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Thread: Wing in ground effect boat

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    Registered User Starman's Avatar
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    Wing in ground effect

    i have a new design project as some of the longer term members here know, I've built some welded aluminum boats and have a bunch of aluminum available. I also live in the Seattle which has great inland waterway access almost all the way up to Alaska.

    What I envision is a four seat craft with a lot of additional cargo capacity, and if possible making this cargo space useful for sleeping two people inside the plane while it's not moving. The cargo/sleeping space could be a partial 'trade' with the two rear seats.

    It also needs to have the removable wing tips that can be switched with longer wings in order to get better range. I want to ultimately have a 3000 mile range so I can use it to go to Hawaii, for example.

    Longer wings will allow flying within ground effect at a higher distance above the surface.

    I want it to have enough wing area so that it will fly slowly enough to be able to follow the contours of ocean swells and remain in ground effect. I think 50mph is a good ballpark figure.

    So far I envision a reverse delta with twin engines on pylons like the Russian BE-103 uses: http://cdn-www.airliners.net/aviatio.../7/1111773.jpg

    I realize that with longer wings it will be able to fly out of ground effect and so will need to be registered as an aircraft, but that's for later.

    I hope to initially use two 40 hp industrial (lawn mower) engines like the Kohler Command V twin. And initially use them with direct drive.

    Later, for long range, I might need to switch to larger water cooled engines, and of course, diesels would be ideal for the long range. I've done some preliminary spreadsheet calculations using rough assumed ballpark figures. With a gross weight of 3000lb and a span of 40 ft it needs to have 150+ hp to get a marginal climb rate, and marginal is OK for it when it is overloaded with fuel. This is assuming 1000lb of fuel, which will give a 3000+ mile range.

    However, those figures are for flying out of ground effect, and flying in ground effect can increase fuel efficiency up to 250% but for now I'm going to figure it as if there is no ground effect, which will provide a large fudge factor.

    There are two types of ground effect, span dominated ground effect, and chord dominated ground effect, and the chord dominated ground effect will provide better efficiency but requires flying lower (unless AR is less than 1, and this won't be)

    Chord dominated ground effect creates an unstable condition, which can be partly compensated for with use of a reverse delta with negative dihedral and a large horizontal tail: http://www.aerospaceweb.org/question/aerodynamics/ground-effect/flarecraft-l325.jpg

    On these types of WIGs the horizontal tail is normally a lifting surface because it helps to automatically prevent the unstable pitching up the occurs when the plane increases it's height above the surface. At low heights the center of lift moves back to about 50% chord so the tail lifts very little, but when higher the center of lift moves to around the 25% point, at which the tail must lift more.

    This site has some discussion of the stability issues and different airfoils used to help with that: aero
    Last edited by Starman; June 24th, 2010 at 01:31 PM. Reason: edit title to remove 'boat'

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    Registered User Starman's Avatar
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    Re: Wing in ground effect

    Here are some preliminary sketches of my idea. Showing a two step hull, I thought of using a hydroski, but if the plane contacted the water while the ski was retracted it would stick to the water and not bounce off.

    My plan is to use welded aluminum boat construction methods for the hull, engine mounts, and main spar and use foam and fiberglass for the top of the fuselage, wings, and tails. The wings will provide flotation.
    Attached Thumbnails Attached Thumbnails Wing in ground effect boat-wig1.jpg   Wing in ground effect boat-wig2.jpg  

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    Moderator addaon's Avatar
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    Re: Wing in ground effect

    Is 80 hp going to be enough to get you up on step? Direct drive, your static thrust will be rather low.

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    Registered User Starman's Avatar
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    Re: Wing in ground effect

    It might not be enough, but I'll try direct drive first, mainly due to impatience I thought it wouldn't be enough but then I saw that the original Airfish 1 got airborne and went 100mph on 13 hp so there is hope. If I need a PSRU I'll make one out of V belts. The smaller diameter is good because it allows a lower thrust line but if I go from a 6ft to an 8ft prop it will only raise the thrust line one foot.

    Obviously when it is reconfigured for long range and a large fuel load it will need more power and thrust efficiency.

    I see that many planes with engines in pods have the prop in front (like the Be-103), but I would prefer it in the back because it allows a lower thrust line. Do they put the prop in front mainly for convenience sake? I guess it allows a shorter prop shaft.

