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About Erwankerauzen

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  1. Erwankerauzen

    Hervey Bay A Class Worlds

    Instead, I think the best sailors would get the most from relevant measurements, compared to the average Joe who does not even compute the shear & twist of its apparent wind . Of course for A-Cat sailors who are involved in AC Cup and/or making A-Cat sails,it can looks a bit trivial. But I feel confident that a reliable set of data would be helpful, not only for the above-mentionned, but also for all others A-Cat designers professionnals or not. Fair winds to all Erwan
  2. Erwankerauzen

    Hervey Bay A Class Worlds

    Hi Everybody, Both the Australian A-Cat Nat & A-Cat world are attracting the best A-Cat sailors, That is why it could be a great opportunity to make a few performance measurements in order to be able to plot a few points and achieve gradually an "A-Cat polar curve" A publicly available EXCEL spreadsheet could be a perfect and simple tool to gather the informations achieve some average /standard deviations if necessary. I feel confident many smart anarchists would bring positive remarks to achieve a reliable outcome. The starting point could be: Which equipment on the boat and what kind of protocol to record the sailing parameters and how to link these measures to the true wind direction and velocity ? Good luke and fair winds to all the sailors. Erwan
  3. Erwankerauzen

    Gay Test

    Obviously this young lady is not chubbby, she has no fat, wherever you are looking at. So the main conclusion I can draw is that this young lady does not eat BigMacs. Whatelse can be noticed ??
  4. Erwankerauzen

    The new sailing twin skin setup

    The Liebeck wing sections can achieve similar high Cl, but their stall behavior not easy to manage and the big Cl can be achieved with a laminar rooftop, not a turbulent one like for our sails or wings. Coming back to the twin skin set_up, it seems we are talking about the main only, but: If you consider the relative size of the jib, the height of the hound, I think we should consider it as a slotted rig : With the jib being the first element and the main sail the second element. Cheers
  5. Erwankerauzen

    The new sailing twin skin setup

    For the CFD and sailmakers geeks who are interested in double skins sail concept, have a look at this workpaper from Princeton University / NASA Librairy, an old one but it remains interesting. Happy reading Cheers EK
  6. Erwankerauzen

    C-Class Little Cup news

    So Canaan is not attending ??? Too bad!! Fair Winds Erwan
  7. Erwankerauzen

    Moth Developement

    You are talking about hindged flap, which aims to modify the camber of a single wing section. It is a bit different than a 2 elements wing ,with a slot between. For sure the size and position of the gap can change the global result of the package, it is well documented in the C-Class litterature. But what I mean is: As the boat is foiling, the apparent wind is strong enough to make a single sail or single wing powerfull enought without complex solutions like a 2 elements slotted wing. In other words if the maximum (2D) lift coefficient of a 2 elements wingsail is around 2.4 The maximum (2D) lift coefficient of a simple sail or single element wing would be around 1.6 But as soon as the boat is foiling, the apparent wind available requires only a lift coef between 0.8 and 1.2 So the extra HP available with the 2 elements wing is useless, Power is not the issue, but below 6 knts TWS. Cheers
  8. Erwankerauzen

    The new sailing twin skin setup

    I am afraid it would never be possible to observe a negative AoA at the top of thse wings, for a simple reason: Assumption: The crew reponsible for the trimming has a minimum understanding of wing section Lift/Drag issues) As it is about symetrics wing sections with a significant thickness for the main one (Element 1) The lift/drag sweet spot for this kind of wing section is probably within -4° to +4° In other words, even if inverted, as it is controlled by a smart crew, I doubt negative AoA to be more negative than -4° ( on a cruise mode of course). So you see random, the actual issue is how to detect on a video this tiny 4° maximum difference between the wing section and the apparent wind ? To see this inversion you would need to be on the top of the wing, checking the alignment of the wind vane with the center line of the wing section. For a 2 feet long wind vane,; A 4° angle means a 4.15 cm gap or around 1.60 inches. Cheers
  9. Erwankerauzen

    Moth Developement

    A 2 elements wingsail like the one which was build from C-Cat mould a few years ago, is probably not the best trade-off between complexity, and performance. The slot wing sail is very effective to deliver extra HP compared to a single sail, but according to the apparent wind available: as soon as the boat is foiling, it is not about power anymore, but about drag. In light winds, when you need the most sail power, unfortunatly the Reynolds numbers are low and the available power from the wing too, as the polar curve goes right (more drag) and down (less HP) on the graph. Cheers
  10. Erwankerauzen

    The new sailing twin skin setup

    random Negative camber is different from inverting the top. GroupamaC which has some common designers with ETNZ has "little streamlined struts" at the top of her wing to control........ top inversion. But wether it was actually used is another story, no too much hands available on this 2 crews boat. Do you aim to replace Doug Lord??
  11. Erwankerauzen

    The new sailing twin skin setup

    Random, Try to googlize the following and you will get the full workpaper, it is too heavy to be downloaded. You can bet confortably that, if there is some theorical advantage to have a bell-shaped lift distribution (with negative lift at the tip), the AC design team have put it at full use. These "rocket scientists" are professionnal you know! NASA/TP—2016–219072 On Wings of the Minimum Induced Drag: Spanload Implications for Aircraft and Birds Albion H. Bowers, and Oscar J. Murillo Armstrong Flight Research Center, Edwards, California Robert “Red” Jensen, and Brian Eslinger Jacobs Technology, Inc., Edwards, California Christian Gelzer Logical Innovations, Inc., Edwards, California. Good reading
  12. Erwankerauzen

    14' Stunt S9 Foiling Cat

    Good feed back, thank you very much. Everybody is happy to see that the boat is still in her development phase.... since 2012. Wish you the best
  13. Erwankerauzen

    The new sailing twin skin setup

    I doubt you can observe a -3° AoA of the sail top on video. I am not sure (because of my Alzheimer), but it is possible Glenn Ashby has mentionned it in an interview, a few months ago. Remember, in addition to his skipper role, he was also the wing trimmer. Happy week end Random
  14. Erwankerauzen

    The new sailing twin skin setup

    The rocket scientists behind the Godzilla wing of the AC 34 used to say that the thick wing sail allowed tacks and gybes with continuous air flow and no separation (very draggy) which is not the case for a classic teardrop mast. I guess the engineers have considered this point seriously as fast tacks and gybes are a significant part of the whole performance in the cup. In addition, if top main sail negative lift is also a part of efficient trim, in order to achieve the so called Bell shaped lift distribution, it is necessary to have a thick sail in order to fit some "inverting devices" in the middle. Cheers
  15. Erwankerauzen

    The new sailing twin skin setup

    Hi Dorox, Your examples of wing sections look like Javafoil outputs ??? Anyway, thanks for making serious homeworks for the benefit of the "sailing geeks" community. In order to check your CFD model (just in case :garbage in/ garbage out issue) here is how I would make a check For 2D drag (wing section drag/ friction drag/ pressure drag) My benchmark is Minimun drag coef=1.7% or 0.017 for a significant Lift coef around 1 It is what I found on different workpapers in the case of a fully turbulent flow over the sail. With 10m/s apparent wind speed for an A-Cat, the lift coefficient should be around: Cl (2D)=1 and Cd (2D)=0.017 so Lift/Drag = 1/0.017= 59 That is very theorical of course but it provides an idea . For AC 50 Wing, you can consider a 20% to 25% relative thickness for Element 1 and 9% to 12% for Element 2. Mark Drela (MIT Prof) has posted somewhere (probably on BDN) a file with such wing section and the drag coef was around 1% but AFAIR it was with NCrit= 9, so not fully turbulent assumption. Cheers