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Kite Anchor Geology, Soil Kites, Design Issues

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  • dave santos
    Anchoring is a major AWE requirement. This post describes how powerful kites are securely moored for safety, reliability, & performance, at minimal cost.  
    Message 1 of 1 , Aug 10, 2009
      Anchoring is a major AWE requirement. This post describes how powerful kites are securely moored for safety, reliability, & performance, at minimal cost.
       
      Fabric Sand Anchors hold tons of pull with ounces of material & can be scaled up. David Gomberg sells a low cost version. Peter Lynn is a proponent. One can improvise a sand anchor by knotting & tethering the corners of suitable canvas. Adding an apex retrieval line can be helpful.
       
      Soil Kites are close analogues to Sky Kites, despite soil's thousand-fold or greater density. The holding power of a tiny soil kite "flying upside down" deep in good soil is impressive. A soil kite may actually dive deeper with increased pull.  Boat anchors suited to soft bottoms, like the Danforth, are soil kites, but generally unsuited to land kites; Lynn points out that a dragging sand anchor is safer than a runaway "hook" when things go wild. The potential is real for super kites to pull down buildings & create mayhem plowing across highways.
       
      Soil viscosity ranges from slurry to broken rock. Under stress soil begins to act as a fluid, so anchors usually fail by leaking soil around edges as flow. Heavier drier more solid soils hold best. Engineering tables crudely predict the holding power of various soils but direct testing & adding a large safety factor is essential. Eight to one is is considered very safe in many structural contexts, but kite surge can be a very extreme peak compared to common dynamic applications.
       
      The life cycle of an anchor is a critical consideration. Hidden galvanic corrosion is a particular hazard to avoid by selecting galvanized & stainless components. Inspection & programmed replacement are long term necessities. Water saturated weakened soil should be presumed even in a dry place. Even earthquake liquefaction may be a design factor.
       
      Powerful soil kites can be made at modest cost with buried steel plates or concrete slabs bridled like kites & attached to the surface with galvanized or stainless wire rope. Delivering a folded or oblique anchor to depth, which then tips crosswise or expands, greatly reduces excavation requirement. "Mud-jacking", pumping concrete under high pressure, or expansion cement around a wire rope clamped or looped in a bore hole creates a "belled" footing & locks into hard soil.
       
      Drilled pins & hooks are suitable for rock anchors. Sea anchors are powerful solutions if downwind creep is acceptable. A "deadman" buried beam or log is soil-kite like & holds well. Stakes are not so good as kite anchors as the pull is generally upward. Spiral stakes like those used for dogs hold better. Kiters use impact wrenches to set large versions. Plants are sometimes used as living anchors. Hobby kiters even tie off on tufts of grass. Trees have an easily hurt living layer under the bark to protect by belting.
       
      A kite anchor has associated connector hardware such as an eye, ring, carabiner, or shackle. Often smaller fittings are ganged on a larger one. Rigging Plates have a set of holes to organize multiple fittings. Quick release hardware, Kite Killers, are a good precaution to douse a berserk kite.
       
      Anchoring situations demand flexibility. A complex anchor field in varied geology will need multiple solutions. Some anchors may be mere dead-weights & even be designed to drag in a peak event allowing other failsafe anchors act as kite killers. Small water or sandbags may even operate dynamically in "teabag" mode as downwind drogues.
       
      The world's top Kite Geologist, a pro soil kiter pro, BobL, is helping KiteLab determine best AWE practice. Ask KiteLab about your particular Kite Geology challenges ;^)
       
       
       
       
       
       
       
       

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