Gyrocopter rotor instead of canvas sail ?

Discussion in 'Hydrodynamics and Aerodynamics' started by CocoonCruisers, Mar 22, 2019.

  1. CocoonCruisers
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    CocoonCruisers Junior Member

    Large rotating machinery within human reach on a moving platform, with powerful electron beams and 50 000 Volts in saltwater spray ... can this thread get any healthier ? :)

    (You might be onto something with such thrusters for boundary layer control though, whatever the wing)
     
    Last edited: Mar 23, 2019
  2. JamesG123
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    JamesG123 Senior Member

    Its not the volts that get'ca.
     
  3. CocoonCruisers
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    CocoonCruisers Junior Member

    Key points for sure! The orders of magnitude i googled up were more like
    - Flettner L/D around 4-8, with underwhelming upwind performance indeed (close to zero VMG) , so better suited for motorsailors, see fig. 13 on https://www.hindawi.com/journals/ijrm/2016/3458750/ for example
    - Modern autogiro *rotor* L/D up to 15 according to https://www.icas.org/ICAS_ARCHIVE/ICAS2012/PAPERS/434.PDF , and reported engine-cut glide ratios of 4:1 to 5:1 for the whole aircraft including the draggy, sometimes open nacelle.

    - I'd think that for a 100m2 rotor as in a 500hp mid-size helo, we'd need something like a disc brake assembly for trucks ? Doesn't really sound unmanagable to me, and the mast will need to be beefy enough to cope with the wheel effect anyway.
    - Not sure if we'd need to brake all that fast actually: on a cruising cat with lots of RM reserves, people would rather be cooking than stand watch sheets in hand to cope with the next gust...
    - Hey wait, maybe we don't need any substantial brake at all: we'll have at least two systems that allow to turn the rotor out of the wind: some kind of mast rotation would be needed to adjust for upwind/downwind/reaching anyway, and we'll also have steering.

    Let it bend then: Curved or inclined mast for enough clearance ? Twin A-frames like for a fairground giant wheel ?

    Autogiro rotors already handle a lot of apparent wind speed differential when they're cruising at 100 knots.

    I fear you are right in assuming that it will be hard to avoid the complexity of pitch control: Simpler aerodynamic and/or aeroelastic tricks for depowering exist (Stall regulation as in Pitch-regulated and Stall-regulated Wind Turbine http://researchhubs.com/post/engineering/wind-energy/pitch-regulated-and-stall-regulated-wind-turbine.html), but is that even possible for a rotor designed to produce lift, not torque ? Would we want the drag (=heeling force) that comes with a partly stalled blade ? And what would be the point of keeping the rotor spinning in a nicely auto-depowered state, if the L/D ratio crumbles to levels that don't really allow to sail anymore ?
     
    Last edited: Mar 24, 2019
  4. JamesG123
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    JamesG123 Senior Member

    You would not. In either case. Ideally, you would want the entire wind powered propulsion system, rotor, mast, etc, to fold away completely (or vanish magically if we are talking truely ideal). But since we don't live in an ideal world, you can't so you get compromises, such as in this case, where the drawbacks have outweighted the benefits of conventional sails. A big one that occurred to me is that a breaking wave or knock down is to demolish your rotor, probably even if it is locked down stationary.
     
  5. rwatson
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    rwatson Senior Member

    Just came across this by accident.

     
  6. rwatson
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    rwatson Senior Member

    Great paper. I will add it ot the Flettner Thread, as it is really useful.

    The "lack" of upwind performance is much better than sails, so that doesnt relegate a rotor ship it to cruiser status.

    If I read Figure 13 correctly, it shows forward thrust at 35 degrees in an 18 knot (5 m/s) wind for a rotor cross section of 112 square metres (diameter and height were 4.0 m and 28.0 m,) as 50 Kilonewtons ( 11,000 pounds)
    (at 90 degrees, that goes to ~200 kilonewtons, 45,000 pounds ) - at minimal heel angle.

    Whereas a quick calculation for Sails :
    Sails of around ~100 sq m, at the same angle (35 degrees ) and wind, produce around ~300 pounds of forward thrust, at a 60 degree heel angle
    (at 90 degrees that is ~ 500 pounds of force of forward thrust)

    SailPowerCalc http://cdn2.hubspot.net/hub/209338/news/SailPowerCalc/SailPowerCalc.htm

    (I put the links here if anyone feels like checking my very quick figures)
    Conversion of force units newtons N mass gravity unit newton gravitational force Newton - sengpielaudio Sengpiel Berlin http://www.sengpielaudio.com/calculator-forceunits.htm
     
  7. Dejay
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    Dejay Senior Newbie

    Sweet it actually works!

    Now I want a giant vertical wind turbine that rotates around the entire ship.
     
  8. CocoonCruisers
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    CocoonCruisers Junior Member

    Hmm, that will depend much on scale. On a cruising cat large enough to avoid the samourai scenario, it means greenwater 4 meters or so above waterline.
    I'd long be running under bare poles, or hanging on a drogue then, with the lower blade solidly strapped down - just like windmills have weathered storms for centuries.
     
