Studing WIG (Wing In Ground Effect)

Discussion in 'Boat Design' started by Geob, Nov 22, 2006.

  1. yipster
    Joined: Oct 2002
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    yipster designer

    a seaplane lands on and takes an angle of attack from the CG and centre of lift above the step
    the second part is only for floatation ( it sloopes up to stay free in take-off)
    (very early seaplane floads had a canoe on its side shape to get the planing pad more fwd)
    see attachments and type "wig" and "stepped hull" in the search button
     

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  2. lohring
    Joined: Nov 2006
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    Location: Eugene, OR

    lohring Junior Member

    The boats go through a hump speed much like seaplanes. The drag is increases rapidly then drops off after the hump speed. Drag then increases more slowly. In tests the motor pulls over 100 amps at the hump speed but only around 60 amps at twice that speed. Our sponsons look very much like the stepped hulls and floats used by seaplanes, but they are designed so the step (therefore the load) is centered between the support booms. The portion behind the step streamlines the sponson and provides attachment as well as static buoyancy. Stability is the most important attribute of the design. I reviewed videos of our electric hydro's high speed runs in rough water and was amazed at how well the boat recovers from bounces. This happens so quickly that it is only apparent in slow motion. I also watched onboard video of the air trapped sponson step. When the boat reaches a high enough speed it doesn't touch the water. Conventional sponsons blow out as well at high speeds, but leave splashes every few feet as they touch. The air trapped design is much more resistant to displacement up or down. The same is true of the main wing, though it lifts much farther out of the water. Again, this is a smooth water design, and in rough conditions a more airplane like design is needed for adequate water clearance. There the center of lift position changes dramatically as the ground effect changes when the airfoils move up and down. This makes stability a big problem. Notice the huge tails on the Russian designs.

    Lohring Miller
     
  3. Geob
    Joined: Nov 2006
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    Geob Marine Engineer

    Thank you for the information, one more time.

    Regard to the steped hulls I didn't know a lot of things. But i have begun to read the links that you give me. As I saw I must use a steped hull.

    Generally at high speeds and especially the moment where the craft start planning, so the forward part or the first step is in the air, there is, as I believe, a critical moment because the second part traps air. So, the thing that i don't know, with the knowledge that i have, is if the traped air help Lift?

    The only thing that I can imagine, is that the compaction of the trapped air push upside the craft. Also as more is the traped air, as less is the wetted surface. So we have low resistance.

    I have to read many things in steped hulls. Thank you for your attention in my subject.

    * lohring : yes the stability is a very big problem. All the tails that i have saw, were huge. But only with this way you keep the craft constand. I believe that many ships that provided as WIGs, were only planning crafts which had a high speed so they had a little contact with water. But they don't fly above the water.

    * yipster : So with a steped hull we keep a constand angle. All the steps must have the same angle ? In order to understand : tha specific angle help us to keep the same angle as the speed increase ? I will search these words.

    Thank you again...



    Geob
     
  4. FAST FRED
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    FAST FRED Senior Member

    "The only thing that I can imagine, is that the compaction of the trapped air push upside the craft. Also as more is the traped air, as less is the wetted surface. So we have low resistance."

    "Trapped" air has little to do with the WIG concept.

    When a wing is less than half its span over something solid (water or dirt) the air can not circulate off the wing tip as rapidly , so the induced drag goes down , but the lift stays the same.

    The hight restriction is so severe the Govs don't call a WIG an aircraft , but a boat , even tho some can hop to a good hight for a VERY short (trade speed for altitude) time.

    Almost as efficient is wing tip tanks , or the modern winglets , where the lesser drag at altitude makes modern cargo haulers.

    FAST FRED
     
  5. Smoothride
    Joined: Sep 2006
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    Location: Washington State

    Smoothride Dog Owner

    Hi Fred and everyone;

    I had a buddy who's dad flew with American, but who flew in the air force before that (even though he was an naval academy grad). He did tests in a dc-3 (C-47) at LOW altitude over the ocean to test reduction of drag in ground effect (collecting lots of data for the engineers). This was in the 60s, I'm pretty sure.
    Every pilot out there knows about ground effect (nothing new), but it's application to modern day marine applications is interesting to say the least. I bet it would be intersting to mount a couple of aviation partner's blended winglets on the ekranoplane, and see if it has any effect on reducing drag/ increasing performance... http://www.aviationpartnersboeing.com/
    hmmmm....

    SR
     
  6. lohring
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    lohring Junior Member

    The use of air traps on the main airfoil makes the flow much more two dimensional when the low aspect ratio airfoil is close to the water. This dramatically increases lift. The main wing is 14 inches wide and runs 1 1/4 inches above the water. The air traps on the sponsons create air pressure under them to make an air bearing between the sponson and the water. We find that the higher the sponson plaining surface angle the faster the boat goes. We have tested up to 10 degree sponson angles. Since the drag of an object in water is 800 times more than the drag of the same object in air, this reduces the power required considerably.

