 2,000 HP – reliably.

      So about a 16-fold improvement in 40 years?

      (Actually, the latest jet engines run at about 180,000HP, so a 15,000-fold improvement in a century and a bit. Still somewhat shy of the required hundreds of millions that the EMDrive inventors are suggesting.)