Skirtless Hovercraft - RC Groups
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Nov 18, 2016, 12:45 PM
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Idea

Skirtless Hovercraft


If we compare a peripheral jet hovercraft to a multirotor craft with rotors pushing directly against the ground? Assuming that we use the same power and the types of fans and rotors that gives the best efficincy for each craft. Which one would be more efficient?
Last edited by Street racer; Dec 15, 2016 at 04:19 PM.
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Nov 18, 2016, 09:29 PM
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Quote:
Originally Posted by Street racer
Which one would be more efficient?
At what?
racing pylons at 100MPH, or carrying a few tanks onto a mine laden beach?
Last edited by xanuser; Nov 19, 2016 at 05:50 PM.
Nov 19, 2016, 07:44 AM
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Where's Shane???
Nov 19, 2016, 07:44 AM
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When you need him lol
Nov 19, 2016, 02:28 PM
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I think this is one of those questions that doesn't have a single straightforward answer. It also depends on what you want 'efficiency' to mean since that's one of those words with many different meanings depending on the context. There are some very specific definitions of efficiency when it comes to wind turbines or thermodynamic systems for example, and much looser definitions when it comes to colloquial usage.

Instead of saying 'we have X amount of power available, how do we use it most efficiently?' I would come at it from the other direction. Define the performance requirements and then start optimising for the minimum amount of power needed. Start with the weight you need to carry and the minimum hover height, then look at how much propulsion is needed and if it needs to fight winds, uneven surfaces, have emergency buoyancy if the motor(s) quit over water etc. I've done design projects in this vein and there tends to be a lot more things to account for than is first apparent. It is also very, very easy to go astray by being over-optimistic about what the machine is going to deliver performance-wise. All human endeavors are littered with failed designs, some of which never stood a chance, some of which came so close but never quite made it. Since we're on the topic of hovercraft the Avrocar is a good example of this.

Anyway, I can tell you that multirotors are not happy at all in ground effect. The turbulence and vortices spilling from under the air cushion wreak havok with the stabilisation and result in the thing wobbling all over the place. It's actually hard to even get or keep a multirotor in ground effect for this reason. I reckon with enough tuning of the flight controller parameters you probably could get it to be somewhat stable in ground effect but it's never going to be great. A well setup peripheral jet hovercraft is almost magically stable in comparison.

I don't know how well helis cope in ground effect. I would guess better since they're not as reliant on very precise computer stabilisation as multirotors are and a heli is also starting from the best possible configuration (single big rotor vs many smaller ones). With a hovercraft you also have the entire surface area of the body for the high pressure air to act on vs trying to throw air directly under a propeller, much of which is going to be immediately blasted out and sucked around again.

I think buried somewhere in the single engine hovercraft thread is a post by Windnsea talking about his attempt at a hovercraft/quadcopter hybrid. I'm going off memory here, but I believe the setup was a peripheral jet hovercraft with 4 lift fans arranged across the plenum as they are in a quad. There was a stabilisation port directly under each prop so some of the direct thrust from the prop would go right through to the ground. I believe this was all setup as a conventional quad with the idea being the flight controller could manage the stability of the hovercraft as it would a quad (autolevel and preventing it from flipping etc. Don't know if there was any attempt at propulsion or strong pitch/roll/yaw control from the props. I'll go digging for this post later). Anyway I recall Windnsea reporting that this setup never worked very well and he went back to a single engine and worked on the split flap design for stability and control.

By the way since the single engine hovercraft thread is locked we could either start a new one or just let this one continue the discussion. I actually did have a fair bit to report on with both my single engine and bixel-hybrid designs. I assume the thread was locked because of excessive length.
Nov 21, 2016, 12:16 PM
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Hi, Fifty, thanks for the detailed answer. I was wondering about this because I think there two modern hovering machines in production that stands out, the Aero X hoverbike and the ArcaBoard hoverboard and both use propellers/rotors to push directly aginst the ground and I wondered if they would be more or less fuel/energy efficient using a skirtless air cushion. As you point out about stability I'm sure they would be more stable if they were hovercraft.

