Power to space use ratio

I reckon…
Having highly active AWES, arrayed in volumes, at appropriate densities will have significant impacts on power to space use.
Much as array patterning & density in HAWT farms does.

Also…
The ability to harvest from the whole height, width and depth of your airspace… Is hugely significant.

Of course I have to state… Daisy, a stackable mechanical drag mode autogyro kite, has rotors working simultaneously in lower and higher level winds. Also stacking seems to make the system more efficient with less drag / kite and more line tension for better torque transmission.

More on all that coming

The ratio mainly proposed since M. Loyd’s seminal publication *Crosswind Kite Power http://homes.esat.kuleuven.be/~highwind/wp-content/uploads/2011/07/Loyd1980.pdf is the power to kite area ratio. @kitefreak proposes the power to weight ratio.

I beleive the power to space use ratio allows to think the AWES farm as a whole rather than addition of unities with their respective long tethers. So a system with high power to kite area ratio, generally a crosswind kite power system with its fast moving tether, will have a very low power to space use ratio. In the end AWES seen as less efficient in regard to their power to kite area ratio will be able to reach a higher power to space use ratio if said space can be maximized, for example, by implementing unities that are close each other, or more simply by implementing very large units.

Loyd and I discussed whether power-to-area or power-to-weight is the first-order AWES number and we agreed on the basics. Power-to-weight remains the most predictive number in aerospace; it just happens not to have been Loyd’s starting computation basis, where power-to-area was easier for him to analyze, and gravity was completely neglected.

Its a testament to Loyd’s genius that his paper remains AWE’s founding classic despite its gaps and shortcuts. Loyd himself was rather mortified that the paper came to be so iconic, because he would have worked harder to polish it. Pierre’s special concern with power-to-airspace was also not treated by Loyd as such, but would be a critical factor where airspace is scarce.

Many critical numbers exist in AWES engineering that Loyd did not introduce, like LCOE which in turn might be driven by Insurance Cost. It was reasonable for Loyd to neglect power-to-weight to begin formal analysis, and its now reasonable for us to consider it, especially in the aviation Scaling Law context that Loyd was well aware of. His “C5-A” wing case would logically have been a soft kite, not a massive aluminum transport wing.

The generalised architecture of a networked kite system volume is a dome.
When scaled up, the central area of this dome is flying higher than it would for a smaller land area network.
Therefore the power per land use area improves with scale of networked kite deployment.

The dome may be a self inflating dome shape, some sorta blob, an Alexander Bolonkin dome, or a Santos mothra shape… All allow for better power to land use in the centre.

Google Photos
These could be a lot higher in the middle to achieve the desired effect

Google Photos
Always fascinated when I see this fish farm cage net lift and make this shape…

An AB dome inflation test by KPower

Now I would compare rigid and soft wings as they fly by figure-eight or circle. I will use rough orders of magnitude. The power of a rigid wing is about 10 times the power of a soft wing by considering the wing area. But it can be the reverse if we consider the power to space use ratio, or more precisely the available power in regard to the tether(s) length. The radius of a turn is proportional to the squared speed, and a rigid wing goes two times faster as a soft wing. So the required (useful and useless) swept area for a rigid wing is 16 times that for a soft wing, knowing that in all cases we are far to the Betz’ limit. Add that from these respective areas, the rigid wing uses a thin annulus while the soft wing uses a much larger part of his smaller swept area.

An illustration of what I try to say is on the two documents below:
https://www.researchgate.net/publication/325831964_Aerodynamic_analysis_of_Ampyx’s_airborne_wind_energy_system : the figure 1 represents a fast wing (Ampyx AP3, 150 kW) using a eight-figure of about 600 m wide and 200 m height.
https://www.researchgate.net/publication/320495787_Modeling_and_control_of_a_Magnus_effect-based_airborne_wind_energy_system_in_crosswind_maneuvers : the figure 7 represents a slow Magnus wing (40 m span, 1.5 MW without taking account of the power consumption) using a eight-figure of about 100 m wide and 75 m height.

1.25 W per m² of occupied area for the first, 200 W per m² of occupied area for the second, while the first is far more efficient per wing area. Certainly the result would be far lower than 200 W by using a classic soft wing, but far higher than 1.25 W. Note that here the occupied space is not yet the space use which takes into account of wind changes.

So the use of soft wings by SkySails or by @Kitepower and @rschmehl makes sense.

Pierre,

Agreed, that a kite’s turning-rate and -radius are key to maximizing harvest sweep in the kite window.

Conflating Skysails and Kitepower is problematic, given stark comparisons between them in scaling and other critical engineering dimensions. Its necessary to respond appropriately to Kitepower’s multiple design failure, as revealed by the crash review.

Tweet media dominance aside, what makes Kitepower attractive technically, in the face of the crash conclusions and LEI kite limits? There are other considerable soft reeling ventures, like KPS.

We must address system topology to judge airspace performance. A rigid autogiro turbine that turns-in-place, or a dense kite network, can in principle maximize airspace. These are old findings are worth repeating, along with new insights into turn performance.

In the context of airspace efficiency here, the most pertinent comparison is with USP3987987fig5 crosswind sweep architecture.

The comparison I made is about crosswind kites flying by eight-figure or circle as it is the method used by almost all companies, and concerns rigid vs soft wings (the US3987987fig5 describing a different rig requiring significant developments in order to face the wind). In the scientific publications I would like to see how the “power to space use ratio” leads to a different efficiency but there is nothing about it.

