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Would this two-rotor hovercraft design work? The bold black line is weighted metal on the lower to stable it. If it helps, this is a human sized hovercraft.

Would it work if:

  1. prop1 lift > prop2 lift
  2. prop1 lift = prop2 lift
  3. prop1 lift < prop2 lift

The difference between prop1 and prop2 lift should be in a range of 0-30%

diagram

NOT TO SCALE, assume that lower weighted bars are equidistant from middle of hovercraft.

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    $\begingroup$ A hovercraft rides on an inflated air cushion and is inherently stable. Do you mean a twin-rotor helicopter instead? $\endgroup$ Commented May 13, 2020 at 23:00
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    $\begingroup$ If all you want to do is fly it around a few inches off the ground, then putting a skirt around it reduces the power requirement dramatically. And voila! There's your hovercraft. $\endgroup$
    – John K
    Commented May 14, 2020 at 0:59
  • $\begingroup$ In other words, use the ground effect, too much weight, it won't fly. Good one, Camille. I would also explore the stabilizing effects of the rotor "disks". They seem to help on bicycles. $\endgroup$ Commented May 14, 2020 at 11:27
  • $\begingroup$ As a matter of interest, are hovercraft on topic on Aviation? They are normally considered ships. $\endgroup$ Commented May 14, 2020 at 16:20

2 Answers 2

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Yes - it can work. Colin Furze (UK inventor & TV personality) built an essentially similar device. Skip to about 1:40 to see some of the problems he had.

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    $\begingroup$ What a death trap! $\endgroup$
    – John K
    Commented May 14, 2020 at 0:58
  • $\begingroup$ What kind of motor do you think he uses? $\endgroup$ Commented May 14, 2020 at 1:15
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    $\begingroup$ You can see that there are two rather cantankerous and unreliable two strokes. Double the risk of failure! And when one goes, even if you stay close to the ground, it flips you over and if you're lucky, you won't have a limb removed when it goes through the running engine's flimsy netting that is all that is between you and your future nickname, "stumpy", during the crash. This Fruze chap seems to have about the same risk tolerance profile as BASE jumpers, who are addicted to near death experiences. $\endgroup$
    – John K
    Commented May 14, 2020 at 1:25
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    $\begingroup$ However the answer to “would this be stable” is a NO – the thing is not stable, and it cannot be made stable. It is controllable (barely), but not stable. No helicopter is stable in hover. It could be made stable by converting it into a hovercraft, that is adding the skirt all around it, which would also reduce the power requirement. $\endgroup$
    – Jan Hudec
    Commented May 14, 2020 at 8:01
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    $\begingroup$ @RobertDiGiovanni, bicycle is not stable. When moved out of the centred position, the deviation grows unless corrected. The gyroscopic effect slows down the deviation increase a bit, which makes it more controllable, but cannot change the way the feedback works. The same applies to rotorcraft. $\endgroup$
    – Jan Hudec
    Commented May 14, 2020 at 21:31
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If the weight is located low enough, it should have "pendulum stability", just like this toy --

enter image description here

If the props are running at different speeds and generating different amounts of lift, then (assuming that is a top view not a side a view), the pilot's weight will need to be off-center to compensate.

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    $\begingroup$ "Pendulum stability" doesn't work. The toy you mention is stable because the center of drag is behind the center of mass. $\endgroup$
    – Mark
    Commented May 14, 2020 at 2:47
  • $\begingroup$ We're going to get to the bottom of this pendulum thing. Too much "fallacy" and Pavlovian dv's. Needs work. $\endgroup$ Commented May 14, 2020 at 5:28
  • $\begingroup$ In other words, an object in an unaccelerated state will have a "pendulum" effect, but Mark is correct, drag, and thrust line also play a role. $\endgroup$ Commented May 14, 2020 at 5:31
  • $\begingroup$ Put a little drag above the prop and watch what happens to hover stability. May be another reason the Army liked to put a radar bulb there. $\endgroup$ Commented May 14, 2020 at 11:33
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    $\begingroup$ @quietflyer, the keel effect, airplane pendulum stability, and the like are all about the relative positions of the center of mass and various aerodynamic surfaces. But your answer is suggesting that the relative positions of the center of mass and the center of thrust are important, which is the classic rocket pendulum fallacy. $\endgroup$
    – Mark
    Commented May 14, 2020 at 20:31

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