I dont understand what you are thinking here. Either a kite network with many tethers and total kite area, or a single kite with a single tether. The AWE architecture should have a massive impact on dimensions. For single kite single tether, the dimensions you suggest are ultra short tether compared to current popular concepts. This is an interesting direction, but its difficult for someone like me to see how that kite would even look…
It is very clear. The flying body is 1 km for one of several tether(s) of 1 km. The discussion goes towards confusion because of numerous irrelevant posts from @kitefreak as for any topics.
You mean 1 km wingspan and 1 km tether? Or 1000 square meter kite with distance kite-ground 1 km?
I agree the difficulty then I am glad you see it.
A sketch is below, here a rotary AWES or several crosswind kites sharing the same swept area. It is not necessarily my choice for an AWES but only a way to represent quickly what I try to say.
So Pierre is proposing WS/TL*=1 as an AWES scaling design principle.
No other critical AWES scaling principle or limit is accounted for, so caution is due.
…. * WingSpan to Tether-Length
The value of 1 is obvious from my first message.
“maximized swept area” (MSA) or WS? How can either equal 1 tether length? WS = MSA?
MSA is two-dimensional. The values are incommensurate.
The dimensions of a swept area are dimensions, not an area as such, and are not measured in km².
Thank you Pierre, for your patience in explaining how you reach your results.
“Swept area” really is Area to be accounted in m2. The confusion is to insist otherwise.
So, I will give an exemple for @kitefreak as he has some difficulties understanding basic things.
Measuring the size of a football stadium in metres, not in m²: the length can be 105 m, and the width can be 68 m. After that its area can be measured in m².
The same stands for the flying body or its swept area. After that the flying body or its swept area can be measured in m².
We speak about size, not about area.
Agreed- L x W = A, given as m2
Again, WS in meters and swept area in meters-squared are not commensurate values, and would not give the same tether length.
KiteForum.com is not the best place to clarify the math contradiction. Its a great source of kite knowledge, that we can rely on for that.
A swept area has dimensions that are measured in meters.
@kitefreak you persist to don’t see any difference between dimensions (in m) and area (in m²). The topic I opened is about the proportions of the dimensions between the tether and the flying body. So the same unity (the meter) is necessarily used.
I am pointing out the difference between m and m2. As a kite scaling expert trained by KiteShip and many others, this is a topic where I can contribute.
For example, there is currently a scaling limit on how large and massive a kite can be handled on the ground without damaging the fabric, somewhere around 1000m2 even on grass. This implies we will have to develop kite assembly mid-air to scale further.
There are many such kite scaling factors to share.
All unit-scaling factors apply to “scaling by size”. It seems reasonable to include tether-scaling here or form a tether-scaling topic.
A vertical scaling limit is the 2000ft airspace ceiling defined by FAA. The horizontal limit is far larger. Lets assume in metric unit an extended horizontal zone of ~500m vertical extent.
A sweeping wing’s pattern must be contained within, so due to normal turning limits, the sweeping wing should be not much larger than 200m WS, depending on specific kite design.
A larger kite could be flown and tapped that does not sweep a full figure-eight or loop, but does Dutch Roll in a tighter higher-solidity airspace. Imagine a powerful buffalo galloping, as seen for the front, tugging PTO lines by its gait. Imagine many such beasts side-by-side, optimally filling the space (by roughly 25-50%, for Dutch Roll sweep and bypass).
Current AWES prototypes like the M600 and AP3 occupy the defined airspace, but very sparsely. It was reckoned by Makani, and agreed by kPower, that a 10x Area soft wing is a rough equivalent by power (at least at smaller scales). Soft wings helpfully turn under power on a tighter radius and can be around 100x greater in Area in the defined airspace. This owes to the severe scaling limits that apply on “kiteplane” “energy drone” classes.
One of the most critical scaling factors is that probable wind velocity remains constant in the defined airspace while the minimum flight velocity of a kiteplane grows with higher mass and wingloading.
Using the scaling laws so loosely based like «mininum flight speed scales with mass» you face the problem that we have no clue to the impact of the scaling law. We all know the world is probably like this, but did we hit the wall at 5 kg mass, or are we hitting a wall at 50 tonnes?
The answer defines whether this is a worthwhile scaling law. As it stands, if you want to convince me (and maybe others), you need to back the scaling law by some reasoning.
Much on the same note, many early AWE texts state that tether drag is less of an issue with scale. With a few simple calculations I was able to figure out that tether length scales with wingspan. Thats quite different from «solved with scale».
To get these nuances right is super important. A lesser discussion is of little interest to me at least
In aerospace we use the case-base range of velocities and masses from scale-model to jumbo-jet for minimum flight velocity data. These data allow us confidence that “minimum flight speed scales with mass”.
It would be “clueless” not to apply this data heuristically. From WP-
The figure above shows «speed» and not stall speed which would be a more relevant metric to make assumptions about lowest possible production windspeed.
The stall speed of the largest aircraft in the chart, a 747, is 75 m/s. The minimum/maximum weight is 272/408 tonnes. Wingspan is 60 m.
The relation between stall speed and AWE performance more or less relates lift to mass, so though a bit convoluted, it should be relevant.
An AWE optimized wing should only weigh a fraction of a 747. Lets assume 1/30 (based on some quick calculations). Thus the stall speed could be reduced to approx 14 m/s. Even with a large tether drag, this aircraft could be suitable for AWE. So my conclusion (based on a really weak foundation) is that AWE should scale to more than 60 m wingspan, which represents an altitude of approx 2.5 km above ground on average. Which does not sound all bad to me.
Nevertheless, the chart is a good one.
(I am considering single wing single tether AWE in this matter)
I see AWE scaling as a very clear subject.