The skew angle causes cosine cubed losses which can be significant:
SKEW ANGLE-DEG. EFFICIENCY RATIO
10. 95.5%
15. 90.1%
20 83.0%
25. 74.4%
30. 65.0%
I think it is better to displace the turbines laterally as I suggest in the topic “Turbine Orientation “
I guess even though the format shows two ways to reply to 1) either a single post, or 2) to the whole topic, I have to highlight the post I want to reply to so it appears as a quote in my reply to it. Oh well sometimes I can be a little slow to catch on… 
Hi Doug,
I have a question about the tested multi-rotor.
The introduction presents a shaft of 70 feet, and seven rotors of 7 feet in diameter. 70 feet = 21 m, and 7 feet = 2.1 m. So the space between the rotors is 21/6 = 3.5 m.
mechanism which allows the shaft to tilt as much as 25 degrees from horizontal
So we will therefore assume that the elevation angle of the shaft is 25 degrees.
Sine of 25 degrees (shaft) is 0.4226. Sine of 65 degrees (rotor plane) is 0.9063.
So the vertical dimension of the shaft between two rotors is 3.5 X 0.4226 = 1.4791 m.
So the vertical dimension of a rotor is 2.1 x 0.9063 = 1.90323 m.
As a result apparently (excepted the first rotor) rotors do not harness fully fresh wind. With a shaft of 21 m and 25 degrees, one can fully accumulate a little less than 5 inclined rotors for a frontal airspace of a little more than 4 surfaces swept on a vertical plane. How do you explain a so high value in these conditions?
Hi Pierre:
The test site was in a windfarm area, on a hill, with the tower projecting up above scattered small trees. Lots of turbulence - it was kind of an insane location. You build shit, try it, sometimes you get lucky.
Would that be your response to a potential buyer?
Doug, SuperTurbine ™ is your product. If someone wants buy it as suggested on your website
SELSAM, customers and also AWE researchers (who are looking at several options), should know the curves according to different conditions (number and diameter of rotors, wind speed and quality, angle, rotor spacing …).
There are hundreds of scientific papers on reeling kites, and not one on SuperTurbine ™ to my knowledge, apart from this report which is not complete because it does not indicate enough data to infer performance under different winds, as well as the different configurations of the rotors under various angles.
Perhaps @Rodread and @Ollie have studied the optimal spacing between the rotors but Daisy architecture is not quite the same.
So I suggest you get in touch with @rschmehl or perhaps @Ollie (if they agree) in order to establish a complete theoretical and experimental document on SuperTurbine ™.
Science has a bright side when it is used intelligently, neither too much nor too little.
Unless you prefer send the same post all days and all years about the supposed failure of reeling kite promise …
Pierre: Kite-reeling seems to be the only remaining AWE idea being commonly pursued. Nobody ever bothered to try a “laddermill”. I debunked many previous outlandish claims, Magenn, Altaeros, etc.
At some point, I was swayed by the claims of Makani - even said it sounded promising, from the claims they were making - I did not realize how bad their latest craft performed until I saw some of their final videos.
All those “smart” people… All those CFD studies, the modeling, the simulations, the advanced design, the number of engineers - How could they get it that wrong? I do not believe they disproved the general concept, just their specific implementation. As I’ve said many times, why do teams try to go so big, so fast? Why not bite off a smaller chunk to start so the inevitable failures do not kill the whole company? Oh well, one more common symptom of the endless P.C. syndrome…
Did you know that citing “a lot of very smart people” is a repetitive symptom of “The Professor Crackpot Syndrome”? Yup, like red spots are a symptom of chicken-pox. Can’t tell you how many times I’ve heard that one. I remember a conversation with one arrogant know-it-all, years ago, where he was talking up a group in a certain country, that he said was developing advanced vertical-axis turbines that were going to make all the regular turbines obsolete. I tried to explain to him that the vertical-axis concept had come and gone decades ago, and was long-disproven, or at least ill-advised by now. His response was “These are some very smart people”. I was thinking “OK but you just said they are pursuing vertical-axis turbines, believing they are superior, but then you said they are “very smart people”. The two statements are in conflict”.
My point is, by the time you are trying to rationalize a claim of future supposed success in a disproven field of endless failure, and you have to threaten with a taunt of “very smart people”, you’re already dead in the water, just showing typical symptoms of a project that is never going to work out.