Quote:
Originally Posted by FiftySlicks
By the way since the single engine hovercraft thread is locked we could either start a new one or just let this one continue the discussion. I actually did have a fair bit to report on with both my single engine and bixel-hybrid designs. I assume the thread was locked because of excessive length.
Good idea. I was a bit disappointed that the thread was closed, now that AlienPodShip has infact built a full scale skirtless craft, and I presume all the hovercraft people here would like to comment on that incredible machine.
Last edited by Street racer; Nov 22, 2016 at 12:55 PM.
Nov 29, 2016, 10:07 AM
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I think I found the answers to my questions about the arcaboard here, : https://www.rcgroups.com/forums/show....php?t=2567792

Still someone needs to make a Skirtless Hover bike

I mean Would'nt Aero-X and the Furze hoverbike work better if they were skirtless hovercraft?
Last edited by Street racer; Nov 29, 2016 at 11:06 AM.
Nov 29, 2016, 10:31 AM
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Quote:
Originally Posted by Street racer

Still someone needs to make a Skirtless Hover bike
Homemade Hoverbike (3 min 51 sec)
Nov 29, 2016, 11:02 AM
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Quote:
Originally Posted by xanuser
I know, and it's an impressive achievement, but Furze's bike is a DuoCopter, not a skirtless hovercraft A hovercraft or hovercraft bike would be less likely to cut off the pilots legs (watch the part when it flips over! Scary stuff)

I have posted about the paramotors a few times in Windandsea's thread, wondering if those could be used to make a skirtless craft, I even found some electric paramotors.
Last edited by Street racer; Nov 29, 2016 at 11:09 AM.
Nov 29, 2016, 11:17 AM
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Quote:
Originally Posted by Street racer
I know, and it's an impressive achievement, but Furze's bike is a DuoCopter, not a skirtless hovercraft A hovercraft or hovercraft bike would be less likely to cut off the pilots legs (watch the part when it flips over! Scary stuff)
yeah i know. point being thats about as good as its going to get for a hover bike, unless there's some breakthrough in energy storage in the future. he probably cant even get it off the ground after a big holiday meal.
Nov 29, 2016, 01:06 PM
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Quote:
Originally Posted by xanuser
he probably cant even get it off the ground after a big holiday meal.
ha ha, true. And you're right, electrisity is even worse, it's by far inferior to gas even though the environmentalist idiots want people to believe otherwise. Anyway, are you saying if those gas powered Parajet motors were used in a peripheral jet hovercraft, like the one AlienPodShip built, it would be less efficient than this bike?(lower hover height with same fuel consumption)
Nov 29, 2016, 01:49 PM
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just trade offs/ more efficient thrust, but with added weight and reduced maneuverability, and increased drag if moving at any kind of speed.

back on topic;
A long time ago (pre lipo o_0) I built an RC hovercraft that worked OK skirtless. -but better with a skirt tho-
this winter i plan on trying again, this time for a single fan/skirtless.
Nov 30, 2016, 04:52 AM
just look at it smokin'
z-matrix's Avatar

re: Skirtless Hovercraft


To hover efficiently you need a skirt, the skirt eliminates the pressure drop caused by the increased distance from the ground, less power will be needed to "float" if you use a skirt on a terrain other than a laboratory table that is perfectly flat.

The skirt also adds additional clearance to the vehicle, so when it hits a bump only the skirt deforms.

If there is no skirt then it is not a hovercraft, it is a multirotor aircraft/helicopter
Nov 30, 2016, 06:37 AM
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Quote:
Originally Posted by z-matrix

If there is no skirt then it is not a Hovercraft
Seriously!?? Trolling much? If not you should get your facts straight, a skirtless peripheral jet hovercraft, which is what this thread is about, is not a helicopter or multirotor!
Last edited by Street racer; Nov 30, 2016 at 06:50 AM.
Nov 30, 2016, 06:44 AM
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Quote:
Originally Posted by xanuser
just trade offs/ more efficient thrust, but with added weight and reduced maneuverability, and increased drag if moving at any kind of speed.

back on topic;
A long time ago (pre lipo o_0) I built an RC hovercraft that worked OK skirtless. -but better with a skirt tho-
this winter i plan on trying again, this time for a single fan/skirtless.
Sounds good what size is it going to be?


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