Power to space use ratio

kPower has always cared about this ratio as a function of “airspace efficiency” and/or “land footprint”.

Just as multiline kites are less likely to breakaway, so are many-connected Kite Networks. All lines to the ground must to fail at one time for a Network to ever runaway. A Network can passively self-kill still anchored as it loses lines, just as arches passively self-kill in place if one side parts.

The simple Network solution to gust surges is passive unit-self-furling. As discussed on the Old Forum, common tree leaves passively feather and even roll-up, to collectively depower in storm winds.

It is true, but no existing companies or scientific publications care about this ratio.

About kite networks, I think some things are possible now, some other no, at least by taking account of the available technology. A lot is to be (re)discovered about it, but it is possible that it is after a first possible commercialization of utility-scale AWES.

I believe there was a talk at AWE conf 2017 that treated looping radius. I remember finding it very interesting, unfortunately I dont remember which talk…

Pierre,

First you wrote “AWE world”, which includes the old discussions. Even so, kPower is an “existing company”, and the Old Forum was “a scientific publication” whenever science was presented, including your own best postings. At least you think our long established concern over power-to-space was correct. Power-to-weight is even more important for kites, and not incompatible with high space efficiency; the best kite designs achieve both.

Tallak,

You are right, that turning performance is now being identified as important in mainstream AWE academia. Had they closely studied Kite Sports, they would have discovered this parameter long before, because free-style C-kite kite-punks and old-school stunt-kiters were so obsessed with turning. Those low-AR wings had superior turning performance by design.

On the two scientific publications I quoted above there is not a single word about the power to space ratio, so much so that the high efficiency of the Magnus balloon in regard to this ratio is not even mentioned. And the hugely huge figure-eight flown by the Ampyx wing shows an absolute
misunderstanding of this ratio which is the most important of all ratios, comprising the power-to-weight ratio.

Some looping radius can be studied here or there, but for other reasons like the optimization of the efficiency of the wing.

I am the only one to completely identify the power to space use ratio as the first main ratio. The official circles make absolutely zero contribution about this ratio, and, ignoring it, are pursuing to the lack of hope of significant result.

Note the picture shows a train of kite you identified as not very efficient (the traction being not multiplied by the number of kites due to wind shadow) in a previous message.

Pierre,

The place to find expert discussion of turning rate advantage is on Kite Forums and Blogs, not AWE papers. Sample-

Our top classic kite scientists are the best, in any case; Hargrave, Chanute, Wittgenstein, Rogallo, Barrish, Payne, McCutcheon, Loyd, Roeseler, Lang, Culp, Ockels, and so on. No one should expect as much from “PhD puppy-mill” kite science. This is well known on the Old Forum-

From: dave santos
To: Yahoogroups
Oct 5, 2017 at 6:04 PM

A few years ago kite surfers identified kite high turn rate as a critical competitive edge, particularly in gnarly dynamic freestyle conditions. For decades, performance soaring has understood tight turning in thermals as desirable. As kitesurfing and soaring are energy-driven, we study every such anecdotal heuristic in AWE, sooner or later. This is a belated start at analysis of Power-Kite High Turn Rate in our AWES context.

Power-kite tight turn capability seeks to maintain high velocity out of the turn. Better-kite can thus zip back and forth across the power-zone of the kite-window, at highest extraction capacity, while not-so-good-kite burbles the turns. Two familiar factors are especially key to high kite turn rate; low inertial mass, and high lift coefficient…

Expect a high turn rate kite wing to have modest aspect ratio (birds like swifts fold wings dynamically to low AR). A long wing is better suited where the Wing Span to Kite Window Width ratio is low, as a design law to guide us in matching wing to window."

High turn rate as a tool to increase the power to space use ratio is not mentioned.

Pierre,

Lots of AWES airspace and land-footprint density references over the years, well before 2017 turn-rate analysis. This quote from 2011, TACO1.0-

"Dense Arrays- Super Density Operations (SDO)

A major class of TA is cross-linked wings in arrays. Such arrays are calculated
to utilize airspace up to a hundred times more efficiently than single-line AWES.
The “tether-scope” requirement of single-line systems means they operate too
sparsely to scale greatly.

