Questioning airfoil design of WIG craft

Discussion in 'Hydrodynamics and Aerodynamics' started by MantaRay, Mar 10, 2013.

  1. MantaRay
    Joined: Mar 2013
    Posts: 19
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    MantaRay Junior Member

    Other than hydrofoil my great interest in marine technology is the WIG crafts. When I saw this design it seemed to present a few unconventional design aspects, one being the replacement of a horizontal tail with a V-tail. The other aspect got me thinking - instead of placing the body or 'hull' of the craft below the wing, place it above. This way there is more cavity space for air to be captured underneath. I can imagine this may reap increased lift but the wings will have to be stronger due to supporting the load of the body when it is not cruising. Also, due to the increase of captured air I suspect this may cause an increased danger of tipping backwards (although assuming a horizontal tail is in use).

    foil.jpg

    I would enjoy reading anyone's thoughts on this.

    EDIT: Just found the classic Lippisch x-112 which shows what I mean in the second illustration of what I call the 'mono air cavity'.

    [​IMG]
     
    Last edited: Mar 12, 2013
  2. yipster
    Joined: Oct 2002
    Posts: 3,486
    Likes: 96, Points: 58, Legacy Rep: 1148
    Location: netherlands

    yipster designer

  3. Submarine Tom

    Submarine Tom Previous Member

    MR,

    You've described a flying wing which is a good WIG design.

    I don't think your link photo to be of very good design other than it "looks" cool.
     
  4. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    any grounds effects machine must fly with the same stability and control issues as any normal aircraft. The effects of ground effects is to reduce the need for the amount of lifting surface, but stability and control issues still remain. A dihedral tail provides both elevator and rudder control but at extra weight as conventional cross tail configuration, also there is an inherent "dutch roll" instability introduced by the configuration. Only a nuisance on conventional aircraft but not desirable at all near the surface necessary for ground effects.

    The V or dihedral tail configuration is more of a fashion rather than having any aerodynamic advantage. There is some argument for fewer moving parts, and perhaps better ground clearance over conventional design, but that is a matter than can be solved by proper design with a conventional configuration.

    I had studied the various tail configurations as part of an engineering study when I was in collage. If an undergrad can determine this from published souses and simple hand calculations (long before the internet), you would think that modern designers would be smarter. Yet the same errors are being made by people who do not study what has gone before, and rejected. There is no advantage, and considerable disadvantage, to a V-tail configuration in an aircraft. It is done only for marketing reasons, an equivalent conventional tail will always perform better.

    And whether the fuselage is above or below the wing is a not necessarily a matter of improved performance, the amount of air under the wings is a matter of the size of the wings, not where the fuselage is located. Ground effects is also a matter of the proximity to the surface, the closer to the surface the more beneficial the ground effect. If the placement of the fuselage allows the wing to be closer to the surface in you flight configuration, that is where the advantage will be, just like the example in video that Yipster posted.
     
  5. Yellowjacket
    Joined: May 2009
    Posts: 662
    Likes: 113, Points: 43, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    A "design" that was done by a "designer" and not an engineer, or at the very least not anyone who is an aeronautical engineer. The "hole" in the lifting surface is horrible since it cuts the span in half, there is essentially no vertical stabilizer, the amount of "V" in the tal surfaces is essentially insignificant.

    In short, It"ll never fly...
     
  6. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 254, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Or if it manages to fly, it will be at such a high speed and so close to the water to make it a perfect suicide machine.

    Gives a new meaning to the term "rescue vessel" - a vessel which needs a rescue team always nearby.
     
  7. MantaRay
    Joined: Mar 2013
    Posts: 19
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    MantaRay Junior Member

    T-Tails seem to be in all ground effect crafts. There are a few that use other configurations such as the canard:



    This 7.2m model rides smooth but I wonder how it will perform with an increased load.
     
  8. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    A T-tail is used to keep the elevator up in clean air, but it can have a very undesirable effect when not done properly. the Piper tomahawk is also known as the "trauma- hawk" since the T-tail looses effectiveness right at the landing flair, usually resulting in over rotation, and much trauma to the occupants. on an aircraft a low horizontal tail is best, it will be in clean air on landing when pitch control is critical.
    On a ground effects machine the air down low is not so clean, so the T-tail could be a good choice.

