Everything Old is new again - Flettner Rotor Ship is launched

Discussion in 'Boat Design' started by rwatson, Sep 1, 2008.

  1. rwatson
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    rwatson Senior Member

    Dinghy comments

    Good observations there.

    I understand that any rotating cylinder, even with conical shaping will certainly provide lift, but as you very correctly pointed out, without "gates" at bottom and top, and even one near the centre, the efficiency will be greatly reduced. This is similar to a plane wings with "tips" or "winglets" and the "flow directors" on the top of the lifting surface on jets. The "gates" do not provide forward lift, but merely control the surface boundary layer on the rotor that does provide the lift.

    The heeling effect is a secondary result, which is greatly reduced by the propensity of a rotor to "claw' its way back to windward.

    I would say that without "gates", this model is suffering from much increased resistance to the wind without the corresponding "lift" of an efficient rotor design.
     
  2. DennisRB
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    DennisRB Senior Member

    A powered airplane creates its own wind to produce lift and will work the same on a day with no wind (after takeoff). A rotor ship still needs apparent wind from an angle to work. So I'm not sure if you can compare it to a powered plane as the rotor ship is converting energy from the wind into power.

    I was going to mention the wingtiplets on air craft wings as a likeness to the gate at the end of the rotor to reduce spanwise flow. The fact is they are proven to work on planes but looking at a large cross section of aircraft in use to day most don't use them so its not like it makes or breaks the design of a wing. Wingsail yachts don't seem to have them usually. Also different shaped wings needed them more than others. Just like different shaped rotors would.
     
  3. rwatson
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    rwatson Senior Member

    Well, I did say "in some sense", in an effort to stress that engines to force wind (artificial or natural) across solid surfaces are by no means counter intuitive or abnormal. I note that jet passenger planes take a lot of trouble to plot courses that encounter beneficial air flow (natural wind) to make huge savings in fuel - so they are not totally divorced from natural phenomena as they can seem.

    Re the wing tips and gates - there are pros and cons for plane wings. Typical boundary layer velocities, drag implications, manufacturing and design expense etc. are all part of a complex equation.

    Flettner himself started with plain spinning tubes, but expert aerodynamicist that he was, he proved that the rotor environment was pecularly suited to "gating" on early models, (see attached experimental vessel - leaning to windward, I note) and the gates produced very real performance benefits.

    Basically, the suitability and benefit of the "gates" for a rotor ship is not an artifical construct or style decision, but based on extensive research.
     

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  4. DennisRB
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    DennisRB Senior Member

    My comments were mainly aimed at Daniel who appeared to think they were required for it to work, therefore dismissing the boat I posted as a Flettner rotor. Did Flettner ever try a tapered rotor?
     
  5. rwatson
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    rwatson Senior Member

    Fair enough - I hope my comments re-inforced the principle too.

    I have never seen a tapered rotor anywhere but in that particular website - and for yachts seeking improved righting moments , it may have real benefits.

    Lots of fun research to do on the whole concept still, I would imagine.
     
  6. DennisRB
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    DennisRB Senior Member

    Makes me want to buy a cheap RC keel boat from ebay and set a rotor up on it...

    I think the taper would also help take care of the probs associated higher wind speed further from the ocean surface? It would appear to be much more difficult and expensive to build with a taper.
     
  7. rwatson
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    rwatson Senior Member

    "thom gates" on Flettner Rotors

    I came across this article from rotor enthusiast and naval architect Joseph Norwood.

    He calculates the co-efficient of drag and lift based on zero to multiple "gates" or "Thom fences " for Flettner Rotors in a discussion on rotor catamaran design.

    I am keen on the idea of trying out rotors on "harry proas", or should I say Joseph Norwood Proas, as he was proposing the large windward hull concept very early on.
     

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    Last edited: Aug 31, 2010
  8. rwatson
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    rwatson Senior Member

    Attached Files:

  9. dskira

    dskira Previous Member

    Don't take it personally, it is not your boat.
    I made a technical observation no less no more, you can call that dismiss.
    Show more proof than a search on Google, and I will gladly change my mind.