A dense kite network could perhaps maximize the space with static or perhaps rotating kites (imho with a lot of problems as the power is involved), but not with crosswind kites. I know it since my participation in Dieppe kite festival. Crosswind kites require high spacing, so each unity should tend to maximize its own space by taking account of the tether length.

The tether fully modifies the topology. “A rigid autogiro turbine that turns-in-place…can in principle maximize airspace”, but not a tethered autogiro turbine.

Differences between SkySails and KitePower are not about the turning-rate by considering an equal wing area. Other things like crash review are not directly connected to the current topic.

Pierre,

As long as Kitepower is invoked here, unresolved questions about their safety culture and poor scaling prospects beg answering. Their Twitter feeds do not advance either this Topic, or un-responded concerns. Even Skysails and KPS, without Kitepower’s crash stigma, are not really central to the topic.

Kite networks do move interconnected units crosswind together better than un-networked kites can coordinate, by coherent lattice waves, as seen in classic trains and arches. I have attended this annual kite arch event for many years near my NW home, Ilwaco, and developed kPower’s lattice-wave AWES ideas from the dynamics on display-

Dave, the video shows a network of static kites in arches. There is no problem as there is no expected power.
I quoted SkySails and KitePower, illustrating my message about rigid and soft crosswind kites. Thanks to produce more relevant observations.

The positive aspect is that existing companies could significantly improve the power to space use ratio without big changes in the rig, keeping their scheme of crosswind kites in figure-eight or circle in yoyo or flygen modes. R&D could focus to more adapted wings.

Pierre,

The kite lattice waves shown are coherent and energetic. These are just toys that fit in a small box, but a system of orthogonal PTO lines could harvest energy.

Wubbo’s SpiderMill is an example of a crosswind network AWES architecture that is not a toy. Extracting SpiderMill energy is by lattice waves. Very exciting.

Mesh of kites lattice wave schematic-

image

Your Ortho Kite Bunch requires resonant lattice waves to operate properly.

Im not sure if the Magnus and the Ampyx rigs are comparable.

Rather than using speed as a metric for turning, I think a factor times wingspan is probably more accurate than speed squared. The factor will of course depend on the design of the wing.

A rigid wing may as well turn really tight loops by rolling in the loop. It seems noone is actively pursuing this (except perhaps Kitemill as I am quite aware of this :wink: ). I am sure rigid wings could reduce the required swept area if this becomes a large issue.

Also, multi kite rigs will be an entirely different story.

The issue with super small radius for any kite, soft or rigid, is the nonlinearity of the inner vs outer tip. The effect is bigger the smaller radius relative to wingspan.

Actually I would argue soft kites like Kitepower have may use more area, as they can more easily fly on longer tethers (the kite being less aerodynamically effective). Different designs give different results I guess…

Turn rate and power during turn are the performance criteria used in competitive power kite sports.

High performance gliders do not roll very fast. They need very long tethers to stay inside the kite window power-zone, and easily overfly the window. If they ever lose velocity, they don’t turn as needed, but fall out of the sky.

If high performance wing motion is constrained by network topology, like twin-kite rigs, then tight turns in less airspace is possible. By extension, high cell-count lattices can host large numbers of wings in coherently phased lattice waves. Wings that momentarily lose phase or velocity remain airborne by collective suspension.

As long noted on the Old Forum, robust networked wing stability statistics are superior to single line single wing instability statistics. The kite arch video shows 2000 unit-kites with low failure risk compared to individual unit-kite topology. Complex individual control is a burden, not a solution. Lattice waves are a control solution as well as a scalable high-density design path.

In the examples I provide both fly by figure-eight. Magnus balloon has a low L/D ratio and flies slowly, while Ampyx wing has a high L/D ratio and flies fast. Magnus balloon has also a high lift coefficient, but its power consumption is too high as the tangential speed is high.

From https://www.google.com/search?q=aircraft+turn+rate+formula+squared+speed&oq=aircraft&aqs=chrome.0.69i59l2j69i57j0l4j69i61.12119j0j7&sourceid=chrome&ie=UTF-8 : " As the aircraft turns , if the airspeed increases with the bank angle held constant, the radius of turn increases with the square of the speed (r=V211.26tanθ ft). Hence, the distance traveled during the turn increases as the square of the speed."

The main reason to make tight loops would be in order to improve the “power to space use ratio” but the AWE world does not care of this ratio.

In fact the swept area cannot be advantageously reduced by using the same long tether because the tether is responsible for the space use. So the rigid wing should scale. Besides significant problems (cubed mass, high risk…) I don’t see how a large rigid wing could reduce the swept area without losing lift, “rolling in the loop” looking to be a dangerous maneuver in the time.

If you think about a network of kites, indeed it is different. I do not think there is an available technology to do it at high scale with safety control enough, because too numerous parameters are involved. Particularly a network would fail with sudden wind changes. The existing objects are not often networks. Aircrafts are not networks, wind turbines are not networks. In the other hand trains are networks but in a linear way.

I could agree but the figure I quoted (Ampyx) is hugely huge. By using soft wings the figure could be only large. And the swept area of the Magnus rig I quoted is quite small in regard to the harnessed power, a current wind turbine being yet better.

It depends on the scale it can reach.

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.