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orion

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Skis may work better but again, it's not as straight forwad as one might think. It's actually what we selected for one of our current developments however tow testing (models) has so far not been all that successful. The next tow test will be next week so I'm hoping the mods I made will have better luck.
 

Bart

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Couple more thoughts:

Add a chine or somesuch to the bottom of the kayak, to give it a step and/or aeration capacity. This would also stiffen it. A variation on that theme would be aerator vents on the bottom of the kayak hull, so when it goes through the water, venturi effect draws air into the flow, so the thing rides on seafoam which is a lot more slippery than just water. Add-on sawtooth bottom of foam/fiberglass would be an option.

Or, just use one of those prefab ultralight floats, perhaps the inflatable type, as the hull. Add wing and empenage + engine/prop.

Spratt controlwing worked pretty well, apparently. Ultralight version should be even easier. Reportedly, such wing absorbs ~90% of gust loads, making it much smoother in rough air. Simplifies control mechanisms, too, since tail feathers are fixed. And, controlwing rotated to negative lift acts as huge speed brake on landing.

BTW, a kayak weighs generally ~25 to ~40 lbs, depending on size, materials, length, etc..


Should be able to make an ultralight controlwing for several hundred lbs. empty weight.
 

ZoomZoom

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Ok, now we have to start talking about crafting some RATO units......:gig:. Hehe, just kidding. By the way, I have seen these blow up raft-craft, with a simple engine and an ultralight or hang glider wing take off and land on the water with a couple of passengers no problem. So is this just a size and weight issue, or are you guys gonna say THAT floppy THING has some kind of helpfull step to get it out of the water easily? Maybe its just light enough to do it?

ZZ.
 

orion

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There's a slightly different issue when using the inflatable dinghies as the flotation hull. It's not really a benefit since the skin friction on those is pretty substantial, but the large displacement capability they have results in a very small amount of volume being displaced. Then, you couple this with a very light wing loading and you end up with a craft that does not depend as much on the hydrodynamic capabilities of the hull - the wing simply starts lifting at a very low speed, extracting the inflatable out of the water before hull drag becomes a too significant an issue.
 

Dana

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One other note - waterborne aircraft do not rotate on take-off....they accelerate at constant attitude until the aircraft flies off the water, at nearly level attitude. This is why I mentioned in a previous post that it is very important to set up the hull and the flight surfaces in a very particular manner or the airplane will simply not fly.
That's interesting; I would have thought that the aircraft could more or less "pivot" on the step, at least to a small extent. But I did learn with R/C models years ago that the float angle is critical (as is waterproofing the electronics! :emb:).
By the way, I have seen these blow up raft-craft, with a simple engine and an ultralight or hang glider wing take off and land on the water with a couple of passengers no problem. So is this just a size and weight issue, or are you guys gonna say THAT floppy THING has some kind of helpfull step to get it out of the water easily?
One advantage those things have is that the pilot can control the pitch of the wing, so that the aircraft can accelerate at zero AOA (and thus low drag), then rotate just the wing to liftoff AOA while the hull stays level.

Some of the very early seaplanes had flat bottom planing hulls, sometimes three (two main floats and a tail float). I'm guessing it worked quite well on calm water but could be problematic in rougher water.

-Dana

Baby oil is NOT made by squeezing dead babies!
 

Topaz

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...Some of the very early seaplanes had flat bottom planing hulls, sometimes three (two main floats and a tail float). I'm guessing it worked quite well on calm water but could be problematic in rougher water.
Actually, if memory serves from some accounts I've read, exactly the opposite was the case. On very smooth water, the 'downward lift' effect on the bottom of the floats that Orion described above could keep them from lifting off at all. On rougher water (to a point), the natural effect of the waves and troughs breaking the 'suction' could help them get airborne.

I've seen photos of early floats modified with a series of wedge-like steps added along their length after initial trials, in order to defeat the 'downward lift.' Early float design was somewhat empirical. ;)
 
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Dana

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Actually, if memory serves from some accounts I've read, exactly the opposite was the case. On very smooth water, the 'downward lift' effect on the bottom of the floats that Orion described above could keep them from lifting off at all. On rougher water (to a point), the natural effect of the waves and troughs breaking the 'suction' could help them get airborne.
You may well be right; nobody seems to be making floats like that today.

Smooth water is hard to get off from; I've heard of pilots having trouble getting airborne, then fast taxiing around the lake a few times to make some waves, then being able to take off.

-Dana

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Be careful while bending the law.....
 

lr27

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Yup. I've seen a guy do that with a low powered Taylorcraft. All that spinning around must have addled his brain, because I also saw him do about 6 turn spins, using up about 3/4 (maybe it was only half, was a long time ago) of his altitude. 6 turn spins with a floatplane! At least I think it was the same guy.

Come to think of it, that location must have been bad for pilots brains, because the seaplane I saw there also did stupid things.
 

Dana

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Eeek... I don't know how a T-Craft on floats would spin. Without floats, though, it's a joy to spin... spins like a top and recovers just as easily. I once did a 15 turn spin in mine; another time, back in my young and foolish days, I got caught on top of the clouds with no holes and no gyro instruments-- I had a turn needle but it was broken-- so I spun down through the overcast (I knew the ceiling was high enough below for a recovery, which didn't take much).

-Dana

Help, I've fallen up and I can't get down!
 

JMillar

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32ft / sec^2 (or 9.8m/s^2 for us metric people) is true, but that's down. Are your airfoils pointed down? Can you pull up in time? You might have been better off in dingy going over that waterfall :D
 

orion

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Built by trial and arror and considered by most to be an accident waiting to happen.

A similar project by another experimenter has been discontinued shortly after an uncontrolled event scared the cr___ out of the builder.
 

Topaz

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Just out of curiosity, what are the pilot certification requirements for WiG's? It doesn't look like this one can leave ground-effect, but it's still 'flying' in that it is wing-borne, rather than a pure air-cushion vehicle.

Their website is claiming that you don't need a pilot's license to fly it, yet this is hardly an 'ultralight' in the Part 103 sense.
 

orion

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The first two classifications of WIGs are considered marine vehicles and as such, fall under Coast Guard regulations. You therefore do not need a license to operate one as long as it is a pleasure craft.

If however the WIG was able to fly for extended periods out of ground effect, then it would become an airplane and fall under the web of FAA authority, at which point you would need all the typical licenses and ratings.

But here's the interesting part - there is no actual definition of WIG height limits. Here in the US we generally consider the WIG operating envelope to be at under 50 feet - over that limit and the FAA takes over. In other parts of the world though that limit is 300 feet and there is some pressure to redefine it here.

The problem with all this is that the ground effect for small craft is in the range of about a foot or two (function of span and chord). If the craft is capable of operating above that height for extended periods of time then it technically is an airplane. But then the question is whether it is still an airplane if it operates less than 50' off the water.

Although several years ago the Coast Guard was working on these issues I don't think the gray areas were ever firmly defined. But then WIG development has virtually disappeared so the subject, for now, may be moot.
 
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