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Low is Beautiful- Altitude & AWE

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  • santos137@yahoo.com
    Model Uncertainty characterized initial AWE research. All kinds of pet schemes emerged & one popular mantra was high altitude wind power, a prejudice based
    Message 1 of 3 , Jun 13 9:54 AM
      Model Uncertainty characterized initial AWE research. All kinds of pet schemes emerged & one popular mantra was "high altitude" wind power, a prejudice based on the greater power higher up the wind gradient with altitude.
       
      Gradually the severity of problems with high altitude AWE became clear. A longer tether is more uncertain, it must be designed heavier for equivalent reliability. Direct control thru a longer tether is sluggish & less reliable due to a greater requirement to anticipate input. Adding actuation aloft adds weight, cost, & failure modes.
       
      Flying higher puts the kites into ever more airspace & greater competition with other aviation. Sure you can high-fly the Sahara or Southern Oceans, but US or European airspace will be dicey. A high flown runaway can cover a lot of ground. You never want to see a monster tether come down on a busy highway or drag a building over. Gaining airworthyness certification will be hard.
       
      A higher kite has greater scope & must be spaced farther from its neighbor. The scope required with height grows faster than the wind speed advantage; bummer! KiteLab's passive-control semi-captive arrays work around this problem, but Makani seems committed to keeping a bunch of non-captive wings clear of each other by active-control.
       
      High flying means visibility is a major issue. One cannot fly in clouds/fog without FAA instrument certifications (IFR capability), a far steeper avionics requirement.
       
      Risky AWE schemes to fly the generator require a heavy conductor tether. Aluminum is the best conductor by price & weight & can even carry considerable loads, but don't heat it up. Required insulation is more weight & drag. Go high & electrical issues compound core uncertainty.
       
      Thus have many AWE startups been chasing their own tail ever higher. Sky WIndPower has languished pining for the stratosphere. Makani has quietly downsized its height ambitions without admitting it ever miscalculated.
       
      Low is Beautiful.
       
      There is a turbulent surface layer that kites must clear but, as Payne pointed out, its only about 50-75 feet in normal winds. Above the surface layer an AWE sweet-zone begins & extends upwards a short ways, then uncertainty issues with height take over. The FAA allows anyone, even children, to fly low mass kite systems in a safe manner up to 150 feet without all the complex expensive restrictions & airworthiness requirements of conventional aviation. That's actually pretty high for an experimenter & there is a lot of power there (a few terrawatts) if you are not too greedy.
       
      Low altitude is the Bunny Slope for AWE where competence can develop & eventually enable practical high altitude methods.

    • christopher carlin
      Dear Dave, I agree. KISS applies particularly in the early days of new technology applications. By the way from some aerospace experience I have a kite at
      Message 2 of 3 , Jun 13 10:29 AM
        Dear Dave,

        I agree. KISS applies particularly in the early days of new technology applications.

        By the way from some aerospace experience I have a kite at 60,000 feet would have the potential if it's tether broke of coming down within a couple hundred mile radius. Could be exciting. Also Aluminum has lousy fatigue properties. Using it as a tether without say Kevlar reinforcement doesn't seem a good idea to me.

        Regards,

        Chris
        On Jun 13, 2009, at 5:54 PM, santos137@... wrote:




        Model Uncertainty characterized initial AWE research. All kinds of pet schemes emerged & one popular mantra was "high altitude" wind power, a prejudice based on the greater power higher up the wind gradient with altitude.
         
        Gradually the severity of problems with high altitude AWE became clear. A longer tether is more uncertain, it must be designed heavier for equivalent reliability. Direct control thru a longer tether is sluggish & less reliable due to a greater requirement to anticipate input. Adding actuation aloft adds weight, cost, & failure modes.
         
        Flying higher puts the kites into ever more airspace & greater competition with other aviation. Sure you can high-fly the Sahara or Southern Oceans, but US or European airspace will be dicey. A high flown runaway can cover a lot of ground. You never want to see a monster tether come down on a busy highway or drag a building over. Gaining airworthyness certification will be hard.
         
        A higher kite has greater scope & must be spaced farther from its neighbor. The scope required with height grows faster than the wind speed advantage; bummer! KiteLab's passive-control semi-captive arrays work around this problem, but Makani seems committed to keeping a bunch of non-captive wings clear of each other by active-control.
         
