Mydauphin,
Some of what you are saying is incorrect.
The Spruce Goose was not designed to only fly within ground effect. The fact that it never got over 70 feet was more of a political decision than a technical failure.
The thing which makes a WIG into a WIG is wing loading. A short, stubby wing with very long chord is a good thing in a WIG, and a bad thing in an airplane. Once you start to escape ground effect, the wing losses cause the WIG to descend again.
There is a lot of very good, interesting reading on
http://www.se-technology.com about what a good WIG is all about, and why it can reasonably fly in ground effect when it's dangerous to fly a regular plane in that space. They can say it much better and more concisely than I ever could, and that's where I learned it anyway.
I have mentioned my UH-18sp hovercraft before, which can be easily converted into a UH-18spw wing in ground effect. I want to contrast this device with a purpose-built WIG.
A purpose-built WIG is designed to take off at a relatively low speed and then accelerate to a much faster speed while never being able to stay out of ground effect, and to do so very economically. Take-off power is generally a lot higher than cruising power.
On the other hand, a UH-18spw is NOT a purpose-built WIG. It is a hovercraft to which you can attach a wing and fly around in ground effect. It is less efficient as a WIG than it is as a hovercraft, which according to the se-technology guys is wrong. The UH-18spw takes off at around 55 mph and then cruises at 60 or so. It holds less payload in WIG mode, has less range and it flies in a much nose-up attitude. All of that seriously irritates any WIG purist.
A UH-18spw can't fly out of ground effect for long even if it has power, because its wings have no dihedral and there is no aileron to prevent it from rolling over. When in ground effect, the nature of ground effect gives more lift to the lower wing and so it is self-righting. When built per plan, they don't have power to escape ground effect for long. They would be a class B WIG by that definition.
There are two groups of WIG people: The academic purists, who hang out on se-technology and the associated forum, and there are the practical WIG people, who just want to go out and fly. The purists have regular arguments about whether a UH-18spw is really a WIG or not because the speed and efficiency do not match the WIG expectations. However, the main critical property of a WIG is there, so in my book it's a real WIG even if it's not a very good one.
The se-technology guys keep insisting that there are no WIGs you can get in the private sector, even though the UH-18spw was listed last time I checked and I know several people who have the WIG version working.
Finally, back to the last point of argument with your post.
IMO, the reason that there are no commercially viable WIGs in use is not because of a lack of stability. That may or may not be there, it's a topic of discussion on the se-technology forum. The real reason though, is that whatever you can load onto a WIG and carry can easily be loaded into a 747 and flown there faster, safer and more reliably. And for less money. Per ton mile, a 747 is more efficient than any WIG which has ever been constructed. They get there by flying high and fast, rather than low and fast. There are no boats or birds or anything to hit, so it's safe. They go in a straight line, so it's fast. They land at airports, so the normal shipping trucks already go there.
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