Seeking Ground Effect Craft Info

[CoryLunn]

Hi,

I am trying to gather all the information I can on ground effect vehicles. Although they have a lot in common with aircraft they are in fact also boats that spend much of their time on the water, so I'm reaching out to the community of experts here on boatdesign.net

I'm working on a project to build a ground effect wing that a rider can stand on while being towed behind a boat. Although a flying wake board might sound absurd, I have a lot of experience designing and building strange craft as well as riding hydrofoils and other towables, and I strongly believe it is possible.

I'm looking for any info on vessels that can fly in ground effect. I'm especially seeking any small, home made type craft. I really would like to find pictures and videos of any that are out there.

Also of particular interest are the specific wing foil shapes used, the construction methods, and the performance (weight, speed, range, hp, etc.).

If anybody has any pictures, links, or info that would help, please send it my way!

If you are interested in seeing the project I'm working on, and discussing the design and offering constructive criticism, check out the link here:

https://www.kickstarter.com/projects/405387784/the-wake-wingtm?ref=category

Thanks in advance for all the help from all the very knowledgeable people on this forum!

 

[cmckesson]

Ekranoplans

I don't have them here at my home (they're at work) but you might look for Kiril Rhozdesventsky's name as author. In addition, Yun and Bliault recently added a WIG book to their series on AMVs. Check Amazon for that one.

 

[rwatson]

For starters, feel free to search for WIG and ground effect on this site. There are heaps of references and information.

Please dont take offense at my direct comments, I just put it down as I see it, without spending hours padding in positive points.

Given the problems of low flying 'craft', can I put up my 'guesstimate' hand, and state and declare that a stand on, towable WIG is a non starter.

Your graphics shows no towing harness, and given the complexity of the nearest activity, Sailboarding, that us going to be your major issue. This is especially a problem with no tailplane for directional stability on a towed vehicle. Having been at the end of many glider launches at the end of a tow plane, I have had some experience.

Likewise, the amount of wing you have to support a body, is inadequate, when compared to any other lifting device. This is especially pertinent given you have built in positive Dihedral in your pictures, the exact opposite of most WIG configurations designed to entrap as much airflow as possible.

By all means, feel free to spend the backers money proving I am wrong, but the absence of any computations or towing system details is a sure indication of no real chance of success.

But - dreams are free. Good luck

 

[CoryLunn]

rwatson,

Thanks for the info and comments. I would like to share some features that I see differently from you, and hear some more of your feedback and thoughts.

Having no harness is essential for the safety of the device. To have either the rider or board attached to the ski rope would be dangerous during a fall. Also, I think wake boarding, and especially foilboarding is a closer sport than windsurfing.

You mention that it has no tail plane. I have utmost respect for you as a glider pilot as I know they can be tricky and require lots of skill to fly well. The design we are talking about has two large vertical tail surfaces, but no horizontal stabilizer. The two tails should provide could directional control, especially when they are trailing in the water. Without the horizontal stabilizer to control pitch the rider would have to shift his weight between his front and back foot. I'm not sure if this is possible but I have ridden foilboards that require similar 3 dimensional control in flight above the water: https://www.youtube.com/watch?v=xaVbsgpjIpw

The wing size is intentionally small because it is only supposed to fly in ground effect and never get higher than a few feet. I have seen ground effect craft with very small wings that seem to work even at low speeds such as the hoverwing.

The positive dihedral seems necessary to me in order for the wing to be able to turn safely in flight. The large winglets might compensate slightly for the lift lost due to dihedral.

The wing has a little over 40 square feet of surface area. That means it needs to generate about seven pounds of lift per square foot, which should be possible in ground effect at those speeds.

I hope I haven't been rude. I would genuinely like to hear your opinion about each of these factors and I sincerely appreciate the time and effort you took to respond to me!

 

[rwatson]

.....

Having no harness is essential for the safety of the device. To have either the rider or board attached to the ski rope would be dangerous during a fall. Also, I think wake boarding, and especially foilboarding is a closer sport than windsurfing.

Thats even worse. Ground effect flying is very sensitive to angle of attack. Its nothing like wakeboarding - the differences between air and water are HUGE.

trying to accomplish this with body balance is not practical at all IMHO

The wing size is intentionally small because it is only supposed to fly in ground effect and never get higher than a few feet. I have seen ground effect craft with very small wings that seem to work even at low speeds such as the hoverwing..

Where is the Math ! This should have been done even before the build. Without the calculations, all the promises in your begging page are just fantasy.

The positive dihedral seems necessary to me in order for the wing to be able to turn safely in flight. The large winglets might compensate slightly for the lift lost due to dihedral..

yes, for maneuvering, positive dihedral is essential - but it totally destroys any ground effect. Imagine losing half of your lift at 30mph at 4 feet. Thats what you are looking at.

The wing has a little over 40 square feet of surface area. That means it needs to generate about seven pounds of lift per square foot, which should be possible in ground effect at those speeds.

Opinion is irrelevant. If you don't have the math skills to work it out, you are wasting your time.

Also, WIG vehicles also utilise lift over the wing, as well as pressure gradients under the wing, and they dont have a pair of feet mucking up the airflow.

But even so, keeping the pressure under the wing will be impossible with this configuration.

I hope I haven't been rude. I would genuinely like to hear your opinion about each of these factors and I sincerely appreciate the time and effort you took to respond to me!

No, I know typing isnt the easiest communication for tact, but its the facts that are critical.

