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Tinbuzzard

Here is a real weirdie that actually flew! These photos were passed on to me by an airport bum aquaintance who is chock full of really good aviation lore. (He worked for Howard Hughes for a time and also pounded fairings and drove rivets on the P-51 prototype)

Time: 1952. Location: Anchorage, Alaska. Power: McCullogh drone engine.
Why: God only knows.

It made at least one runway flight of several hundred feet with no turns reported. The front rudder behind the engine nacelle was movable and may have controlled roll in conjunction with the vanes along the sides. I don't know if the vanes moved, or acted as slots on a very low aspect ratio surface. Sometimes human... er, aah, cough..... ingenuity is amazing!
 

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orion

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I've actually seen similar attempts years ago. If it is along the lame lines of thought, essentially this is a flying life raft. The narrow span allows it to be stored easily but at the same time it has lots of area so amazingly enough the induced drag is not all that bad.

You want to go fishing? Just drop this in the water or at an airport, take off and fly to your favorite fishing hole and land.

On this one though the undercarriage would have to drop off for that to work. Interesting he got it to fly with what looks like quite a bit of anhedral.

Good for him!
 

apogee

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Is this one of those flying above water things which fly on a cushion of air? The Russians used to build huge ones. The 'Caspian sea monster' as the US called it was huge.
 

orion

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Good question but no, it doesn't look like it's intended to fly as a WIG (Wing In Ground-effect), although it probably could. And BTW, WIGs don't really fly on a cusion of air - they fly in a very narrow operational envelope where they gain benefit by being in close proximity to the surface, the net result being a slight lift advatage due to the shifting of the wing's lift curve and a reduction of induced drag.
 

Bart

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Barny Wainfan, in an early article about his Facetmobile, mentioned some early (1930s?) NACA studies on very low aspect ratio aircraft. It seems that as aspect ratio decreases, wing efficiency decreases...to a point, then improves at even lower aspect ratio. This apparently because the vortex from each tip, as it rolls up, is countered or opposed by the vortex from the other wing. Low aspect ratio wings would have all sorts of advantages and weight savings. An inflatable plane would be a lot easier, with transport and storage as major benefits.
 

ZoomZoom

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:grin: This is moving towards my secret kayak with a wing attached design concept!! What a great floatplane! Get the lightest onepiece glass or plastic kayak you can find. Add your wing and motor up front with some ply internal bracing. Get a rudder and elevator in the rear and your set to go floatplaning!!:shock: Might have to be a two placer to get the balance right though!:gig:

ZZ.
 

Bart

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:grin: This is moving towards my secret kayak with a wing attached design concept!! What a great floatplane! Get the lightest onepiece glass or plastic kayak you can find. Add your wing and motor up front with some ply internal bracing. Get a rudder and elevator in the rear and your set to go floatplaning!!:shock: Might have to be a two placer to get the balance right though!:gig:

ZZ.
That's what I've been thinking about for quite some time: Off the shelf kayak, add ultralight empenage and bolt-on wing, windscreen, plus small pusher engine, and go flying! I have a couple of Tupperware store-bought kayaks at ~35 lbs. each. You can whack them on rocks with no prolemo. Eddyline makes their kayaks out of thermoformed stuff called Carbonlite, which seems like some sort of colored polycarbonate. Anyway, I have a sample of the stuff, and you can hit it repeatedly with a hammer and it won't penetrate. Could be very good stuff for homebuilt airplane uses.
 

ZoomZoom

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Wow, who knew so many creative/warped minds were thinking along these lines. Sounds like we need to start a new thread!;) Im curious as to the weight of these kayaks, as this ties in with the viability of the idea. My concept would be with a fixed foam composite wing that bolts onto the added internal framing of the kayak(wi/tractor motor config)., but each of these sounds like a cool concept! The tow idea sounds kinda like the german auto-gyro that they used on U-boats to spot convoys! Anyway....cool ideas guys!:grin:

ZZ.
 
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ZoomZoom

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Thats an interesting point Topaz, and one which crossed my mind as well. You're obviously brighter than me cause I just ignored it and moved on...hehe.:gig: Perhaps someone here who knows a bit more about the dynamics of floatplanes may chime in with some helpfull advice. I have a feeling though, that if the craft is kept light enough,(this is a pretty tiny...ie kayak sized bird), that although a step might help, it might not be necessary to get something so small and light to break with the water and get airborne. Anyone else have any wisdom?

ZZ.:whistle:
 

orion

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Well, it might actually be harder than you think but like with most things, the specifics depend on a number of variables. To start with, the typical kayak is essentially designed as what's called a displacement hull. In other words the shape of the hull is more like that of a sailboat more than anything else. These hull shapes are very efficient for the speed they were designed for (referred to as "hull speed") but any attempt to go faster results in a very rapid drag rise. For instance, a standard sailboat may be very efficient at eight to ten knots but most likely can't go too much faster without substantial modification or increase in power. But even that has its limits since the drag curve is so steep - while the boat sails well at ten knots, it might take 500 or more horsepower to go twenty.

The second issue to keep in mind, which is actually coincident with the above, is the fact that a displacement hull is essentially an airfoil turned upside down. Thus, the faster you go the more negative lift you will generate. This lift will exceed than the hulls buoyancy quite quickly and it may actually suck the hull under water.

But there are exceptions. One type of hull that might have limited application is called wave-piercing. It is essentially a very long but narrow shape, best illustrated maybe by something like a hull used by the Hobie-Cat catamaran. These shapes have a much higher "hull speed" and could potentially have application in a light craft such as you are describing.

