Comparisons - Split Junk and Cambered Panel Sails

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  • 30 Sep 2014 23:00
    Reply # 3112630 on 3103628
    Deleted user

    Hi David,

    I was feeling quite smug with myself at having excluded the mast in my MK III rig and felt that i would consequently have less error/  turbulence to mess with the flow, but of course in real life we still have to have masts - sadly, so yes to your suggestion i will experiment with a mast of similar scale held both above and below the battens at the  luffs as you suggest.

    Weather forecasts tonight suggest the jet stream will be coming south over UK this weekend heralding the start of unsettled weather and strong winds.

    It will be too soon for me to use, but good to know that it's coming. I have never looked forward to winter so much.

    Ash

    Last modified: 30 Sep 2014 23:06 | Deleted user
  • 30 Sep 2014 20:41
    Reply # 3112494 on 3103628

    Ash, I don't think anyone has mentioned yet that you'll need to do a 'mast to windward' and 'mast to leeward' test for each panel except the wingsail. That will in any case be useful in its own right, to establish whether there is a 'good tack' and a 'bad tack'.

  • 30 Sep 2014 19:22
    Reply # 3112430 on 3103628
    Deleted user

    Cheers Arne, Ash

  • 30 Sep 2014 17:56
    Reply # 3112364 on 3112335
    Anonymous member (Administrator)
    Ash Woods wrote:

    I made a  mistake in my MK II  Test Rig as  posted on Technical Forum - Illustrations, it won't work, got it wrong - sorry. 

    But the good news is - I have now designed a MK III that will work ok and is capable of measuring LIFT and DRAG,  so in a moment i will describe it in more detail, but first i should briefly reply to Arne's post above (3104043) in which he ends with "What have i missed"?

    "Nothing Arne", what you say is spot on.  Mark also makes a similar point re a  windsurfer. I agree a very good 'feel' can be achieved in flying the panels as you describe, and i can see how a video will be able to record the batten angles against the horizon. But i think the flow of tell- tales and the actual loads of drag and lift would not be easily remembered by me for accurate comparison over a period of several days.

     

    Ash, if you re-read my posting you will see that I suggested you to read out loud the state of the telltales. Sound pictures, you know  -  invented over 80 years ago ;-) .. 

    Last modified: 30 Sep 2014 18:05 | Anonymous member (Administrator)
  • 30 Sep 2014 16:51
    Reply # 3112335 on 3103628
    Deleted user

    I made a  mistake in my MK II  Test Rig as  posted on Technical Forum - Illustrations, it won't work, got it wrong - sorry. 

    But the good news is - I have now designed a MK III that will work ok and is capable of measuring LIFT and DRAG,  so in a moment i will describe it in more detail, but first i should briefly reply to Arne's post above (3104043) in which he ends with "What have i missed"?

    "Nothing Arne", what you say is spot on.  Mark also makes a similar point re a  windsurfer. I agree a very good 'feel' can be achieved in flying the panels as you describe, and i can see how a video will be able to record the batten angles against the horizon. But i think the flow of tell- tales and the actual loads of drag and lift would not be easily remembered by me for accurate comparison over a period of several days.

    Yes impressions could be gained, but i want to try to obtain something that is more accurate, less subjective and provides data that I can consider long after the test rig has bitten the dust.

    I enjoy the process and will learn a lot even if is a total cock up, the materials are scrap or readily available. The  Junk rig is so user friendly and relatively easy to make as compared to a Bermudian sail so I feel it is worthwhile having a go.

    Realistically - this is likely to be the last boat and sail I will construct, i want to know that within reason that it has been my best shot, not to be sitting in the cockpit thinking 'now if only i had done...x, y and z'!

    How I hope to set up and use the MK III test rig.

    1. With sail and battens pointing head to wind and spilling, DRAG will be generated, caused by friction. With no 'Horizontal Mast', as in the Mk I design to provide an anchor, the sail and battens will be pushed downwind, tugging and swaying whilst held up on their vertical rope supports. Water is then added to Bucket "D" (drag) to oppose the drag and start to settle things down.

    2. Simultaenously gravity will be pulling the sail cloth and battens downwards so a little water added to Buckets "LA" (lift aft) and "LF" (lift Fwd) until they hold the rig level, so balancing out the force of Gravity.