    When I used for work for a large aircraft manufacturer here in the Puget Sound, there was an engineer who thought having a small one or two seat ground effects machine might be an advantage in the Puget sound. It would allow him to own a much less costly house on the far side of the sound, and commute across the sound at 80 to 100 mph just above the water. Faster and much smoother ride than a speed boat, and presumably lower operating cost. With three wheels he could drive it on the street registered as a motor cycle, with short stubby wings under 8 feet there would be no wings to fold up. Interesting idea, he never built it, but it would be a blast to skim across puget sound just above the waves at 100 mph.

    I am not aware that anyone has made a commercially viable ground effects aircraft. It seems the promise would be much faster ferry service and smoother ride, with much less lifting surface and induced drag in operation. It seems a floating ground effects machine could be viable since it would be faster than a conventional ferry, but presumably less costly to operate than a conventional short hop aircraft. but I am not aware of any that are in operation.
     
  9. yipster
    Joined: Oct 2002
    Posts: 3,486
    Likes: 96, Points: 58, Legacy Rep: 1148
    Location: netherlands

    yipster designer

    I'll put that idea fwd to a girlfrend that likes to travel around those lakes
    you mention a land borne motorbike wig, asume its ment to fload as well
    a hoovercraft wig flys land and water but unlikely gets roadlegal registered
    last up in my gallery a 2 wheel driven water riding bike that fits the same idea
     
  10. tom kane
    Joined: Nov 2003
    Posts: 1,767
    Likes: 48, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Any winged craft operating in the confines of ground effect area is going to be dangerous when turning
    as at some time the wing tips will contact the water or ground and a spin will happen. I doubt that a flat turn in ground effect would be possible. An air boat with a horizontal fan or a converted helicopter for ground effect work would be a different story.
     
    Last edited: Mar 12, 2013
  11. Submarine Tom

    Submarine Tom Previous Member

    Horizontal fan's suck.
     
  12. DennisRB
    Joined: Sep 2004
    Posts: 1,270
    Likes: 26, Points: 48, Legacy Rep: 228
    Location: Brisbane

    DennisRB Senior Member

    I'd say they blow :p
     
  13. Michael Y
    Joined: Oct 2010
    Posts: 29
    Likes: 1, Points: 3, Legacy Rep: 14
    Location: Pennsylvania

    Michael Y Junior Member

    A tricky thing with the aerodynamics of WIG is that when in ground effect, the center of pressure on an airfoil is at the half chord position. As you come out of ground effect, the center of pressure moves forward to the quarter chord position. This is destabilizing, particularly if the center of lift and the center of mass swap positions. One fix for that is to make the horizontal tail big enough to compensate for the shifting COP on the main lifting surface, and to put it well out of ground effect itself, i.e., have a big T-tail.

    Another approach which I'd thought about, and it seems this design uses, is the idea of using a canard to make the WIG naturally stable. As the AOA increases the canard way up in the nose of the craft comes out of ground effect and loses lift and so wants to drop back down, creating a restoring moment. Cool!

    Supposedly an inverse delta planform is less susceptible to the moving center of pressure issue.
     
  14. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 254, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I have just noticed that MantaRay has opted for another photo to illustrate his ideas in the OP.
    The new photo puts my and Yellowjacket's previous comments completely out of context. We were commenting the original photo:
    http://www.boatdesign.net/gallery/showphoto.php/photo/10570
    Perhaps it's just an unnecessary pedantry, but sometimes I feel a need to dot the i's and cross the t's. :)
    Cheers
     

  15. MantaRay
    Joined: Mar 2013
    Posts: 19
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    MantaRay Junior Member

    Thanks for clearing that up for me. I personally hate the T-tail for aesthetic reasons. However, the alternative canard configuration also serves for increased efficiency. The designer of the WISES ('Kaien-3') model (the video above) commented - "A horizontal tail does not exert lift. Moreover, large tail prevents the ship to take large angle of attack at the moment of takeoff, and it increases drag and weight. For commercial services we should minimize the size of horizontal tail if stability can be obtained from other devices. I am using a specially designed wing section for stability."

    Here is another look at the WISES model. It looks as if the wing span is smaller on this model. I have contacted the designer/developer and will ask if this model is accurate according to their math, ect. I am tempted to build a model myself.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.