    The boat goes through three stages when accelerating from a stop.
    1 A large wave builds up in front of the wing and sponsons.
    2 The planing lift on the wing underbody and sponsons lifts the boat over the bow wave.
    3 Air flowing over the wing and under the wing and sponsons lifts the boat clear of the water except for the rudder and prop.

    By the way, we ran a lifting rear wing at several angles of attack to see what effect it would have. It did very little for overall stability and barely lifted the back of the boat. Its drag slowed the boat one or two mph.

    Lohring Miller
     
  7. yipster
    Joined: Oct 2002
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    yipster designer

    recall "If one sets out to support the weight using aerodynamic lift, one typically picks a much larger wing span than the width of the hull. But even then, it takes a wing span 15 - 20 times the width of the wetted planing area to have the same drag due to lift." from the wingboat thread, and really blowing my mind is this one, than again, foam, a fwd prop on top, it seems everything is possible...
     
  8. kach22i
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    Location: Michigan

    kach22i Architect

  9. Geob
    Joined: Nov 2006
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    Location: Athens - Greece

    Geob Marine Engineer

    * lohring : Ok. You mean that we have less resistance, because the craft is in the air. Did you make any test about the power that the craft need before take off and after the take off. I believe that when the craft is in the air it use less power (low resistance) am i right ? Please tell me if you have any test about Power and the machine that you use.

    * yipster : you mean that in order to calculate my wing span i must calculate the wetted surface? So i need to know the speed before the take off in order to calculate the wetted surface. In my mind i have a WIG craft with a prop on the top of the craft about the center. I just start to make a drawing of the wing that i have in my mind to show you what i want to make ( with some changes of course in the future...). This threat looks very good. I will read it. Than-x!

    *kach22i : These are the wings that the WIGs use... I saw simillar types in many WIGs craft. Is this wings simillar with the reverse Delta wings? Please give more information about the wings if you have. I have many questions about the wings. Did you know if this wings build with the DHMTU series?

    One of these days i will attach a first drawing of my WIG. Thank you one more time... I have learn many new things from here...
     
  10. Geob
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    Geob Marine Engineer

    Dear yipster the video that you attach is perfect...! Thay can fly many meters above the surface (water, ground, etc) But i have a question : Are they use high Power machines or they fly from ground effect?
     
  11. FAST FRED
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    FAST FRED Senior Member

    "By the way, we ran a lifting rear wing at several angles of attack to see what effect it would have. It did very little for overall stability and barely lifted the back of the boat. Its drag slowed the boat one or two mph."

    Not a new tale , aircraft tails are considered to do Negative Work .
    The wing wants to climb and the tail creates drag forcing the AC to a level altitude.

    Only better built aircraft like a DC8 could transfer fuel in flight to an aft cg (too far rearward for take off) and get the tail loaded enough to pay its way.
    A good crew could save about 2% fuel burn on a 5 hour flight.

    Todays aircraft don't have the transfer system or crew ability to use one.

    FAST FRED
     
  12. Smoothride
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    Smoothride Dog Owner

    Fred;

    The MD-11 and 747-400 have fuel transfer systems that transfer to the tail.
     
  13. lohring
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    lohring Junior Member

    We tried the tail both to add more lift and to act as a stabilizer. The sponsons counter the pitching moment of the main airfoil and more tail lift just loaded them a little more. It was interesting that the tail drag slowed the boat so little. It backs up the conclusion that rudder and propeller drag is by far the greatest component of the drag. In the test model we could move the batteries to vary the cg as well. Below is a graph of one acceleration run. The current draw is a good indication of the power applied to the prop. Voltage times current is the input power. You can see where the prop "hooks up", the current increases as the boat gets to the hump speed, then drops and raises until the peak speed is reached. In later testing with a larger prop we went 93 mph.

    Lohring Miller
     

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  14. Sean Herron
    Joined: May 2004
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    Sean Herron Senior Member

    Burp...

    Hello...

    Keep going - there is a lot going on...

    Kack - where are you doing your bits...

    SH.
     

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  15. fhrussell
    Joined: Dec 2004
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    Location: Long Island, NY

    fhrussell Boatbuilder

    Here's some info on the Flarecraft which was my cousin's company. He folded a few years ago because the USCG decided that it was not a boat, but a plane, therefore requiring a license and expense to operate. also, it was deemed that they were too fast at that low altitude and run the risk of hitting boats and other obstacles.

    http://www.se-technology.com/wig/html/main.php?open=showind&code=0&ind=16
     
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