Polymer kite

by Pierre Benhaïem in Airborne Windenergy Forum · · 5 Replies · View last reply Respond
Pierre Benhaïem
Pierre Benhaïem

As AWES should work 24h/24 all days, the lifetime of fabric power kites is expected to be too low, about 2 months.
I tested  http://www.supreme.co.in/xf-films-products.php    (“Multilayered Cross Laminated U.V.Stabilised Films”): after 14 months outdoors the 70 gr/m² film  was good as new, while the lifetime of a current blue tarp does not exceed 12 months. Perhaps flexible kite lifetime is low due to the fragility and the finesse of the wires constituting the fabric, as wires resist badly in both UV and mechanical constraints. So a polymer (for example XF-film or a specific material) in one piece could be more durable.
See https://www.youtube.com/watch?v=-YSHOXKAasU : a plastic paraglider is possible. See page 49 of http://paragliding.rocktheoutdoor.com/wp-content/uploads/2015/06/RELAZIONE-DEF-1.pdf  : “This means that the real efficiency (in normal flight condition with frontal wind) is about 5; not bad for a plastic paraglider! “. Initially it is about 7. So one can deduce that a high lifetime plastic XF film kite should be also possible. Bands receiving suspension lines are welded. Building giant polymer kites can also be less expensive thanks to an economy of time.

Pierre Benhaïem
Pierre Benhaïem

http://kiterepairs.blogspot.fr/ :" The reason that repetitive creasing is bad, is because it will start to form cracks in the coatings on the fibers."

Supposing fibers are the lifetime problem. There is no fiber when a polymer is used.

Pierre Benhaïem
Pierre Benhaïem

After some deeper investigations, discussions and other tests, in my opinion it is possible to produce some temporary conclusion about airborne wind energy systems: ripstop has appropriate mechanical properties but its lifetime is too short; and plastic films, including xf-film I mentioned, has a higher lifetime but their mechanical properties are too low. So a mix could be (and already have been) studied, but the task is not easy as the film-fabric complex should be light, and durable in spite of possible cohesion problems between components.

Pierre Benhaïem
Pierre Benhaïem

http://www.beautiful-light.eu/en/characteristics and http://www.faiteslepleindavenir.com/2015/06/18/du-soleil-dans-les-voiles/  represent other possibilities as the integration or encapsulation of photovoltaic film. AWE kites, at least static lifting kites, could be equipped.

Pierre Benhaïem
Pierre Benhaïem

As temporary conclusion rigid power kites are more appropriate, their lifetime being far higher among other advantages and also disadvantages like crash risk. Concerning flexible kite, some suggestion: a complex including a polymer fabric (for mechanical resistance) between two layers of the same polymer but as film (for lifetime as it hides and protects the fabric), possibly multilayered cross laminated UV stabilised film.

Pierre Benhaïem
Pierre Benhaïem

After a deeper analysis of different combinations, including laminated complexes with layers of film and ripstop, I can assert that the fabric-film lifetime remains far too low. Indeed with the time and humidity the external films become more porous, making failure due to the lack of cohesion of the whole. 

It is the reason why we can prefer a robust uniform plastic film like the multilayered cross laminated UV stabilized film, even by considering its lesser mechanical properties (about 1/3 of ripstop with equal mass). By the same I suggest the implementation of bands in reinforcements by extra thickness of the same material in order to assure the cohesion. So a high lifetime could be reached (see above that I tested xf-film tarp for more than a year outdoors) but with a relatively heavier film. If this option of an uniform film is not appropriate enough, searches should go massively towards rigid wings.