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    Registered User Dan Thomas's Avatar
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    Re: Wing in ground effect

    Quote Originally Posted by Starman View Post
    It might not be enough, but I'll try direct drive first, mainly due to impatience I thought it wouldn't be enough but then I saw that the original Airfish 1 got airborne and went 100mph on 13 hp so there is hope. If I need a PSRU I'll make one out of V belts. The smaller diameter is good because it allows a lower thrust line but if I go from a 6ft to an 8ft prop it will only raise the thrust line one foot.

    Obviously when it is reconfigured for long range and a large fuel load it will need more power and thrust efficiency.

    I see that many planes with engines in pods have the prop in front (like the Be-103), but I would prefer it in the back because it allows a lower thrust line. Do they put the prop in front mainly for convenience sake? I guess it allows a shorter prop shaft.
    On any waterborne aircraft, an aft prop ends up eating a lot of spray and splash. Water does terrible things to propellers, like splitting them apart and eroding them, and any big gulp of water can cause sudden deceleration of the crankshaft and damage things.

    So the pusher props we do see on amphibs tend to be mounted up high and above the wing or above some strakes to try to keep the water out of it.

    Dan

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    Registered User Starman's Avatar
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    Re: Wing in ground effect

    Thanks Dan, I'm aware of the importance of keeping water out of the prop. When I mentioned putting the prop in front I meant in front of the engines, which are still in back. On this design I'm relying on the prop being above the big fat wing root and hopefully once the craft gets going fast enough to cause some spray that it will rise up to where all the spray will go under the wing. The Be-103 accomplishes this by using a delta shaped wing root that reaches fairly far forward, Reverse delta WIG craft accomplish it by having the large wing root at a high incidence.

    In this case, whether the engines are oriented with the props in front of or behind them, it is still a pusher craft since the props and engines are behind the passenger compartment; and if water went over the wing it would hit the props no matter which way the engines are facing.

    I imagine that wood props would split and erode but that aluminum ones wouldn't split but may get eroded a little?

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    Registered User GESchwarz's Avatar
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    Re: Wing in ground effect

    Wing in Ground = Cartwheel Effect
    If you see something, say something.

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    Super Moderator orion's Avatar
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    Re: Wing in ground effect

    The biggest problem WIG craft continue to have in their development is simply that the hydrodynamic forces at play will drive the power requirement, more so than anything flight related. If we look at an idealized planing flat plate at a positive angle of attack, the optimum L/D occurs at or near 5 deg in relation to the waterline. The max L/D value at this point is approximately 5.5:1. But this is idealized and assumes a perfect flat surface. Introduce typical environmental issues and realistic hull design values, including things like dead-rise, the max L/D value will most likely be around 4.0:1 or even less. So, for your 3,000 pound craft you will be generating about 750 pounds of drag. Below this trim speed you will be in displacement and/or transition mode and after this point it'll be assumed that your wing will be providing lift thus reducing the weight the hull has to lift.

    Then your dynamic effects come into play - as a rule of thumb, it's a good idea to have a substantial thrust margin at this point so as to avoid porpoising. For the sake of discussion let's round off the thrust required to get off the water to be at about 1,000 pounds. Given your two 40 hp motors with moderately small props, it's doubtful that you'll generate more than about 250 pounds of static thrust, give or take a bit. Maybe with an optimized low pitch prop you can do a hair better, but you'll still be woefully short of the mark.

    And regarding your 250% increase in fuel efficiency in ground effect, simply stated, in your dreams. While it is true that a wing in ground effect does generate less drag and to a limited extent a bit more lift (requires very small h/c values) than in free air, remember that you're dealing with induced drag only. Because of speed and performance issues though, you generally have a large wing so your cruise lift coefficient is relatively small, thus making the induced drag number relatively small. You still have the fact that it's a low aspect ratio design and you are still carrying the rest of the vehicle. Those numbers do not change.

    But here's the basic problem, you need power to get off the water but you then don't really need it to cruise (BTW, I think a more realistic cruise speed goal for you will be around 80 to 100 mph). On a large scale craft like the Russian KM that means you carry ten large turbofans for take-off but then you idle eight of them for cruise.

    On a smaller vehicle like the failed Flarecraft you will then have a tendency to overpower the craft, which can greatly destabilize the vehicle (long story here and not a very pretty one).

