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Cheap Practical AWE

AWE research has tended to envision high-altitude energy kites as based on sport-style or aerospace-composite traction wings sweeping figure-eights under active robotic UAV control. This mindset enabled valuable analysis and demonstrations but technical kiting and experimental robotics experience suggests that such schemes are only about a tenth as reliable as advanced UAVs, which are themselves about a hundredth as reliable as human piloted aviation [1]. Most of the causes of failure are inherent in the immature technology and will persist for years. Capital and maintenance costs are particularly high for aerospace airframes, active controls, and high-altitude flight. An impasse looms.
 
Low altitude Passive Flight Automation (PFA) based on traditional single-line kite stability is proposed as a way forward. Passive methods are cheap, have major performance and safety advantages, and don't need batteries or many other active-control failure points. PFA is the lowest-mass aloft solution, essential in good kite systems. KiteLab has proven that a PFA based lifter kite can hold aloft unstable hot power generating elements that would otherwise crash far more often.
 
Low altitude research is also essential to move forward rapidly. Low altitude kite flight is preapproved by US standards and can be rapidly adopted by small players everywhere. KiteLab has working systems operating under the 150 ft FAA approved kite ceiling, while performing numerous small-scale experiments aimed at higher altitudes with active elements. Low altitude practice is a vital stepping stone to higher-altitude competence.
 
Micro-actuation trim-forces applied to a PFA lifter can begin to bring back active approaches for eventual wide adoption. What's desired is an actuation-starved agent for a tiny bit of "chaotic control" over a real-world wind-field case-base for a PFA lifter-kite. Even a primitive low-dimensional sampling of the Inflow Wind Field may give such a controller a chance to poise the kite against perturbation by inflow turbulence or to make small kicks to dampen threatening aeroelastic oscillations. Kite-killing in runaway event will be an essential safety function of minimalist actuation.

[1]Safety Considerations for Operation of Different Classes of UAVs in the NAS

CoolIP                       ~Dave Santos             Apr 5, 2009           M51

Comment and development of this topic will be occurring here.       
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  • I'm somewhat leery about excess complexity such as computer control over kite-electric technology. My preference would be to keep the technology as uncomplicated and as straightforward as possible. Less complex technology almost consistently delivers higher reliability and lower long-term operating costs.   ~ Harry
     
  • Hey Harry,    a generator system I am developing is designed to be a modular type of device such that it can work on the simplest pulsating power input like the flipper wings Dave Santos prefers to the much more complex multi inputs from tower turbine, solar steam, and pretty much any type of mechanical energy. On the simplest level it can be completely self governing by mechanical means or with the more complex multi input arrangements it can be computer controlled to manage the power ins and outs as programmed for priority needs. I'm still working to get the prototype built as my finances will allow and will make public the details when I can get the proper IP stuff documented. I do intend to make all my stuff open source but I want to make sure that it is covered first so as to not let it be taken over by those who are not as willing to share the tech with the rest of the world.   -brooks
     
  • I am surprised at the absence of standard aerodynamic terminology in the models described.  I would like to hear about your; span, wing loading, air foils, cables, speeds, power, L/D, weight, scale limits and materials; these are the main issues I deal with in my designs.    ~mike fallwell
     
  • Mike,

    The referenced post was a semantic abstract, not a technical specification. Specs are available online off JoeF's AWE site.

    If you are asking about Lifter Kites, standard types like Morse Sled & KiteShip's OL are used. Specs are published. DaveC or I can answer specifics.

    If you are asking about Membrane Wingmills- practical spans range from a few cm to several hundred m.,
    composite membrane & carbon battens preferred but even cardboard & bamboo is practical.
    my biggest membrane wingmill has been 3 m span, 50 cm at max chord, a new wing under construction is 10 m
    foil type is curved plate with turbulators & other tricks.

    "cables" are SpectraŽ or DacronŽ.

    Power has ranged from milliwatt to a couple of hundred watts, these are small fast & cheap experiments, kw prototypes are under construction.

    Membrane Wingmill concept intended to scale beyond all others.

    L/D of most of the wings are in the 4-8 range, some are close to 15 or so, torsional dampening by swept battens is allowing higher L/D.

    What sort of AWE designs are you working on?

    ~DaveS
     
  • Sounds interesting, Brooks . . . I wish you success. At the present time there seems to be great merit in combining airborne aeronautical working apparatus with ground-based electrical generation equipment. Large generators/alternators would yield greater output and increased longevity over small, lightweight airborne electrical equipment.
     
    Ground based electrical equipment may also be easier to insulate/isolate from lightning at some locations.
     
    ~Harry
     
  • Excellent point on the lightning issue although now you just triggered the gerbil in my head spinning on some new ideas on how that power could be harnessed. My dad worked with some folks who had made some attempts many decades ago but I just had an idea that they may not have tried regarding the many ways to store and convert energy. I'll keep you posted.       
    -brooks (and the gerbil that controls him)
     
  • Hi Brooks,  You'll need some incredibly large capacitors to store a charge of lightning . . . . or even multiple strikes.  Harry
     
  • When I said "new ideas they may not have thought of " it was a hint to the common method of extracting/storing energy via direct electric energy is not the only form of energy that can be extracted from a lightning strike. Giant capacitors would probably be the most efficient if they could be charged fast enough to absorb that energy but as someone who has restored old buildings with damaged lightning rods I can tell you energy can be take many forms. I'll have to check my my chief number cruncher to see if the projects he worked on could do the job as well as the methods that have been tried by the electrical extract/storage method. There has been some research in the direction I'm thinking,  but not public common knowledge. I'll have to check on how public before I say more.                         -brooks
     
  • The fatal problem with lightning power is low capacity factor and high capital cost of the equipment, which overwhelmingly sits idle but has to be massive to handle brief peaks.
     
    Persistent atmospheric charge across altitude seems too diffuse to usefully collect by any sort of flying conductive web. Convective cells are big capacitors & might conceivably be discharged at a reasonable capacity factor (pulsed ionizing energy beams)?, but not anytime soon.
     
    Synthetic lines in a non-saline atmosphere are not lighting attractive. Aerostats have woven metal jackets on their tethers to handle lightning. Lightning arrestors are bypass conductors that will protect a kiteboat or ground generator from damage.
     
    Ultra capacitors are generally only cost effective as load/supply leveling
     buffers, not as primary storage. Composite structure can double as capacitor. Ultra capacitor airframes might charge/discharge by contacting along skycable networks.
     
    Wind power AWE will be far more practical for a long time than secondary energy harvests such as from solar thin-film or static-charges. Piezo hummer ribbon mesh might be a "solid state" collector someday. A wing yanking on a generator is current best option.

    ~DaveS
     

  • No debate here on all these points, Harry just got the gerbil  running on that treadmill in my head, but I have some new ideas on the storage and transmission of energy. Actually old ideas revisited with a twist.

    -brooks