Multiline Arrays also have key safety advantages over single line systems.
Redundancy of tethers makes flyaway safely improbable. Land and airspace is
conserved, minimizing obstruction issues. Conspicuity is greatly
enhanced."

http://www.energykitesystems.net/CoopIP/TetheredAviationConOps.html

Finally, a recent Old Forum kPower post, referencing your interest (2019 Jun 6 at 8:08 PM)-

"[AWES] kPower Testing showing SS Power Kites Turning Tightest under Power

A few weeks ago, at Pierre’s suggestion, the subject of kite turn-rate recurred in the evolving context of maximizing airspace. kPower started working through its encyclopedic power kite quiver to compare turn rates, to validate heuristic prediction in favor of slower, lower-mass wings.

Using parafoils for session comparison, as the hotter higher-mass baseline, SS kites of the three major types (NPW, OL, and PLSS) were observed turning tighter and faster by equivalent wing area and wind velocity. The hotter parafoil somewhat overshot the heart of the Power Zone, where the SS more closely ruled, especially when both fly short-lined. With Rigid Wing kites based on super-hot gliders, the wide-turn effect is even more pronounced, as any glider pilot can predict. Hot wings can be made to roll and pitch a tight turn, but its an extreme maneuver that depowers and slows the hot aircraft, which then has to re-accelerate up to speed.

This anecdotal kPower result will be easy to directly confirm by third parties. It suffices to watch power kite and glider videos for non-dimensional pattern-flying laws. Its not just the higher inertial mass that makes turns large, but also common lack of vertical keel and/or wingtip/winglet area, so drastic roll-pitch input is needed instead."

In summary, power kite pros naturally evolved high turn rates and high airspace density twenty years ago. This is still advanced AWE knowledge, hardly yet published academically. kPower is the closest AWE venture to expert kite culture in all its variety, as well as closely following academic AWE R&D. Its really all one fantastic AWE world.

I will nuance strongly my answer in that kPower “land footprint” is different as kPower envisaged secondary uses and the presence of inhabitants below AWES (I remember some sketchs and texts of AWES above towns) unlike me. Even you criticized my poster in AWECBerlin2013 about land and space use.

I precise it again. There is no scientific paper about the power to space use ratio. Beside it the turn rate was studied by classic kite players, but not for the purpose of a better power/space ratio for an AWES to generate electricity at utility-scale. I see the turn rate as an element among others to improve this ratio.

It was true several years ago. It is true now. I am the only one to regularly say that a high efficiency by crosswind flight per wing area is nothing when several km² are used, preventing secondary use.
When a second player will understand it, a step will be reached.

Indeed the photo shows a multiplicity of power kites with short tethers (10-20 m) and driving the users. It is very different when the tethers are 1 km length and with stationary rigs. If the proportions remain constant as I advocate, the wings would be gigantic, which may be necessary for a good power/space ratio under acceptable control conditions. Such a configuration can be studied as a mean to improve the power to space use ratio.

Multiline Arrays could perhaps be a mean to maximize the space, but in this case a forest of long tethers would hardly be manageable. And in the same time you indicate the power-to-weight ratio as the first one. I consider things in another way: the first ratio is the power/space ratio, then multiline Arrays is a (not the best imho) mean to reach this ratio. Other means can be multiline-single kite, and even single line (in several parts)-single kite.


I agree. There are relevant observations and analysis. Thanks.

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I precise that I wrongly or rightly interpret a “rigid autogiro turbine” as a not yet tethered device like an autogiro or something like a wind turbine, thinking it uses only its own space with its swept area.

But as the autogiro is tethered, even when it is stationary, the tether could move the autogiro far away according to wind conditions. So the tether fully modifies the topology within the environment of the complete device.

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DaveL and GrantC’s SkyMill is our best tethered Autogyro AWES model. I helped them test prototypes on the US NW Coast. Not much airspace was needed.

AWES kitefarms require a forest of tethers as much as kite sport events. However, instead of complex individual control, network interconnection aloft (topological stability) is simpler, and enables passive dynamic stability, including lattice waves. Many such stable topologies work without fuss, like drop-stitch construction as a model. Its the common many-single-line topology that requires the greatest spacing and most concerns.

You are finding that absence of AWE scientific papers is not always absence of AWE science. Initial AWE spatial density and turn-rate science exists in the texts cited. Do not wait for AWE academia to catch up, just keep moving ahead.