    Daniel
     
  10. rwatson
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    rwatson Senior Member

    I think the documentation by Joseph Norwood, at post 52 will provide some usefull info on the effect that the "gates" or "fences" have on the rotors.
     
  11. dskira

    dskira Previous Member

    Interresting, I agree.
    I was talking about this version, which I find difficult to beleive.
    I will need some more proof than a video.
    But as I said I can be wrong

    Daniel

    [​IMG]
     
  12. apex1

    apex1 Guest

    As I said, all I remember was that he planned a Flettner Rotor on Calypso. The picture is not a artists impression, but was the NA´s proposal.
    Have never been a great fan of Cousteau, so I did not follow the process further.

    Thanks for the deeper insight you provided on the topic in general!

    Although I personally don´t think it can outperform the Skysail system (which definetively does NOT have the disadvantages you describe), it is at least a valid solution and may be the better way of alternative propulsion on really large vessels like Ore carriers or Tankers.

    Regards
    Richard
     
  13. Clarkey
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    Clarkey Junior Member

    Interesting paper here on the Flettner Rotor ship:
    http://naca.central.cranfield.ac.uk/reports/1925/naca-tn-228.pdf

    The endplates certainly improved efficiency in these early experiments but are by no means necessary for the rotor to work. Like winglets on 'planes it is probably more efficient to just add span (height) to the rotor if it is not limited by other factors.

    I think that the rotor on www.rotorboat.com is an elegant solution - the tapered form should help reduce the loading at the top of the rotor and mitigate to some extent spanwise flow. It works for wings and since a rotor is very much like them the idea probably has merit. The boat performed at Weymouth speed week and was timed over the 500m course. I forget the exact speed but at least it has been verified in a credible setting.

    The problem I see with small rotors is that in high winds they must rotate very fast to maintain the necessary ratio between circumferential velocity of the rotor and the speed of the wind. As this ratio dips below about 1.7, the l/d becomes marginal for upwind sailing. mind you, this also happens with conventional rigs as you reef them.
     
  14. DougCim
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    DougCim Junior Member

    I'm not sure what would be the reason for using multiple disks like that, since as others noted, the loss of pressure differential can only occur off the ends of the tube. Perhaps there was a structural reason?

    Two other questions about that boat spring to mind:
    ....the text notes that "with only 600 watts, it could sail faster than the wind"... but they don't say how fast the wind was. Will that boat go 30+ knots in a 30-knot wind? I'd bet not. (especially on a cloudy day)
    ....I also immediately wonder how fast an identical boat would go in the same conditions that still had the regular sail rigging on it... -or even had a rigid wing sail of comparable area instead.

    The problem with all the info I've seen so far is that none of it is a real-world comparison. For that you'd need one boat hull (or multiple otherwise-identical boats) and the ability to switch between using the three different types of "sails"--fabric sails, a rigid wing sail and Flettner rotor. Has this ever been done?

    -------

    I still maintain that the Flettner rotor is a motor drive, not a sail.
    The rotor is entirely dependent upon rotating to function, that much is agreed on--but since nobody seems to be able to figure out how to rotate the rotor using wind power, that leads me to believe that the motor is putting more power into rotating the tube than the tube is producing in lift. It's highly unlikely the rotor is functioning at 100% efficient energy conversion, and even more unlikely it's working at over 100%.
    ~
     

  15. Clarkey
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    Clarkey Junior Member

    I need to find the source but I remember reading that this yacht:
    [​IMG]

    Raced around a triangular course with a conventionally rigged yacht of the same type. Apparently the conventional rig just won but it was a close competition.

    I think most of the available data shows that a rotor is able to extract considerably more power from the wind than is required to turn it. I am not sure that I would characterise this as 'greater than 100% efficiency' because the energy driving the boat comes from the wind, not from the motor. By the same measure a conventional sail would be infinitely efficient - and that is a good thing!

    My interest in rotors is due to their ease of handling and maneuverability, not performance (although this seems to be reasonably good). Of course I also like them because they are different but I would not pretend that they are the best thing since sliced bread for every application.
     
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