RotoKite

An almost new video from RotoKite:

The difference with the older video is in the mode of wings retraction:

It would need power aloft to furl in kites like that …so, potentially a lot of weight in the ~“nacelle”
onboard gen or power up the cable? both heavy
Lot of volume in that centre = drag… lot of kite in the centre of rotation = slow kite & low lift…
On such a short flight path will it have time for cyclic pitch control without serious wear on components?

Don’t get me wrong… power aloft is fine if you’re generating and using it efficiently … Very keen to explore how much I can add into a higher power daisy wing and how little power I need to control it.

You need a motorized pulley for this i believe…

Good question. A cyclic pitch control can be better with huge soft wings.

The rotokite can be dismissed for now. There are just renderings and the concept is flawed.
Something similar is certainly possible and someone should work on it.
What I see as the main problem, which Rod has pointed out, is the cyclic pitch control. - on soft kites. I’d buy it if the kites were rigid but even then a lifter would probably be the better solution.
I don’t see volume in the center as a problem. That’s where the slowest part where drag matters the least.

The cyclic pitch control on soft kites is quite possible, by using two opposite wings with their respective kite control unit that are similar to the wings used by KitePower http://www.kitepower.eu/technology/3-sytem-components.html . A lifter would add an expense of energy during reel-in phase.

1 Like

But the two opposite wings could have a lower efficiency than a single wing flying crosswind.

Cyclic pitch control is done on helicopters, a fact making probable that this is also feasible for such a kite rotor, given some invention and engineering.

1 Like

I’m not saying it’s impossible. But doing it on soft kites of such a small diameter and corresponding rotational speed is hardly worth it, in my opinion.
Make it rigid and the diameter at least three times as large and I’d say it is worth pursuing in order to simplify flight control in contrast to yo-yo.

There also needs to be some positional control when reeling in, which the current design does not have, unless it’s lighter than air, which it probably isn’t.

In the first video there is an unpowered aerostat. Is it a viable answer to the positional control you mention?

A similar concept with rigid blades but also with bridled wings is described on
http://cdn.pes.eu.com/assets/misc_new/peswindissue17talkingpointskylimitpdf-891355291894.pdf.

I’ve written to @gianni from Rotokite and he replied and sent me the attached files:

Dear Luke

Thank you for let me know of the forum I will follow it carefully and I will point it out to those who have thought about this project
I’ll tell you some things about this idea
I had some flying experience for a gliding patent and when Massimo ippolito ( Kitegen ) who was my partner in an electronics industry start to
work on kites to make energy, I thought a wing on a leash would have a lot of problems with cable resistances
Of course the rotation is not very efficient but if you can go higher maybe you can have power with a simple system
A light central balloon with the effect of increasing the diameter and simplifying flight control and takeoff
Having electricity the hydrogen needed to maintain the pressure, I do not think it’s a big problem
The closure towards the center was suggested to me by Olivier Caldara who wanted to make a prototype but I closed the bio air technology
A generator placed between the cable and the rotating part can feed an electric motor for the recovery at the center of the profiles and also for on-board eletric services
I send you attaced a short presentation of the project
Every cooperation to develop this project would give me much pleasure but first of all it would be important to produce renewable energies
Best regards

gianni v

Rotokite 3.19.pdf (1.1 MB)

We had presented ( 2010 ) a project to the European Union with Cimsa and I received this contribution from them.

I share their opinion that with a slow rotation speed it takes a lot of wings

the ROTO project, have a very hight drag coefficient.

For an average wind speed of 15m/s, a parachute having a
nominal diameter of 3m, leading to an inflated diameter of 2m
approximately, will generate a pulling force of 170kg. If the
wind speed is 20m/s, the force generated is 300kg

@gianni has now joined us on the forum. Welcome! :slightly_smiling_face:

2 Likes

Below is a video of some experiment of autorotation with only one wing, using a two lines 0.7 m² kite which was held by only one line during the rotation.

@Gianni: I think these values (170kg and 300 kg) work with an inflated radius of 2 m, so a diameter of 4 m.
This approach can be interesting for other reasons: a lesser space use, so a better power/space ratio, and also a more regular force which is obtained by using a low radius loop, compensating the lesser efficiency.

