Understanding Wing Technology

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

  1. tspeer
    Joined: Feb 2002
    Posts: 2,268
    Likes: 236, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    I've learned a bit since I developed that technique. It was originally intended for someone to design a mast (I had landyachts in mind at the time) without recourse to a computer. It was based on the idea that the windward separation bubble was basically unavoidable and a smooth curve to the lee side would minimize drag and maximize lift.

    Now, programs like XFOIL are available that can analyze wingmast-sail shapes and do inverse design of mast shapes. XFOIL can handle small amounts of separation, such as separation bubbles. So anyone can do inverse design, now, and come up with a better mast shape than reflecting a known airfoil. The reflection technique might still be a good way to get a starting shape, however, as well as a reasonable sail shape to go with the mast.

    The other things I've learned are it's better to have two small separation bubbles on each side than one big one on the windward side, and trimming the mast so the stagnation point is near the leading edge is a good way to go. If the Reynolds number is high enough or the mast thickness/chord ratio low enough, it's possible to design a mast that has attached flow on both sides, eliminating the drag of the separation bubbles completely. And putting the stagnation point near the leading edge reduces or eliminates the leading edge suction peak that is a major source of skin friction. Together these mean the mast should be operated with less rotation than the smooth lee-side criteria, and the mast shape should be different.

    Possibly the next major advance in wingmast technology would be the ability to twist the mast. Especially with a sloop rig, it's not possible to trim the mast so it is at the best angle at the head and the foot. Separation on the mast could be reduced if it could be twisted. And twisted quite a lot - something like 20 deg or more.
     
  2. tspeer
    Joined: Feb 2002
    Posts: 2,268
    Likes: 236, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Opening the gap reduces the aft loading on the wing and allows the flap to develop a strong leading edge suction peak. A thinner flap will have a stronger suction peak and need a correspondingly smaller gap to suppress it. so you're right about moving the pivot aft for thinner flaps.

    A tab on the wing like the C-class use is very effective in controlling the size of the gap independent of where the flap is hinged. The tab can be slaved to the flap deflection so the pilot still only has one flap control.
     
    2 people like this.
  3. Erwan
    Joined: Oct 2005
    Posts: 377
    Likes: 15, Points: 18, Legacy Rep: 97
    Location: France

    Erwan Senior Member

    Large Twistable Mast & Bubble Ramp

    Thank You Prof Speer for this suggestion, it meets some of my intuitions:
    From a pure theorical point of view, without any consideration for technology or feasablity, I would like to know if it makes sense to imagine :
    1- A large twistable mast 20% 25% of the chord with 5% thickness.

    2-The mast section could be derived from the S 1223 airfoil, and refined with XFOIL as you suggest.

    3-Because this airfoil has a laminar ramp at 20% of the chord, I wonder if it would be smart to make the mast-sail junction around the laminar bubble's place where the friction coefficient is close to zero because of the inverse air flow at this place ?

    4-With a 25% mast chord, the last 5% could be a kind of morphing lips, which foster the sail angle relative to the mast and provide smooth continuity between mast & sail at any camber.
    As a result, managing the mast-sail camber could be like managing the laminar bubble ?

    For other fluid dynamics benchwarmers like me, who would like to have good references about low reynolds and laminar bubble, I suggest to googlize " Mark Drela + Low Reynolds Airfoil Design for the MIT Deadalus prototype"

    Also "Low Reynolds Number Airfoil Design, Lectures Notes+ Michael Selig)

    Also interesting study (Phd I guess) about morphing wing section: (Development of a design tool for aerodynamic shape optimization airfoil + Secanell Gallard) In this study the Reynolds number range is 250K to 1500K, quite similar to beach cats.

    Regards to all

    Erwan
     
  4. tspeer
    Joined: Feb 2002
    Posts: 2,268
    Likes: 236, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    (Thanks for the promotion, but I'm not a Prof.)

    Yes, that makes sense, but you have to consider the mission, too. From what I've read, everyone that has taken a large wingmast to sea has come back saying, "Never again!" It's too much un-reefable area.

    [/QUOTE]
    2-The mast section could be derived from the S 1223 airfoil, and refined with XFOIL as you suggest.

    3-Because this airfoil has a laminar ramp at 20% of the chord, I wonder if it would be smart to make the mast-sail junction around the laminar bubble's place where the friction coefficient is close to zero because of the inverse air flow at this place ?
    [/QUOTE]
    That wold give you a starting point, that technique was intended for people that do not have access to an inverse design method. I would use XFOIL to redesign the shape to meet your requirements. Arvel Gentry has an excellent article on mast design. You can follow his design philosphy to its logical conclusion with XFOIL to produce a mast without separation on either side.

