Collapsible Flettner Rotor Project

Discussion in 'Projects & Proposals' started by Yobarnacle, Jun 4, 2014.

  1. rwatson
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    rwatson Senior Member


    Would you get them stiff enough without reinforcing ? nothing worse than a floppy rotor :D

    The rubber is very, very heavy too
     
  2. Sailor Alan
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    Sailor Alan Senior Member

    First you need to decide what area you think you need. A Flettner rotor’s surface area is very roughly equivalent to a sail’s area. Use this as a starting point. i.e. take the sail area you think you need, divide it in two, because i think you will need two masts (for control), and this is the surface area of your rotor. They are going to be quite large, the ones shown on ships are really a joke, or publicity stunt.

    We did work on this for power generation, not lift or propulsion. On land, with lots of width, we could use guys to the top, but for ship/boat use, not so much. A reason it does not work for airplanes is the lack of consistency in lift. We could not predict performance with consistency in the ‘real’ world. i.e., small differences in angle of attack made big differences in lift force and vector. A ship/boat would not care so much, if only due to inertia. But, its now the average force forward which helps. Cdr Beebee stated in his book “Voyaging under Power” that he realized he had used an average of just 5hp whilst racing from LA to Hawaii, and this led him to his long range boats. But, he had to install about 100hp to get that 7?hp into the water reliably, windage, wave motion, etc.

    Others are plowing this area as well, its currently popular, but we didn't see much worth in it. We were mildly amused Airbus was associated with “Think’ in their patent etc. http://www.thiiink.com/advantages-rfr-technology/

    and http://gizmodo.com/the-mega-ships-of-tomorrow-may-be-driven-by-technology-1583330087

    As far as i can remember, dimples or riblets do not help much, but this might change with experiment, certainly ‘Think’ do not seem to mention them. i.e. you will need a really smooth surface, no joint ridges etc.

    I cannot open your spreadsheet, so do not know what it contains. i think the CP of the rotor is roughly half way up, slightly less than exactly halfway, because of tip loses. The ‘end plate’ or ‘fence’ at the top is not perfect. Getting the rotor close to the deck should increase end plate effect at the base too. Given that the CP is higher up than, say, a triangular sail, the load on the mast, and it must be free standing i think, is going to be worse than a sail. Equally, we may not stand much ‘bend’ in this mast, bearings do not line up etc. So immediately we are fighting a weight issue. Welcome to airplane design, see below.

    Second question, after area, is weight. You can probably make it fairly light if it is not retractible, but retractible, especially telescoping vertically, will be intrinsically heavy. i can’t offhand think of an easy way to do this, but time will tell. Think have clearly patented some of these things, tipping as well, which is easier to arrange..

    I usually favor reducing windage up high rather than weight, but you guys might know better.

    I was thinking of a stack of plastic buckets, the kind/size sold at Home Depot for holding tools. They nest, and could be extended by some suitable means. So could stacked, telescoping drum chassis. Wild thought, an “A” frame mast perhaps? A cloth tube with drum chassis inside to hold its shape, hanging from the "A" frame mast?

    Ive seen photos of paraglider like chutes on ships, but whether ‘real’ or photo shop, i do not know. The problem is, they, and Flettner rotors, need such a lot of area to be effective, then they are really hard to control in weather, makes it tough to rely on such. if i understand correctly, the ‘clippers’ of old, with their clouds of sail, only really got up to speed in near storm conditions.

    There was a brilliant RIB made in NZ that used truck tarpaulin as the casing, with a separate inner tube like a truck or tractor. This meant the outer skin was tough and could be repaired easily, whilst the inner tube could be patched, or replaced easily. They were bought by various armed services too. Perhaps this could make a cheap, tough, vertical inflatable tube for experiment. Load's at the base will be high unless there is a 'shaft' or mast inside?
     
  3. Sailor Alan
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    Sailor Alan Senior Member

    More thoughts.

    If cloth were used, and it needs to be air-proof, it could be held in vertical tension like a sail, from a central mast, or “A” frame mast. Hoops might work, certainly drum chassis would, though they are fairly small. I don't think we could use a raked mast unless we taper the rotor (which might be a good idea, given the loads involved. I think we need to start with a 3-4’ diameter for this project to be practical.

    With cloth, and hoops/drum chassis, and a ‘mast’, the whole held up with a halyard, we could think of ways to hoist and ‘reef’ this, slightly like a rotating, circular, Chinese lugsail?

    Notice i am thinking in terms of the mast continuing to stand, just the rotor being reefed. This MIGHT make the whole scheme light and simple enough to be practical, especially if we taper it as well.
     
  4. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Thankyou everyone. thankyou daiquiri and moderator for correcting title of thread to Flettner.