The counterpart is an a lesser efficiency per wing area. A compromise can be found to achieve barely less efficiency as my experiments of autorotation with only one wing show on the video I have attached above RotoKite .

Roto-Kite: a study for theoretical and experimental validation by Enerkite

The work of Enerkite, with a preliminary study, has allowed to validate the project for the
generation of energy up to the order of MW, obtaining assumptions of weight and cost
of the system and LCOE parameter.
Output power peak 20 kW 1 MW
Nominal wind speed (m/s) 9 9
Kite wing opening (m) 6.5 46.2
Rotor area (m2) 130 6,700
Kite weight (kg) 9 650
Annual production (KWh) 74,885 3,744,292
Total cost generation system(*) (€) 11,320 160,000
Electricity cost (€/KW, less than) 0,025 0,02

Authors: Dipl.-Mat. Max Ranneberg; Dr.-Ing. Alexander Bormann; Dr. Bernhard Kämpf; Dipl. Des. Christian Gebhardt Dipl.-Ing. S. Skutnik.
Dok.Nr.: EK_FT_0018 Date: 26.06.2014.

As a preliminary observation It appears that the rotor area is the area swept by the rotor (it is normal) and that the full opening of a wing matches its wingspan. Thus, a wing takes the radius of the swept area. A brief calculation confirms that matches the respective values of the rotor area.

Now the paper on Betz limit indicates:

“AWE drag power systems can harvest up to 16/27 of the power available in the wind.
AWE lift power systems can harvest up to 4/27 of the power available in the wind.”

The “Output power peak” values (20 kW for 130 m², 1 MW for 6,700 m² rotor areas) are far above 4/27…

As a result only one kite (instead of three) could be sufficient as I suggest here.

This is nice but the presentation has me a bit worried: pumping water rather than creating electricity? That swivel is not going to be easy to make. And finally; 1 MW is a lot of power. That needs to be backed up a bit more if I am to bite the hook…

Roto-Kite project
• A simple project characterized by a few kg of fabric and cables, a balloon to keep the
system in height even in the absence of wind, a ground-based generator
• The rotation produces a lifting force which is transmitted to the ground by the bound
cable and transformed into electrical energy
• The rotation principle and some technical aspects of flight control are commonly used in
helicopter flight technology
• The size of the rotor can be modified to adapt to the intensity of the wind

So this system looks to be for creating electricity. Apart from that, I think that the central aerostat can lead to a maintenance problem more than an automated piloting system, especially since a computerized control will always be necessary, even if the AWES produces in passive mode. So I can prefer a low radius loop system with only one controlled kite.

It is my opinion that the Roto-Kite system will not work because of cosine cubed losses. Skymill’s schematic shows a tether angle of at least 70 deg. This means that they only achieve 4% of potential power! Gianni’s analysis shows approximately 45 deg. which will achieve 35% of potential power. In addition, their analysis does not include the weight of the tether.

Yes, but I think its only to show a farm of AWES in the picture. Generally crosswind and rotating AWES (comprising my experiment of low radius loop) fly at a tether elevation angle of only about 30 degrees, achieving 65 % of potential power. So it can be the same for Skymill and Roto-Kite systems.

Seems we’re a tough crowd.

I’d like to add the drag of the aerostat (and blades) will require compensating lifting force in order to avoid high wind blow down. This has not been shown?

I’m not writing this idea off. Rotating wings have a hell of a pull force (technical talk) and can stack.
They can be flown on a single line… I’ve flown old Daisy rings on a single line… Interesting…
Your concern may be the induction of twist onto the pulled single line… Not a problem if you modularly add sets of ClockWise and CounterCW rotors onto the line. Just ensure they power and depower at similar times for stroke actuation. The powering can be furled, banked or pitch actuation.

Adding the sets onto a lift kite line isn’t too hard a technical challenge.

Sending the lift kite out on a steady 1/3 wind speed at a low angle isn’t too hard a challenge.

To me it looks like a good way to take the rotor kite advantages to altitude… I rate this project

1 Like