Slip Wand for foiler height and roll control

Discussion in 'Boat Design' started by ozandy, Jan 5, 2014.

  1. ozandy
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    ozandy Junior Member

    Hi folks.

    I am currently building a small experimental foiler and would like to run an idea past the more experienced designers out there...a kind of pre-reality sanity check.

    The foil setup is similar to the current racing Moths with T foils front and rear, with a wand setup to control flaps on the front foil.
    (The front foil is supported by two struts so is more "H" than "T")

    The change I am adding is to have 2 flaps on the main foil with each one controlled individually according to the amount of side slip detected by the wand, which has a keeled paddle on the tip to keep it tracking straight even when heeled. The wand will be allowed to rotate about 20 degrees to the left and right whilst also doing the 90 degrees forward-backward movement with 45 degrees the designed trim height angle. The two flaps have +/- 4 degrees, are full span and are about 1/3 chord.

    If the wand is deflected to windward then the flaps will try to roll the boat to windward and visa-versa, the idea being to tune it to maintain balance between the sail force and the weight of the boat.
    When wind picks up (or sail sheeted in), boat is "under leaned" and so the wand will slip to windward, causing roll until balance is achieved (no more slip).
    When wind drops off (or sail sheeted out), boat is "over leaned" and so wand will slip to leeward, again causing boat to roll off to balance (hopefully prior to crashing sideways!).
    This should also work to balance simple turns under power provided the bow does not pivot around the main foil struts so as to reverse the slip...some powered tests should sort this out. I will test it using simple power setup to get the main trim sorted and confirm it will foil prior to putting sailing rig, which is a modified 12M racing sailboard rig.

    My main worries are the roll authority of the flaps as compared to the rest of the boat, whether a stable trim can be achieved for most speeds so it can take-off stable without becoming unstable at speed. There is also the effect of heeling on the wand slip detection and tracking.
    I'll have to play with the gearing of the slip vs the height, and also play with adding mass to the wand tip as a damping mechanism.
    ...and whether my dodgy fiberglass prototype foils will survive the maiden outings! (hardwood core, router jig, CF and vac-bag unit for next ones...planing/sanding sucks!)
    Have I missed anything?

    Boat and foils are painted, wand tip printed, and I'm nearly ready to build the wand system...so at this point I thought a sanity check would be a good idea. Any comments or suggestioins welcome.

    Cheers,
    Andy Howard
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Drawings would help-not sure I get the point? My gut feeling would be that
    roll authority would be questionable using just the flaps and that the whole foil might have to be bigger than a "normal" main foil.
    You didn't say how big or heavy the boat is and I wonder why the crew can't provide all the roll authority you might need?
    But your experiment sounds intriguing-wish you good luck!

    PS- when heeled on foils(Veal Heel) one of the biggest advantages is the increase of righting moment-how do you think that would be impacted by the
    "roll control flaps" ?
     
  3. ozandy
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    ozandy Junior Member

    Hi Doug,

    I'll put together a diagram soon...sorry, verbals are not the best. The mechanism relies on pushrods up from flaps, a 90 horn with about 5:1 reduction, then pushrods to bow mounted wand root.. The left and right rods connect to each side of an smaller arm that sets the left right differential.
    Re-reading this makes it clear I need a diagram! (it is really not much more complex than standard Moth setup)
    The point is to balance an unstable craft so it turns much like a balanced aircraft or motorbike via yaw/roll coupling. Just as a training aeroplane will bank automatically (via dihedral) with rudder input, I want the boat to roll into turns without additional pilot control. Whilst 3 axis aircraft always perform better than 2 axis with coupling, 2 axis craft such as paragliders and hang gliders work better as recreational craft: PGs bank auto based on yaw, HGs auto yaw based on roll. Both are easier (and more fun?) to fly than 3 axis sailplanes.
    The main foil is rather large and fairly high aspect (2 struts allow for slightly more length). I wanted a reasonably light foil loading so it gets up easily at lowish speeds.
    Also the flaps (OK, ailerons, or more correctly "Flaperons") are fairly large so will produce a pretty big change in lift between max up and down deflection. Given they protrude out well beyond the COG centerline I'm hoping they have the authority to balance the boat. I'm sure some crew body language will be required in more extreme conditions though. (I hope so!)
    The boat is only about 3M long and will be single handed...hopefully without quite the skill and effort required to pilot a Moth!
    The Veal heel angle is the intended "neutral point" of the slip/roll mechanism and will depend on the amount of side force (from whatever source, sail or "G" forces): If over or under heeled then slip will result which *should* be self correcting...leading to neutral flap setting (both at same deflection) that equtes to a simple height only wand. Thats the theory anyway!
    The boat will hit the water within weeks, so I'll only be able to theorise a little longer! :)
     
  4. philSweet
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    philSweet Senior Member

    Yes, pictures would help. And yes, I think you may be missing something.

    Reducing sideslip, in and of itself, is not the objective. In fact, it is completely irrelevant. The objective is to maximise the drive and minimize all of the resistance terms caused by the wind, which includes the induced drag of the foils and the drag of the hull.

    If you are going for hydro control of roll attitude, you would probably have more authority if you operated inertially against the center of mass, like the way a motorcycle casters. I would think you need to roll the boat by shifting the keel out from under the CoG, not by trying to directly torque the whole mess over. That means the lateral wand response would be the opposite of what it sounds like you are proposing. <edit> I'm not sure exactly what you are proposing. During the adjustment maneuver, if you apply a force to scoot the keel out from under the boat, the sidelslip will temporarily increase. Where it settles out after the adjustment is a bit of a mystery.