    The difficult task in designing a WIG is simply that there is not enough reliable information out there to do a good job of it. If you're designing a plane there is tons of data, text books and reference papers that you can dig through to get just about anything you need. For WIGs there is virtually nothing. I've been doing WIG development consulting for over about fifteen years now so I've seen most of the programs in the Western hemisphere. Some have potential and some are downright scams but all have the same issues - not enough data and not enough money to do it right.

    The bottom line of this is that the project you have in mind is ambitious and there is a lot more to it than a cursory glance might reveal. I certainly do not wish to dishearten your effort but just want to make sure you understand what you're getting into. People and organizations have been after a functional WIG craft for years, especially a Class B. So far though, no luck. FlightShip came closest but it too ran out of money, mainly due to creative bookkeeping by the developer. That program did go through sea trials and certification but once the money got pulled, it just disappeared. Last I heard it was sold to someone in Turkey but there it seems to have gone nowhere.
    Last edited by orion; May 23rd, 2010 at 11:44 PM.
    "To live is to learn; to learn is to live" (author unknown)

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    Registered User Kristoffon's Avatar
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    Re: Wing in ground effect

    Quote Originally Posted by Starman View Post
    I want to ultimately have a 3000 mile range so I can use it to go to Hawaii, for example.

    I want it to have enough wing area so that it will fly slowly enough to be able to follow the contours of ocean swells and remain in ground effect. I think 50mph is a good ballpark figure.
    Did you even do the basic math? 3000 miles at 50 mph is a 60 hour trip! Do you plan to sleep in the middle of the ocean?

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    Super Moderator orion's Avatar
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    Re: Wing in ground effect

    One thing I forgot to note above: The hull L/D value is for an established planing configuration. To get there though you have to deal with your bow wave so getting up on plane requires a lot more thrust than the planing L/D value might suggest.
    "To live is to learn; to learn is to live" (author unknown)

  11. #11
    Registered User Starman's Avatar
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    Re: Wing in ground effect

    Quote Originally Posted by Kristoffon View Post
    Did you even do the basic math? 3000 miles at 50 mph is a 60 hour trip! Do you plan to sleep in the middle of the ocean?
    Yes, land in the middle of the ocean and put up a strobe light on a short mast to hopefully prevent being run over by an ocean liner. Actual distance between Seattle and Hilo is 2655 miles, from San Fran to Hilo is 2318 miles. But 3000 miles should be minimum potential range (for the long wing, long range version only).

    Anyway, 50 mph is more like hopeful minimum practical flying speed if I want to follow larger ocean swell contours but I envision the Pacific being pacific enough to allow flying at a planned long distance cruise of at least 100 mph while still benefiting from some ground effect. I expect to plan trips when the ocean is relatively calm and so allow faster speeds while flying low (watch out for rogue waves =). So that is 27 hours, meaning flying overnight or spending one night parked in the middle of the ocean.
    Last edited by Starman; May 24th, 2010 at 11:26 AM.

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    Registered User Starman's Avatar
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    Re: Wing in ground effect

    Quote Originally Posted by GESchwarz View Post
    Wing in Ground = Cartwheel Effect
    Yes, I expect to put skis on the tips of the reverse delta to help prevent cartwheeling but I didn't draw them in there yet. With the long wings I'm on my own There won't be any skis on the tips of the long wings, but maybe some end plates.

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    Registered User Starman's Avatar
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    Re: Wing in ground effect

    Quote Originally Posted by orion View Post
    The biggest problem WIG craft continue to have in their development is simply that the hydrodynamic forces at play will drive the power requirement, more so than anything flight related. If we look at an idealized planing flat plate at a positive angle of attack, the optimum L/D occurs at or near 5 deg in relation to the waterline. The max L/D value at this point is approximately 5.5:1. But this is idealized and assumes a perfect flat surface. Introduce typical environmental issues and realistic hull design values, including things like dead-rise, the max L/D value will most likely be around 4.0:1 or even less. So, for your 3,000 pound craft you will be generating about 750 pounds of drag. Below this trim speed you will be in displacement and/or transition mode and after this point it'll be assumed that your wing will be providing lift thus reducing the weight the hull has to lift.