        High flying means visibility is a major issue. One cannot fly in clouds/fog without FAA instrument certifications (IFR capability), a far steeper avionics requirement.
         
        Risky AWE schemes to fly the generator require a heavy conductor tether. Aluminum is the best conductor by price & weight & can even carry considerable loads, but don't heat it up. Required insulation is more weight & drag. Go high & electrical issues compound core uncertainty.
         
        Thus have many AWE startups been chasing their own tail ever higher. Sky WIndPower has languished pining for the stratosphere. Makani has quietly downsized its height ambitions without admitting it ever miscalculated.
         
        Low is Beautiful.
         
        There is a turbulent surface layer that kites must clear but, as Payne pointed out, its only about 50-75 feet in normal winds. Above the surface layer an AWE sweet-zone begins & extends upwards a short ways, then uncertainty issues with height take over. The FAA allows anyone, even children, to fly low mass kite systems in a safe manner up to 150 feet without all the complex expensive restrictions & airworthiness requirements of conventional aviation. That's actually pretty high for an experimenter & there is a lot of power there (a few terrawatts) if you are not too greedy.
         
        Low altitude is the Bunny Slope for AWE where competence can develop & eventually enable practical high altitude methods.



      • harry valentine
        California restricts windmill towers in residential areas to an elevation of 30-feet (thirty). Allowing kites to fly at 150-feet is a definate improvement as
        Message 3 of 3 , Jun 13 12:04 PM
          California restricts windmill towers in residential areas to an elevation of 30-feet (thirty). Allowing kites to fly at 150-feet is a definate improvement as it can allow for kite-based wind energy technology to access the higher velocity winds that blow at even that low altitude.
           
           
          Harry

          To: airbornewindenergy@yahoogroups.com
          From: santos137@...
          Date: Sat, 13 Jun 2009 09:54:40 -0700
          Subject: [AirborneWindEnergy] Low is Beautiful- Altitude & AWE



          Model Uncertainty characterized initial AWE research. All kinds of pet schemes emerged & one popular mantra was "high altitude" wind power, a prejudice based on the greater power higher up the wind gradient with altitude.
           
          Gradually the severity of problems with high altitude AWE became clear. A longer tether is more uncertain, it must be designed heavier for equivalent reliability. Direct control thru a longer tether is sluggish & less reliable due to a greater requirement to anticipate input. Adding actuation aloft adds weight, cost, & failure modes.
           
          Flying higher puts the kites into ever more airspace & greater competition with other aviation. Sure you can high-fly the Sahara or Southern Oceans, but US or European airspace will be dicey. A high flown runaway can cover a lot of ground. You never want to see a monster tether come down on a busy highway or drag a building over. Gaining airworthyness certification will be hard.
           
          A higher kite has greater scope & must be spaced farther from its neighbor. The scope required with height grows faster than the wind speed advantage; bummer! KiteLab's passive-control semi-captive arrays work around this problem, but Makani seems committed to keeping a bunch of non-captive wings clear of each other by active-control.
           
          High flying means visibility is a major issue. One cannot fly in clouds/fog without FAA instrument certifications (IFR capability), a far steeper avionics requirement.
           
          Risky AWE schemes to fly the generator require a heavy conductor tether. Aluminum is the best conductor by price & weight & can even carry considerable loads, but don't heat it up. Required insulation is more weight & drag. Go high & electrical issues compound core uncertainty.
           
          Thus have many AWE startups been chasing their own tail ever higher. Sky WIndPower has languished pining for the stratosphere. Makani has quietly downsized its height ambitions without admitting it ever miscalculated.
           
          Low is Beautiful.
           
          There is a turbulent surface layer that kites must clear but, as Payne pointed out, its only about 50-75 feet in normal winds. Above the surface layer an AWE sweet-zone begins & extends upwards a short ways, then uncertainty issues with height take over. The FAA allows anyone, even children, to fly low mass kite systems in a safe manner up to 150 feet without all the complex expensive restrictions & airworthiness requirements of conventional aviation. That's actually pretty high for an experimenter & there is a lot of power there (a few terrawatts) if you are not too greedy.
           
          Low altitude is the Bunny Slope for AWE where competence can develop & eventually enable practical high altitude methods.




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