A semi wig

Discussion in 'Boat Design' started by creosote, Jan 17, 2011.

  1. anthony goodson
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    anthony goodson Senior Member

    In all of this there has been no consideration that whatever is driving the boat ,any of these boats ,must at least partially be immersed in water.
     
  2. creosote
    Joined: Dec 2010
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    creosote Junior Member

    Anything goes

    Except oars;).

    At the upper end of the scale, such as the Caspian Sea Monster, multiple jet engines were used.

    Smaller startup companies making wig craft use air propellers and some are powered by outboard motors with their props in the water.

    The semi-wig craft was a modification of whitewater jet boats, so they use water jet drives. Yes it needs to be in the water to provide thrust. Of the two traits that I suspect the semi-wig to have, roll correction doesn't involve the jet drive leaving the water.

    Since the jet drive thrust is angled to increase the chance of a pitchpole event, I would hope that the drive loses thrust in that event.
     
  3. Easy Rider
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    Easy Rider Senior Member

    I've done a lot of flying ultralights and I don't think those sponson like things attached to the boats creosote has been posting are going to have have enough lift to pay for their weight and drag. That big almost flying boat that was posted looks like a good and serious effort to make a very fast and more efficient boat or much more efficient (than an airplane) ground effect airplane that dosn't fly. There once was an "air" taxi service here in SE Alaska that connected Anette Is just SW of Ketchikan to Ketchikan. There was no airport at that time (in the 50s) in Ketchikan)) There was a large military air base during the war and after the war the base on Anette Is was used as the Ketchikan airport. After DC6s & 7s landed at Anette It was a short shuttle flight to Ketchikan. I know much use was made of the Grumman Goose and I think the old PBY was used as well. They said of the PBY "take off at 90, fly at 90, land at 90. Well to get to the point many of the shuttle "flights" were'nt flights. They were loaded to the point that the trip to Ketchikan was in fact a 15 to 18 mile taxi as they couldn't take off. Not much to view out the window as the aircraft was shrouded heavily in spray. Anyway to get serious lift one needs lots of well designed wing area and lots of speed. Forty knots need not apply unless the craft is extremely light (mini payload) or lots of speed. It would seem to me that to get really efficient one would need to actually fly in ground effect. Also without the ability to bank maneuverability would be poor so avoiding logs in the water ect would next to impossible. And creosote, I think if a hydroplane had it's sponsons aft rather than fwd they probably would recover from a 90 degree flip up too. As long as the CG was far enough fwd.
     
  4. cthippo
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    cthippo Senior Member

    The large WIGs used the jets to get it moving and off the water, but cruised on only a couple small engines. Once you get it in the air WIGs are very effiecient. The reason the engines on WIGs are placed at the front of the craft is to blow air under the wings to create additional pressure for lift.

    The hull also provides some aerodynamic lift, especially at high speed. Look at what happens whey hydroplanes get a little air, it tends to be followed by a followed by a lot of air and a really big splash. At the kinds of speeds we're talking about the lifting moment of the hull is non-negligble. The sponsons also add lift, but I also wonder if they don't also impart stability somehow.
     
  5. keysdisease
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    keysdisease Senior Member

    Just to clarify, you mean the intake for the jet drive needs to be in the water, not the jet nozzle, right?

    Steve
     
  6. kroberts
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    kroberts Senior Member

    I don't think they use the term WIG the same way that WIG guys would. I think it's more of an exaggerated tunnel hull in normal use.

    I don't think they're trying to get much lift out of them. Maybe it gets them a couple inches lift to clear rapids, but I think that's minor.

    I think what they're after is some sort of control for when the boat gets squirrelly. Face it they have 1000 hp or so, why do they need efficiency on a boat that size? I think they're trying to induce high drag when the boat points in the wrong direction. They're using an air surface because when a boat like that gets in trouble it's because it isn't touching much water.

    The shorter the wings on the WIG compared to the chord, the faster take-off and supposedly (unless I'm missing something) the lower altitude it flies.
     
  7. cthippo
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    cthippo Senior Member

    A WIG, or properly "Wing In Ground effect vehicle" flies over the water within the ground effect which extends up to (I think) twice the wingspan. Rather that being entirely dependent on conventional lift the WIG floats on a cushion of air trapped between the wing and the surface of the water. Once the vehicle is up on this cushion it takes very little energy to keep it there. Likewise, if it gets above it's cushion (out of ground effect) it has insufficient lift to actually fly.

    The best comparison I can think of is a hovercraft. Both ride on a cushion of air, but where the hovercraft generates it's cushion by forcing air into it's skirt, the WIG does it by forcing the air under it's wings.

    The advantage of the WIG, especially the large ones, is that it combines the speed of an aircraft with the carrying capacity of a ship. The Soviet Orlan class WIGs could carry 400 troops at 180 MPH for over 4300 nm and had a top speed of 350 MPH. They could also fly right up onto the beach to discharge cargo like an amphibious tractor.
     

  8. kroberts
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    kroberts Senior Member

    cthippo,

    I have a hovercraft (Universal Hovercraft UH-18sp) that can be easily converted into a WIG. It's a fairly good hovercraft that makes a not so good WIG. I have not made the conversion but I have ridden on the WIG version (Universal Hovercraft UH-18spw) and driven several of the pure hovercraft version in addition to my own.

    Legally speaking in the USA, the maximum altitude for class B WIG is 50 feet. Technically speaking it's supposed to be half the wingspan where the ground effect is no longer significant. According to some WIG guys, it's much lower than that for ideal operation.

    Those boats have more than enough power to blow over wings or not. They're not going faster than they could go without the wings, as far as I can tell. The wings are for something else then. Moreover, they're not getting completely airborne even if you discount the prop/jet. They're definitely making hard hull contact with the water. If they were after anything like a WIG then they would try to avoid that, and they would have a much, much smaller engine.

    For example, my UH-18sp is 18 feet long and is considered over powered because it has a 119 hp engine on it. It will go 70+ mph easily enough. F1 unlimited-class racing hovercraft have 200 hp or so tops. A good WIG would need less power to go faster than that. So if these are WIGs in the movie, then why 1000 HP? Why hull contact?

    I agree that they use WIG principles, but I don't agree that the normal goals of WIG design has anything to do with it. It's gotta be there just to provide some sort of stability and to control the boat when you do get airborne.
     
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