Kite-reeling? Well it seemed like the most basic idea any kid flying a kite using a reel powered by a DC motor would come up with - power the reel to make life easier, then, hey wait it is making power as it reels out! The part I thought was clever was flying the kite back-and-forth to increase swept area. One red flag I noticed early-on was how many teams jumped in to pursue kite-reeling. I mean, how many teams are needed to check this idea out, really? I compared it to the old graffiti saying I would read on outhouse walls as a kid: “Eat s***. how can a million flies be wrong?” Not that I could identify any specific deal-breaker with the technology, just that it seemed a bit desperate - grasping at straws, and not very imaginative. Kind of a “hail-Mary”, like “We can’t think of, or build, anything better”.
But, as with Makani, the numbers I was hearing DID sound VERY impressive. So I opened my mind to the possibility that kite-reeling had “cracked the code”. I am still open to the success of kite-reeling. That is why, every year or so, I ask yet again “So how is kite-reeling going these days?” I’m not saying there is anything wrong with it when I ask this question. I just ask the question.
In this case, we had containerized, supposedly turnkey, supposedly quickly-deployed kite-reeling systems, with one supposedly shipped to a point of use maybe 6 months ago or so, and as one of the biggest fans of AWE, I’m curious to know how things are going with that system. I mean, has anyone run the system yet? If so, how is it working? If not, why not? Seems to me when asking followup questions after a parade of promotional press-releases is seen as a problem, there may be more at play than just modesty. Too much resistance to such simple questions might be a sign that the hype was just that, and nothing good is emerging as a result. All I did was ask “What’s new today?” Not looking for an argument, just wondering how things are progressing after being exposed to all that “great news”. Hopefully things are going great, everything is working fantastic, and someone would be happy to share the good news. 
Hi Doug, this topic is about SuperTurbine ™ and you pursue to write about kite-reeling. Perhaps a deeper analysis of this multi-rotor system could help to realize some ideas in AWE.
Hi Pierre
I was just responding to your comment:
I am still curious to know how the systems are doing.
And you mentioned:
“There are hundreds of scientific papers on reeling kites, and not one on SuperTurbine ™”
Yes, well, all those “really smart” people, all those “scientific papers” - if all those papers are worth the paper they are printed on, then what’s holding things up?
Maybe the missing paper about SuperTurbine ™.
If I knew what is the optimal space between two rotors and their angle, maybe it would help me build one or two AWE versions.
Of course we can stick to the theoretical losses because of the cosine and deduce the distance between two rotors, but it seems that there are other parameters that a finer measurement would help to discover. I still don’t explain why the measurements of the report are so high while the rotors are covering each other a bit.
Yeah I was surprised too. I had originally planned to use just five (5) rotors, which should have been enough to generate the 3000 Watt target output. I added two more rotors and extra driveshaft to support them, at the last minute, which turned out to be unnecessary.
Do you mean that the power was the same with only 5 rotors compared to 7 rotors?
No. We did not run it with 5 rotors during that project.
It would not have made as much power as 7, but it would have been enough to fulfill the stated goal of the project.
Pierre: I’ve long surmised that favorable wake interaction from one rotor to the next could be at play. The wake of a rotor spins in the opposite direction of the rotor’s own spin.
The top of the wake from rotor 1 hits the bottom of rotor 2. The bottom of rotor 2 is traveling in the same direction as the top of the wake form rotor 1, therefore the wake from rotor 1 helps spin rotor 2, and so on, up the line of rotors. This effect would imply that the line of rotors enjoys advantageous wake interactions, somewhat like a line of geese flying in formation.
Doug: it looks like an interesting feature. I remember (rightly or wrongly) @Rodread was also seeing very good performance from Daisy while the rotors were close together. Maybe he can confirm or deny it.
I have no idea
about many things
There’s nothing conclusive in the very wide ranging and very few results gathered so far on my systems.
Yep generally I reckoned rotors were more efficient stacked.
I put it down to less line drag / blade
I’m planning to be testing for more exact detail by around this time next year.
Roddy: Wind-watch.org is an anti-wind-energy website. Their concern is noise and convincing people how bad it is…
The main vorticity of a wake is it rotates opposite to the rotor spin, (Wake vorticity, wake swirl.) by Newton’s third law:
Newton’s third law: If an object A exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A. This law represents a certain symmetry in nature: forces always occur in pairs, and one body cannot exert a force on another without experiencing a force itself.
Here is an interesting video at around 1:26 or so.
One rotor downwind and offset from another rotor.
The graphics are nice, colors fun, but it really doesn’t convey much except confusion.
