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  #31  
Old 08-29-2010, 02:57 PM
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TeddyDiver TeddyDiver is offline
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Quote:
Originally Posted by DougCim View Post
the NOTAR system uses the Coanda effect, as the tail boom of the MD-500 does not revolve. The Magnus effect is a property of boundary layer flows around a rotating tube.
So what.. as I said, another implement (whatever the name) and the aerodynamic principle and outcome is the same..
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  #32  
Old 08-29-2010, 03:03 PM
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TeddyDiver TeddyDiver is offline
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Originally Posted by apex1 View Post
Albert Einstein was a true admirer of Flettners Rotor, maybe he had a better understanding of the system:
Interesting..
actually about 200 years old invention..
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  #33  
Old 08-29-2010, 06:19 PM
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rwatson rwatson is offline
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Quote:
Originally Posted by apex1 View Post

I have never come across any mention of rotors being driven by exhaust gases.

In every case they were rotated using small auxilliary motors.




Your link:

http://www.oldsaltblog.com/2010/08/1...nally-arrived/
Aha - now I know what you where referring to

The info " Exhaust gas from the engines power a downstream steam turbine, which drives the four Enercon-developed Flettner rotors"

makes me think the steam turbine (small motor) is directly driving the rotors, so the heat from the exhaust is creating the steam for the steam turbine ( not gas turbine).

I reckon the primary source of rotation is the steam turbine, while the *energy source* is the heat from the gasses.

Certainly, there is no risk of exhaust back pressure problems using this process, as another contributor was concerned with

Last edited by rwatson : 08-29-2010 at 06:21 PM. Reason: extra info
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  #34  
Old 08-29-2010, 10:01 PM
mydauphin mydauphin is offline
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It would seem to me that the structure of the rotors especially if they rotate would have to be substantial considering the forces acting on it to propel the boat. So the amount of weight and high cg may affect boat in some undesirable ways. I would not want to be out in a storm with them. How do you drop the sails? I believe the kite-sail idea is much more flexible and safer. Perhaps inflatable rotors could be develop that can be deflate if winds exceed a certain amount.
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  #35  
Old 08-30-2010, 04:05 AM
Tackwise Tackwise is offline
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Quote:
Originally Posted by DougCim View Post
The Flettner rotor is a solution in search of a problem.

......It is most certainly not a sail, if it needs engine power to function--it is only a method of converting engine power.
>>Energy conversion (simplified):
Old fasion sail => Wind flow over sail = Propulsion force
Flettner rotor => (Engine) rotational power + Wind flow over rotor = Propulsion force
How you define 'sail' may be a matter of discussion (to be discussed in other threads). Defining a flettner rotor as a method of converting engine power may also be a matter of debate, to my humble opinion ...


......If it generates seven times as much as an airfoil the same size, they why is it not used on any production aircraft, or as the propulsion method for any aircraft? I've seen a number or articles about experimental models, but for some reason all those dumb guys over at Airbus and Boeing keep sticking with the same old airfoil wings (-and airfoil engines...).
>>Very true, however the reason behind this is not that the flettner rotor is not effective. Think about the problems of engineering a rotating wing . (I would not want to sit in such an aircraft, think of what would happen if the rotation stopped during midflight... oeps) For many applications a flettner rotor will be impractical due to the rotation aspect, and various other reasons. However I feel it is not fair to rule out the flettner rotor for all applications, especially since 'new' technology is making a lot more possible/practical/economical viable/etc.


......DIY boatbuilders are free to try anything they want, and yet there's a sizable list of other innovations that are far more common than Flettner rotors: Kort nozzles, winged keels, keel bulbs, hydrofoils, rigid-wing sails, torpedo tubes and variable-pitch props to name just a few. Other than this publicity stunt by Enercon, the original Flettner boat and the Cousteau boat, how many Flettner-rotor boats even exist? I'd bet not very many, compared to anything else in that list.

.....I've no doubt the principle works, but it's not as useful as inferred. Enercon themselves doesn't even make any wind turbines using Flettner rotors.
~
>> The Kite has been around for how many centuries???? Only just recently is it being put to use as a viable aid to propulsion of ships.... Do not write off the flettner rotor just yet, some smart *** may invent the perfect solution!

For those interested v.d velden has recently introduced an application for the flettner rotor as (bow)rudder:
http://www.vandervelden-marinesystem...DEFINITIEF.pdf

greetings

Tackwise
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  #36  
Old 08-30-2010, 06:18 AM
apex1
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Quote:
Originally Posted by mydauphin View Post
It would seem to me that the structure of the rotors especially if they rotate would have to be substantial considering the forces acting on it to propel the boat. So the amount of weight and high cg may affect boat in some undesirable ways. I would not want to be out in a storm with them. How do you drop the sails? I believe the kite-sail idea is much more flexible and safer. Perhaps inflatable rotors could be develop that can be deflate if winds exceed a certain amount.
The weight is about the same as a mast of the old square riggers (when comparing power they can provide)

One cannot drop masts, so, the argument is mute.