    Then your dynamic effects come into play - as a rule of thumb, it's a good idea to have a substantial thrust margin at this point so as to avoid porpoising. For the sake of discussion let's round off the thrust required to get off the water to be at about 1,000 pounds. Given your two 40 hp motors with moderately small props, it's doubtful that you'll generate more than about 250 pounds of static thrust, give or take a bit. Maybe with an optimized low pitch prop you can do a hair better, but you'll still be woefully short of the mark.
    It looks like I'll need some PSRUs then, keep in mind the two 40 hp engines are for a more lightly loaded, short wing, shorter range version and direct drive is mainly for first sea trials. The figuring I did suggests that I need at least 150 hp to get even a poor climb rate, which would be acceptable for this since there are so few mountains in the ocean.

    This is how I'm thinking of going at it, in very rough figures:

    First 'flight' attempt:
    1200 lb
    20 ft span
    150 ft wing area
    80 hp w direct drive

    Local cruising in Puget Sound and up behind Vancouver Island:
    2000 lb
    20 ft span
    150 ft area
    80 hp w PSRU (might need more hp)

    Going to Hawaii:
    3000 lb
    40 ft span
    250 ft wing area
    160 - 200 - 250 hp w PSRU

    Thank you for the planing boat L/D figures, that helps. One thing I wonder about is the ideal planing angle - are you pretty sure that the ideal angle is 5 degrees? Previously, and over a decade ago, I had read that the ideal angle is 10 degrees. Possible 5 to 10 is close and is the ideal range? 10 degrees though would mean a little bit less wetted area in a hypothetical ideal situation.

    I'll get back to the rest.

    I just edited the title to include the word 'boat' so expect a whole new bunch of lurkers here. =)
    Last edited by Starman; May 24th, 2010 at 11:54 AM.

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    Super Moderator orion's Avatar
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    Re: Wing in ground effect boat

    The ideal planing angle usually resides between 4.5 and 5.5 degrees. Yes, there is some variance as a function of Froude Number and finesse ratio but for a conventional hull, that's about it. Beyond that the drag rise is fairly substantial. Also keep in mind that the hull imposed trim angle will initially be much higher as you approach the planing speed so the actual amount thrust you'll need is dramatically greater.
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    Registered User Starman's Avatar
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    Re: Wing in ground effect

    Orion, I'll respond to your other statements here without quoting all of them.

    I got the 250% efficiency increase from the website I linked to, and I didn't believe that it's possible in a real world situation. Maybe it is possible on smooth water at very low h/c where the air under the wing completely stagnates and generates a full pressure recovery. In any case, when I figured the range I assumed no efficiency increase due to WIGE just to be on the safe side.
    On a smaller vehicle like the failed Flarecraft you will then have a tendency to overpower the craft, which can greatly destabilize the vehicle (long story here and not a very pretty one).
    I'm aware of the excess power situation that WIGs have, but could you state briefly what the source of the destabilization is when overpowered. High thrust line?

    The difficult task in designing a WIG is simply that there is not enough reliable information out there to do a good job of it. If you're designing a plane there is tons of data, text books and reference papers that you can dig through to get just about anything you need. For WIGs there is virtually nothing. I've been doing WIG development consulting for over about fifteen years now so I've seen most of the programs in the Western hemisphere. Some have potential and some are downright scams but all have the same issues - not enough data and not enough money to do it right.
    I've had my eye on WIGs for about 25 years now and it seems there are plenty of them that have acceptable functionality. I have no desire to start a company and sell these, it's just for me, and so no scamming. In any case scamming is against my nature and ethics is very important to me due to my 'situation' Here's something I wrote about ethics on my website: The Way of the Immortal - Ethics

    The idea that there isn't a lot of design info is fine with me because I like seat of the pants designing and going into the unknown appeals to me a lot. I'll build scale models of this craft before cutting too much metal.

    I'm curious though about this website The WIG Page - information about Ekranoplan and Wing-In-Ground effect craft that I linked to earlier, which is a clearing house for the latest WIG design info. They require a fairly substantial membership payment to access the info. Have you heard of them and/or are you a member of it?

    I don't mind ambitious projects, and I like the challenge so don't concern yourself with disheartening me =)

    It's too bad that the Flightship was the victim of more scamming and went under as it looked very good to me.

    Also, keep in mind that with the longer wings this vehicle is intended to be an actual 100% aircraft (amphibian) able to fly out of ground effect - with a lifting tail.

    Now I need to find out how to make a good model that is waterproof, I suppose balsa wood doesn't fill the bill.

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