    From the very beginning I intended a tripod mast and a suspended rotor. I am thinking roller furling gear used for staysails as the bearings.
    The cylinder diameters I input the calculator were 0.3 and 0.4 meter, = roughly 12 inch and 16 inch drum shells. And I used minimum wind I could get an output, 7mph or 6 kts

    Except in the tradewinds or near the great capes, zephyr days with light winds are more common than half gales. I need the mast to be able to set conventional light air sails as well as the rotor.
    I'm not looking for a universal panacea with the Flettner rotor.

    I have/had a plan for collapsing the drum shell rotor by gravity. I'll post it for curious sake, but drum shells are too small to be effective.

    The inner tube rib sounds great. Is it still made?

    Bicycle inner tubes still aren't a meter-n-half diameter but 26 inch dia is common. I'll play with that diameter. An accordion stack of bike tubes in a herculon sleeve might work. A bike rim at top and bottom for rigid drive components.
     
  5. rwatson
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    rwatson Senior Member

    Based on what info ?

    Totally unnecessary. One will be ample from all I have read.

    Are you talking about the E-Ship ? Based on what information. http://www.enercon.de/en-en/2224.htm



    A great idea and a great site. Thanks for the link
    "The system has been developed and tested both in tank tests and in full-scale sea trials. It is suitable for inclusion in new-build designs and ,importantly, can be retrofitted on existing vessels"



    has an important caveat "If the vessel which is to be retrofitted is using a fixed pitch propeller, the efficiency gains would certainly still be positive while using such a system, however not as positive as they could be if the blade angles themselves could be optimized while underway."



    Dimples have been tried without good effect as I recall, but end and intermediate fences seem to be important from data I have seen

    I can save and send it in another format if you know how to load it. What is your version of excel and version of windows ?


    What is CP ? Do you mean CE, centre of effort ?





    I usually favor reducing windage up high rather than weight, but you guys might know better.

    I was thinking of a stack of plastic buckets, the kind/size sold at Home Depot for holding tools. They nest, and could be extended by some suitable means. So could stacked, telescoping drum chassis. Wild thought, an “A” frame mast perhaps? A cloth tube with drum chassis inside to hold its shape, hanging from the "A" frame mast?

    ummm - the US navy wouldnt charter a photoshop boat, I am sure
    http://www.msc.navy.mil/sealift/2008/November/kite.htm


    That wasn't the experience of the Flettner Boats. They were reportedly very controllable in high winds, even more so than conventional sail.



    It seems feasible in my mind too. That little catamaran in the vidoe seems to be doing just that.
     
  6. rwatson
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    rwatson Senior Member

    Hmmm - will that be robust enough ? Agricultural engineers can supply strainless bearings much stronger


    If you can get hull speed in light winds, thats a great result
     
  7. rwatson
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    rwatson Senior Member

    Possibly some relevant info

    "Lift coefficient from the sailing rig compared to the flettner rotor is a factor of 1 to 13, including the unique power control difference between the 2 sailing systems where as the sail system has to be reefed taking away the possibility of maximising power according to rapidly changing wind conditions, where as the flettner rotor just has to regulate its rpm according to the corresponding wind speed leading to the much higher utilisation of the different wind conditions."

    http://www.thiiink.com/flettnerrotor/
     

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  8. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Has anyone evaluated magnus effect from a flattened rotor?

    A continuous band spinning around two separated skinny rotors?
     

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  9. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Since magnus effect results from wind friction, and lack of, with a moving surface, does it have to be circular? Why not triangular or pentagonal? Would make tensioning the fabric rigidly an easier task.

    I understand a rigid steel cylinder has ONE moving part and robust enough for large ship forces.

    As Sailor Alan pointed out, many of our future advances won't be due to discovering new principles, but to new materials allowing more efficient applications.

    For a 25 foot plastic boat, some sailcloth spinning over several rollers (one powered) might be just such an innovation. Take that same fabric panel and twist it up into a cable and you could lift my boat with it. :)
     
  10. Yobarnacle
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    Yobarnacle Senior Member holding true course

    A multi roller rotor might even be adjustable if that benefited. The thom gates at the top of the fabric might have to be fixed, causing a chafe problem. Need to think on it.

    In the crude diagram the grey areas are high pressure. Not shown but on opposite side would be the low pressure zone producing lift.

    Am I understanding the magnus effect correctly?

    I'm comparing a single large rotor to a multi roller rotor in the sketch.
     

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  11. Sailor Alan
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    Sailor Alan Senior Member

    This is about the single vertical tube version. The halyard tension to hold a cloth tube taunt over this distance (height) will be high, so the compression on the mast system will be high too. A multipart block halyard will help. Though an “A” frame mast, or a tripod sounds good, getting the top together and leaving room for the necessary ‘end plate’ will give excessive unused height, or a kind of ‘bridge’ which will not handle compression very well. Therefor i was thinking of a free standing single mast, hence the zipper etc.