The power to make them rotate is not very much, btw.

And to answer another question, how many of these systems are built. There have been at least two dozen of them in the past 30 years. All have shown the system works as assumed.

One correction of my statement about the rotor on Cousteau´s boat:

He decided to install the original Flettner Rotor on Calypso, and that was all I did know about. Here a sketch of the old plans:



I was not aware that his successors developed another (derivate) system.

Regards
Richard
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  #37  
Old 08-30-2010, 07:38 AM
DougCim DougCim is offline
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Quote:
Originally Posted by TeddyDiver View Post
So what.. as I said, another implement (whatever the name) and the aerodynamic principle and outcome is the same..
The Coandă effect and the Magnus effect are not the same.

The Coandă effect occurs over any smooth surface or flow plane, while the Magnus effect only occurs over a smooth rotating cylinder.

-------

I have been trying with some effort to imagine anything that a Flettner rotor would be good for. The only advantage I can see it has is that since it is symmetrical (from above) it doesn't need to ever be aimed into the wind at all. That omnidirectional ability takes a big toll on overall efficiency, however.

The practical problem it has is that since the propulsive force it generates is always perpendicular to the prevailing wind (think about that limitation for a moment!) it is only ideal for crosswinds, and would be much less useful with the wind in any other direction.


If you just think it's interesting from a scientific standpoint, I understand that. From a geek standpoint, I like the idea of running my house off solar panels,,,, but I know enough to know that for most people (including myself) it's not really economical to do, compared to the boring old way of just paying to get electricity from a wire hooked to my house.


If you think it is a grand solution that's vastly more efficient than anything else out there, then ignore the fact that after 88 years no airplane company, windmill company or most boat companies are keeping the lights on by building the things, and go ahead and build yourself one--but don't get too surprised when kids on Hobie cats and lasers run circles around you. Because I would bet very much that they will (and even at that, they're gonna tell you it's not a sailboat, too...).
~
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  #38  
Old 08-30-2010, 07:54 AM
apex1
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Quote:
Originally Posted by DougCim View Post
The practical problem it has is that since the propulsive force it generates is always perpendicular to the prevailing wind (think about that limitation for a moment!) it is only ideal for crosswinds, and would be much less useful with the wind in any other direction. ~
As I already pointed out:

you don´t understand it.
(and I am not wasting my time to elaborate on it)

What I do not understand is why you are fighting against a well proven concept, with really childish arguments? Your Hobie cat will not run circles around a 200 meter ore carrier, be sure!

Regards
Richard

and:
http://www.google.com/images?q=flett...w=1024&bih=607
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  #39  
Old 08-30-2010, 12:26 PM
Clarkey Clarkey is offline
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I have been fascinated by Flettner rotors for years, it is very interesting to see some coming in to use.

There is a good source of information here by someone who spends less time wondering about things and more time actually doing them:

http://www.rotorboat.com/

It is worth taking some time to understand some of their unique features like no need for trimming and 'self reefing' properties as windspeed increases.

I have long been of the opinion that they would be an elegant solution for a sailing river launch, able to take full advantage of gusty, shifting, inland breezes. If powered from a solar panel I see no reason why this should not be considered 'sailing'.
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  #40  
Old 08-30-2010, 05:35 PM
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DennisRB DennisRB is offline
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Quote:
Flettner's spinning bodies were vertical cylinders; the basic idea was to use the Magnus effect. The idea worked, but the propulsion force generated was less than the motor would have generated if it had been connected to a standard marine propeller.
From wiki, which is not know for accuracy. However I would like to know the relationship between power produced by magnus effect compared to the power used to turn the rotors. Obviously when run from wasted power as in that quad rotor ship it would be worthwhile, but what about when you must pay for the fuel to drive the rotors? I wonder how the heeling moment of the rotor compares to a sail that develops the same power?

Here is a link to a small rotor boat. Apparently it points VERY well and uses very little power.

http://www.rotorboat.com/



Quote:
The main fact is that the current rotor, 3.6 metres long, uses in the region of 20 watts of electrical power to drive the boat to hull speed even in light winds.
Wow that is a small amount of power used to get to hull speed on what looks like an 11 foot dingy.
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  #41  
Old 08-30-2010, 08:17 PM
dskira dskira is offline
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Quote:
Originally Posted by DennisRB View Post
From wiki, which is not know for accuracy. However I would like to know the relationship between power produced by magnus effect compared to the power used to turn the rotors. Obviously when run from wasted power as in that quad rotor ship it would be worthwhile, but what about when you must pay for the fuel to drive the rotors? I wonder how the heeling moment of the rotor compares to a sail that develops the same power?

Here is a link to a small rotor boat. Apparently it points VERY well and uses very little power.

http://www.rotorboat.com/





Wow that is a small amount of power used to get to hull speed on what looks like an 11 foot dingy.
Something is wrong in this demonstration.
No end plate, the rotor can't propels, since the difference of pressure is sliding away on the top.
The rotor is conical, can't have any propulsive effect. Doesn't make sense.
I don't think it is what he want us to see.
A rotor will not make the boat heel. Perhaps the windage on a very high wind can have a heeling effect, that I don't know.

