HAL9000v2.0 wrote: no profit for the investers.
"grant by Coke Zero..." sonds like moneyloundry to me.
What I have missed?
katou wrote:How about hidden wheels? I can guarantee a working prototype if we can make this small change.
Jeremy posted the paper by Ian Brooks, which I would recommend too. Ian is writing about integrated craft, where one fan is used for lift and propulsion. Even if you concentrate on the lift only, it's difficult to get below about 4 hp on a practical craft.
There's more at http://www.hovercraft.org.uk including useful resources and papers in the "links and downloads" section.
I am in fact currently working on an electric lift system for a hovercraft, but I'm intending it as a hybrid, with a gas engine as the primary power source.
Jeremy Harris wrote:Be aware that the lift calculator on the Hoverhawk site makes some assumptions that are based on "normal" sized recreational craft with cushion pressures that are much lower than those that would apply to a very small area, high mass craft. When trying to use on line resources it's worth remembering that these may all have been optimised for the typical cushion pressure found on recreational and commercial hovercraft, typically around 10lbs/ftÂ². Once you get to around 15lbs/ftÂ² you start to run into axial fan blade loading problems and if you go higher than around 20lbs/ftÂ² you may well have to switch to a centrifugal fan in order to get the required pressure rise without encountering blade stall. Your craft looks as if it may well be over 20lbs/ftÂ² cushion pressure, which is going to cause considerable loss of efficiency and high mass flow rates through the hover gap no matter what you do. As the skirt deforms over small obstacles a cushion that is running at this high a pressure will leak more air than one running at a more conventional pressure, as any skirt will become less flexible as cushion pressure increases, just like a tyre.
Another issue associated with high cushion pressure that you may need to look at carefully is skirt bounce. This plagued early bag skirt hovercraft that were operating at high'ish skirt pressures and was only really ameliorated by adding fingers. The problem with finger skirts is that although they are nice and stable and will pass over obstacles well they leak more air so need more lift power. The most successful bag skirt craft around are probably the Sevtec range. They get good stability and a low lift power requirement from running at a very low cushion pressure, but this isn't an option for a small area craft.
You really need to go back to first principles to calculate mass flow rate and pressure, then look at the complex interaction of varying flow rates on fan performance curves to try and get a feel for the power requirement with different fan types over the range of anticipated operating conditions (fans have a tough time with variable loading in a hovercraft). This will then give you a realistic estimate of power required and hence battery size. What you'll find, I'm sure, is that the true power requirement will be much, much higher than the simple on line calculators might suggest. An acquaintance of mine, Ian Brooks, wrote the attached paper that may help you. It applies to the sort of craft you're looking at, an integrated one where lift and thrust are provided by the same power source, except he looks in more detail at a separate thrust duct system, which you may or may not wish to consider: .
Jeremy Harris wrote: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 Harris wrote: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.
Jeremy Harris wrote: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.
Thanks very much for this comment. It help me to think about my ideals.
Tks again and pls keep posting.
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.
auraslip wrote: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.
auraslip wrote: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"
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