Foiling radio control trimarans

Discussion in 'Multihulls' started by PerthMini40man, Jun 9, 2016.

  1. PerthMini40man
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    PerthMini40man Senior Member

    OK - will do that this Sunday. Not so easy as the wind blows across the lake and I am sailing upwind into the wind shadow of the windward bank of the lake, but will do what I can. I will not foil beating to windward unless the wind strength is EXACTLY right for the rig.
    More later
     
  2. Doug Lord
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    Doug Lord Flight Ready

    =================
    Way to go!!
     
  3. Linussss
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    Linussss New Member

    Hello everyone,
    I am trying to build a foiling mini 40 for my school project.
    I was wondering if any of you had plans I could use and a few tips on how to make it,
    Thanks linus
     
  4. PerthMini40man
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    PerthMini40man Senior Member

    Hi Linus - I have sent you an email - free plans are available at rcsails.com, and I have also sent some tips on construction
     
  5. PerthMini40man
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    PerthMini40man Senior Member

    Video of Secret Service in action again

     
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  6. PerthMini40man
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    PerthMini40man Senior Member

    And this one is specifically about three sets of foils being tested

     
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  7. UpOnStands
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    UpOnStands Senior Member

    Looking good. Are you still thinking of active foil control?
     
    Last edited: Feb 19, 2018
  8. PerthMini40man
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    PerthMini40man Senior Member

    Hello UpOnStands. No not at present. I think there is still a lot to learn about the fixed foils, and I am keen to keep the boat as simple as possible. I get a lot of enjoyment out of the boat as it is right now, just want to refine the concept.
     
  9. UpOnStands
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    UpOnStands Senior Member

    If possible, can you tell us what is the weight split between front and rear foils?
    Front 2 together carry XX grams and rear foil carries YYY grams.
     
  10. PerthMini40man
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    PerthMini40man Senior Member

    I can weigh the boat on the foils and rudder when static if that is what you want (on Sunday when it is rigged), but not sure what that tells you as surely it is the dynamic loads that are important. I am going to guess that 80% of the static load is spread between the two foils.
     
  11. UpOnStands
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    UpOnStands Senior Member

    Thanks, that data and static trim when afloat, visual, will be very interesting for understanding the key step of rising up on the foils.
    You are right about the dynamic loads but w/o load cells and a towing tank static will have to do.
     
    Last edited: Feb 20, 2018
  12. PerthMini40man
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    PerthMini40man Senior Member

    I was working briefly in the Netherlands Ship Model Basin in Netherlands during the 1980's when all the America's Cup syndicates were testing tanking 12 Metres after Australia II had won the cup. It was hilarious as there were 4 syndicates all using the same tank and NSMB had to have separate workshops for each syndicate as it was all top secret. The syndicates were all staying in the same town but only one at a time allowed at the tank. We were testing the towing of an oil rig to be installed in Norwegian sector of the North Sea - boring by comparison. Anyway - no such facilities in Manila!
     
  13. UpOnStands
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    UpOnStands Senior Member

    many years ago was I was involved with the construction of semisubmersible drilling rigs and the installation of offshore oil production platforms in Asia. That side of life was definitely not boring.
    I was thinking that it might be possible to realize poor mans tank testing of foils by using a pulley system on a lake to move the hull/foils without sails. Very light weight fishing line should be sufficient. Trouble is the the CoE is 50cm+ above water surface and hard to replicate the complete sail forces, also changes with foiling. But better than nothing.
     
  14. basil
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    basil Senior Member

    Many moons ago I watched an old boy towing a model launch behind his outboard powered dinghy. He used a set of spring loaded scales tied to a line on the model to measure drag. When he built the launch it had the sweetest flattest wake going. The only issue I see with what you're proposing is how do you sort out the towing angle when the hull rises on its foils? As the hull rises the towline will be trying the pull the bow down - though a very long towline should/might address this.
     

  15. David Cooper
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    David Cooper Senior Member

    Does the height of the attachment point matter? If it's high up, you put more weight at the back of the boat you're testing to keep it level. If you're pulling it along from ahead and to one side (rather than from directly ahead), you then have to put the weight at the opposite side (and towards the back). A low attachment point with the weight more central should lead to the same behaviour as a high attachment point with the weight far back. The same applies to any side angle in the tow line with the weight needing to be further out to the opposite side if that attachment point is moved higher. So, I don't think the height of the attachment point is important, and if you anticipate a change in it when the boat rises up on foils, you'd simply distribute the weight for the foiling height rather than the displacement one. What must matter though is the direction you pull the tow line in, because there's always a force to one side when sailing unless you're going directly downwind, and you want that sideways force to be acting when testing your foils. In a test tank, I imagine that you would apply a constant sideways force in addition to moving the boat forwards and allow the boat to move sideways at whatever speed the resistance from the foils allows it to, and if the foils are generating sideways lift, that must also be allowed to move it to either side.

    Without access to proper test tank facilities, you probably want to tow the model from another boat (or vehicle on land) located both ahead of it and a long way to the side. Any measurement of the force on the line will be dominated by the sideways force, so it may not give you the information you want, particularly if the tow vehicle follows a straight path and can't be pulled off line (or allowed to move the other way if the force on the line reduces due to the foils slipping sideways). I wonder then if it might be better to do the testing using fast-flowing water while the model is held more or less in one place - it could be allowed to move sideways, ... or perhaps it could be held between (and slightly ahead of) the bows of a catamaran while motoring along (on flat water) so that you can change the speed and avoid turbulent flow. You could then build a relatively cheap device to hold the model and apply a sideways force to it just as you would in a test tank, but without having to build anything fancy to enable forward movement. It may then be possible to measure the fore-and-aft force separately from the sideways one, giving you much more informative numbers.
     
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