    I do not think the bicycle tubes are stiff enough, they rely on the restraint of the tyre for their function on the bike. Pump them much over 20psi without the bicycle tire in place, and they bulge all over the place. I do not think bicycle wheels are very good either, they are not very good at lateral loads.

    I would try a sailmaking approach, and make a tube from low stretch sailcloth. It could be a complete cylinder with a seam, or with a zip for easy installation on the single mast. The seam, or zipper, will be a ‘bump’ in the smooth surface, who knows to what detriment. Every 2’ or so, place a batten pocket around the tube. These should have either wooden battens, cane or willow, or fiberglass rods in them. At some future date, two (or several) of these batten pockets could be tied together, using more cringles, to ‘reef’ the tube.

    The lowermost and uppermost ‘batten pocket’ will have a row of cringles round it, and each of these cringles has a stranded steel wire (or low stretch cord) at about 30-45deg to a bearing system in the center. As suggested by Rwatson, you could raid the agricultural engineers, or construction (cranes etc) parts box for a suitable high tension roller bearing system. DO NOT use the roller furling system, it is not designed for continuous rotary duty. Besides they are expensive for what you get.

    This will need a lot of tension vertically so the tube does not twist with torque, and ‘bend’ laterally with wind pressure. Modern sailcloth, especially that with a lot of filler in it, is very stiff and stable, so should do this duty. We should ask a sailmaker whether it should be cut on a bias for greater stability, and torque transmission.

    The multi-roller idea would dramatically increase the lateral load on the rollers, and though you could support them at the ends, the middle will tend to sag together. Perhaps we could discuss slitting the vertical cylinder, or triangle tube, into easily handled vertical sections?

    Be careful though, the multi-roller system sounds like a Van de Graph machine, a static electricity generator of some effectiveness. After running it for a while, you might get lightning bolts across the mechanism.
     
  12. Nick.K
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    Nick.K Senior Member

    I knew an elderly engineer (he died a few years ago) who had a passion for flettner rotors and believed that they could be used as fuel saving devices on trawlers. He designed and patented an inflatable rotor ( http://www.google.co.uk/patents/US4401284 ) and built a small scale version which was fitted to the stern of his old admiralty Pinnace. Unfortunately when I knew him the boat had become decrepit and I never had a chance to see it in action but I did spend an afternoon with him where he showed me the plans and photos and explained how well it worked and what a difference he thought it could make to fuel consumption in fishing vessels. The inflatable element evidently was designed to overcome the weight and size of a rigid rotor.
     
  13. Sailor Alan
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    Sailor Alan Senior Member

    Clearly this principle has been around for a while, and fascinated people over that time as well. Apparently, it was originally dropped as diesels, and water screw technology became better. (see below)

    Here is another attempt at a reefing rotor system.

    http://flettner-rotor.de/rotor-yacht/reffbarer-rotor

    This one appears to be opaque plastic sheet formed into a cylinder, using aluminum extrusions as formers/frames for shape and support. Sound and well engineered, as one would expect from a university.

    http://www.shipspotting.com/gallery/photo.php?lid=437967

    Having a ‘fixed’ endplate is completely new to me, I've never seen it before. It clearly makes the mast support system a bit easier.

    http://en.wikipedia.org/wiki/File:Flettner_Rotor.gif

    From Wikipedia, which I'm sure you have all read.
    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.[1] These types of propulsion cylinders are now commonly called Flettner rotors.

    It was found at the time that the rotor system could not compete economically with the diesel engines that were also being developed for ships in this era. Flettner turned his attention to other projects and the rotors were dismantled. Baden Baden was destroyed in a Caribbean storm in 1931. Due to the rising cost of fossil fuels, as well as environmental concerns, there has been renewed interest in the concept in the later 20th century, starting with Jacques-Yves Cousteau's Alcyone in 1983.

    Clearly Diesel engines have improved greatly since then, as have propeller design, as have materials, but have these changed to the point where the Magnus effect can compete with slow speed screw propulsion? I realize this vessel will have its own screw running in ‘neutral’ i.e. exactly water speed for minimum drag.
     
  14. Nick.K
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    Nick.K Senior Member

    By memory, the drive disk at the base of Ken's rotor was about 18 inches across, the inflatable element packed down to almost nothing on top of it when deflated. The boat was a heavy displacement motorboat of about 30ft length. I don't remember the actual figures, but I do remember him saying that it worked very well either to drive the boat or as an assisted drive.
     

  15. rwatson
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    rwatson Senior Member

    This statement is obviously wrong, and the reference that it cites does not support that.

    Considering that seize of the vessels that Flettner converted, and the that the cylinders were driven by such small motors, it doesnt make any sense.

    I modified the Wikipediea page to reflect that - it will be interesting to see what happens.
     
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