Understanding Wing Technology

Discussion in 'Hydrodynamics and Aerodynamics' started by Doug Lord, Sep 18, 2010.

  1. RHough
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    RHough Retro Dude

    There are other tools that allow you to use different profiles but they are not as user friendly IMO.

    XFoil

    Just for grins, have you looked at the numbers for a near zero thickness foil with 12-15% camber? (think soft sail)
     
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    One of the first things I tried! The ultimate undercamber!
     
  3. RHough
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    RHough Retro Dude

    That's why soft sails and high speed under sail are not a great match. :idea:
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ==============
    But soft sails hold the world speed records under sail on water over 500m(kite) and one nautical mile(hydroptere). So lets keep it in perspective.....
     
  5. Cheesy
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    Cheesy Senior Member

    To add a bit more complexity to the mix (or maybe less) all of the wings developed so far (that I am interested in, C and Moth) have been limited by sail area and or the requirement of one sail, leading to the slotted wings to provide maximum lift off the wind (additional reasons for slotted wings?). Now if you had a class that had a sail area restriction of 13m2 and on top of that a 20m perimeter down wind sail, would a slotted wing still be the optimal solution? Would it be worth looking into the engineering of a single asymmetrical element and relying more on the soft sail for off wind legs, although then there will be a point where speed is limited by the drag and apparent wind angles of the soft sail.
     
  6. Gary Baigent
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    Gary Baigent Senior Member

    Cheesy, I don't know the answer but hard sail C Class cats are the most efficient and still the world's fastest round an Olympic type course even though they have (by new AC huge rig standards) a moderate sail area. Their "magic" is that they are ultra light resulting in high Bruce number figures and the slotted wings superior to any other sailing rig on the planet. Ask the C Class guys if they would want soft downwind sails (if the rule allowed them). My guess is they wouldn't be interested. But a C Class with a 50 foot hard rig (to put it in AC territory with double hull length rig height) - would you need extra downwind sails for a monstrous, death wish beast like that?
     
  7. RHough
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    RHough Retro Dude

    Doug, you make it too easy... :p

    Perspective:

    126 MPH Sailing on land in 40 MPH wind (3.1 times wind speed)

    What multiple of wind speed are the wet sailing speed records? Less than 2 times wind speed? One of the limiting factors is the drag of the rigs.

    IMO the basic physics of the Sail Rocket program have it about right. Once they get the control issues sorted the kites and displacement foilers like hydroptere won't have a chance. The MkII boat is under construction.
     
  8. Gary Baigent
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    Gary Baigent Senior Member

    IMO Sail Rocket should reduce the rig incline ... which will reduce the aaiiieee factor of looking over the bow and at high clouds simultaneously.
     
  9. Windmaster
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    Windmaster Senior Member

    Wingsails etc.

    Hi All

    Read this thread with interest. All welcome to view my website at http://www.sailwings.net if you've not been there already. I've been doing experiments with wings for a few years.
    I'm particularly interested in developing automatic control. Let the wind do the controlling instead of all that pulling on ropes!
    One idea is "windthrusters" which you can check out on this page; http://www.sailwings.net/windthrusters.html and http://www.sailwings.net/windthrustersfaq.html

    Peter Worsley
     
  10. Doug Lord
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    Doug Lord Flight Ready

    ===================
    Geez, Randy-I forgot the word "water" even though I remember thinking I'd better be specific or you'd nail me for sure(since corrected). And you did.
    Ah, never heard the term "displacement foiler" before-is that your invention?!
    Hydroptere sails at fairly high multiples of wind speed for a water borne boat doing twice windspeed frequently-I think she did something like 1.49 windspeed for her record. Same with the Moth or Mirabaud.
    But I agree,generally, about soft sails vs wings-though I don't think soft sails can be completely ruled out just yet -especially in classes like the A Cat and Moth.
     
