Wing in ground effect boat

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Starman, May 20, 2010.

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  1. May 31, 2010 #21

    57Marty

    57Marty

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    Have you seen this one? Universal Hovercraft has what I think you are talking about. Two videos


    From what I remember on the Discovery channel the craft is "flying" in Canada and does not require any kind of pilots license due to the limited height above the water. Interesting idea and definitely not an airplane.
    Marty
     
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  2. Jun 1, 2010 #22

    Starman

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    Re: Wing in ground effect


    Thank you Ekranoplan, I have seen most of those videos, but not of the one from Korea. I really like the style of that one and also the overall layout, type of wing, etc.

    It is easy to see that there are many of these WIGs that have been made and that they have flown and flown well. The idea that many of them have crashed was disappointing, but then I suppose that most airplane designs have crashed as well.

    It seems to me that if the horizontal tail is large enough and the wing is a reverse delta that the stability problem shouldn't be too much of a problem. Possibly it can be more of a problem at higher speeds well above takeoff speed.

    One thing I've thought of is to have a surface follower that will automatically control the elevator to maintain the craft a certain height above the surface. This could be a mechanical follower or it could be electronic, using a radar or sonar mechanism. I prefer mechanical ones.

    One thing that was disappointing was that during the German contest that none of the WIGs was able to take off due to the water being slightly rough. If I make one of these I want it to be able to take off from the middle of the ocean, not when it is rough and stormy, of course, but when it is calm to moderate. Taking off in moderate swells would be kind of like taking off in a regular plane from a undulating runway built on gently rolling hilly terrain because ocean swells are actually pretty far apart. If all it takes is a lot of power then I'll give it a lot of power. I'm not afraid of using a lot of power, but then that evidently can be destabilizing.

    Most of the videos I've seen show the craft operating only on smooth water but some of the advertisements claim that they can operate in waves of various heights. This video Aron-7 Wing-in-Ground-Effect (WIG) Seaplane Video shows the Korean Aron 7 taking off from relatively rough water at one point (40 seconds). It also looks like it is underpowered and requires a long time to take off. The Aron & however, has a relatively long wingspan and therefore would probably not be able to qualify as a boat. The good thing about the long wingspan is that the wing chord is smaller and therefore the stability problem is lessened. It has a relatively small horizontal tail but it is pretty far back. In the videos you can see that it appears to be constantly changing it's pitch attitude.

    It is good to see that the Airfisch * has been taken over by a Singapore company.
     
  3. Jun 1, 2010 #23

    Starman

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    I've seen these and what is remarkable is that it has such a poor wing which the designer evidently just guessed at, the horizontal tail is small and close to the wing, which has a large chord, and yet it seems to be quite stable.

    If it can fly to 50 ft as it says in the video then it must be registered as an aircraft whether or not the driver chooses to fly it that high, unless it's light enough to qualify as an ultralight.
     
  4. Jun 14, 2010 #24

    Starman

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    Hi, I solved the stability problems for WIG craft :) :ban::ban:
     
  5. Jun 14, 2010 #25

    Inverted Vantage

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    orion, apologies if you've heard this question before (I'm sure you have), and I'm not very educated on boat design...what research has there been on using hydrofoils as boosters to push the hull up out of the water, reducing drag and thus reducing the required thrust to pull the vehicle completely out of the water?
     
  6. Jun 14, 2010 #26

    orion

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    It has been explored and is considered a promising (our concept uses the idea for instance) however it is not popular because a similar idea was incorporated into a test version of the X-114, which crashed because the pilot forgot to retract the foils and they dug in during a turn, destroying the craft.

    The other problem is that in order for them to be fully functional they have to be submerged, even as the craft leaves the water. This however means that they're likely to be submerged or in water contact as the craft approaches the takeoff/cruise speed so the system does require some form of retraction so as to allow a low drag transition to flying speed. Our system is looking toward an automated retraction - without that the scenario of them inadvertently contacting the surface is very real.
     
  7. Jun 14, 2010 #27

    Inverted Vantage

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    What about a forward swinging spring mechanism? While the craft is water bound, the hydro pressure of the water, coupled with a mechanical lock, keeps the hydrofoils locked backwards. When the pilot pulls a lever, it decouples the lock, allowing the legs to swing forward automatically via the spring. The biggest issue you'd have is making the spring strong enough to pull the foil forward, while at the same time weak enough so as to let them stay stuck down.
     
  8. Jun 14, 2010 #28

    orion

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    While certainly a viable possibility, the problem is that it still requires pilot action. The retraction itself is not so much an issue - it's more so finding a way to guarantee that said retraction will take place every time.
     
  9. Jun 14, 2010 #29

    Inverted Vantage

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    If it absolutely must be automated, you could have a pressure sensor on the struts. When the craft lifts up out of the water, the hydro pressure stops and an electrical signal is sent to the latch to disengage and pull up the foils.
     
  10. Jun 15, 2010 #30

    autoreply

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    And when any of those systems (pilot included) will fail you're in a serious crash.
     
