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I've read a few different explanations of how hovercrafts hover, and they all mention a low-pressure cushion of air. This confuses me though: If there is low pressure under the hovercraft, why doesn't it get sucked to the ground?

Also, if air is being forced into the space under the craft, why is this air cushion not high-pressure?

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    $\begingroup$ Purely guesswork on my part, but it may be that "low pressure" actually means "a low amount of pressure above ambient" rather than the literal interpretation "below ambient pressure". $\endgroup$ – IanF1 May 3 '15 at 16:35
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I can't speak to what sources you were reading, but the air under a hovercraft is higher than ambient air pressure, not lower.

Wikipedia:

Hovercraft use blowers to produce a large volume of air below the hull that is slightly above atmospheric pressure. The pressure difference between the higher pressure air below the hull and lower pressure ambient air above it produces lift, which causes the hull to float above the running surface.

http://en.wikipedia.org/wiki/Hovercraft

Here is Wikipedia's image of a hovercraft: enter image description here

If this craft weighs 500 kg and has 2 square meters of area, it would need a pressure of ~2500 Pascals to hover. Atmospheric pressure is ~100,000 Pascals, so the hovercraft needs to be few percent above atmospheric pressure to work.

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  • $\begingroup$ That makes perfect sense. I just wonder why so many different sources say "low pressure." $\endgroup$ – ItsTimmy May 3 '15 at 16:57
  • $\begingroup$ I don't know, sorry. Wikipedia is usually a good first place to look. $\endgroup$ – Mark Eichenlaub May 3 '15 at 16:57
  • $\begingroup$ Might be that they mentioned gauge pressure assuming that the person could gather from context $\endgroup$ – Triatticus May 3 '15 at 18:05
  • $\begingroup$ I suppose they call it "low pressure" because it's lower than "high pressure". $\endgroup$ – Mike Dunlavey May 3 '15 at 18:55

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