RotoKite

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 - #12 by PierreB .

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

http://www.sequoia.it/wp/en/wp-content/uploads/2016/10/wind-full.pdf, page 11:

Making a kite capture energy with cables as long as a kilometer is like
racing a greyhound on a leash hundreds of meters long.

Generally it is true, but not if its wingspan or swept area is a kilometer wide, for example by using tied flexible wings.

That report is a really enjoyable and honest read
it does suggest that a rotary design has a swept radius sweet spot …
Their tests with a single kite could not sweep a tight enough radius to be efficient.
Their analysis showed that sweeping too tight a radius with 2 kites linked at the tips is inefficient.

We’ve demonstrated that Kite rotors still work when you remove the central parts and replace the wing to wing connection with tensile line like the slightly later picture posted on tied flexible wing

That enables a tight autorotation with high speed on all blade elements and lower blockage with less chance of hitting your own wake

I recorded on 08/21/2016 (H6EA1G8_152234) an unpublished design about tied wings (see also the video of tied opposite wings and central parachute; it would suffice to tie additional identical wings on each side):

This design concerned rather C-shaped semi-rigid wings. I forgot this for two reasons: no single C-shaped wing has ever flown to my knowledge; the second reason was not correct because I thought that the tied wing blade could have a huge span while it remained narrow, being not able to fill the swept area, forgetting that the narrowness could be compensated by the number of the tied wing blades. So gigantic rotors could be built by tying very small flexible wings.

@Rodread , concerning your method by removing “…the central parts and replace the wing to wing connection with tensile line…”: indeed the wing power is more fully used (about 2 times per wing area for a complete rotor compared to a rotor of Rotokite or mine with tied wings everywhere, and it is a proven method but at small scale. I do not know if entanglements could be avoided at high scale without a fine computerized control as for any dancing kite systems.

Indeed tensile lines are efficient but only in traction, while tying flexible wings on the full span provide a supplementary shape cohesion by wind force over the entire surface of the rotor, giving also the possibility to add some lift in the central part comprising the central parachute.

In some way tying wing of the full rotor would reproduce the classic configuration of a three-blade ground-based wind turbine where the central part also does not produce much power, although it produces lift for the AWES version.

Now concerning the Rotokite report on my previous comment, I think the table 4.2 page 50 is a bit optimist.

Peak Power Output Class 20 kW 1 MW
Nominal Wind Speed 9 m/s 9 m/s
Wingspan Of One Kite 6.5 m 46.2 m
Rotor Area 130 m2 6700 m2
Kite Weight 9 kg 654 kg
Elevation Angle 30◦ 30◦
Reel-Out Speed Coefficient 0.38 0.38
Partial Load Efficiency 0.33 0.33
Nominal Force 5800 N 290 kN
Induction Factor 0.9 0.9
Nominal Ouput Power 20 kW 1 MW
Nominal Tether Length 150 m 300 m
Tether Safety Factor 5 5
Tether Weight 3.7 kg 360 kg
Hover Power 80 W 4 kW
Drag During Reel-In 1.1 1.1
Area Reduction from Rotor Area Solidity x 0.05 Solidity x 0.05

Knowing that in reeling yo-yo mode the power coefficient (CP) cannot be higher than 0.15 (4/27, so 1/4 Betz limit as documented), that leads to a value of 439.857 kW, then 285.731 kW by taking account of cosine³ coefficient (0.65) with an elevation angle of 30 degrees as stated, then half due to recovery phase, so about 1/7 the value of 1 MW as stated. It is true that 9 m/s wind speed is rather a low nominal value.

1 Like

That’s odd, I don’t remember seeing this in Milan but one of them is from the Politechnico …?

(having seen their video)

Theres no Planet B!

Ok, having dealt with the global warming discussion, i have a few questions

1: Launch and land?
2: Scalability?
3: Has it been tried already and what happened?

This is an interesting one though as it checks off the «high altitude wind»
box…

Also, why would that give power to poor people, rather than these?

All these questions and more answered in the 2016 paper «Design space exploration of gyrocopter-type airborne
wind turbines»

http://dx.doi.org/10.1002/we.1873

This paper presents a multidisciplinary framework for the design and analysis of gyrocopter-type airborne wind turbines. In this concept, four rotary wings provide lift to a flying vehicle, and excess power is extracted using gearboxes and generators before being transferred to the ground through electrical conductors embedded in a structural tether. A physical breakdown of the system was performed, and five models were constructed: wind model, rotor aerodynamics, structural mass, electri- cal system, and tether (structures and aerodynamics). A stochastic optimizer in the framework enforces interdisciplinary compatibility and maximizes electrical power transmitted to the ground under various operating conditions. The framework is then used to explore the design space of this advanced concept in numerous flight conditions. The effect of implementing new technologies was also studied in order to evaluate their effect on the overall performance of the system. It is shown through a 1.3 MW design that a gyrocopter-type airborne generator could provide more power than a ground-based wind turbine for a given blade radius, although only a fraction of the available wind power can be harvested using off-the-shelf technologies and components. The work presented in this study demonstrates the challenges of designing a high altitude wind generator and shows that performance is affected by complex interactions between each subsystem.

The company that already did this was Sky Windpower. https://www.skywindpower.com/

That page does not seem to have been updated since 2011?

Just because you are poor doesn’t mean you have access to good wind.


needs a couple more bridles supporting these poles to the main tether

1 Like

Actually I am not sure humility is a good indicator for innovation either…