Land footprint is not just one set of crude assumptions. The same footprint unworkable today by crude art becomes workable tomorrow by superior art. That is how to analyze footprint maximization, based on all critical factors. Yes, AWES will someday fly over populations, just like most aviation. Kite Networks have desirable advantages for populated places. One can walk around the 2000 kites set on arches much more confidently than if they were each single line.

Thanks if you find earlier references to AWES space maximization issues than those I provide.

Hello @rschmehl,

Thanks for the references. I will pursue in the present topic which seems to be more appropriate, Makani’s wing being a special case of crosswind flygen rigid wing, multiplying the risks. It can be a reason why both Fig.4* and 2.2.1 Zoning concept in [2] and Fig. 16.6 and 16.4.1 Spacing of Units in [3] concern “flexible wing systems” ([3] mentioning also rigid wings in the introduction, but not elsewhere) as you indicated. By this one can deduce the acceptable risk for flexible wings would not be as acceptable for rigid wing. It is a secondary point which should be more studied.

Now let us come to the main points. Fig.4 and 2.2.1 Zoning concept in [2], and Fig. 16.6 and 16.4.1 Spacing of Units in [3] are similar and both describe a sort of tilted and reversed cone delimiting the danger zone, allowing some uses under the kite flying. IMHO it is quite unrealistic:

  • Wind direction is assumed to be the same for the whole kite-farm. But various winds in direction and intensity can occur in each place of the kite-farm, leading to a likely collapse. The probabilities of such variations could be studied, combining stochastic and real wind data for example, or lead to more spacing, or even to the implementation of a single larger unity.

  • The safety issues are mainly computerized. The scheme of a farm of crosswind kites lack passive safety. The computerized management failing would likely lead to a full collapse.

  • Knowing that the tethers move fast under several tons of tension, that at a low elevation angle of an average of 30-40°, people under such tethers would likely not be accepted. I remember safety instructions from Enerkite during AWECBerlin2013 for the few kW-range wing: “nobody under the kite!”.

Currently the industry is only about preliminary testing and theoretical studies, excepted @Kitewinder.
I am afraid that my estimate is well below the security imperatives that will not fail to occur, at least for a while. Indeed a fall zone should be added.

A tether of 1 km is a little like a tower of 1 km, but in addition the rope is moving and is under high tension. So more compact designs should be studied. But it is only my opinion.

Figure 4* [2] from V. Salma, F. Friedl, R. Schmehl: “Improving Reliability and Safety of Airborne Wind Energy Systems”. Wind Energy, in production, 2019. doi:10.1002/we.2433 . Preprint accessible as pdf :

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Yeah, I must be rubbish at getting this message out… I’ve been trying to communicate this for quite a long time…
Refresh of old drawings a little more polished to show how networks improve land and air space usage.
The elevation on these stacks is shown too high


This next one is V old… the stacks are way too steep high


But compared to reality… Yeah, they can be fairly steep and still work ok

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Rod correctly identifies networked kites as the highest theoretic power-to-airspace AWES basis.

Networked kites with many-connected topological-stability also solve unit-kite runaway risk, single-line unit-kite scope-interference, and promise best overall plant economy-of-scale. Networked unit-kites can also have the highest turn-rates, densest spacing, and may in large numbers spontaneously develop coherent lattice waves, for powerful pumping outputs.

Wubbo’s SpiderMill is a 2011 networked kite concept offering these inherent virtues. kPower proposes cross-linking SpiderMills into metamaterial networks. Pierre’s Ortho-Kite-Bunch is another early AWES network concept. Rod’s kite network concepts cover a further range of ideas. Its time for serious research into high power-to-space AWES kite networks.

Another commonly overlooked advantage of this awes is the constant output without lines which wear out by running over capstans, pulleys, fairleads and drums.
In terms of power to space… The modularity also lends itself to changing land use cases… the ground footprint could be rearranged depending on… season, late payments … other

The best thing about kite turbine architecture efficiency is the match of deployment of material, to its potential to work the wind power window.
A system with 1 kite here sucks VS A system with a network of kites working right in the power zone.


That’s level 1 efficiency advantage to networks
Then level 2 is the farm stability

I spent last week snow-kiting, we should all be doing it and flying more kites more often.
Power, tension, turn rate, control authority all ramp up in that green zone… Get in there.

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A video to highlight how the placement of your kites in the wind window affects potential to work.