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Iâve made a few changes, simplifying the whole thing and developing a few points. The last sketch :
New conclusion for my preprint:
It turns out that pumping mode is not viable with the system described: the enormous mass of air inertia would lead to a control shift that would be manageable in mild weather conditions, but unmanageable as soon as thermal ascents or descents occur. Stationary use is therefore essential, as a lifter to support AWES or/and photovoltaic film
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OK this is kind of sad. The death of an AWE system. Maybe there is still hope? I will say though, I am reminded of a day I was supposed to launch on a tandem flight from Crestline (1 mile high). My flight was cancelled. âWe had a fatalityâ. This was on June 29 at 1:29 PM a few years ago. Think about that date and time: The highest thermic activity imaginable, and this site has a LOT of thermic activity, which start out at ground level as âdust devilsâ. The dust-devils often climb up the mile-high hill.
Well, a pilot named Larry, not known to be some super-pilot, but a regular flyer, had decided to launch into the great thermic conditions. There were a couple of bystanders who happened to be there talking to Larry and watching the launch. According to them, the entire flight lasted about four (4) seconds. Larry launched, his glider tipped over sideways and did a 180 right back toward the hill, slamming into a tree that people would typically tie off to at the top of the hill. I guess he was killed instantly.
Today there is a plaque on a bench at the launch, acknowledging Larry, as well as a female paraglider pilot who had âgone inâ after getting drunk on her birthday and flying. She was doing some sort of stunts and apparently got stuck in a diving spiral from which she could not escape. Then it took a long time to find her.
Anyway, that part is not really relevant - letâs stick with Larry: Thermic activity can ruin your day. You could have 100 perfect flights, then one day, it all goes bad. Just a roll of the dice. As one guy teaching me had confided âIf you could see the air, you wouldnât flyâ. ⊠
I knew the issue of thermal ascents by making Solar balloon jumping. A balloon of 400 mÂł leads to an inertia mass (mainly air) of about 460 kg. The game is using the kinetic energy of the balloon when it is climbing to lift someone when the rope is taut. The buoyancy is about 200 N (20 kg). So the jump is about few meters height. But if a thermal ascent occurs, the height can be far higher.
The problem is far more serious with utility-scale Magnus balloons inflated with air, whose the volume can reach hundreds of thousands of cubic meters. During the descent phase of pumping mode, if a thermal descent occurs, the balloon will no longer be able to recover, and the crash is assured, with destructive effects: the one-kilometer balloon contains 31,400,000 mÂł, which corresponds to an inertial mass of around 35,000 tons.
From High Altitude Wind Energy | HAWE | Project | News & Multimedia | FP7 | CORDIS | European Commission (Omnidea):
[15] e) Instead of the expected 5-10% energy consumption from the ABM (to keep it rotating), nearly 20% of the average power production was needed. This effect is due to the balloon bending between its âcantilever typeâ fit in both ends, an un-anticipated effect and is considered, by the HAWE team, a very important experimental result as it is now known that it has to be minimized. Bending can be minimized with higher internal pressure, with bigger rims (structural reinforcement of the tops) or a different rotation system that has been developed throughout this project and tested at sub-system level. In this alternative ABM rotation system, the cylinder is anchored in a third point (through a ring in the middle section) and rotated through this ring. Further info can be obtained in Deliverable 10.4.
âThe cylinder is anchored in a third point (through a ring in the middle section) and rotated through this ringâ: this could refer to a belt transmission as studied in this topic.
I dont quite get what the problem was that you discoveredâŠ
My explain is on Preprint: Towards a gigantic Magnus balloon with motorized belts - #111 by PierreB.
Another major issue due also to the huge inertial mass of air is the slower accelerations of the balloon during ascent phases alternating with descent phases, leading to significant loss of power during very long transition phases.
As I find that Magnus balloons are interesting because they can be stacked easily (Omnidea shows two stacked balloons on the video at 1:50 ; see also stacked Sharp rotors) and perhaps could fill the space, I maybe will open a topic on âMagnus balloon laddersâ.
I find it strange that a huge magnus cylinder does not also have a huge aero lift to match a huge moment of inertia.
I was expecting the problem was starting and stopping the rotation of the cylinder itself.
Both moment of inertia (rotation) and kinetic energy by linear displacement during vertical pumping cycle are mainly due to the mass of air of the balloon. The mass of the envelope is very small compared to the air mass. The inertial mass increases with the volume, so a magnitude more than the âaero liftâ which increases with the area. So the âaero liftâ ends up being insufficient when the balloon scales up.
Beside this, a neutral (slightly positive) buoyancy for the vertical pumping mode is better. With a huge buoyancy the descent phase would consume too much power. And varying the heating according to the phases is not an option, nor is the use of hydrogen or helium.