But I can be wrong.
Daniel
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  #42  
Old 08-30-2010, 08:29 PM
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DennisRB DennisRB is offline
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Na mate. Its certainly a Flettner rotor type of propulsion. There are even sailing vids and theory pages.

You should read the page. He came up with this idea independently from his studies in aviation. He only found out later that this had already been applied to ships. Going by his report the idea scales all the way to RC boats too as he developed an RC boat first. The magnus effect is what curves a balls flight in the air when hit with a spin, so it would surely work on a sightly tapered tube if it works on a sphere. There is no need to have an end plate for it to work. My guess is he chose to taper the tube instead of use an end plate to reduce the vortices's of the top of the mast. It appears to work quite well. If he not heard of the Flettner rotor ships before he dreamt up this idea I am sure he would have used a straight tube with an end plate too. That is the beauty of not having preconceived ideas to cloud your mind from other possibilities which may be valid. (did I just sound like questor?)
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  #43  
Old 08-30-2010, 10:51 PM
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rwatson rwatson is offline
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Fletter Math Calcs

Quote:
Originally Posted by DennisRB View Post
....

Here is a link to a small rotor boat. Apparently it points VERY well and uses very little power.

http://www.rotorboat.com/



Wow that is a small amount of power used to get to hull speed on what looks like an 11 foot dingy.
Wow Dennis, thank you so verrrrry much for that link. I will follow that up with alacrity.

In the interest of the topic, I am posting three scans of actual formulae that perports to to calculate the propulsive force of a rotor.

Its been some years since I immersed myself in the study, but hopefully my rough notes wont obscure the text. If anyone needs to have indecipherable bits resent, pleaselet me know.
Attached Thumbnails
Everything Old is new again - Flettner Rotor Ship is launched-calcs01.jpg  Everything Old is new again - Flettner Rotor Ship is launched-calcs02.jpg  Everything Old is new again - Flettner Rotor Ship is launched-calcs03.jpg  

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  #44  
Old 08-30-2010, 10:54 PM
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rwatson rwatson is offline
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Quote:
Originally Posted by apex1 View Post
He decided to install the original Flettner Rotor on Calypso, and that was all I did know about. Here a sketch of the old plans:



I was not aware that his successors developed another (derivate) system.

Regards
Richard
It does indeed have a rotor on this artists impression, but I am positive that the boat that Coustea ( not Calypsos successive owners) visited the USA in had the large chord wing masts, as I vividly remember a documentary on it.
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  #45  
Old 08-30-2010, 11:26 PM
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rwatson rwatson is offline
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Rotor Physical Performance in Storms, and Kite/Sail Use

Quote:
Originally Posted by mydauphin View Post
It would seem to me that the structure of the rotors especially if they rotate would have to be substantial considering the forces acting on it to propel the boat. So the amount of weight and high cg may affect boat in some undesirable ways. I would not want to be out in a storm with them. How do you drop the sails? I believe the kite-sail idea is much more flexible and safer. Perhaps inflatable rotors could be develop that can be deflate if winds exceed a certain amount.
The rotor idea was created due to the desire to reduce crew costs handling large sail areas. I have seen vidoes of kite launching from decks of large ships, and it can take up to three crew, and at least one full time monitoring person PLUS the helmsman. We all know how difficult kites can be, even with new parafoil designs. Deploying and retrieving is at least as problematic as raising and lowering sails. The time lag in retrieving a Kite sail could be cause for concern in an emergency.

Regarding perfomance at sea, I attach two scans of documents based on the actual results of the Buckeau at sea,

Remarkably, the vessels stability performance actually improved with the rotor conversion as graphed at the top of page 78.

Some points to regard -
1) Page 77 "At 40 to 60 mph wind velocity , the wind pressure is not any greater than at 25 to 30 mph. This represents a tremendous advantage .... over ordinary sail."

2) top of page 78 - "when the rotor is shut down, the wind pressure is far less than that of (standard) rigging, even after the sails have been removed"
(see graph of Buckeaus stability curves)

Note that "reducing sail" on a rotor ship is a matter of reducing the motors throttle, which is done in seconds. Compare that to the compexities of either Kite Sail or standard rigging.

For those who find the concept of powered aerodynamic devices a bit strange, consider the illustration of a modern jet wing.

True, the lifting surface does not rotate, but the engines force high velocities of air over a curved surface due to the velocity of the crafts forward movement.
Because a boat is unable to achieve the velocities needed to generate lift across a stationary surface, Mohammed goes to the mountain, and speeds up the lifting surfaces to achieve the propulsive effect desired.

So, in some sense, as a sailboat is like a glider, a rotor ship is like a powered airplane.
Attached Thumbnails
Everything Old is new again - Flettner Rotor Ship is launched-performance01.jpg  Everything Old is new again - Flettner Rotor Ship is launched-performance02.jpg  Everything Old is new again - Flettner Rotor Ship is launched-engine.jpg  

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