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What happens when the wind stops?
What happens when it is struck by lightening? Do you have to land and take off each cycle? How do you propose to change the swept area? What sort of wing will you use? How long is each power stroke? What frequency are the power strokes? How long will the string be? How fast will the string be pulled out? How strong will the string be? How thick will the string be? How long will the line last? What do you call the wings? How will you control the kites? Why do you use a reciprocation motion rather than a continuous loop of wings? How long will the wings last? How will you change wings that are damaged? Can it survive in strong winds? How does it deal with turbulence? What happens if the string breaks? How much will it cost? How long will it last? Is it computer controlled? How many wings can you have? Why is this scheme particularly suited to offshore placement? Is there a risk to aircraft or birds? How would you overcome such intermittent power production? Can a stand alone unit provide smooth power?? How will the reduction in air density with altitude reduce the energy content of the wind? ? 
Thomas Berger  "The art and science of asking questions is the source of all knowledge."
Frequently Asked Questions:
What happens when the wind stops? Nil wind at altitude is rare. However, in these circumstances the wings can be kept aloft by a scheme called "step towing". With this scheme, energy is transferred to the wing by a careful combination of winching in and paying out. To top... What happens when it is struck by lightening? The control electronics will be kept in a faraday cage, which with protect the sensitive electronics from the effects of the lightning. The tether rope will be constructed from a synthetic fibre with a Dielectric Strength greater than that of air. This means that the lighting would "prefer" to travel through the air instead of the rope. To top... Do you have to land and take off each cycle? No. A cycle will occur between two altitudes that have been optimised for maximum power production. To top... How do you propose to change the swept area? The term "swept area" comes from HAWT design. The term usually means the area of a disc that the turbine blades trace during one revolution. This figure is important because it directly relates to the power that can be generated by the turbine. Tethered airfoils do not have a directly comparable figure. Tethered airfoils can alter the power production by altering the position within the power zone or altering the total surface area of the wings. To top... What sort of wing will you use? A high strength to weight ratio is essential, therefore construction techniques from the Free Flight (Gliding) industry will be used. To top... How long is each power stroke? The distance will depend of the wind strength. To top... What frequency are the power strokes? A power stroke will be in the order of minutes rather than seconds depending upon the operating conditions. To top... How long will the string be? This will depend on many factors. But of course primarily depends upon operating height and distance from the base station. To top... How fast will the string be pulled out? Roughly half the wind speed. To top... How strong will the string be? This will depend on the rated output of the generator system. A system that matches one of the largest current generation of turbines (2MW), 277,000N would be placed on the lines. Four 25mm (1 inch) diameter Dyneema ropes would be able to take this force at 20% of their breaking strain. To top... How thick will the string be? The thickness is directly related to question 10. To top... How long will the line last? With fatigue cycle loads of 20% of the breaking strength, 15 years is possible. To top... What do you call the wings? At avian energy we call them traction kites. To top... How will you control the kites? Computer controlled autopilot with ground station communication. To top... Why do you use a reciprocation motion rather than a continuous loop of wings? Research to date suggests reciprocal motion is more efficient. To top... How long will the wings last? It may be possible to build one to last 15 to 20 years, however the commercial and weight factors may favour a shorter lifetime. To top... How will you change wings that are damaged? The wings will be lowered and fully landed. To top... Can it survive in strong winds? As the wind speed increases, the wings can be flown in low power areas of the power zone. If the wind speed approaches the VNE of the wing, the wing will be landed. The design of the wing is such that this VNE condition of the wing should only be reached a given number of times per 100 years. To top... How does it deal with turbulence? The wing will have active and passive attitude correction. To top... What happens if the string breaks? Lines will be used with a five times safety factor (similar to bridge construction). To top... How much will it cost? An accurate costing is difficult at this stage, however the intention is to use less expensive raw materials than those used in state of the art HAWTs. To top... How long will it last? See answer 16. To top... Is it computer controlled? Yes. To top... How many wings can you have? The upper limit has not yet been established. To top... Why is this scheme particularly suited to offshore placement ? Currently, offshore wind farms have to be placed in shallow water. This is due to the foundation requirements. The wind is constantly trying to push over a traditional wind turbine. This dictates substantial foundations. A tethered airfoil is being pulled up by wind. This can be resisted with an anchor to the seabed. To top... Is there a risk to aircraft or birds ? Risk to birds is lower than that of HAWTs. This is due to the wings flying significantly slower than the tips of HAWT blades. The FAA have included provision for sailplane winching areas, which are shown on air maps. For nighttime, it will be possible to comply with FAA lighting regulations of high obstacles (such as TV antenna). To top... How would you overcome such intermittent power production ? The power stroke and recovery stroke can be imagined like an internal combustionengine: "In a 4 stroke engine there is only 1 power stroke every 4th stroke. On a single cylinder engine a large flywheel is usually required to deliver smoother power. However, often multi cylinder engines are used to deliver smooth power as in a 'normal' 4 cylinder car engine. In the same ways multiple generators running with power cycles arranged like a car engine will deliver smoother power without the need of a massive fly wheel or similar short term energy storage device. To top... Can a stand alone unit provide smooth power? Yes but like a single cylinder internal combustion engine (See question how would you overcome intermittent power production.) it would require a large flywheel or similar short term storage device to deliver smooth power. To top... How will the reduction in air density with altitude reduce the energy content of the wind? The energy content of a wind of 20mph at sea level will be greater than one of 20mph at 10,000ft, however wind speeds tend to increase with altitude. If the wind is 20mph at sea level it is likely to be far stronger at 10,000ft. The fact that energy content of the wind, through a given area, is proportional to the wind speed cubed means that the energy content is likely to be far higher at 10,000ft. To top... |
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Avian Energy, Stretfield, Bradwell, Hope Valley. S33 9JT. | Email: info@avianenergy.co.uk | ||||