So the ascent phase is assured by aerodynamic lift by Magnus effect. And as the huge inertial mass of air can operate in the two directions of translation, up and down, the Magnus effect alone should absorb both change of directions and thermal currents, by taking account of a very low rate of acceleration of the vertical translation of the balloon and its rotation, due to the huge inertial mass of air. The enormous kinetic energy of the rising or falling balloon is an aggravating factor.
Even re-establishing the rotation to obtain positive lift will not be enough if the balloon descends too quickly due to the winding phase combined with a thermal descent.
A 1 km balloon hitting the ground at 10 m/s would generate a small storm in the surrounding area.
I didnât say it explicitly, but this inertia in starting and stopping and that of the air mass, and the difficulty of starting and stopping the rotation was one of the reasons I said this:
How much rotational inertia the balloon would have in addition to that of the envelope is still an assumption I think. I donât think itâs that high from the air mass rotating with the balloon, but I think you would like to get it higher, using internal baffles for example, to get smooth operation and to be able to convert the rotation of the balloon into rotation of the generator.
This moment of inertia from the air mass would also work against crosswind flying I think.
Those things combine I think to make a train of smaller radius, and shorter, balloons flying crosswind a better option. Youâd still need to find a way to land and launch it.
I used this example of a non-rotating balloon to show the problem of an inertial mass of air in a balloon of several hundred thousand cubes, concerning the translation issue, up and down during vertical pumping mode, not directly concerning the moment of inertia (due to the rotation) which is another issue. That said the moment of inertia mainly increases with the volume (as the inertial mass of air) so the air mass (the mass of the envelope being very small compared to the air mass), so a magnitude faster than the area of the balloon, leading to slower starting and stopping of rotation.
I am introducing a preliminary sketch:
All this obviously leads to smaller balloons with lower radius. As a secondary consequence the effect of the centrifugal force (âto a very limited degreeâ refers to it) would increase:
And in addition the vertical trajectory can perhaps facilitate stacking.
However I prefer vertical trajectory due to a higher potential of maximization of the space. And I think that the turns (in figure-eight), as well as taking up space, hinder and slow down rotation. I experimented crosswind flight with turnings with 3 Sharp rotors under a kite flying crosswind by figure-eight : the coefficient of lift seemed lower than that of a same but static rotor.
That said a re-examination of the WindFisher trajectory shows that there are no turnings as such, only changes in the direction of rotation of the cylinders, which removes the problems mentioned above.
See also the poster and the aerodynamic coefficients (bottom right and enlarge image) on
In all these Magnus balloons, the rotation is motorized and is used to generate lift: the higher the spin ratio (tangential speed/wind speed), the greater the lift and drag, which overall increases the power of the system.
That said, horizontal crosswind Magnus balloons could avoid any turn be reversing the direction of the rotation after each transversal trajectory, avoiding (in addition to possible loss of rotation speed and maximization of the space) some gyroscopic effect destroying stability. The reel-in phase occurs at an edge of the flight window, after each transversal trajectory and change of rotation direction, or after several return trips. Compared to a vertical trajectory, the horizontal trajectory doubles the amplitude of the flight on either side of the approximate center of the flight window. But the management, a little like that of OrthoKiteBunch is very complex, including takeoff and landing:
And âconventionalâ spin motors are used instead of motorized belts. These motors can be settled at the top and bottom of the set.
This only means that a 10 m diameter magnus cylinder needs 10x longer distance to stop than a 1 m cylinder. This should be expected
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That sounds about right.
And to think that kinetic energy made me happy for solar balloon jumping. Now itâs just the opposite.
Thatâs what AWES is all about: thereâs always something that sticks, even on paper when you look at it closely.
Fortunately, there have been quite a few experiments and scientific publications. Now a good bureaucrat can perhaps find solutions by juggling the parameters, avoiding the pitfalls, and ending up with something viable. But itâs not a foregone conclusion!
The features of the path of the crosswind Magnus cylinders of this sketch seems to be close to those we see on the animation of Wind Fisher.
Indeed there is no reverse position of the cylinders as they go forth and back, just a rotation in one direction and then in the opposite direction, alternating with a recovery phase at each edge of the flight window. Interesting!
Now of course we can forgive the teeming throngs of neophytes, maybe a few âjournalistsâ, who look at this and are convinced they are witnessing the future.
But, people like us, well, weâve seen one or two of these types of ideas, or more to the point, a never-ending parade of such ideas, so we know better, right? Right? Well? âŠ
We know that the future of wind energy looks like the present: ground/sea-based 3-bladed wind turbines.
But we are on an AWEforum. So weâre discussing all sorts of concepts, including Magnus balloons, even things with multiple rotors.
Interesting piece of «fact» there. Though I propose one should not trust 100% in what the future looks like.
I am not here to discuss a non-practical means of wind power generation. I am here because I think AWE may still be realized.
Its important to be clear about these things because if someone is on the forum just due to idle curiosity, that would make sense maybe in a creative way, but not interesting to me