But like Topaz indicated, the best solution is something like a stepped hull. Unlike a sailboat hull, this design is configured to slide on top of the surface much like you see in ski boats and other high speed marine craft. The purpose of the step is essentially to kill the aforementioned lift due to the hull's shape, thus acting sort of like a spoiler on a wing. As you accelerate, the step allows the fore part of the hull to plane on top of the surface and the aft part of the hull (which you need for flotation), to be totally separated due to the aeration caused by the step.

But the design of a sea plane of any sort is a rather complicated mixture of variables. For instance, a planing hull requires only a very narrow range of angle of attack for maximum lift-to-drag performance. In reference to the keel line, this angle is in the neighborhood of five degrees.

Now, to this number you have to properly set your wing angle so that the airplane flies just at the right point, lifting the craft out of the water. The speed of the planing hull must be matched to the wing performance if this is to work right. If the incidence is too low the wing will not develop sufficient lift until you reach a very high speed, which may not be possible since the drag rise even on a planing hull is pretty steep.

You also need a fairly high amount of static thrust. Your best lift-to-drag ratio during takeoff will be about 3.5:1, although if not optimized the number can easily be substantially lower. Another thing that might cut this number down is an improper hull design for the very low speed spectrum, forcing the craft to deal with a large magnitude of "hump drag" where the hull has to first overcome its own bow wave before it starts planing.

Now all of this is the "ideal" case. There's nothing that says that you can't play around with this through trial and error. Who knows, you might hit upon just the right combination of variables that might allow you to get off the surface. All I'm trying to point out here is that it's not as easy as it sounds. I am going through just this exercises right now and even with expert help, my first hull shape had just a bit too much curvature in the aft body which resulted in less than desirable performance. On to model number three......
 

Topaz

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Brighter? Nah. I just read a lot. And I stayed at a Holiday Inn last night. ;)

I imagine reshaping the forebody of a kayak with foam and glass and, in the process, adding a shallow step wouldn't be the end of the world, both from a construction standpoint and from its usability as a paddled boat, either. Probably wouldn't be anywhere near optimal for getting off the water, but it might be better than a plain hull, for all the reasons Orion pointed out.

'Course, at that point, might as well make a new hull from scratch, and that leads you back into seaplane hull design...

This is why I never build anything... -sigh-
 

Topaz

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BTW guys - Just this weekend saw one of the two Martin Mars flying boats in existence, converted to a water bomber, take off from Lake Elsinore and go 'round the pattern. AWESOME sight!!!!!!
 

ZoomZoom

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All good points!! Well rounded and fully addressed. Wonder if one of the V shaped hulls I've seen on a few of these kayaks would help? Your addition of a foam and glass step suggestion is also a good one Topaz. A lot of questions regarding weight/hull shape and power will continue to go unanswered, that is until someone just builds it.:) Then we'll know for sure. I'll be happy to intellectually assist any brave soul who tries.:whistle: Of course this offer has its limits. hehe

ZZ.
 

orion

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The "V" shape on the kayak is there for better stability and tracking. It however is still a displacement hull and thus will still have a very steep drag rise beyond the designed hull speed.
 

DaveK

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Who would have thought so many people have thought of the same thing!

I passingly thought about it and than rejected it because by the time you add the wing and engine you would be displacing much more weight then the hull was designed to do. Add to this that even with a step the angle between the back edge of the step and the back of the hull would likely prevent you from rotating for takeoff or flaring properly for landing. All your landings would have to be very flat approaches which would limit where you could get into.

The only thing I could come up to fix this would be some form of hydrofoil that you could extend into the water for takeoff and landing. The foil could get you up on "step" pretty quickly and could help ride over chop on the water. Probably some control issues involved, but I looked into it and a Lake anphib was outfitted like this as an experiment many years ago. It apparently worked pretty well.
 

orion

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The application of a hydrofoil to flight vehicles (airplanes and WIGs) has been tried numerous times but usually with marginal or even disastrous consequences. While a lifting surface does have the ability to get you out of the water quickly, the problem it encounters is that regime of operating envelope where it has to transition between being an under water lifting wing and a surface planing ski. In the transition it loses about 50% or its lift, usually resulting in a porpoising motion or simply the craft just falling back onto the surface. To counter the behavior you either need a lot of power to brute force your way past the transition, or it just has to be designed right. Actually, it usually tends to be sort of a combination of both.

The Lake trials did have marginal success but operationally the configuration was determined to be too problematical. There was also a WIG craft that used the foils (X-114) which did work as advertised, until the point where the pilot did not retract them fast enough. The craft touched back onto the surface, buried one foil, and then proceeded to make expensive noises and pieces all over the surface of the water.

One of the biggest operational issues with hydrofoils is simply the stuff that tends to float on top of the surface. One piece of sizable flotsam in the wrong place will simply knock the whole apparatus off the airplane. And if you design it big and strong enough to resist impact, then the weight will most likely work against you too.

One other note - waterborne aircraft do not rotate on take-off. The reason is that the hull needs to be at the optimal angle of attack (keel line in reference to the water line) all the way through lift off. Any significant change of angle and the drag rises quite steeply, resulting in the aircraft settling back down onto the surface. If you look at amphibs and float planes in operation, 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.
 

DaveK

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All good points, Orion. I would imagine that to avoid the transition problem between lifting and a planning foil you would run the plane up to some speed beyond stall speed (wing) with the foil below its maximum lift capability and then rotate to allow the foil to accelerate you up out of the water. Kind of a pop up maneuver that would transition the foil from lifting to completely out of the water in a split second. Probably pretty violent to the structure though. I could see some major problems with landing, especially if you "wheelbarrowed" it in. Any knowledge of using a retractable ski?
 
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