Collapsible Flettner Rotor Project

Fortunately I have thought of a simple method of quickly and easily reversing the buckets on a Savonius rotor AND simultaneously reversing it's spin relative to the wind, and all without stopping or reversing the motor. The motor drive and bearings are in the center suspension mechanism.

This system simplifies a lot of concerns and is cheaper to boot.

No fancy motor controls or brakes.

No problems of cabin top supporting weight of rotor.

No engineering free standing rotor.

The rotor is horizontal passing through eye of wind so NO chance of dangerous heeling forces.

The height of rotor can be reduced, in a gust, by half instantaneously, or when desired and propulsion also ceases, both as an additional benefit of using this same solution. Also good for passing under low bridges.

The aluminum spars are reduced in length by at least half, so cheaper, and less weight and windage aloft. There is now 4 spars rather than 3 as before but still a large savings.

and hopefully it is a wind generator at anchor or dock as well as motive machinery underway.

See sketch below. I declare this open source and all may use or improve upon, provided THEY agree to make it open source.

 

Sketch below demonstrates attitude of rotor passing through winds eye while tacking. Also emergency reef in a strong gust. Rather like scandalizing the gaff in a gaff-rig as an emergency reef.

I am looking at building a custom low rpm (200-400 rpm) PM motor as part of and internal to rotor for direct drive. Make the rotor a big outrunner motor.
Actually this is TWO rotors joined at the middle via the drive hub. Perhaps they should have separate motors. Speed one a tad faster to eliminate vibration harmonics.

The two A frame supports, one port other starboard, their aft legs can be unstepped and swung forward, allowing rotor pivot down and aft, to rest horiontal on gallows frames above cabin top. Or perhaps aft legs telescope for same result.

 

So it is no more a Flettner rotor project, looks like it has evolved into a Savonius rotor project?

 

Perhaps it's both. Savonius never tried to use the split cylinder as ship propulsion as Flettner did with smooth cylinder.
Simply changing the rotor from smooth cylinder to half cylinders offset into Savonius configuration, doesn't eliminate Flettner, I think.
if the rotor is still used for propulsion.
Does it?
After all, Flettner's contribution was a spinning rotor as propulsion, not inventing the cylinder.

Do you like the somersault rotor concept at all?

The intent now, and originally, is to lower the rotor quickly when needed. Folding into itself, telescoping, we exhausted all possibilities that came to mind.
We still may yet come up with a novel idea for telescoping.
Meanwhile, this works. It doesn't telescope but it comes down. It collapses. It's simple and quick. And solves other issues.
And the rotor is ridgid which Rwatson will approve of I bet.

 

I am trying to understand.
So, it is a half-flettner half-savonius, where savonius provides the spin and flettner the thrust? Am I interpreting it correctly?

 

Hub motors

I know bike hub motors were sorta mentioned before...

There are some big innovations happening in that space.

This unit is from the top dogs in the ebike world:
http://www.ebikes.ca/product-info/grin-products/cycle-analyst-3.html

It can do very advanced control of a hub motor.
Braking, temp monitoring, speed limiting.

All off the shelf plug and play.

Their website also had some info on the waterproofness of the hub motors.
Can't find it at the moment.

I bet there would be a way to enclose the motor in the Flettner rotor somewhere to keep it safe.

I'm thinking *next* to the rotor shaft, not on the shaft. Use 2 cogged pulleys with short Gates toothed belt.

 

No sir.
Please pardon my unclear explanations.
The rotor will be electric motor powered as intended from post #1.
From the pdfs I posted about 6 posts back, I read the Savonius develops more lift and drag (more Magnus) than a smooth cylinder because of the air flow through the center. They were powering their rotors with Magnus effect to spin itself.
I AM NOT.
But I like the idea of the greater Magnus effect force of the Savonius for use in a FLETTNER rotor propelling my boat, spinning twice wind speed by electric drive.
When NOT propelling my boat, it can spin from wind power as a VAWT (Vertical Axis Wind Turbine) and recharge my batteries. Maybe to all above .
If the Flettner doesn't do much or enough, I will at least have a wind generator for my investment. The PM electric motor serving as a generator. Perhaps?

Thanks Kommando. I'll check it out.

PS: I DID check it out. Nice hub motors. I may use a couple of these. I am still exploring possibility of building my own one meter diameter hub motors.

 

http://www.prh.fi/stc/attachments/innogalleria/savonius_kirja.pdf

This is by Savonius and contains lots of information. I'm posting a screen capture of excerpt from page 11 and 12 below. Among other attributes, the Savonius style rotor doesn't need nearly as large end plates as a smooth cylinder.

 

I am not reading them that way. I am actually failing to see any comparison with the Magnus rotor in the papers you have posted. They all deal with the use of Savonius rotor as a vertical-axis wind-turbine generator, hence are trying to maximize the power efficiency at a given wind speed.

