After carbon fiber you have access to fiberglass which is still strong and more flexible than carbon. Also, steel is very strong and cheap also. If you can concentrate forces to a small area, steel seems to be a material as good as it gets imho.
AWE sparks new industries with the tethered rigid kites and also automation tools. It is great to see companies like Makani, Kitemill, Ampyx, Windlift, Skypull and others developping these new products, that after having tested sport power kites.
Small anecdote: Yesterday me and my friend were out kiting. Me on an inflatable LEI kite (incidentally leaking slightly) my friend on a bridled foil kite.
The foil kite had a broken bridle rope, and he was unable to control it. He managed to get ashore by putting the kite in the power zone where it inflated temporarily.
Two failures with two modern power kites with less than 50 hrs use each. On the same session. Out of a total if two kites.
So to answer the title of the thread: definitively not, unless you could build it more robust.
Tallak, LEI kites do leak air. I don’t know why TUDelft likes them so much. Its a bit like fixing a bike tire, people still use bikes. Compare with a crashed composite kiteplane before deciding. The broken bridle-line should have been a quick repair, even in the water. Don’t put a fancy kiteplane in the water.
Pierre, It is great that so many teams are doing rigid wings. Its not so promising that they failed with soft-kites first, but no one can say that rigid wings are not being tested for survivability.
Anecdotes and appeal to the technical authority of ventures are poor arguments compared to power kite data such as is. Ship kites are high TRL COTS. No rigid wing seems able to compete either in availability, robustness, or performance calculations that include Area and Mass factors.
FAA and ICAO regulations based on mass and velocity are also bad news for rigid wings compared to power kites. Like insurability, they reflect deep underlying aviation reality and scaling laws. No on in AWE is planning to scale rigid wings further than the marginal versions currently struggling. Lets see if any of them survive hundreds of hours of logged flight, like power kites achieve.
I dont think there exists any data for rigid wings being tested at sea, so I don’t see how you can conclude that this option is infeasible. Sirely if a fixed energy kite were to succeed, a rigid wing project for vessels would be sure to follow.
I dont agree to your argument about existence of data for ship kites relative to any design being superior to another
This is a detailed study comprising scability concern about Ram-air wings. Page 532: " A prime example of the scaling process is documented nicely in the X-Fly family
of Ram-air precision cargo delivery systems from Airborne Systems North America
[9, 11]. The development originated as an Advanced Concept Technology Demonstrator
research program from Natick Soldier Systems, whereby iteratively heavier
weight requirements were levied (0.25 ton, 1 ton, 2.25 tons, 4.5 tons, 13.5 tons, and
finally 19 tons). The wing sizes were 36 m2, 102 m2, 250 m2, 350 m2, 900 m2,
and 1,040 m2, respectively."
So scaling the flexible kite leads to a mass penalty, although far lesser than for the rigid kite.
Apart from this paper, it looks that the power kite can deliver high power by translation like for kite ship, while the rigid wing would be suitable for energy production, but there is no still definitive answer.
The reason I think a high G_e (glide number or lift-to-drag ratio) kite may have its place in ship propulsion is that only with high G_e will it make sense for fast travelling ships, which most large vessels ate these days. Which again might imply something composite based
The power kite can have a lower cut-in wind speed.
So far composites are not recycling well.
True the lightweight kite can fly better in low winds. But because wind energy is w^3 there might not be too much to gain by flying in these low winds.
The large nylon (?) foil kites that need to be replaced every 4 months for 25 years will also contribute to a lot of garbage. Plastic is not a perfect environmental garbage either…
A low cut-in wind speed also allows to avoid some take-off and landing operations that can use energy.
There is of course the scaling by number option available to “rigid” kites too.
On a kite turbine network, the much more efficient/kg “rigid” drive blades scale by number.
There are many variations in “rigid” as discussed.
I’m currently testing with “blue” cut foam with 2 carbon tube spars through the fuselage sockets, and a badly ironed on skin… Far from high tech.
