A "crackpot" design

The “crackpot” term is often used by @dougselsam. It refers to both crazy designs and conformist attitudes.
I will try to produce a design as crackpot as possible. I may have done this in several (if not all) previous messages.:wink:

So two counter-rotating bladeless rotors rotate two balloon filled with helium, using angle gears, that produce thus some Magnus effect. The force is used during the yoyo reel-out phase. During the reel-in phase the direction of rotation of the rotors is reversed.

I would guess some methods now well reputed will enter this rubric.

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I say lets keep an open mind and provide honest feedback. One can only have an opinion. The idea owner can choose to listen to feedback or not.

I usually think: You can prove something is possible, but it is often difficult to prove something is impossible. Therefore one should be critical to “naysayers”, if you think something is possible.

Of course, negative feedback is most times a signal that the idea is not that good. But often bad ideas have some useful insight that might be used at a later time.

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Some extract of the last interview:

_What do you plan?
_Simulations are promising. As we are careful and informed 50 small 100 MW unities will feed the East Coast.
Indeed we prefer begin small before starting GW scale.
_ You plan it for when?
_ The next year.
_ But you told it one year ago.
_ Right, we told “the next year” one year ago, then now we tell the same, always “the next year”.
_ And now, besides “the next year”?
_ We are studying a project for remote areas.

The downwind rotor contains blades with variable pitch, producing the stall-returning effect. The flow is not slowed as for devices that are subject to Betz limit. By the stall-returning effect the flow bounces back as soon as it crosses both rotors, keeping its kinetic energy. So the flow is multiplied in layers as the Betz limit is multiplied, becoming 2.5 instead of 0.59, but not more due to the losses by bouncing back. The Cp is expected to be about 2.

Here is a topic for Crackpot thinking and projects. What about a reeling Magnus rotor connected to a Darrieus turbine?

Hello Pierre: Connected in what way? What do you mean?

Hi Doug,
I tried to gather some crackpot features (Magnus rotor, Darrieus turbine, reeling).

More seriously (?) the figure 4A represents a Darrieus rotor (460) around the (not reeling) Magenn balloon https://patents.google.com/patent/US20060251505.

In a similar way, but not as an AWES, the figure 53 on http://students.iitk.ac.in/projects/wiki/lib/exe/fetch.php?media=2014:seifert_flettner_apps.pdf represents an Hybrid rotor comprising a cycloidal propeller around a Flettner rotor.

Oh OK that’s what I thought you meant.
Looks like it would work GREAT as long as it remains as ink-on-paper, where everything does what you want it to, rather than doing what it does.
I would say the wind-shadow of the sausage-cylinder would beat the Darrieus blades to death.

This is probably true.

I experimented a rough (attached photo) and not very efficient Darrieus rotor of 0.5 m x 0.5 m, blades Naca 12, carrying on a side an expanded polystyrene Savonius rotor of 0.27 m diameter and 0.5 m span, and on the other side an expanded polystyrene cylinder of also 0.27 m diameter and 0.5 m span. The weight was above 0.5 kg: with a wind of 5-7 m/s the set had a small elevation angle of 10°.

Then the test was made without the Darrieus rotor, with only the Savonius rotor for an elevation angle of 35°- 40° as a kite; then with the Savonius rotor and the cylinder side by side for an elevation angle of 40°.

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I wish you could post some more photos of your setup. This looks super interesting, but I am having trouble visualising what you have done here.

While many of the papers listed are interesting, my feeling is that they are a bit off. Here is my thinking on the subject (which I hope may be useful for your project):

  • like a wing for a plane, keep the aspect ratio long, eg >5 to mininize the effect of the tips
  • the different technologies datreius, savonius and magnus cylinder all have slightly different optimal TSR. The diameter should be matched so that each section is running optimally (eg a savonius rotor should have 1/4 radius of a darreius rotor, or similar radius to a magnus wing)
  • the area of the kite must be dimensioned so that the power into the magnus wing section(s) must be equal to the power generated by harvesting sections

I am assuming they are all fixed relatively in rotation sharing a single shaft.

The TSR values and harvesting energies may all be found by looking up tables.

Interestingly, the optimal harvesting device here is not the one approaching the Betz limit, rather the one producing most power for the least drag and weight. Probably this would mean high efficiency wings, I believe favoring a HAWT over darreius over savonius. And actually I believe a scaled down turbine like @Rodread’s Daisy might be a good option, with a gearbox.

So I just introduced using rotational AWE systems for on-wing power harvesting.

Let me explain some reasons why:

  • weight to power may be excellent
  • the turbine will self inflate and find its own shape without further rigid structure
  • you are not looking to go high altitude
  • you probably dont need the lifter, or at least it may be tiny
  • with effective blades, the drag should be the smallest of the competing options (that I am considering right now)

Super envious that you are getting some testing done. Looks like fun. Unfortunately I am super time constrained these days myself…

On my previous post I spoke about a 0.5 m x 0.5 m Darrieus rotor with a 0.27 m x 0.5 m Savonius rotor on a side, and a 0.5m x 0.5 m cylinder on the other side.

Unlike a Magnus rotor (and in some way a Savonius rotor due to its Magnus effect) the Darrieus rotor does not need a high aspect ratio.
Theoretically the spin ratio of a Magnus rotor can go with the TSR of any device assuring its rotation. Practically (and according to my rough experiments) exceeding a value of 1 is difficult without motors, leading to a higher diameter of an efficient wind turbine in regard to the diameter of the driven cylinder.

On the photo I attach it is the same Darrieus rotor (0.5 m x 0.5 m) and with a smaller (0.17 m (instead of 0.27 m) x 0.5 m) poly Savonius rotor in the right to allow a better understanding. In the left there was a 0.27 m x 0.5 m cylinder.

As the TSR of my Darrieus rotor was rather low, between 1 and 2 at the best, the proportions between rotors can be too approximative.

However the Darrieus rotor adds drag, and has no lift unlike the Savonius rotor at least with the following dimensions I experimented:

  • a (0.27 m x 0.5 m) Savonius rotor alone leads to 35° elevation angle;

  • (0.27 m x 0.5 m) Savonius + cylinder rotors lead to 40° elevation angle;

  • the same cylinder + (0.5 m x 0.5 m) Darrieus + the same Savonius rotors lead to 10° elevation angle.

In fact the Darrieus rotor(s) could fly but with longer Magnus rotor(s) or/and Savonius rotor(s) or/and Sharp rotor. In the other hand the Darrieus rotor is more efficient than the Savonius rotor for electricity production: an appropriate balancing between these rotors could be studied, comprising their respective diameters and spans.

It would be true if all components (Darrieus and Magnus rotors) have the same diameter. But the diameter of a Darrieus turbine is higher (you confirm this by the TSR requirement), so some rigid structure is needed to hold the blades. And for a HAWT a mast as axis is needed.

However Magnus and Savonius rotors can have the same diameter, but a Savonius rotor is not easy to build in soft material and will be still less efficient. And the Savonius rotor TSR would be a little slowed down by the Magnus rotor.

At small scale HAWT + Magnus rotor would be a possibility, but at higher scale an inflatable balloon like Omnidea’s in reeling (yoyo) mode could be a better solution, but with some needed adaptations.

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