Pierre,
The excess ST rigid mass is simply shifted to the spacer spars needed to hold the lines apart, much like Rod and Christof apply spars. Let these designs try and scale further for the square-cube scaling penalty to be starkly revealed.
Compare with this better Metakite model-
You see a problem for scaling. I see a problem for the management. You can be right. The photo is nice but where is the power generation?
Scaling has always been a critical Aerospace/Aeronautics Engineering concern. My scaling analytics fundamentally derive from that culture, not subjective personal insight.
It will be nice as more AWES developers acquire a specialized aviation scaling background to inform their assumptions.
Scaling is a problem to solve, rather than guess at and get wrong. We must scale AWE successfully to power the world with wind.
Iām currently recycling 2x 3 blade Daisy rings, into a 1x 6 blade hexagon configuration.
Scaling by number has the advantage of modularity.
But another advantage occurred to me which I donāt think has been mentioned here. Flutter.
Surely because a short span section is stiffer it will suffer less from flutter at the speeds it will be going.
Can use of short span sections in our speeds eliminate flutter?
@rschmehl would you agree with this?
Your paper Aeroelastic analysis of a large airborne wind turbine goes deep into flutter analysis.
The most basic quote from Variations of flutter mechanism of a span-morphing wing involving rigid-body motions
ChaoHUANGa
ChaoYANGa
ZhigangWUa
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As anticipated, a continued decrease in the flutter speed accompanying the increase in span length is observed.
Iām going to attempt to sound knowledgeable by saying BFF means Body Freedom Flutter not Best Friends Forever
and BTF bending torsional flutter not ā¦?
In the kite Turbine rotors Iām making, there is cyclic loading on the tethering and through the blades.
The 5 point bridling is quite wide spread and set in 1 position for stable driving through the rotation despite gusts. Havenāt noticed flutter. Wouldnāt have a clue till it hit me on the head though.
Is this idea of flutter prevention by span reduction at our given speeds a valid supposition?
Also, it was the recent post with mention of using a hanglider put me onto this flutter researchā¦
http://forum.hanggliding.org/viewtopic.php?t=3863
Operating at higher altitude will give increases likelyhood of flutter ā¦ is that right?
At altitude, where TAS is higher than IAS, aerodynamic damping is weaker than at lower levels (damping is proportional to IAS) whereas inertia-induced disturbances are stronger (inertia grows with acceleration, which is the time derivative of TAS).
Read more: http://forum.hanggliding.org/viewtopic.php?t=3863#ixzz6ExoPxD9M
I suggested it before, thinking it can be a simple way to scale in number (and rotor diameter ?) without adding too much complexity and weight. That said I have no answer in regard to the flutter issue, but @rschmehl likely has it as you guess.
Thanks @PierreB
Yeah, the ring design always had 6 lines down and @Ollie said the solidity was so low with those blades that the 6 blades on that diameter and speed would be fine.
Hopefully, weāll know more soon. Some fine knot-work and duct tape bodging on the wayā¦ Iāll wear a helmet.
Hi @Rodread, it sounds like a fair general conclusion that stiffer blades increase the flutter speed. You should find some information about this from wind turbine aeroelasticity studies. Best, Roland
Scaling in size can be limited for rigid wings due to the cubed mass increasing as they scale. So scaling in numbers look to be a good way if unities can avoid collisions each other.
So I wonder if using suspension lines to relieve the structure can be a way to connect the units. In such a way the area could increase without cubed mass penalty. Connection elements should be flexible enough to avoid breaking everything.
The sketch below does not show the dihedral angles due to the force of the wind between the fixings on the respective fuselages.
If this concept is workable some other combinations can be found, such like other wings
instead of stabilizers, or biplanes.
In scaling a wing that long at high speed,
I suspect flutter is going to be a problem
That was one of the key points in Florian Bauerās analysis of the Makani archivesā¦
Remember that the Makani wing system had a split bridle to the sponsons/fuselagesā¦(canāt remember their term)
True. Perhaps using a flexible and hollow hinge between the cords of two wings, and the same for the other wings, but it is likely a not workable solution.
Scaling in numbers is interesting to mitigate the square-cube law. But it is not easy to put numerous small unities close each other, due to the tethers then risk of tangle, above all if unities work crosswind.
There were many discussions about (Magnus effect based) Flettner rotors. Limits of inflatable Magnus cylinders lead to a high power consumption even at a low spin ratio (below 1) where the coefficient of lift (CL 2 at the best) is far to be optimized.
However things are likely different with rigid cylinders (CL above 5, and a far lesser power consumption) which are not likely to widen under the effect of the wind. Some data are mentioned on the pdf that is available on:
https://repository.tudelft.nl/islandora/object/uuid%3Aae200352-5d8b-4551-900b-3d316cc5fd49
As a result small unities could be realized in order to avoid a too much weight penalty. thanks to cylinder topology, an unlimited number of cylinders could be put side by side or/and stacked. As the control is mainly rpm control there is no issues of turn and also of depower (in yo-yo mode, as shown by Omnidea balloon).
An example of scaling by number of Flettner rotors is given below:
Im thinking these cylinders seem heavy. Could they be standing tall on a carriage? Power take out on the carriage wheels or similar? It seems feasible that these magnus towers could be quite tallā¦
If cylinder diameter is too low, losses by frictions occur, leading to an inefficient device. So the diameter should be about 1 m, leading to a probably heavy cylinder, perhaps unless a lightweight construction including foaming epoxy systems is envisioned.
This really silly thing about wannabe AWE, and crackpot wind energy in general, is people never stop suggesting long-disproven ideas as though they are some new concept.
As shown by Omnidea, and different publications, and also recent ship realizations, the use of the Magnus effect is an AWE option among others, considering that lift is used. Advantages are the possibility to stack cylinders in all directions, and a lesser risk as the lift is increased by the rpm, not by moving the flying body both at very high speed and crosswind. A better knowledge of Magnus effect use would allow to aim the practical limits in regard of the peripheral speed and the involved power consumption.
I can see how magnus effect makes sense enough on a ship.
What I donāt like about magnus effect devices for AWES power generation
This could be a list
misalignment of motion (a spun cylinder goes sideways under a marginal lift effect)
the need for internal rigidity of a huge flying sausage
Even in a network like drawn
https://forum.awesystems.info/uploads/default/original/2X/4/42394048365916f307add6f85c5a90abdaf01f2d.png
How do you coordinate all of that?
However in the second AWE book two chapters (12 and 13) were dedicated to the Magnus effect based cylinder. Below is the chapter 12:
https://hal.archives-ouvertes.fr/hal-01759173/document
Also Omnidea shown a positive power (see at 9:50 on the video below) in spite the low spin ratio, in spite of the power consumption (about 1/4), but also with helium:
On my sketch each group of (top to bottom) superimposed cylinders has its own tethers, ground station, in such a way that misalignment can be permanently mitigated by rpm control of each cylinder. That said to put and control cylinders side by side looks to be more easy than top to bottom where a rigid frame is required to avoid touching each other when the wind falls.
Another concern is the stability which is good when the balloon is filed with helium. But I prefer avoid the use of helium, so the stability is achieved with large disks which are stabilizers in addition to add efficiency.