Way more effective than the old ram airs. I can’t wait for a chance to test the next (old tech) wing tech upgrade.
There is no claim here that rigid kites cannot work at sea, only the conservative observation that soft ship-kite TRL is higher, with years of operational data; as a competative advantage. Its also worth repeating that marine operations are far more costly, in general, than equivalent work onshore. Offshore is properly classed as an extreme environment for reliable automation, and woe to delicate overly-complex AWES that seeking an early haven offshore from inherent hazard and noise challenges.
Both soft and hard kites will need to be recycled properly. Simple polymer kites are the better cases for recycling compared to complex kite-planes loaded with structural resin and toxics, especially ocean crash fall-out like NASA’s Pathfinder crash caused.
Again, both rigid kiteplane and power-kite AWES architectures are placing competing bets on reliability, LCOE, and so on. The high TRL power kite has the definite advantage of so many COTS applications and similarity cases. Lets let rigid wing AWES crash statistics inform us how close they are to power-kite life-cycle statistics. Don’t be fooled by conservative human-rated soft-kite hours. Many of those kites still look and work like new when retired from human-lifting, and would easily live on many more hours at rated loadings.
I am not impressed by aerospace novices who dabble clumsily in soft kites and then choose rigid wings, as if responding to venture pitches rather than real-world flight factors. My own lifetime in aviation has progressed in focus from powered rigid-wing actively-piloted aircraft to gliders, sailing, parachutes, and soft kites flying passively. Again, COTS TRL-9 power kites lead early AWE by best-scalability due to highest Power/Area-to-Mass, and best-robustness, for all the resulting operational and economic advantages.
I believe many traditional power kites have fabric stretch issues and need to be modified after prolonged use (skin tuck to compensate for stretch). I fail to see how handling a sewing machine is compatible with on site maintenance…
“Soft ship-kite TRL is higher” as a means of translation from time to time, but not as a stationary means of wind energy electricity production all the year. It is the same for sails.
Boats use soft sails or kites since hundreds years, while windmills and wind turbines use rigid blades.
Tallak, Fabric-stretch is NOT a serious issue in power kiting (search popular Power Kite forums). At worst, stretch will be a small loss of performance in AWE, a minor derating factor that really only matters in elite kite racing. Fly a power kite quiver to rated conditions to avoid any hint of a problem.
Crashing is by comparison a serious issue for rigid AWE kites, as Makani’s crash history first proved. If a kite does need sewing off-site, more likely for a repair than stretching, at least it packs in a bag and ships easily, unlike rigid wings.
I would rather sew outdoors, onsite, now that you mention this great idea. Sailors have always sewn their sails, above or below decks, so why not us? What exactly could prevent outdoor sewing but a lack of will or aptitude?
Pierre, The Race for Water circumnavigation with Skysails’ North Sails Power Kite, did generate electrical power, and even hydrogen. Its very odd to fear ship kites somehow, in principle, can’t make electricity on land. Of course they can, but reeling upwind-downwind is not the best way; Payne’s crosswind motion is the best way for slower but super-powerful soft kites to beat faster smaller weaker rigid kites.
Have you available information about it? If yes please provide a link.
For a same power, a soft 1000 m² kite can be more dangerous as a rigid 60 m² kite: it can take everything in its path with its huge traction and its tethers and bridling, even after a crash.
Soft kites have a low lifetime, and soft blades are not used for energy systems like windmills or wind turbines. Moroever large and powerful planes like airliners are rigid.
But soft kites are suitable for sport, or towing.
No Pierre, modern kite-killers completely prevent runaway. Also, multi-line architectures make runaway very improbable. kPower proposes both methods together. A 60m2 rigid kite is not only far less powerful, but it can’t be killed like streaming fabric, but will kill whatever it crashes on, at likely high velocity. Let FAA rules for mass and velocity apply as well.
It already occured.
It would be still worse.