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Hovercraft question regarding propeller and motor

  1. May 18, 2012 #1
    Hi there i was thinking about trying to build a light hovercraft that can transport one person and I had a few questions about the propellers and motors and how they work.

    The first question is, is it possible to run a hovercraft with an enclosed fan, for example like that found in a jet ski, where it would suck air in and then propel out the back?

    The second is regarding the propeller, for the idea above, would the blades have to be a certain size to work effectively or would a small propeller suffice?

    The third, what size motor would I need if I didn't want it to go any faster than 15/20mph, and could the engine be electric and would it need gears?

    thanks
    kind regards
    dan
     
  2. jcsd
  3. May 19, 2012 #2

    NascentOxygen

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    A hovercraft needs air pressure for both lift and propulsion. I think batteries for an affordable all-electric hovercraft would add too much weight. All electric might be practical if you can tether the craft to a mains AC outlet via the power cord. :smile:
     
  4. May 19, 2012 #3
    Do a search on utube. People have built them but the problem is even with the light lithium type batteries is you still can't carry enough batteries on it to get any decent range. We are going to have to have much better batteries before an all electric hovercraft will be good for anything much more than just a operating display of the technology.
     
  5. May 20, 2012 #4

    NascentOxygen

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    If you aren't chasing speed, lightweight forward propulsion could rely on pedal power to rotate the propeller. The amount of air needed for continuous lift varies according to the surface you glide over. On a smooth polished floor, you could design a close-fitting skirt that loses comparatively little air, so a low powered motor could provide sufficient flow (and battery operation may be feasible). Whereas, if you wish to travel over rough surfaces like roadways, or lakes or grassy fields with bumps and hollows, then a lot more air escapes under the skirt and this has to be quickly replaced, so the high power/weight performance of the internal combustion engine is mandatory.
     
  6. May 20, 2012 #5

    Danger

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    Try a search through the forums here. A few years ago, Russ Watters posted either a chart or a link to a chart that is truly amazing. I designed a vehicle about 20 years ago, but could never afford to build it. I was planning to use a 500-600 hp engine to drive it, split between lift and propulsion. According to the charts, the lift required only about 15 hp. I can't remember any details now, because it was so long ago, but it's on record. Since my design was for a 4-passenger fully enclosed winter closed-highway avoidance device, with wheels for street-legal operation and a top speed of over 100 km/h, with weight well in excess of 1 tonne, I have a feeling that you can achieve lift with electric motors and a reasonable battery pack (look into scavenging from cordless power tools). Anything left over from lift is available for propulsion and control systems. A lot of hovercraft use one fan with thrust vectoring to provide propulsion. I prefer to keep the 2 systems separate, but that's just a personal kink. And do keep in mind that it is preferably a fan, rather than a propellor, for the lift factor. A propellor would be best for propulsion. That's pretty much a matter of semantics, and I don't want to confuse you. What I mean is that you want a multi-blade unit with a fairly steep pitch, wide blades, and low rpm's for lift (think C-130 propellors). For propulsion, something like a Beech Baron or Cessna 310 uses would be more efficient. If you use only one, though, go with the fan. Bleed airflow from it and channel it horizontally to provide your propulsion.
    I'm not an expert, but from my limited experience I believe that it's the best approach.
     
  7. May 20, 2012 #6

    NascentOxygen

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    As a point of reference for weight/power/duration/cost, consider the modern cordless electric lawnmower powered by a pack of lithium cells.
     
  8. May 22, 2012 #7

    Danger

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    When in doubt, throw in a Hemi... :biggrin:
     
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