As a start: a balloon 6 m long and 0.95 m diameter
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Are you actually building this?
I used HDPE film 30 microns (0.03 kg/m²) for Solar balloon jumping but Magnus balloons could also work, only for experiments. I have yet a reel of 3 m round film tube. So I cut the two ends then the balloon is made, like on the photo.
Magenn Mars was limited by using torque with a Savonius-like turbine for a small area around the balloon, and heavy and slow generators aloft. But that does not mean balloons that use Magnus effect are not efficient.
Magnus effect balloon should use lift like Omnidea does. With an appropriate arrangement it could become a (if no the) promising AWES, being inflated with air, and being able to scale in any dimensions.
Wrt stabilizing a magnus based kite, Peter Sharp mentioned a relevant patent of his to provide dihedral effect to a magnus wing by tapering the radius of the wing.
This could be an important implementation detail as dihedral effect will let a kite be stable in a loop in the roll axis. Ultimately it could remove the need of active roll control.
The other way I figured out was to use wing sweep. This method though seems more difficult to implement, in particular wrt the end plates.
Below is an interesting paper and a summary about experiments on a Flettner rotor. The pdf is available.
Highlights
• Flettner rotor CL affected by Reynolds number in critical regime.
• Flettner rotor CD affected by Reynolds number in critical and supercritical regime.
• Flettner rotor power consumption scales with cube of tangential velocity.
• Power consumption found insensitive to Reynolds number.
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So for a thought experiment: imagine a diameter D, length H magnus cylinder used as a single AWE wing in a lift mode rig. Its flying speed is v = n w, where n < G_e (the glide ratio). n accounts for cosine loss and roll/centrifugal losses. We’ll disregard mass.
The power of the AWE rig, with one third reel out speed (and small solidity is:
P = \frac{w}{3} \frac{1}{2} \rho C_L n^2 w^2 D H
The magnus power consumption is (from eq 3 in the paper):
M = C_f \rho (k n w)^3 \frac{1}{2} \pi D H
\frac{M}{P} = \frac{3 C_f \pi k^3 n}{C_L}
If we further assume k=2 and n = 5, C_L = 6, and C_f = 0.007 from the paper:
\frac{M}{P} \approx 0.4
It seems infeasible…
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The first equation about the power of the AWE rig is understandable for me. Some light note: k = 2 matches Cl= 4 as shown on the figure 4, so not 6, for what I think to have seen. So with Cl = 4, I obtain 1966 W with your first equation, instead of 2949 W with Cl = 6. I assume wind speed is 13.85 m/s, and k is 2 like you mention, thus the tangential speed being 27.7 m/s for 530 rpm (figure 13) that in order to match the figures 4 and 13. The cylinder is 3.73 m x 1 m.
The second equation about Magnus power consumption matches eq 3 if we muliply by n cubed, so 0.125, as you did, I think. But that should work if another wind turbine like Savonius rotates the Magnus balloon, not if a motor is used, in which case the coefficient n has not to be used. So by using eq 3 I obtain 1044 W. The ratio P/M is now 1966/1044: it is not so good but 1000 W is the value shown on the figure 4 for 530 rpm (27.7 m/s), so not too far from 1044 W. But here for the power of the AWE rig the coefficient n² has also not to be used for what I think, since it is still the motor which rotates the balloon. So it becomes 7865/1044. It is not too bad and a better value is not expectable.
I think the eq 3 gives a far higher value than the equation given by the chapter 12 page 293. This is due to the cubed value of the tangential speed while only the wind speed is cubed in the chapter 12, not the spin ratio X (here k).
The Omnidea balloon has a Magnus power consumption of 1/3 or 1/4.
Please correct me if I am wrong.
Im sorry I mixed losses with speed to windspeed ratio. After adjusting n from 0.5 to 5, it no longer seems feasible due to power requirements. The smallest useful n for AWE would be around 2, in which case the power ratio ends up around 16%, which is maybe feasible, but in total the whole concept seems a bit marginal…
I have edited my post to correct this
n = 0.5 seems to be a possible value as it is the cosine with 60° elevation angle. The cosine of 0.8660 with an elevation angle of 30° is often used as a reference for crosswind kites.
n = 5 seems to be a ten times too high value.
