Turbine Orientation

I think the focus on % loss is a little misguided. For any AWE, it is quite likely that zero elevation angle is plain impossible.

Conparing with a HAWT (regular windmill) yes you have losses, but you have benefits as well.

Cosine loss only means that you need more wing area to achieve the same power. This is bad, but other factors may be limiting the scale also, like tether strength, power rating of the ground eqipment etc.

And, for a superturbine type og windmill, if you point the rotors horizontally, you need to add an extra force to counter tether downwards pull.

Also remember higher elevation would mean more altitude and higher average windspeeds.

Im not sure cosine losses is the best place to start a design…

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Unfortunately the cosine cubed losses are more than the gain from increased wind speed. For example, increasing the tether angle will cause a cosine cubed loss of 46% whereas a 10% increase of wind speed will increase the power by 33%.

It is also possible to increase the altitude without modifying the angle of elevation by lengthening the tether.

But other issues would occur such like higher space use, and tether weight.

My example suggests increasing the tether angle from 30 deg to 45 deg. It would be even worse for greater tether angles.

Yo-yo mode requires crosswind action. Why not replace the turbines with arrays of kites which are lighter and cheaper. Kites will naturally turn to face the wind during crosswind action providing more power. This is similar to your Orthokitebunch system with a different power takeoff.

The parachute on chinese umbrella description.pdf (1.3 MB) does (did) not use crosswind action during yo-yo phases (The most basic airborne wind energy system).

Multi-rotor could make the same, enjoying a higher lifetime as the rotors are rigid, and also perhaps easier to implement. Indeed thin rotors are around the tether without transfer issue, only thrust. So the rotors are not connected and are adapted to different wind conditions according to altitudes.

It is true. The same is not easy for rotors excepted for facing rotors like for Makani or FlygenKite.

Like something you’d see sketched in the margin of a junior high school kid’s notebook

Indeed, because as you just wrote:

Yes Pierre, it definitely has the advantage of simplicity, and I’m probably one of the kids who sketched it in the margin of my notebook way back in the '60’s or '70’s. Also underwater versions. By the time I got to college all my margins were full of wind-energy-themed art, mostly just very vague themes.