  11. Jun 15, 2010 #31

    Inverted Vantage

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    Uhhh...yea. What's your point? If your engine, control cables, fuel cap, flaps, landing gear fail, you're in a serious crash. That's why you have to design them not to fail. That's kind of like saying you shouldn't fly because if your wings fall off you'll be in a serious crash.
     
  12. Jun 16, 2010 #32

    Kristoffon

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    That's flawed logic. Even if it can be designed "not to fail" it still requires maintenance. And adds cost and complexity. Certified aircraft are required to be maneuverable with only rudder or only aileron for the case of one of those controls failing.

    Even if they were failure proof a collision could make them useless. 747s have triple-redundant hydraulics. This was originally considered excessive. However at least one aircraft was saved shortly after the 747 entered service when a collision rendered two of the systems useless but it landed safely on the third one.

    The only failproof device you can build is a granite chair.

    The mission most aircraft spend 95% of their time on is cruise. I question whether the added weight, cost and complexity of such a system would be worth it. Water is usually the longest available runway and if the space is so short a device like that becomes necessary then maybe that spot isn't so good for operating aircraft out of.
     
  13. Jun 16, 2010 #33

    Starman

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    One of the reasons for the hydrofoil idea is not just short water runways, but it can make a big difference in WIGs or flying boats that have marginal takeoff power.
     
    Last edited: Jun 26, 2010
  14. Jun 16, 2010 #34

    autoreply

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    Not as serious as when your hydrofoil accidentally hits the water, turns you over and your aircraft explodes.

    An engine/control/fuel/flap failure should all result (in most cases) in zero damage, or light damage due to an offfield landing. Landing gear failure is expensive, but in most cases not dangerous for pilots..
     
  15. Jun 16, 2010 #35

    orion

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    There were only two cases of hydrofoils on WIGs that I've seen - one result was positive the other not so much. There was a Japanese POC scale vehicle that used small hydrofoils on the hull. These retracted at cruise. In this case the foils were successful in that they demonstrated a much quicker transition to flight.

    In the case of the X-114 the hydrofoils did indeed get the hulls off the water much sooner but the take-off run itself ended up being substantially longer than on the conventional hulls. The accident killed the program so no analysis was conducted as to why but the guess was that the aft foil (located on the wing trailing edge at the craft's centerline) raised the vehicle too high thus reducing the angle of attack, which in turn resulted in the need for more speed before the craft actually flew.

    Also, I was wrong about the foil actuation it turns out - the foils on the X-114 were fixed, not retractable. At low speed their impact with the surface was OK due to their incidence however, at cruise speed where the craft flew at a lower angle of attack, the incidence angle of the foils was actually slightly negative, which is why they caused the serious crash. As they contacted the surface they immediately sucked that side into the water, disintegrating the structure.

    The idea of using a water drive for take-off assistance may be useful but will have to be done carefully since it needs to be in operation until well into flying speed. If it cuts out just as you leave the water and all you'll be left with is the small air engine, the drag of the higher aoa, plus any inadvertent contact with the water, may actually settle you back down into the water. At best this could be annoying - at worst it could set up a porpoising motion, which could be quite destructive.

    As far as a 60' takeoff is concerned, not likely. Given you mass, your bow wave and hull drag, I'd hazard a guess at takeoff of about 700 to 1,000 feet. A properly designed hydrofoil will help that significantly (down to about 400 to 600 feet) but now your drive system gets more complex since the props will need to stay in the water as your craft gets foil borne.

    And finally, for that power a typical water prop is turning about 2,500 rpm, maybe a bit more. In other words, you'll still need a reduction gear on that rotary.
     
  16. Jun 16, 2010 #36

    Inverted Vantage

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    Its not flawed logic, I was saying that mentioning something was a bad idea because it required maintenance is stating a given (in the aircraft industry) as a negative to an idea. Essentially, any system you add will require maintenance and safety procedures if it breaks - so saying that it shouldn't be done because you'd be required to perform that maintenance and learn those procedures is, in my opinion, pointless and not a real detractor.

    In my opinion, anyway. :)
     
  17. Jun 17, 2010 #37

    Starman

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    Does anyone have any other ideas as to how to reduce drag for takeoff?

    If I were to rely entirely on a front surface follower which contacts the water then the craft could be a conventional design and not the canard/tandem wing style.

    Why aren't surface followers used already?
     
    Last edited: Jun 29, 2010
  18. Jun 18, 2010 #38

    autoreply

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    How about this idea, since it's used on quick torpedoes and might work in a smooth sea.

    When blowing air in the boundary layer on the underwater hull drag is seriously reduced. When released from a pressure vessel weight penalty is pretty low while it might give a real decrease in required runway.
     
  19. Jun 18, 2010 #39

    orion

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    This actually has been tried in several forms, as has a film energized boundary layer. The latter does show promise but the air system never worked.
     
  20. Jun 18, 2010 #40

    Starman

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    I've decided to keep this idea under wraps until I get it flying.
     
    Last edited: Jun 29, 2010

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