    3. The 3 buckets and their water contents will hopefully by now be holding the panel fairly steady, each will be weighed (without detaching them from their rope). These initial weights will provide a zero starting point ; and they will be deducted from any weights of water found during subsequent tests. That is to say: only the additional weights will be used as they represent the subsequent forces generated.

    4. The interesting part can now begin as we 'sheet in' - by adding water to bucket "LA". The leech will be raised and wind deflected, applying a downward force to the sail and battens. This downward force is LIFT.
    We will also need to add water to bucket "LF" to maintain our required Sheeting Angle, the weights at "LF" and "LA" reflect the total LIFT generated and is being delivered via the Luff and Leech ropes.
    As we are now deflecting the wind, a greater DRAG will be created - consequently more water will be added to bucket "D" until it stops the rig being dragged downwind. The stabilized sail panel can now 'sail' quietly, hopefully generating measurable LIFT and DRAG, corroborated by tell-tales which will indicate the moments when : the starved, attached and stalled air flows.
    These comparisons will take place at varying sheeting angles from horizontal up to about 30 degrees or more until DRAG  outweighs LIFT.

    5. I hope to be able to mount a total of 3 panels at a time, side by side, to fly in the same wind conditions and record their data at varying sheeting angles. There will be a total of 4 Test Panels: Flat, Arne's Cambered Panel ARNE'S, Slieve's Split Junk Slieve's and David's Swing Wing with a hinged batten.David's 

    6. I aim to be able to obtain a LIFT vs DRAG Ratio of each panel's performance for comparison and to be able to make changes to panels in order to find the optimum shape for each one. Trying out different ideas - maybe varying the amount of camber, the position of that camber, the entry angle, the size of a slot, or the sheeting angle of a jiblet. I will also watch the effect of clipping 2 meter long x 30mm wide pieces of ply vertically to the battens to see if they limit the escape of pressure from the high to low pressure sides and what effect they cause. No doubt anomilies will occur and further tests may need to be carried out for clarification.

    Lastly I just want to comment that my quest is to enable me to decide which design of sail to make, and is peculiar to me, 'very peculiar' I know! 

    In no way am I wishing to set up competition or to judge a winner. We all have different requirements so my eventual selection may not be yours. I think it's very much 'Horses for Courses'.

    I do appreciate all the fantastic info available on JRA and the unselfish and honest help I have had from many of you since posting this subject a few days ago.
    In particular to David Tyler, Arne Kverneland and Slieve McGalliard, their encouragement and advice has prompted me to rethink this all through again and has, I hope, resulted in the my MK III being a more realistic test rig.

    I am really enjoying the process in any event, so fingers crossed that half reasonable results can be obtained.

    I have managed on this occasion to post an illustration of the MKIII Rig in Technical Forum Illustrations and also hopefully as a link Here

    Thanks again, Ash

    Last modified: 30 Sep 2014 17:38 | Deleted user
  • 22 Sep 2014 23:04
    Reply # 3106025 on 3103628
    Deleted user

    Thanks a lot David for uploading the photos - I must learn to make links.

    Having thrown open my proposed tests a couple of days ago, it has turned into an amazing 'Think Tank'. My brain has been imagining windsurfers, kite flyers, tugs of war, pivot beams and proas all doing in some way exactly what i want to achieve.

    It all ran away from me in the sense that before i could reply another suggestion / comment had come in, but a sincere thanks to all who took time to post on this forum and also directly by email.

    I think I have designed a better rig which will take into account both lift and drag and also the forward power created. I have made a drawing to explain labelled MK II which sits in Technical Forum Illustrations and I again invite comment please.

    I can see that it may be a bit too twitchy initially 'till water loads nearly equal forces produced. I may need to fit a damper or two to stop over reaction. 

    I hope having viewed it you don't burst my bubble with some obvious failing that I wish i had noticed myself, but then of course - I hope you do if there is a problem.

    Another 'non aerodynamic problem' had an answer that was so obvious i am ashamed to admit how long it took me to find, was spurred into being by Roy's post.

