CoolIP index                                                          Most recent edit: Wednesday October 24, 2012

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Advanced Tarpaulin Kites (Megascale Rope-Loadpath Method)

Simple Tarp-Kites rigged as playsails, have the greatest COTS power-to-cost performance; but also shortcomings, like the crudeness of playsail wing geometry, and short service life of an overworked tarpaulin. Better tarp soft-kite designs are a wonderful breakthrough. Few AWES engineering challenges will be so rewarding as perfecting these tarp-kite platforms. What is cooler than a cheap low-tech mega-kite of decent geometry and robustness?

The New KiteLab megascale tarp-kite method is to first create a large rope-loadpath structure in a desirable kite geometry (like KiteShip's OL), and hank the many tarps into place between the loadpaths. This way each tarp only experiences its local loading and the loadpaths carry the big accumulated loads. A large powerful Kite-Arch can be made by running a row of tarps along two or three ganglines, like a constrained laundry line (ease the leech-line to tune for high lift). The really great thing about the megascale loadpath method is that the essential "tailoring" of the wing is merely in the length of the cords: A kit can thus consist of just a box of tarps and a set of cords cut to the right dimensions.

CoolIP*                      ~Dave Santos                 10Feb2012                     AWES5603

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  • Notes:

    A key to to large tarp kites is to control luffing by any suitable combination of the common methods.

    KitLab's favorite stability method is to fly the kite "staked out" by an anchor circle, and belay it around to match the prevailing wind.

    Telone is Italian, and Manta, Spanish, for Tarpaulin (AWES news hint).

    UV resistant tarps with cordage sewn in all around the edge are best. Some high-duty tarps have a sewn-in diagonal belting (webbing), for reinforcement. A similar advantage is by setting a rope X across the tarp to windward, allowing the tarp to billow away from the rope. Alternatively, one can let the sail rest against the rope X (belting best), as long as the shape is acceptable and friction does not cause premature wear. An ancient method is to back up a cheap tarp with a thin plastic netting, as a sort of primitive rip-stop. In fact "stone-age" Maylay style leaf kites use a handmade netting to backup a fragile fabric of tiled leaves.

    All sorts of tricks are useful. One can "tailor" a tarp with tucks and gathers secured by skewers, tapes, and glues to avoid sewing. Tie-offs can be made anywhere on the tarp with just string and small wood "pebbles" tucked in the fabric. Grommets are cheap and easy to use. For gust compliance, elastic lines can be set to the leech (trailing edge) of a tarp, even just using smaller stretchy nylon cordage in conjunction with low stretch polyester rope run to the luff (leading edge).

    KiteLab has built and flown large scrap-kites (made from old tents) that fly shoulder to shoulder with commercial wings. Every year, my old friends (Ortiz/Renteria Kite Kartel) in Austin build a giant kite in half a day from just bamboo and used construction plastic, to usually win the "largest home-made kite" category at the local kite festival. Bamboo kites >100sqm are part of active traditions, from India and Japan to Guatemala. Traditional designs would fly just as well with tarp sails as they do with paper and cloth.

    The largest stock tarps run as large as 10,000sqft; thats far beyond bamboo scaling. The only way to use such a tarp and expect it to last a while is with a full loadpath netting behind it. The advantage of such a monster tarp is in light winds, by its lower weight (by area) and porosity compared to open tilings of smaller tarps (suited for higher winds).

    A flat floppy rectangle requires some cleverness to make into a great wing. The playsail rig pulls hard, but flies with high drag at a low angle and is prone to luff. A general notion is to modify the flatness with a pleating that sets a good chord-wise curve while pressurizing the billows.

    There are endless other tarp variations to discover and test. The design language should be elemental, or one might as well use raw fabric. KiteShip's OL or NPW (NASA Power Wing) are good models for Tarp Kites: If you can get tarps to fly comparably or better, that's awesome.

    An basic design is a "staked out" rectangular tarp gathered along the leading edge to shorten it, creating a delta plan-form with a suitable chord-wise curvature. A powerful kite arch might consist primarily of tarps rigged into a composite ribbon-arch, with the required longer trailing-edge as a natural feature, and the tarps able to furl by draw-lines, just like curtains draw open.

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    The modern poly tarp is incredibly cheap, as little as a dime per square foot for medium duty UV resistant versions with sewn rope borders and grommets every two feet or so. Value-priced kites run ten times higher by the square foot, mostly as a reflection of lower volume production by higher skilled workers. Quality rigid wings run almost one thousand times the cost of the common tarp, by area. This is why Dave Culp pondered if there was not some way to use tarps for kite energy; the "Village Blue Tarp" AWES concept.
    Anyone who depends on tarps as canopies knows that the larger sizes are more vulnerable to blow-out by the concentration of far higher forces. Strangely, tarp prices seem flat across their size ranges, for a given fabric weight, so one can buy a box of many smaller tarps at a comparable price to one larger tarp. The small tarp formats that sell as many as thirty to a box are very easy to individually manage and can be aggregated by setting in a large rope load-path network, a minimal surface with about 30% projected solidity. Furling of the networked kites could be as simple as pulling lines on window blinds. Cheap tarps do require early replacement, but the UV protection that allows a five-year warranty life promises a year or two in AWES service.
    The 1500ft or so of tarp to a 150 dollar box is enough lift in a medium breeze to lift about five hundred pounds at low wing-loading. One could lift an adapted 10-50kw HAWT and hundreds of feet of conductor with this amount of wing. A "lift-ready" HAWT payload might look like an airboat rotor on a sleigh-runner. Such a freaky turbine can win by reaching far better wind than a HAWT tower can. One can also imagine lounging aloft under a tarp array like royalty on-the-cheap, the lowest-cost human aviation of all, persistent and renewable.
    Cheap pioneering DIY sky-sailing methods are only workable by considerable rigging and piloting skills; they are the opposite of wishful AWES where one merely flips an On switch and walks away. Endless novel experiments in rigging are possible, and the end result may be highly refined purpose-built AWES wing arrays.

    An 1873 French magazine sketch depicts an unattributed South American kite lifting design with three taglines managing a heavy load bag. The kite itself is a large framed rectangle with elaborate eddy flap and rear bridle pennants. Two side pullers hauled on the wing while a third puller had a tag line to the load.
    A. M. Clark in 1875 patented what is obviously a PlaySail, a simple rectangular tarp with taglines spreading from it to four pullers, and a payload suspended under the sail. Clive rashly opines that this is "impracticable"; luckily no one told that to those Nebraska kids on YTube ("The Furry [sic] of the Wind"), who totally rocked.

    The classic tarp-flying video: 
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