  9. CocoonCruisers
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    CocoonCruisers Junior Member

    Yes, there are quite a few examples of these windmill-to-propeller experiments around the web, and just as the flettners, wingsails and canvas, they are relevant alternatives for a viability/efficiency shootout.
    But my initial question was more about a simpler, freewheeling rotor that produces lift (forward force) directly like a sail.

    I would have looked at the same links for the quick numbers, so won't be of much help for checking them :). I do see two biases though:
    - Comparing a 28m flettner with a 16m tall sail rig seems a tad unfair: structural and stability challenges are so different that they could hardly be installed on the same boat.
    - 35° sound nice, but they are given at rest (TWA) for both flettner and sail. AWA at some speed might push us into narrower angles, where the flettner might not be able to operate. (Cruising-style canvas sails won't go much further either, but an autogyro-style rotor should: at cruise speed, they operate at single-digit angles).
     
    Last edited: Mar 24, 2019
  10. rwatson
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    rwatson Senior Member

    One of the big problems is the variables in that sail calculation site. Sooo many factors that could be tweaked.

    It's only virtue is that it supports the rule of thumb, the Rotors produce about 7 times the power of a sail the size of its silhouette, and the other is to show that they have an equal or better beating angle.
     
  11. Angélique
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    Angélique aka Angel (only by name)

    Seems hard to invent something new, I've just read this on Dudley Dix' website . . .

    ‘‘ . . . It is often said that there is nothing new in yacht design, that whatever we come up with that is innovative has been done by someone else in the near or distant past. That applies to radiused chine hulls as much as to anything else. . . . ’’
     
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  12. tspeer
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    tspeer Senior Member

    Although you are interested in a freely autorotating sail instead of a wind turbine linked to a propeller in the water, I think it's interesting to consider the geared cases as well. A wind turbine geared to a propeller will allow the boat to sail directly upwind. A water turbine driving an air propeller is the way to go for sailing dead downwind. Both of these modes were demonstrated on land with the record-setting Blackbird. So it makes sense that in between these two extremes, i.e. reaching, the rotor should operate in a freely autorotating mode to produce a lift force like a conventional sail. I've never seen any study that looked at the crossover performance of these three modes of operation to determine when it is best to go to autorotating sailing vs driven propulsion.

    Instead of adopting an autorotating sail as an object in its own right, how about designing a boat to a set of requirements for which the autorotating sail is the best engineering solution? Say you want to be able to sail at any direction to the true wind. An example might be an autonomous vehicle that needs to station keep over a fixed location, or needs to be able to travel a precise path that precludes tacking and gybing. The ability to blend seamlessly between turbine/autorotating/propeller modes by changing rotor pitch (and, ideally, rotor twist) and rotor azimuthal orientation, would be well suited to computer control. Such a craft could also maintain control at low speeds when a conventional sailing craft would be stalled out.

    The ability to navigate precisely gives the craft the ability to maintain formation with other like craft. This opens up the possibility of a swarm of autonomous craft that use their ability to maintain relative position and cooperate to achieve their mission. The missions could range from a military surveillance network with overlapping coverage to vessels that handle each end of a boom seining plastic garbage from the ocean.

    The multimode rotor sail would be an enabling technology for tackling these missions. While I think the autorotating sail is an interesting project by itself, I believe its real value is as a building block to the multimode rotary sail. The obvious hazard of a rotary sail to people working on deck probably makes the rotary sail more suitable for autonomous vessels than crewed ones. But for the long endurance autonomous application, the rotary sail could have some powerful incentives.

    One thing that a rotary sail can do that a conventional sail cannot is to generate electrical power for onboard systems in addition to propelling the boat. So when you start pulling on that thread, all kinds of new possibilities open up.
     
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  13. Angélique
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    Angélique aka Angel (only by name)

    Like eg the Energy Observer . . .

    [​IMG]

    [​IMG]

    boat info starts at 1:28


    The Energy Observer vertical axis wind turbines are of the helical · Darrieus type (video), like eg the Gorlov* helical water turbine.

    * note the naming of vertical vs horizontal turbine axis-orientation of that one.
     
    Last edited: Mar 30, 2019
  14. Dejay
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    Dejay Senior Newbie

    Wait, do vertical wind turbines also produce lift sideways to the wind direction that allows the energy observer to sail with them?

    BTW I love how both photos make the energy observer look huge. That tiny lighthouse got me!
     

  15. Angélique
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    Angélique aka Angel (only by name)

    A vertical axis wind turbine like horizontal axis wind turbines give the boat also a direct force in the direction of the apparent wind, and when that's sideways then the boat needs to be able to provide sufficient leeway resistance to keep course. If the apparent wind comes from aft than that direct force adds to the propulsion, if it comes from the front than it's a negative propulsion force.

    Efficient wind turbines directly efficiently geared to efficient means of propulsion can sail in all directions of actual wind. So when sailing the speed of the Energy Observer will always benefit from working wind turbines, but for an apparent wind against the course that's only so if the wind turbines are efficient enough and if there are not too much loses in the system that links the rotary energy to the propulsion.
     
    Last edited: Mar 30, 2019
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