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Quiet Hovercraft? Answered

Long-time lurker, first-time poster. I very much enjoy this community of happily-twisted imagineers & feel strangely at home when I visit.

Been toying with an idea & need some outside-the-box thinkers. One primary issue with recreational hovercraft design is propellor noise. Could a blade-free ("Dyson-ring") fan design be adapted to a hovercraft application? By ducting the required volume & pressure of air into the ring the primary source of noise is...gone. Safety would be vastly improved, eliminating the need (and weight) for protective screening. Fewer mechanical parts also means the craft becomes cheaper/lighter.  And if, rather than one large ring, two smaller rings were swivel-mounted they could further simplify the steering (directional thrust) and give the hovercraft another very unique feature. By quickly counter-reversing the two rings 180 degrees, the hovercraft would have BRAKES! I've never seen a recreational hovercraft with the ability to stop quickly (with the obvious exception of crashing into a large, heavy object!).

All input is appreciated. Thanks very much!       


I'm failing to frame my question correctly. Imagine two independent engine/propellor systems on a recreational hovercraft. One for thrust, another for lift. The "Dyson ring" question is related to only the thrust system. The lift system will be more or less conventional.

The fan(s) feeding the ring(s), being smaller & more efficient, can be positioned to maximize balance, safety & quiet operation (perhaps under the craft's hull?) because a tube (duct) carries the air flow. The rings are open toward the front of the craft allowing for the "suction effect" to add to the air flow. No screens are required because there's nothing spinning & chopping air (or arms) within the topside ring's diameter. The rings can also be mounted to pivot at their base providing both steering & stopping. Yes, I'm familiar with reverse vectoring systems used on aircraft. Agreed, it's not a 4-wheel disc kinda' braking. But physics says, once forward momentum is overcome, it'll slow the craft as fast as it was accelerated. That's better than coasting & little different than reversing and gunning an outboard motor to stop a boat faster.

The air cushion system contributes relatively little to the noise of a recreational hovercraft and it isn't very turbulent. Its signature force on to the water as it escapes from beneath the craft actually smooths rough, choppy water. If it were excessively turbulent, it would increase chop, not calm it. It takes much less horsepower with a much smaller propellor to maintain only lift. There are no baffles in a dual lift/thrust craft, only a skirt.

So, I AM trying to buffer thrust propellor noise because the ring doesn't spin and/or chop air. I'm also trying to buffer fan (turbine?) noise because the ring "ductability" may allow the fans to be positioned below deck.

The rings as thrust only is a good idea. If your able to build a ring that can handle the amount of air needed to move the vehicle. In this since the ring is little more then a ducted fan. But the added benefit of additional air being sucked through the ring isn't going to add much if anything to the thrust. 90%, or more, of the work is being done by the ducted fan in the base of the units. So you might as well use a conventional fan system and duct it through a ring setup. It just seems to me there would be some loss of efficiency ducting the air through a tube and then bending it around a ring. I would think a better option would be to duct it through a single large tube up out of the top of the vehicle then through a 90 degree pipe that can be rotated 360 degrees. It would still be fairly noisy even as a larger dyson ring. To get the thrust needed you would need a much larger fan which would create allot more buffeting. The great thing about the Dyson rings is it uses a much smaller fan then a conventional desktop fan and pushes a good amount of air. But from what i've seen the dyson on high doesn't match the airflow of a regular fan on high as far as air velocity goes. But the dyson does seem to cool you better with that lower voracity air flow.

As I understand it, the "Dyson" ring's exhaust area is an air foil (wing) of sorts creating thrust (re: breeze) from air being forced into the ring from a duct at the ring's bottom. So there IS a blade in the fan's base connected to an electric motor compressing air thru the duct, into the ring & out the ring's opening. There must be something moving the air. But there are no moving parts in the ring.

Yes, the THRUST propellor is a primary noise source much like that of a small airplane. It's the loud, dangerous part. The engine that turns that prop makes "some" mechanical noise but can be acoustically muffled & exhausted beneath the craft. The air cushion (via the higher RPM LIFT engine & its propellor) is being blown into an inverted bowl shape (the craft's hull) and is acoustically insulated by rubber (the craft's skirt). That craft-lifting air cushion is a more generalized, snugly contained area of higher-pressure (relative to the atmosphere) and isn't near as turbulent (or noisy) as the less-contained chop-chop-chop of the slower-turning thrust propellor mounted topside.  

The Dyson bladeless fan isn't blade free and isn't quiet either. Its quiet compared to conventional desktop fans but you still here the fan in the base of the system. It uses a very efficient and small fan to draw air into the base. The air flows up a tube and around the ring and is directed outwards. As the air flows out it creates a suction drawing air from behind the ring through it. Thus adding to the air flow.

In order to take advantage of that the back of the rings would have to be open to the top of the craft. The weight of the craft would force any air buildup that might occur in the cushion out through that opening. The Dyson fan has no fewer mechanical parts that any other fan. No weight is saved since protective screening would still be needed to cover the fan feeding the rings. Not to mention the added weight of the rings themselves.

As Kiteman mentioned the air cushion the craft rides on has allot of turbulent air and the baffles where the air is allowed to escape flap around creating additional noise. If by some miracle your able to silence any buffeting noise from turbines or fan blades you still have the cushion and the noise from the motor. You can use materials to help dampen the noise but that will only go so far and adds to the weight of the machine which isn't good.

As for stopping... Commercial hovercraft and some aircraft already redirect there airflow 180 to help them stop. Some craft are able to turn there engines/fans around 180 degrees while others use flaps to redirect the airflow to the front of the craft. The size and momentum of the craft prevents this from being a fast breaking system. It takes time for that jet of air to overcome the craft's forward momentum. If you want a recreational hovercraft to stop quickly then throw an anchor off it and hope it catches something solid like a tree.

Is a Dyson ring truly blade-free?

And is the propeller truly the main source of noise? What about the air-cushion? That's a lot of turbulent air right there.