    Exactly. In fact, you can do the morphing ahead of the sail track with a concave recovery region on the mast.
     
  5. BigCat
    Joined: Jan 2008
    Posts: 73
    Likes: 1, Points: 0, Legacy Rep: 27
    Location: near Seattle

    BigCat Junior Member

    Bumpy whale fins

    How about this?

    Bumpy whale fins set to spark a revolution in aerodynamics


    March 21, 2008 It seems despite man's endless ingenuity and the incredible modeling power available to inventors through CAD systems, we keep looking to nature to find ever more effective ways of doing things. Millions of years of evolution's trial and error approach have resulted in some incredibly effective designs that are ready to be incorporated into human constructions if we can only identify, understand and replicate them. The random-looking bumps on the humpback whale's flippers have just inspired a breakthrough in aerodynamic design that seems likely to dramatically increase the efficiency and performance of wind turbines, fans, flippers and even wings and airfoils. WhalePower's tubercle technology seems like nothing less than a revolution in fluid dynamics.

    The humpback whale can weigh as much as 13 Hummer SUVs - and its unexpected levels of agility in the water have puzzled scientists for many years. Dr. Frank E. Fish (believe it or not) was browsing through a gift shop, when he noticed a group of small bumps on the leading edges of the fins of a humpback whale statue. Thinking it an error by the sculptor, he commented that the bumps seemed to be on the wrong side of the fin, starting an argument that would eventually lead him to discover an entirely new way of looking at the role of fins and wings in fluid dynamics.

    Current theory would state that the leading edge of a fin, fan or turbine blade should be absolutely straight and smooth for best effect - a 'fact' that has been taken for granted for decades. But the more Fish studied the odd leading-edge bumps, or Tubercles, the more it became apparent that evolution's work on the fin was far ahead of man's best efforts. Airfoils fitted with tubercle bumps showed much higher lift efficiency and greater stall resistance than identical airfoils without them. Turbines fitted with tubercles to the leading edges of each blade are able to produce more power at low fluid speeds, are quieter, and perform much better in turbulent fluid streams.

    It seems the bumps have the effect of channeling air into smaller areas of the blade, resulting in a higher wind speed through the channels and a number of rotating airflows on top of the blade which increase lift. Furthermore, the bumps eliminate the tendency of air to run down the length of the blade's edge and fly off at the tip, causing noise, instability and a loss of efficiency. In fact "bumps" is probably the wrong word as these are not small protrusions - on a utility scale (50 meter) blade for example, each tubercle would be about the size of a VW Beetle.

    After discovering the Tubercle effect, Fish worked with Phil Watts to invent and patent a new type of leading edge for airfoils and hydrofoils. WhalePower was then formed in collaboration with Stephen Dewar with a view to applying these designs to all types of turbines, pumps, compressors or fans.

    Wind power generation turbines stand to gain greatly from the discovery; because they can be used at a greater pitch angle with much less drag and much less tendency to stall, they allow turbines to continue generating power at wind speeds that are much too slow for traditionally shaped turbines to operate safely in. Importantly for the turbine market, tubercles can be retrofitted to the leading edge of conventional blades. Real world performance is proving very impressive, leading several major wind farm manufacturers to seek retrofit kits for their existing designs.

    The technology is in the early stages of commercialization by WhalePower, which is initially focusing mainly on the wind turbine market as a means of establishing itself. Currently Tubercle Technology is being licensed to manufacturers like Canada's Envira-North who will bring out the first big fans (24 feet in diameter) in April this year. Definitive R&D testing at the Wind Energy Institute of Canada (WEICan) is also about to take place and negotiations are in progress with a number of manufacturers who make everything from hovercraft fans to the tiny fans that keep laptops cool.

    While the company doesn't expect it to be easy to break into the market, WhalePower co-founder Stephen Dewar is confident that the commercial benefits of the technology will be so easily apparent that we'll soon see bumpy leading edges on a range of household and commercial goods.

    "If we've got what we think we've got, then the range of applications is staggering," said Dewar in an interview with The Star, "I'm honestly scared of making claims at this point. The results are so good that we know everybody who knows anything about aerodynamics will think we're salting the goldmine."

    We look forward to discovering how this nature-inspired technology stands up as a commercial product, and seeing its applications diversify as it matures.

