Hoverboard Product Manager Position

[Jeremy Harris]

The biggest impact on lift power is the combination of the mass flow rate of air escaping from the cushion and the cushion pressure. The hover gap air escape area is determined by the distance around the perimeter of the skirt and the hover gap (typically between 1/2" and 1") and the cushion pressure is a function of the effective hull area and the total weight.

There is a "sweet spot" when it comes to working out hull size for a given weight of craft. This tends to be around the 5 to 10lbs per square foot cushion pressure zone. The trade off is that the greater the hull area, the lower the pressure for a given weight, but the greater the peripheral distance, and hence the larger the air escape area.

Fans also have pretty non-linear performance curves, which means that their efficiency varies a great deal with rpm, pressure rise and flow velocity. Fan manufacturers produce performance curves that help to choose the best combination of fan diameter, pitch and rpm for a given pressure rise and velocity, but with a hovercraft the conditions will often vary wildly as mass flow rate changes when going over rough ground or when banking or pitching (which changes the hover gap area). This means you need to have a substantial excess of power over the notional power given by simple calculations if you want the cushion pressure to be adequate under all conditions.

Getting better than around 70% efficiency from a lift fan is tough, and its efficiency will drop down to maybe 30 to 40% as soon as it is operated off the peak efficiency point, which will happen a lot in normal hovercraft operation.

I'd guess that a small, around 5 ft diameter, weighing around 300 to 350 lbs in total, hovercraft might need about 4hp theoretically, but probably closer to 6 or 7hp in reality, because of the high cushion pressure, poor fan efficiency that's inherent for a fan working at such a high blade loading and highly variable mass flow rate changes.

Jeremy

[katou]

I would think that the minimum would be (for lift only) about 4 hp with a straight bag type skirt, and a bit higher, say 5 hp for a segmented skirt. Segmented skirts do look way more cool though.

For a fan, I would recommend (since we're just spitballing) a variable pitch large diameter propeller around say 4 ft dia.

If it could be built so that the operator stands on some wire mesh over the propeller intake duct, you could get max pressure directly under the craft.

Of course, the inflated skirt (only alternative to jupe style) concept requires that the pressure in the skirt be higher than the pressure under the craft. Dang. Still can't get max pressure under the craft!

I do like the picture of a driver (rider) standing over the intake of the 4 ft propeller.

Katou

[Jeremy Harris]

For stability you don't want max pressure under the craft, you want maximum pressure in the skirt or at the peripheral jets. You do want a skirt design that provides a righting moment when deflected, though, which is one reason why fully segmented skirts are so popular. Some designs of bag skirt can tuck under when the craft leans, which makes the craft lean even more, as the centre of pressure will move in the wrong direction. A properly designed segmented skirt (or some low pressure bag skirts) will deflect outward on the downward side of the lean, effectively moving the centre of pressure of the cushion in that direction and giving a correcting moment to bring the craft back upright.

High pressure tends to make the cushion less stable, particularly with a bag skirt, and can make the craft bounce around a lot. It also makes the skirt less flexible (particularly bag skirts) which makes it harder for it to conform to the shape of irregularities without increasing air loss.

I believe that the Bertin jupe system was able to operate at higher cushion pressures, whilst retaining good stability, than bag or segmented skirts, which was one of its attractions and why I suggested it as an option for this small, high pressure, craft. I believe this is because the jupes are inverted conical sections, so when compressed on one side the centre of pressure automatically shifts in the right direction to provide a correcting force. The feeling that they run at higher pressures is borne out by the video of these craft in use; they seem to produce markedly more water spray than the loop and segment skirts used on the similar sized SRN craft and my guess is that this is in part due to their higher cushion pressure. Somewhere I have a analysis of the Bertin system that was published in "Flight" magazine around 40 years ago, back when I was still very interested in hovercraft. If I can dig it out I'll scan it and post it.

Jeremy

[HoverBoarder]

For stability you don't want max pressure under the craft, you want maximum pressure in the skirt or at the peripheral jets. You do want a skirt design that provides a righting moment when deflected, though, which is one reason why fully segmented skirts are so popular. Some designs of bag skirt can tuck under when the craft leans, which makes the craft lean even more, as the centre of pressure will move in the wrong direction. A properly designed segmented skirt (or some low pressure bag skirts) will deflect outward on the downward side of the lean, effectively moving the centre of pressure of the cushion in that direction and giving a correcting moment to bring the craft back upright.