 

[CoryLunn]

The wing actually has almost exactly 43 square feet of surface area (12ftx4ft minus the sweep of the wing). The wing will weigh about 50lbs and carry up to a 250lb rider. That equals 300lbs that the wing needs to lift. 300/43=6.97. So the wing needs to generate 6.97lbs of lift per square foot. Hang gliders routinely fly with as little as 4.5lbs per square foot as slow as 20mph and small Cessnas generate about 10lbs. A piper cub with a Clark-Y airfoil has a wing loading of 6.84lbs per square foot.

Those numbers indicate to me that even if it used the good old Clark-Y airfoil it should fly.

I still agree with you that control may be a serious issue that may be difficult to resolve. Do you think it's possible to find a solution? Any ideas?

 

[Leo Lazauskas]

Here are three references to start you off...
(Chris's suggestion of Rhozdesventsky is a good one, but he started
with help from E.O. Tuck).

If you can't handle the simpler formulations, you might struggle with
the more advanced work...

Newman J.N.,
Analysis of small-aspect-ratio lifting surfaces in ground effect,
J. Fluid Mechanics,
Vol. 117, 1982, pp. 305-314.

Widnall, S. and Barrows, T.M.,
An analytic solution for two- and three-dimensional wings in ground
effect, J. Fluid Mech., 1970, pp. Vol. 41, pp. 769-792.

Tuck, E.O.,
Non-linear extreme ground effect on thin wings of arbitrary aspect
ratio, J. Fluid Mech., Vol. 136, 1983, pp. 73-84.

 

[CoryLunn]

Thanks Leo!

I'll see if the math is too advanced. I appreciate the references.

 

[FAST FRED]

The space tyou fly is about 1/2 the wing span above the water.

Thats why the Russian attempt was so huge!!!

 

[rxcomposite]

Thats even worse. Ground effect flying is very sensitive to angle of attack. Its nothing like wakeboarding - the differences between air and water are HUGE.

trying to accomplish this with body balance is not practical at all IMHO

yes, for maneuvering, positive dihedral is essential - but it totally destroys any ground effect. Imagine losing half of your lift at 30mph at 4 feet. Thats what you are looking at.QUOTE]

I agree with you. Flying wing is very sensitive to angle of attack and location of center of gravity. The first flying wing is unstable. Even by todays flying wing standard, it is still unstable. Fast acting computers control the airplane.

Airplane type wing needs longitudinal control and is served by elevators located far aft.

The Lippisch design is much more stable longitudinaly but still needs elevator. And if remember it right, Lippisch design has a lift of 64 lbs. per square foot.

 

[CoryLunn]

Fast Fred,

I'm not sure if you are trying to tell me that my design will be a problem because it needs to be so close to the ground? If so, I believe that is part of the reason it's safer than other flying towables. I've read that ground effect is most effective when the wing is within 25% of the length of the chord of the wing from the ground.

I sincerely appreciate the constructive criticism, (if it's constructive) I'm receiving from everyone but what I'm really looking for is pictures and video and detailed info on real WIG craft that have already been built and are working.

 

[rxcomposite]

I sincerely appreciate the constructive criticism, (if it's constructive) I'm receiving from everyone but what I'm really looking for is pictures and video and detailed info on real WIG craft that have already been built and are working.

Here.
http://www.academia.edu/461506/Anal...tions_for_a_Commercial_WIG_Craft_based_on_CFD

 

[CoryLunn]

rxcomposite,

I'm sorry, but I believe balancing by shifting body weight is possible. I have a lot of experience on foilboards and I don't think flying in the air should be any harder than riding a foilboard, maybe even easier. The foilboard travels through water, a MUCH denser medium than air, and requires extremely fast responses from the rider to "stay ahead of the curve".

The positive dihedral may sacrifice some ground effect lift at low angles of attack and as it gains altitude. That shouldn't be a problem because at high angles of attack (low speeds) and low altitude, the raised wing tips will actually rock back and get closer to the water, restoring ground effect when you need it most. I think it's a good thing to rapidly lose the ground effect boost as speed increases or altitude increases, thereby restricting the wing to VERY low flight. Also, lift wont be suddenly lost at 4 feet. It will rapidly diminish as the wing tries to climb above 4 feet, which is desired.

You're right, most modern flying wings are very unstable. However, there are thousands of flying wings working everyday without computers or moving parts. Hang gliders are simple, high lift, low speed devices that maneuver using weight shift, and they work especially well in ground effect when landing or ridge running. My design is clearly not a hang glider, I'm just pointing out that it IS possible to create a controllable flying wing.

You say it needs longitudinal control with elevators aft. I'm assuming you mean pitch control? Again, I believe this will be possible with weight shift and handle movement as I've shown with foilboards: https://www.youtube.com/watch?v=xaVbsgpjIpw

If the lippisch design required 64 lbs. per square foot then it needs to fly at much higher speeds than what I'm trying to achieve. My goal is very low speed flight, close to the water only.

 

[CoryLunn]

rxcomposite,

Thanks for the link. After briefly scanning it, I see a lot of helpful information, especially on the shifting center of lift as angle of attack increases. The Lippisch design has many advantage in this respect, but it's not the only factor I have to consider in my design.

I really do appreciate the helpful info! I'm still looking for pictures, video, and details of actual craft that have been built.

 

[Leo Lazauskas]

rxcomposite,

Thanks for the link. After briefly scanning it, I see a lot of helpful information, especially on the shifting center of lift as angle of attack increases. The Lippisch design has many advantage in this respect, but it's not the only factor I have to consider in my design.

I really do appreciate the helpful info! I'm still looking for pictures, video, and details of actual craft that have been built.

I found a lot of images by googling for "ground effect vehicle".
Or were you after something different?