    From: http://www.gizmag.com/bumpy-whale-fins-set-to-spark-a-revolution-in-aerodynamics/9020/
     
  6. Erwan
    Joined: Oct 2005
    Posts: 377
    Likes: 15, Points: 18, Legacy Rep: 97
    Location: France

    Erwan Senior Member

    Sorry for the confusion

    I apologize, it is a confusion with XFOIL Forum, where users mention Prof Drela. As your communication is so academic and your explanations are so crystal clear, I always believed you were in Phd environment.

    My bet is large wingmasts are not worse than wingsails, for Moth or A-Cat application, not for cruising with family.

    Thank you for the Arvel Gentry workpaper, when considering the conclusions (basicaly a blunted front face of the mast section), I cannot avoid to make comparison with well known High Lift solutions:

    When looking at the maximum lift airfoil like the famous Liebeck Cl=3 thin airfoil section (for 3 000 000 Reynolds), also I have somewhere on my old laptop this Liebeck wing section revisited by Prof Drela for (300 000 Reynolds). Both have a blunted leading edge.

    The Steve Killig workpaper on C-Cat technology also provide interesting insight on leading edge design philosophy for C-Cat wing 1st elt.

    When looking at distribution pressure for slotted flap wing section (available on ABOTT) or for Stratford-like recovery, one could find they are quite similare but the first one exhibits a kind of pie-slice gap at the slot position.

    All these high lift solutions, using a slotted flap or a Stratford like recovery distributions exhibits a blunted leading edge.

    This common feature for high lift solutions provides an interesting side-effect. There is enought space in the leading edge to house a telegraphic-mast, like for any kind of twistable wingsail.

    Of course in the Arvel Gentry workpaper, the mast's leading edge velocities are trimmed down by the jib effect, while for other solutions aboved mentionned, it is the aft pressure distribution which decreases the leading edge velocities and therefore the friction drag. (At least it is what I understood)

    I don't know if my comments make sense or not, but what I am sure is that one year ago, I was not able to compare any distribution pressure nor to understand relation between leading edge velocities and drag.

    So if you are a fluid dynamic dummy like me, do not desesperate, it is just a matter of time reading forums and workpapers.

    Thank you BigCcat for the info, this point has been addressed here, but at this time no effective demonstration was available.

    This kind of tubercle bump could be a smart solution to provide aerodynamic fairing for wingsail hound. It would decrease the drag of the hound and the downwash as well.
    May be the new Aethon wing's hound seems to have addressed this problem with a similar philosophy.

    http://www.boatdesign.net/forums/sailboats/sail-aerodynamics-457-16.html



    Regards to all

    Erwan
     
  7. rattus
    Joined: Feb 2008
    Posts: 61
    Likes: 4, Points: 8, Legacy Rep: 74
    Location: US

    rattus SeƱor Member

  8. Gary Baigent
    Joined: Jul 2005
    Posts: 2,991
    Likes: 114, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    My friend Jim Keogh, (Auckland Arty Farty *******' commodore) built a humpback fin-type rudder for his stripped down Hartley 18 maybe a decade ago .... but he could not observe/feel any difference to the boat's performance - plus he had to wedge the blade because of the leading edge protrusions - which was annoying (wedges come loose) in the longer chord case so he returned the blade to a conventional shape. But it looked really cool initially.
    To be practical, the bumped leading edge boards/blade/keel/rudder would have to be fixed down, maybe a pivoting rudder would be okay. If I remember correctly, there were some New York guys who did an experiment with bumped appendages on their mono - and they were impressed by the performance.
     
  9. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    All the things I've seen compare foils with separation problems to the same foils with the warts. They seem to focus on prolonging stall to a higher AoA (and CL). I have not seen a L/D comparison for low AoA and low CL. I suspect there is a drag penalty.

    It comes back to evolution. We don't see the bumps on other animals. Hawks and Buzzards have a need for slow flight in tight circles (thermals close to the ground) and a need for high L/D (to glide between thermals) they don't have lumpy leading edge wings. As I understand the way whales use their fins, they are are mostly aids to tight maneuvers in close quarters and they are not extended full span when moving at higher speed. I don't see how this is applicable to rudders or or other foils on boats that do not get retracted when high CL is not needed. I think a multiple element, camber changing foil would have a better L/D curve over the same range as the whale fin clones. The whale's fins evolved that shape for some other reason than hydrodynamic efficiency or it would be a common feature in nature.
     