High pressure tends to make the cushion less stable, particularly with a bag skirt, and can make the craft bounce around a lot. It also makes the skirt less flexible (particularly bag skirts) which makes it harder for it to conform to the shape of irregularities without increasing air loss.

I believe that the Bertin jupe system was able to operate at higher cushion pressures, whilst retaining good stability, than bag or segmented skirts, which was one of its attractions and why I suggested it as an option for this small, high pressure, craft. I believe this is because the jupes are inverted conical sections, so when compressed on one side the centre of pressure automatically shifts in the right direction to provide a correcting force. The feeling that they run at higher pressures is borne out by the video of these craft in use; they seem to produce markedly more water spray than the loop and segment skirts used on the similar sized SRN craft and my guess is that this is in part due to their higher cushion pressure. Somewhere I have a analysis of the Bertin system that was published in "Flight" magazine around 40 years ago, back when I was still very interested in hovercraft. If I can dig it out I'll scan it and post it.

Jeremy

The French persisted with separate internal skirt systems for a few years, take a look at the Bertin Jupe skirt system, as an example (here's a video with some images of the jupes: http://www.dailymotion.com/swf/xbwted&related=0 ). The idea was that by breaking up the plenum into smaller areas, partially sealed from each other, they could gain stability and help resist bounce. The system works fairly well, but tends to eat up valuable hull area, as most of the cushion pressure is retained by the jupes, with a lower pressure in the interstitial spaces between them that doesn't significantly contribute to lift.

The Jupe system does sound interesting...

Here is some of what they have been talking about in the Design of ACV book on Bertin Jupe system:

...An individual Jupe is a fabric cone with a wall angle of 5-10 degrees to the vertical. When inflated with air from inside, it provides a relatively stiff cushion up to the point where the bottom edge begins to crumple or fold up; beyond this, restoring force reduces quickly. the Sedam series craft had cushions with a series of jupes.

The highly compartmented cushion provided great heave, pitch and roll stability. Jupes are not responsive to waves as a bag/segment skirt and so give rather higher drag, resulting in higher installed power. Significant water scooping drag in the rear area of the stern jupes also reduced the acceleration at hump speed. As a result, the design has been superseded by the bag/segment in the industry. This could be minimized by adjustment of flow to the cells, but nevertheless still caused significant wear in this area - larger than for a bag segment skirt.

The peripheral cell jupes skirt, a mixture of the jupe as applied to the French ACV and the bag and segment skirt, has been applied to one of the prototype LCAC craft, the JEFF-A. Excellent longitudinal and transverse stability was obtained. Maintainability and reliability were improved over a bag and segment skirt with internal stability skirts, since the greater stiffness of the pericells allowed the inner stability skirts to be deleted even though the LCAC is a high-density craft...

Rigid hinged skirt systems have been tried and are extremely wasteful of lift power, as when passing over a pebble, for example, a whole section lifts and allows air to escape rather than just the part of a flexible skirt that deforms over it. All designs moved away from rigid structures like this back in the very early days of hovercraft development, primarily for this reason.

I would really like to properly address this, but I don't have the time to delve into the details on this now. I was not looking at making a fully rigid skirt system for the design I talked about. I was looking at a soft bottom for the skirt system, which would have less air loss than a completely rigid system, with a lot of connected narrow carbon fiber panels to allow one section to lift up without lifting the hundred plus other sections on the board.

However, this could be made even more responsive to small changes on the surface by using a long line of metal or carbon fiber poles while still using a flexible but durable rolled up carbon twill on the bottom.

This would be somewhat like having a rolled up carbon fiber mesh rope connected to poles that act in a similar fashion to the toy shown below:

[HoverBoarder]

Hi,

Thanks very much for this comment. It help me to think about my ideals.

Tks again and pls keep posting.

Thank you for your post.

I am going to continue to work on my hoverboard designs, and I might even work on building part of one of my hoverboard designs this summer.

The most important decision I have to make is which hoverboard skirt design to go with. The losses of air from the hoverboard skirt is one of the most important aspects to look at for the design of a hovercraft type hoverboard because of the smaller plenum chamber size. I want to work on the calculations of air losses from a few different options, and it would probably be good to build a few scaled down models to test out the various hoverskirt designs that I have selected for this project.

These hoverboard skirt test models may include a Jupe system, a combined bag and finger system, and an overlapping articulated carbon fiber panel system with springs and incased carbon fiber twill.