    Problem: I was going to need stakes to hammer into the field with guy ropes to hold the rig down, just as soon as had done so the wind would veer or back, then night would fall , i would have to dismantle it so that the vagabonds didn't nick the good bits....and put it all up again on the morrow.

    Answer : My boat sits in a launch trolley, which sits on a 4 wheeled road trailer in my front drive. Jenny will never notice if i just slide the boat and launch trolley off, then tow the Road Trailer to the Test Site. I can rig the whole show on the road trailer, using ratchet tie downs through the holes and fixtures provided to hold cars in place, the veer when it comes can be dealt with in a moment by hauling the trailer round a bit, at night i can tow it into a secure yard, and if the Autumn Winds fail: Roy can drive, i will ride shotgun as we roam the streets and tunnels of Surrey at 3am. The job of explaining to the nice Officer 'what we think we are doing' will fall on Roy as he is the driver. Sorted!

    Last modified: 30 Sep 2014 16:53 | Deleted user
  • 22 Sep 2014 18:40
    Reply # 3105812 on 3103628
    Anonymous member (Administrator)

    Sketches of Ash's proposed test rigs are now on the Technical Forum illustrations page

  • 22 Sep 2014 16:59
    Reply # 3105719 on 3103628
    Deleted user

    Thanks to everyone's fantastic input my 'little grey cells' have been working overtime, and i have honed my original suggestions a lot in a way which i will describe as soon as possible.

    As i have never sat down to learn how to make a link - i have instead placed a couple of photographed drawings of my revised ideas and placed them in 'My Members Profile' in the hope they assist in explaining my thoughts. I am sure the words make it seem complicated - i am good at that - but just imagine how hard it would be to explain how to ride a two wheeled bike. SORRY MY MEMBERS PROFILE UPLOAD FAILED. 

    Last modified: 22 Sep 2014 23:07 | Deleted user
  • 22 Sep 2014 16:45
    Reply # 3105706 on 3103628

    Encouraged by Roy to air this thought:

    Whenever I've daydreamed about this sort of thing, I've envisaged a Tug Of War trial.

    Picture if you will a kind of land-going proa. A triangular frame with a bicycle wheel and a mast at each of the leeside corners, and some ballast and a further bicycle wheel at the windward corner. Tether it so that it doesn't travel but you can see which way it wants to travel. Rig two test pieces, one  on each mast, opposing each other. By adjusting their sheets, get each one pulling at its best, and may the best rig win. Conduct a series of round-robin or knockout trials.

    This compares the lift, but not the drag of two test pieces. You would have to add a load measuring device somehow, to measure the drag.


  • 22 Sep 2014 16:11
    Reply # 3105669 on 3103628

    Purely on the basis that a daft idea might contain a granuloma of brilliance, I will share part of an email I sent to Ash earlier.

    Now, I am not going to air this on the website, as it is a stupid idea.  Thinking about your wind sail experiment, and not entirely sure about the concepts of lift and drag, but here goes :-

    Borrow a pickup or flat back waggon and driver.  Build a frame cantilevered over the starboard side (port if you wish) so the sails can be flown above the frame, attached by light lines, possibly over friction free pulley blocks, down to spring balances to measure the load at each corner.  At the blocks a crudish home made protractor allows the angle of set of the lines fore and aft to be read, allowing calculation of vertical and horizontal components of loads (analogous to lift and drag?) with the aft lines being able to be let in or out, to correlate to sheeting angle.  The forward lines could be attached to the battens at a midway point, analogous to parrels at the mast position  The next bit needs a long straight flat area (disused airfield, carpark on a Sunday, road tunnel at 3a.m., etc.) and reasonably calm conditions. The Researcher (you) suitably attached with a lifeline, rides in the back of the pickup/flatbed, and the whole is then driven at a steady speed, same speed for each sail setup, and he (you) pays in and out the sheet lines, taking measurements of the loads and angles for varying angles of attack.  Camera mounted on opposite side of vehicle for photos.  There may be turbulence effects from cab structure, but this will be the same for all sails tested.  This allows constant wind conditions for each setup (admittedly not wind tunnel constant) with only one sail at a time to deal with.

    OK, stop laughing, and never breathe a word about this, to anyone.
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