  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    - Hi Peter! Hadn't realised that was you! I still haven't tried out a wing-sail but it's on my list ... Terry Haines
     
  12. RHough
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    RHough Retro Dude

    Yes I coined "displacement foiler" last night. It nicely describes boats like Hyroptere and foiling Moths. Boats that trade induced drag from lifting foils for hydrodynamic drag from wave making or planing hull shapes are "displacement foilers".

    In the sub 50 knot speed range, 3.0 times wind speed is possible on water with wing sails. As the speed goes up the multiple goes down. In land yachts they are getting into the "terminal velocity" area where aerodynamic drag is the limiting factor for the whole system. Increases in speed under sail come from reducing drag. A human kite boarding is not a particularly low drag system, yet that has yielded the highest speed on water to date (at some fairly low multiple of wind speed). Once they figure out higher L/D water foils that work in the 50+ knot speed range, reducing the drag of the human and the kite will be the focus. At some point the limit will be the high AoA that soft sails/kites need to hold their lowest drag shape. A rigid sail/wing that has high L/D at low AoA will be needed to increase speed beyond that point.

    The FoilSim applet gives a feel for this. Use a C-Class limit of 300 ft. sq. and find the highest L/D configuration you can at 70-100 knots wind speed. Then reduce the thickness of the foil to near zero. Look at the pressure distribution at the leading edge, you will not see pressure distributions that will allow a soft sail to hold its shape.

    This is what lead to my statement that high speed under sail and soft rigs are not a good match.

    (not bad getting back on topic eh?) :D
     
  13. Doug Lord
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    Doug Lord Flight Ready

    UWT-Tom Speer

    From SA-

    Posted Today, 09:10 PM

    Amati, on 27 October 2010 - 01:21 AM, said:

    ...
    When you split one wing into 2 wings, don't you create 2 foils with lower re than the bigger wing would have? Or does the whole (split up) unit unit dictate re? Another way to put it is if Cogitos wing were one piece or 2 pieces, but the same planform size, would they both have the same re?


    Yes, the chord Reynolds number for each element is halved because of the definition of the chord Reynolds number. The chord Reynolds number is defined to be the freestream velocity times the chord, divided by the kinematic viscosity.

    But there are many different Reynolds numbers, and they are more useful if you want to start digging into the differences between one element or two. For example, one commonly used Reynolds number is Re_theta, which uses the boundary layer momentum thickness as the length measurement instead of the chord. This takes into account that the boundary layer may have experienced a different history of development by the time it gets to the point of interest. Re_theta varies along the chord, but given points in two different boundary layers can be compared if they have the same Re_theta. The problem is, you need to calculate or measure the boundary layer velocity profile in order to calculate this Reynolds number.

    Ultimately, Reynolds numbers are just a way of categorizing different flow situations. The more the configurations differ, the less useful it is to compare the two configurations at the same Reynolds number. The differences between a single element section and a section with a slotted flap are far more significant than the differences due to cutting the Reynolds number in half
     
  14. Doug Lord
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    Doug Lord Flight Ready

    UWT-Magnus

    From SA-Magnus Clarke--

    I am not going to contribute to this thread endlessly but here goes on a generic decent wing.

    40' boat, do a rig that stands about 70' off the water.

    Main element, NACA 0020 with a 20% tab on the back, Flap element, NACA 0009. Flap chord is 45% of total chord.

    Hinge Flap 15% of ME chord from TE of ME.

    Max chord of 12', min chord at tip, call it 3-4'

    That will get you around a race course just fine. I am sure you can figure out the details from the other threads.
    Cheers

    MC

    I cut it twice and it's still too short
     

  15. Doug Lord
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    Doug Lord Flight Ready

    UWT----Miss Nylex

    Interesting paper on Miss Nylex posted by coxcreek in a series of jpegs-I can't copy so that the result is legible but if you go to SA you can read it:

    http://forums.sailinganarchy.com/index.php?showtopic=115386 posts 3& 4


    *if somebody was good enough with computers to put this in a pdf it would be a public service.....
     
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