I have a pretty good idea of what motor controller I want to use, the batteries I want to use, the fans I want to use, and I already have a number of pieces for the structure.

[auraslip]

Much easier to do!

Or you could combine some off road skate board wheels with a the "hover board" - So that the wheels more or less skip along the ground. Think of it more as a skateboard that can handle rough terrain rather than a "hover board"


Each wheel could be controlled by sensors that detect how you are leaning. Lean forward and the wheels go forward. Lean back and it slows down or reverses. Lean sideways to turn. Since each wheel is independently powered, you could turn in place. It's about all the functionality you're gonna be getting out of a "hover board" but much easier. Heck, just a skateboard with 4 independent hub motors and the lean sensors would be pretty cool IMHO. It'd be intuitive and with out hand held controls, yet small and inexpensive and capable of being powered as a normal skateboard for extra range.

[Hillhater]

Those "omni directional " wheels have a practical application in industry ..
http://www.youtube.com/watch?v=vAiwLRGsNrE&NR=1
http://www.youtube.com/watch?v=OfVhb7r37UY

[auraslip]

Yeah yeah yeah - it cracked me up when I saw the sidewinder forklift in the new star trek movie. Oooooh how futuristic

[REdiculous]

Heck, just a skateboard with 4 independent hub motors and the lean sensors would be pretty cool IMHO. It'd be intuitive and with out hand held controls, yet small and inexpensive and capable of being powered as a normal skateboard for extra range.

If their little motor and transmission works then there'd be no real reason to go hub motor unless you get more power. You don't want to turn like a tank anyway since it would make high speed turning difficult. Much cheaper ($750-ish) and lighter that way. All you'd need to do is hack the control it comes with and mount it on the board instead of holding it in your hand..just turn the lean direction into a forward/reverse throttle signal.

[HoverBoarder]

Much easier to do!

Or you could combine some off road skate board wheels with a the "hover board" - So that the wheels more or less skip along the ground. Think of it more as a skateboard that can handle rough terrain rather than a "hover board"


Each wheel could be controlled by sensors that detect how you are leaning. Lean forward and the wheels go forward. Lean back and it slows down or reverses. Lean sideways to turn. Since each wheel is independently powered, you could turn in place. It's about all the functionality you're gonna be getting out of a "hover board" but much easier. Heck, just a skateboard with 4 independent hub motors and the lean sensors would be pretty cool IMHO. It'd be intuitive and with out hand held controls, yet small and inexpensive and capable of being powered as a normal skateboard for extra range.

That sounds like a fun project aurasip,

I have been thinking about modding a scooter or electric skateboard, and I really like the idea of lean sensors.

Still, it kind of takes the fun out of actually hovering... Unless of course I took an electric scooter or skateboard and modified it to be able to hover on flat ground and drive up hills.

I could build one of the leaf blower models that can be made in a day like the one shown here: http://www.youtube.com/watch?v=W4N-CLPXF8w&feature=player_embedded#at=11

However, I want to make a model that has reduced noise and more control.

I have four decent sized fans that could work as side thrusters, and I am working on making a model of the hoverskirt that I designed, but I am not entirely sure as to what controller to use. I would like to get a wireless controller, and I have had a lot of trouble finding a good controller that I can use. The primary thing I am waiting for is find a suitable motor controller and get the batteries.

Just for fun, here is a trailer video from Jason Bradbury from the Gadget Show showing off his jet powered hoverboard (you have to pause the video at 0:28 to see it). This kind of goes against the idea of developing a quieter hoverboard, but it is fun to watch.



Cheers

[auraslip]

Cool hoverboard videos! I think we were all expecting the second model to sink into the pool, but it was still hilarious when it did! I guess it takes a LOT of power to truly "hover"

[HoverBoarder]

Cool hoverboard videos! I think we were all expecting the second model to sink into the pool, but it was still hilarious when it did! I guess it takes a LOT of power to truly "hover"

Yeah it does! To get the power for a hoverboard to be able to move on water, It really all comes down to the skirt and fan.

My design is a lot more ambitious, and it is going to take a fair amount of time and money to complete. I am also working on parts of my project at a time since I cannot buy everything at once.


I have a pretty fun design for the side powered fans that will be pretty cheap and easy to build and I plan to make them soon and test them out this summer. I am going to put a few of these on the back of my bike for fun .

[GCinDC]

[MikeFairbanks]

These are fun.