The problem with crosswind flight for a Magnus rotor is the power consumption to spin the rotor. Indeed the tangential speed³ is the wind speed X the glide number (lift to drag ratio as simplification, generally between 2 and 3 for a high spin ratio) of the Magnus wing (that to obtain the apparent wind) X the spin ratio.
Power consumption (equation (3)) : 0.007 X 1 X 3.14 X 1.2/2 X 50.6³ = 1708 W.
Power harnessed: 2/27 X 1.2 X 1 X 1000 X 3.8 X (2.53)² = 2162 W before losses by cosine and by mass @tallakt includes in his calculations.
So it appears that for a Magnus rotor the higher apparent wind due to crosswind flight is the killer in regard to the required power consumption.
The turbosail was also seen as an alternative to the Flettner rotor. This is (in theory) a very high lift sail. I remember a lift coefficient of 6 but some problems of implementation occurred. Perhaps the turbosail can be a start for R&D for AWE wings.
For what I experimeted and and took into account analyzes in scientific publications (see the links above), rigid Magnus effect based rotors could be more efficient than inflatable ones and require less power consumption for an equivalent spin ratio.
Magnus / Flettner vertical cylindrical spinning sails have been tried for many years. As far as I am aware, they use more power than they save, because it takes energy to spin the sails.
It depends on the peripheral speed (reasonable power consumption until about 10 m/s for an inflatable cylinder, about 20 m/s for a rigid cylinder, see Fig. 13) of the balloon during the rotation. See the curves at 9:50 on the video below:
I re-read this chapter 12, and just noticed that the authors were referring to friction in the pulleys, pages 286 then 287.
Page 286:
We have noticed that friction in the pulleys is significant. The increase of mechanical friction forces is a well known physical phenomenon when scaling down.
Page 287:
Fig. 12.8 The measured
tension in the tether as a
function of the tether length r
for different angular speeds ω
of the Magnus rotor and tether
speed ˙r, for a wind speed
vw = 6.2 m/s. The zone A is
the possible force difference
that can be used to produce
energy. This zone is reduced
to zone B due to the pulleys
friction. This gives an idea
of the feasibility of a positive
power production cycle and
what one could potentially get
if this friction is reduced
About LTA 20-1, an old project from Magnus Aerospace Corporation of Ottawa, Ontario, Canada, a spherical Magnus effect-based balloon, inventor Frederick D. Ferguson, also founder of Magenn Power and inventor of the well known AWE Magnus balloon which is discussed in the present topic:
Now an old article provided photos of a Savonius AWE kite? shaped Magenn rotor:
An excerpt:
In testing, Magenn has achieved a coefficient of power that is better than 0.22, which is basically the efficiency of catching wind energy and converting it to rotational power output. “The advantage of the large floating cylinder is the economic efficiency of building such a large unit to catch a massive amount of wind as compared to existing wind turbines,” says Ferguson.
This design looks to be more efficient because the blades are relatively larger and well-shaped. That said the generator is aloft, just like other Magenn embodiments.
This design is also represented in pages 25, 26, 27, specifications page 28, of the following publication which resumes the tested Magenn rotors:
Excerpts page 25 and 26:
100 kW MARS prototype (2009)
In comparison to the Alpha prototype, the 100 kW MARS was a
significantly different design, referred to as the “clamshell” blade
design. The moveable “clamshell” style blades were operated with
compression cylinders, allowing them to pivot open and then retract
during each rotation cycle. This novel design is not described in any
of Magenn’s patents.
In testing, Magenn noted that the 100 kW MARS “…achieved a
coefficient of power that is better than 0.22, which is basically the
efficiency of catching wind energy and converting it to rotational
power output. ….The advantage of the large floating cylinder is the
economic efficiency of building such a large unit to catch a massive
amount of wind as compared to existing (terrestrial) wind turbines."
I wonder if a rope drive transmission, for example by using the lateral tori (the inflatable torus on the two sides), in a similar way as on the picture above (but for a single unit to start), would be possible.
I’m skeptical of that Cp of 0.22 figure.
What did they use for “swept area”?
The whole rotating apparatus, including the blimp and “blades”?
Or did they just consider the area of the downwind-traveling blade when unfolded?
And 100 kW? Sounds very dubious. That’s a lot of power.
I’m sorry. but for anyone who knows anything at all about wind energy, the Magenn project was doomed from the start - nothing but one more “La Brea Tar Pits” joke. Good for a laugh, and nothing more. Just because one more "Professor Crackpot’ is promoting an idea, doesn’t make it a winner. For “real wind people”, it was just more of the same old crackpot noise that never quite goes away.
Also, with the top part of the blimp rotating downwind, that might be good for lifting the entire apparatus against gravity, but it goes against having the “blades” open automatically by gravity, as they would if it rotated with the bottom traveling downwind.
All in all, it is such a losing idea it’s hard to imagine anyone taking it the least bit seriously, let alone producing the endless favorable articles and promotions over it. That level of publicity says as much about the lack of technical acumen of the publications themselves, as the idea they were describing.
I think they could have tried the rope drive transmission instead of having a heavy and slow generator in flight.
Certainly these projects do not seem to have been followed up, but the same is true for the other projects in progress.
We should not wait for AWE to compete with HAWT, but try to see how each method can be improved, the difficulties encountered differing depending on the method.
All very interesting, Pierre. The sad thing is, for anyone familiar with the whole spectrum of wind energy devices, everything in the Magenn publicity statements and claims read like typical disease symptoms: “Bird and bat friendly”, “remote islands” “disaster relief” “higher capacity factor at thousands of feet in the air” - all easy claims to make, but all these claims have one basic purpose: To impress potential investors and maybe regulators, who don’t know any better, and who are hearing these claims for the first time.
Such a target audience has a knowledge background consisting of mostly easy-to-understand, highly-publicized yet dubious concepts such as birds, bats, global warming, and supposed ready deployment and ostensiible ease of use, without the slightest understanding of what it takes to actually generate reliable and economical electric power from the wind.
They are living in a complete fantasy-world, trying to attract others with a similar lack of grasping even the most basic conceptual understanding of any simple fact regarding the purported subject matter. The real subject matter is extracting money from gullible people.