  10. Doug Lord
    Joined: May 2009
    Posts: 16,651
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Understanding Wing Technology-Steve Clark wing

    Here are some comments from SA by Steve regarding the wing design he is doing as an open design available to the public. See the image below:

    There will be some provision for moving the hinge axis to tune flap gap.
    The thing will turn into 4 pieces at the end of the day such that it will fit within the footprint of a Weta or Hobie 14.
    Leading and trailing edges are carbon foam moldings, pretty simple. The trailing edge pieces are built straight and bent into a gentle curve by the ribs.
    The ribs are kite tubes cut to length and fit into sockets on the D sections and trailing edges.
    Long term, it can be disassembled into 4 leading edges and 4 trailing edges, a pile of kite tubes and a few other bits.

    The flap will twist as per Patient Lady system, leading edge will not.

    Other details are in the works.

    SHC

    Beatings will continue until morale improves.


    click on image ,and then again on resulting image:
     

    Attached Files:

    Last edited: Dec 8, 2010
  11. Doug Lord
    Joined: May 2009
    Posts: 16,651
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Attached Files:

  12. Doug Lord
    Joined: May 2009
    Posts: 16,651
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Understanding Wing Technology----Moth Wing

    According to Matt Knowles the wing in the Moth class needs much more work-it is not the end of the soft sail as many had predicted and the major developer in the Worlds and "advocate" for the wing-Gulari-will not use the wing in the Moth Worlds.

    Knowles writes:

    "A lot of people have been asking about (or speculating about) the wings. Bora is busy working hard on his final push to try to regain his world title, so I'll clarify things a bit. Since we've arrived our container has been an open shop. We've given full and honest answers to all the questions people have had. We're trying to help the class gain the data it needs to make an intelligent decision about wings in the long term. There's no gamesmanship going on. The three identical wings the US team brought to Belmont have shown great promise in certain conditions, but also considerable weakness. The biggest weakness is light air (marginal foiling). The wings also struggle at times downwind; if they are not set up and trimmed perfectly, they are quite slow downhill. In breeze, they are very hard to beat upwind. Nevertheless, the plan right now is for Bora and Bear to run soft sails for the Worlds. Charlie McKee is going to sail with a wing for the whole event. As he puts it, "someone has to do it" to help the class see what we're dealing with".
     
  13. Erwan
    Joined: Oct 2005
    Posts: 377
    Likes: 15, Points: 18, Legacy Rep: 97
    Location: France

    Erwan Senior Member

    polar curve sinking problem in light air ?

    Thanks Doug for the info,

    Comments regarding wing performances sparks a candid question in my little brain:

    Can the half chord-Reynolds compared to a soft sail in moderate wind speed and therefore low reynolds numbers, dampen the performance of the slotted 3elts wing sail in such a way that the theorical pick-up in performance is offseted by the lower Reynolds effects ?

    Thanks to Matt for his transparency, our comitment should be to brainstrom
    until we gather enough information for Matt and other wing-mates to improve their project.

    Doug you can be our Pastor!!

    Regards and Happy New Year everybody

    Erwan
     
  14. Doug Lord
    Joined: May 2009
    Posts: 16,651
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ---------------------------
    Happy New Year, Erwan! This news from the Moth front along with the A Class experience makes me wonder if the C Class could benefit from a modern incarnation of a soft sail? When they switched to wings the soft sails were no where near as good as they can be now. What do you think?
    ---------------
     
    Last edited: Jan 8, 2011

  15. tspeer
    Joined: Feb 2002
    Posts: 2,268
    Likes: 236, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    I doubt it. For the same lift coefficient, the peak local speed on the wing main element can be lower than the soft sail, and require less deceleration to the main element trailing edge, than the same region of the soft sail. So there's no reason why the wing can't perform well at the lower Reynolds numbers.

    The fixed luff length of the Moth will neutralize one of the advantages wings have enjoyed, which is the ability to have a taller rig and still maintain accurate control of twist and camber. So you may not see as big a difference between wings and soft sails in the Moth class as you do in other classes.
     
Loading...
Similar Threads
  1. jmf11
    Replies:
    3
    Views:
    863
  2. brian eiland
    Replies:
    14
    Views:
    2,929
  3. JMayes
    Replies:
    6
    Views:
    5,356
  4. Slingshot
    Replies:
    9
    Views:
    946
  5. schakel
    Replies:
    4
    Views:
    1,072
  6. WSW2016
    Replies:
    17
    Views:
    2,020
  7. Surfer Naval Architect
    Replies:
    6
    Views:
    1,533
  8. Wally2
    Replies:
    3
    Views:
    923
  9. pmudesign
    Replies:
    14
    Views:
    1,168
  10. Will Fraser
    Replies:
    12
    Views:
    2,009
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.