The fundamental difference between the Magnus and Savonius turbines is that the former is essentially a lift-generating machine with collateral drag and torque effects, while the latter one is fundamentally a torque-generating machine which creates nearly equal (and pretty high) amounts of drag and lift. So the max. Lift/Drag (L/D) ratio of a Savonius rotor is around 1.5-2, which should be compared to L/Dmax= 4-5 of a Magnus rotor.
See the graphs in this test report, which is by far the most complete one I could find in internet: http://www.dtic.mil/dtic/tr/fulltext/u2/643160.pdf

So if we wanted to compare them to sails (because that's how you intend to use them) a Magnus rotor would be somewhat like a man+jib setup, whilst a Savonius rotor is much more akin to a main+spinnaker. Unlike sails, unfortunately, you can't have them both on board. So you have to decide if you want to optimize your propulsion for the close reach or for the broad reach/run. In the first case it can imo only be a well-designed Magnus rotor, in the second case it can be either a badly-designed Magnus or a well-designed Savonius rotor.
Cheers

 

I may indeed be reading them wrong.

The pdf you posted was a water tank test of S rotors as potential water stream watermill devices. They did conclude that because it didn't work well in water it wouldn't in air either. Does that equate? Although they did not test in a wind tunnel, only water tank. Would Magnus effect occur in uncompressible water?

They also erred in details about Flettner's ship. Careless. Not even the name correct. Unless used alias Buckau. The 3 rotors are obvious in photo.

There was a rotor ship named Barbara with 3 rotors, but not Flettner's..
"Because of this success, the Transportation Department of the German Navy
ordered the construction of another rotor ship, the "Barbara". She was 92m
long and fitted with three rotors. Each rotor was 17m high, 4m in diameter
and driven at 150 rpm by a 27 kW electric motor. The "Barbara" carried 3000
tons of cargo and a few passengers. She plied between Hamburg and Italy for 6 years."


But thanks for the post. I gleaned one juicy bit from it. I didn't know he tried it as propulsion. Thanks. Is Savonius' opinions considered objective? Or hype?
Screen capture from this 1966 pdf, below. Red box is mine, contains interesting statement.

 

Yes it would. The fluid type is not important, and at the speeds of interest the air compressibility plays very little role anyways, so what you see in the water is the same thing you'd see in the air - if the Reynolds numbers is the same.

Regarding the Savonius' claim about his rotor giving more thrust than a Magnus rotor, I would be cautious there. We don't know in what conditions did he measure that thrust, and how did he made a comparison with the Magnus rotor. Even in that nice book written by Savonius, which you have posted at the previous page, the drag of his rotor is shown to be higher than the drag of the Magnus rotor, for the same lift. Like I said before, a spinakker will perform better than a mainsail, but only for certain sailing points and wind conditions. Apples and oranges at work here,I believe, and one has to decide what he wants to eat.

Cheers

 

Okay. I only need a mechanism to close the Savonius into a cylinder. Something that works a little like parallel rules. It doesn't have to be quick acting. Even unboltable and reconfigurable would serve.
Then I can have both options and test both types of rotors. When it's ready to test, maybe some Florida forum members will witness and attest results.
We want data, not my opinions.

 

Smart idea. Though it will add some more to the cost and the complexity of the project. I'll see if I can help you to come up with something along those lines.
Cheers

 

Shouldn't add much to cost. Two half cylinders = one whole of equal surface area..

 

I looked at rotor control systems for small boats a fair bit a couple of years ago, before I got sidetracked into building us a new home (which is why I've been a bit quiet on here of late).

The rotor flipping idea would work, I'm sure, but there are going to be some nasty precessional consequences from flipping the rotor and translating the gyroscopic forces, plus there will be a fair bit of top hamper with the thing at the mid-point.

I felt it was better to have a stout unstayed mast inside the rotor, make the rotor from very light material so that the rotational inertia was low and then use a reversible motor. I went as far as building and testing a brushless motor controller that would reverse a big model aircraft outrunner motor on the fly, even at maximum rpm. The motor would stop and reverse direction in far less than a second, even at full speed (but this was a bit brutal!).

My idea was to fit a relative wind vane to the top of the mast, above the rotor, and use this to control the rotor direction. Coupled with hand speed control (more or less the equivalent of adjusting sheet tension in a sail) such a system would allow a rotor boat to be safely sailed at any point. Should there be a risk of an unintended gybe or tack, then the rotor would quickly just stop and reverse direction as the relative wind went through the critical point where rotor lift only provides a strong roll moment.

If the rotor was made from lightweight composite, much as Stephen Thorpe did with his tapered rotor on his dinghy, then I think it should be fairly easy to control the speed and direction quickly enough, as even a small boat would take a second or two to luff up or gybe, which should be plenty of time to stop and reverse the motor.