Foiling radio control trimarans

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

  1. OzFred
    Joined: Nov 2015
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    OzFred Senior Member

    Google is your friend:
    A Class catamaran foils - Google Search https://www.google.com.au/search?q=A+Class+catamaran+foils&tbm=isch&source=iu&ictx=1&fir=MY53ula_qMq5QM%253A%252Cqqwsqea3JVBE4M%252C_&usg=__qZKMvfOYp5ybIVXf3YCEWWYBakk%3D&sa=X&ved=0ahUKEwiE79_yzvLXAhVIvbwKHUnJAlgQ9QEIODAD&biw=1164&bih=636#imgrc=MY53ula_qMq5QM:

    There is quite a variety of shapes, from more C like to Z like. I also know of attempts at flaps on the lower section to add lift at low speeds.

    A significant restriction on the shape of A Class foils is that they must be inserted from above, so the whole foil has to fit through the case. Hence why the tip is always down. It likely also has less turbulence, since an upward tip would form an acute angle with the adjacent part of the foil, though with the C shape that's less of a consideration (but fitting through the case is).
     
  2. David Cooper
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    David Cooper Senior Member

    That's because Z foils aren't really Z-shaped, but merely have two bends in them and two vertical sections. Z foils have two vertical sections joined by a sloping section (which has some similarities to a Z on its side) but with obtuse angles between them instead of acute angles.

    It may well be that an upward tip would be better on full-size boats, angled at 90 degrees to the sloping section rather than vertical, but videos of models show them to be more prone to jumping clear of the water, and that's where a downward tip would help them avoid being blown sideways (and being rotated because the rudder is still catching).

    No - I'm just trying to work out where foiling may take us in the hope that we can jump there sooner. The Moth has homed in very quickly on the best way to use T-foils, but I think there's still be a fair bit of room for manoeuvre with passive foil designs. I've ended up looking at something that's close to being the equivalent of a passive T, but staggered to provide the heave stability that passive T-foils can't. If you look at this new diagram, you'll see how the staggered foil (orange/brown) should properly be compared with the Z foil (red) - they would provide much the same vertical lift as each other, but the staggered one produces less horizontal lift and has less horizontal variation in the centre of lift as it rises. (The green and blue foils would provide a lot more lift, so they don't make for a fair comparison.) The yellow bits are places to experiment with endplates.
    morefoils.JPG
    The more-steeply-sloping of the brown/orange sections is not shaped to generate lift (but it will produce some because there will be a higher pressure on one side than the other, which means the shallow-sloping sections could be shallower in their slope). On a model, I doubt staggered foils would pay off unless the windward one can be raised when going upwind (which would require a means to lock and unlock the foil height by remote control and to adjust the angle of attack - you could use the foil's own lift to raise it and then use its weight to lower it when the angle of attack is set for zero lift, but this is obviously much more practical on a full size boat with a human crew). If foil adjustment is not available while sailing, I think you'll always be stuck with the red foil shape, leaving you to experiment with endplates and foil section (this having a different meaning of the word "section" from the one I used earlier).
     
  3. PerthMini40man
    Joined: Jan 2014
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    PerthMini40man Junior Member

    Thanks David and OzFred - we are on the same page. I was not aware of the rule that OzFred has clarified, namely that A Class foils have to be installed from above - its a good practical requirement for a singlehanded boat, but clearly puts a lot of restriction on the shape.

    Our experience of rc boating makes us firm believers in simplicity. The fewer moving parts (and definitely as few electronic bits as possible!), the less chance of breakages! I am also limited here in the Philippines; I live in a rented furnished apartment and my workbench is a plastic picnic table, so I do not have the ability to construct intricate wand-controlled mechanisms, so I am concentrating on refinements of the "red" foil shape for the foreseeable future. Wand-controlled foils will one day come (back) to the class (noting that the F3 of Doug Lord came and went decades ago) - Michael Scharmer in Germany currently appears to have the most promising concept, but he has to reduce his cat's overall beam to make the foils fit inside the Mini40 max beam rule before he can contemplate using them in races. I understand from Michael that he won't be sailing again until the New Year so unfortunately no more developments from him for a while.

    I realise that restricting myself to a boat that fits within the Mini40 rules (max beam and length) might seem a bit unnecessary, but I like to work with a vision of how the concepts can be applied, and right now the Mini40 Class - or our little One Metre design - are the only places where I can see myself applying whatever we come up with. I don't want to create another class, as we have precious few rc multihullers around the world.
     
    Corley likes this.
  4. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    =========================
    I was one of three people who tried to start the multiONE class in the US about 2001. The class rules allow a one meter LOA with a 1.22m beam. The idea was to facilitate designs using wands. It doesn't appear like there is any development in that wannabe class. Wands used for speed may be doomed in classes where beam is restricted unless movable ballast is used as in the fullsize Whisper and S9 cats where the crew provides the majority of RM, not the foils on relatively narrow platforms.

    http://www.rcsails.com/download/MultiONE.pdf
     
  5. David Cooper
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    David Cooper Senior Member

    I would avoid wands too as I'm looking for a low-maintenance solution - hence my preference for passive rather than active foils. It might be possible to make some gains though by being able to adjust the angle of attack of the (passive) foils by remote control so that you can set the windward one to generate less lift, although it would be unlikely to pay off if you're never on the same tack long enough for it to be worth the trouble, added to which, the weight of extra motors could cancel out any gains anyway - that's a fundamental difference between racing models and full-size crewed boats (where the motors, built into the crew, are always present and might as well be used).
     

  6. Doug Lord
    Joined: May 2009
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    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    "high maintenance" is not a factor for a well designed, well built wand system. There is a least one 17 year old F3 still using its original system.
     
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