# What principles does an air glider use?

I just saw this video which was kind of nifty. What principles govern this? Is it simply that 700 lbs of air pressure are exerted from that little 1 HP blower? What would you have to take into consideration to adopt the same principles to move something like a car on a turntable?

Is moving something with air more economical than moving it by other means?

I'm just thinking out loud...

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This "air glider" works as a hovercraft, using air pressure to lift itself and its load.

From a commercial model we get the following specifications:

• 8-1/2 in. x 36 in. (22 cm x 91 cm) dual pads (0.4 m2 total area).
• 750 pounds (~3500 N) of lifting capacity.
• 1.75 HP blower.

The required (relative) pressure to lift 3500 N of weight using a 0.4 m2 platform is

$p_{\rm cushion} = \frac{3500\,\mathrm{N}}{0.4\,\mathrm{m^2}} \approx 9000\,\mathrm{Pa}$

We can take the air inside the "cushion" as stagnated to calculate the velocity of the exit flow. Then the dynamic pressure at the exit of the gap must be about 9000 Pa, giving an air velocity of

$\frac{1}{2}\rho_{\rm air}\,v_{\rm gap}^2 = 9000\,\mathrm{Pa}$

$\frac{1}{2}\cdot 1.205\,\mathrm{kg\cdot m^{-3}}\,\cdot v_{\rm gap}^2 = 9000\,\mathrm{Pa}$

$v_{\rm gap} \approx 135\,\mathrm{m\cdot s^{-1}}$

If we assume the gap is about 0.2 mm (just a guess), the flow rate will be about

$Q = 4\cdot(0.22\,\mathrm{m} + 0.91\,\mathrm{m})\cdot 0.0002\,\mathrm{m}\cdot 135\,\mathrm{m\cdot s^{-1}} \approx 0.12\,\mathrm{m^3\cdot s^{-1}}$

and the required power

$P = Q\cdot p_{\rm cushion} \approx 0.12\,\mathrm{m^3\cdot s^{-1}}\cdot 9000\,\mathrm{Pa} \approx 1100\,\mathrm{W}$,

below the specified 1.75 HP (1305 W).

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How does this hovercraft adapt to different clearance under the furniture? – Georg Jul 14 '11 at 10:24
@Georg: I'm guessing that the upper part of the skids inflate to fill the space above them (up to some limit, of course). – Colin K Jul 14 '11 at 13:09
@Colin Yes that is rather reasonable. This would allow the device to adapt to non-flat undersides of furniture too. – Georg Jul 14 '11 at 14:08

Holding the glider in the air is Bernoulli's Principle. This basic principle of aerodynamics states that fast-flowing air has lower pressure than slow-flowing air.

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Interesting. You compliment MMC but You did not understand his answer!. You are wrong. Bernoulli is "working" at the edges of the Hovercraft, and works against lift! – Georg Jul 15 '11 at 8:16

The relationship between the velocity and pressure exerted by a moving liquid is described by the Bernoulli's principle: as the velocity of a fluid increases, the pressure exerted by that fluid decreases.

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Have you ever seen an air-hockey game? It just gets rid of friction by putting a layer of air between the object and the surface. If you have a large enough area, it doesn't take much air pressure.

A layer of oil or grease or water would work the same way, but air is cleaner.

It's got nothing to do with Bernoulli.

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Everything that applies to gliders are: 1. Fluid friction 2. Gravity 3. air resistance 4. center of gravity 5. Bernoulli's Principle 6. Lift & Thrust

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## protected by Qmechanic♦Apr 8 '13 at 0:34

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