And also n is not mentioned in eq 3.
The Omnidea balloon has a Magnus power consumption of 1/3 or 1/4.
Have you some explains please?
n is the ratio of speed of the kite vs windspeed. So anything n < 1 is not crosswind flight. To find n, one would start with the glide number, divide by cosine loss and roll losses, possibly also sideslip losses. n=1 would approximately represent Omnidea.
There is still room for optimization, eg reducing k to 1.5 or optimizing C_L to be even bigger. Still seems like we are hitting a wall here. I will try to run some simulations to see what kind of power one could expect…
Looking at the fan-wing, if the power use is similar to magnus, I find it uses less power. The formula for mangus power we used previously gives us 344 W while experiments show very approximate 150W.
Source: «Study on Helicopter Antitorque Device Based on Cross-Flow Fan Technology», Hindawi Publishing Corp, 2016
It is not free unfortunately.
Anyways, given the better C_L and G_e of the fanwing, it seems a more probable fit for AWE rather than magnus. Though it is not easy to build…
Thanks for the explain for n.
For what I know there are two recent significant experiments on the Magnus power consumption: one concerning Omnidea on Analysis of Experimental Data of a Hybrid System Exploiting the Magnus Effect for Energy from High Altitude Wind, and now one other on
https://www.sciencedirect.com/science/article/pii/S0167610518307396 I put again.
In some way it would be good the formula matches these experiments. However as I mentioned the formula are a bit different:
I think by just browsing through papers it is difficult to make any real conclusions. A better study supported by experiments would be required. The data we have though, suggest that there are some real possibilities, though somewhat limited.
I think the paper is consistent and the equations overlap the experiments.
And even in spite of its 1/3 Magnus power consumption, a Magnus balloon like Omnidea’s could lead to an efficient device if it can scale more than others devices.
The age of airships set operational scaling limits for inflated tubes. To survive storms they needed giant hangars. This is not an economic option for cheap energy.
A power kite packs quickly in a small bag or sleeve when conditions are threatening. A large inflated structure is slow to deflate and pack.
It turns out that Cl of a wing has many specialized competing formulations. This is especially tricky for a tumbling wing that undergoes cyclic phases of negative Cl or a spinning cylinder where lift is boosted by the power input. The premises for anomalously high claimed values of Cl for Magnus need to be closely studied rather than accepted uncritically.
There is also the powerful buckling force on the center of a Magnus kite rotor that gets worse with scale. Scaling up internal pressure is not a practical option.
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A 50 m long 5 m diameter magnus wing could produce a MW of energy at 10 m/s windspeed (really rough estimate).
Quite a lot smaller than « The largest airship, the LZ 129 Hindenburg at 245 meters length and 41 meters diameter, dwarfs the size of the largest historic and modern passenger and cargo aeroplanes.»
Using the hindenburg as magnus power plant would produce a whopping 40 MW… If you did that I believe you could afford to build a support structure (manned) on the ground for rainy days, or just use a pump to exit the air…
As we are designing a power plant rather than a lighter than air cargo ship, the design limitations are just all different…
I believe the magnus AWE rig could fly with a pretty long tether, as it already has a low glide number it is relatively less affected by tether drag…
It has been mentioned before, @kitefreak, that just throwing around arguments can easily cloud the discussion rather than add to clarity. At this point we are interested in reasons why this could work or not. At a later stage, one would have to compare with other architectures. All arguments should be backed by some analysis to the relevance of the arguments put forth. Eg: why would a kite at the size of a 747 perform like an airplane? At the very least we should be able to get rid of the seats and fuel? You have many good points, but it is impossible for me to assert how important they may be. Better for the author to provide a small analysis rather than all readers having to
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Lets agree you are forced to settle for the modest power and dimensions given the engineering trade-offs known.
A medium large city would need about 5000 of the units. It will all come down to the economics, including lifecycle and land sprawl.
Lets hope that 10MW power kites with tighter land/air footprint and lowest cost prove out. That’s still 500 units for the example case.
I think I’d settle for a 1 kW rig today if I knew the technology could scale 
Low power-to-mass predicts poor scaling.
Magenn MARS was a ~kW device; scaled rather large but weak.