    The Veel heel is just a maximum drive/resistance set up. It has no magic target geometry for arbitrary points of sail, and more to the point, it has no particular relationship to sideslip. I just don't see how you can convert sideslip into a control response in general. Veal heel does not necessarily reduce leeway. It just loads the foils in a way that minimizes resistance. It reduces displacement a bit via aero forces. It increases the righting moment allowing more power. The best combination of these will provide the maximum drive to overcome viscous forces. Also consider that hulls provide useful lift if they have the proper angle of attack to the wind. This is worth exploiting. Leeway is a means of controlling the hull's angle of attack to the wind during upwind work.

    Once fully trapped out, more Veel heel would suggest a higher average side slip, not less. The heel would be determined largely by required RM. Higher heel indicates higher RM, and that means more sideslip. So it looks to me that you may have a range of speeds and loads where the relationship between sideslip and heel tends to go one way, and then a reversal at higher loads.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    ========================

    Phil, actually Veel Heel produces the primary lateral resistance for a bi-foiler(in addition to increasing RM) by unloading the daggerboard and using the mainfoil for lateral resistance (and vertical lift). The greater the Veel Heel, the greater the contribution from the main foil for lateral resistance.
    I don't think sideslip is an issue for a well designed bifoiler.
     
  6. Skyak
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    Skyak Senior Member

    I have given the double strut 'H' as you call it some thought. I call it inverted pie. My motivation was to give more control by moving the struts outside the hull and to alleviate the need for exotic materials for stiffness. Small trim tabs don't have enough force to provide all the righting you need if the foil is an efficient length. The force might be very welcome in making the boat easier to sail though.

    I do have some ideas that might help you greatly though -if you have two struts external to the hull they are free to move -independently. You don't need flaps at all, you can warp the wing like the Write brothers did on the first airplanes. I would recommend that you keep the two wands, but have them adjust the angle of attack of each strut directly. The hydrofoil build becomes a simple single piece with some clever fiber orientation (unidirectional between the struts with some 45 on the ends). There are more benefits in operation but it does give more of the righting power you are asking about.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    For reference here are two foilers being developed with two vertical struts on the main foil(and the rudder foil as it happens) :

    The one on the left is Seb Schmidt's, the one on the right is the Pi 28 which is sailing now but I don't have any pictures with it on foils. Features a telescoping main foil
     

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  8. Skyak
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    Skyak Senior Member

    I have been holding on to what I thought was my great idea but I had a feeling it was too good for others not to reach the same conclusions. My efforts were toward low cost of manufacture. These appear to be all out speedsters.

    Pi 28 looks fierce. Do you know where I could get more info? I would be very interested in their control plan.
     
  9. ozandy
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    ozandy Junior Member

    Quick diagram

    I hope the attached picture gives a better idea of what I'm building. One wand with two rotation axis. There is a small paddle with 3 blades on the wand tip to keep it tracking straight when heeled.
    I considered two wands with one on each strut, surface peircing "whiskers" attached directly to flap and a trailing slip wand as well as a leading height wand but settled on this for it's relative simplicity and the fact that it is a modification of a live system that works. If the rotation doesn't pan out it can be configured as a standard Moth type height setup and I'll use additional foils on ammas to handle roll in a more "brute force" fashion.
    I also considered foil warping but I believe this may be too sensitive to sub-millimeter build faults for my meagre building skills. A 1/2 degree AOA change can make a huge difference at speed and flaps, though less efficient, are more trimmable and less dependant on build accuracy.
    Thanks for the replies. :)
    Will get to them shortly (at work...should really do some.)
     

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  10. ozandy
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    ozandy Junior Member

    In reply to Phil:
    Rather then trying to torque the whole mess over, which I agree sounds unlikely, I see the righting moment as more like a bike where you pivot the support around far underneath the center of mass. This arrangement does not work in a static fashion...it will (hopefully) only work as dynamic stability, like a bike (which can balance without gyroscopic effects). Counterintuitively, the taller the better (with limts) for stability. Its the "long ruler easier to balance then short" situation. It does rely on the struts *not* imparting much sideforce to allow this "sliding around underneath" to happen. At speed this should not be a problem.
    You may be right though and it may be that flaps on the lower struts are more appropriate...got to build and test to be sure!
    I'm not sure about "sideslip is completely irrelevant" when on foils. For any stable flying craft sideslip is certainly relevant! In this case I intend the main foil to take all the lateral load...the struts will take no sideforce at all when the craft is in balance. If they do start taking any load, the wand should cause roll to eliminate it. Once flying I intend the center of mass of the craft, including pilot, to remain at the centerline with little to no hiking or weightshift required.
    You may be right about stability issues at different speeds, but just as a plane can be banked in a balanced turn at any speed so too should this stabilise at a heel angle that is appropriate to the total side forces (wind plus others) imparted...thats the theory anyway. I do see issues with overall balance when heeled at the back-end. Not sure if standard setup of a bit of weather helm is OK...will a rudder banked at 45 degrees behave? The Moths seem to manage it so I'm sure it is doable. Will definately need rudder trim. Maybe shims are too simple (sigh...another build).
    I love the idea of a telescoping main foil! I abandoned the idea because the control linkages became impossible to route: not a problem if you have a ladder foil setup to control height instead of submerged foils with wands. I also considered this and will revert to a ladder setup if needed. Very simple and good for strength too, but no slip/roll coupling which is what I want to explore.
    I'm with you Skyak on the build simplicity. This is why I went for two struts along side the hull rather than fancy cases.
    On my setup the rudder foil will slide up and down like a standard daggerboard and the front foil will only pivot forwards (at very slow speeds!) for stowage and launching/landing.
    I also like the idea of a double strut, one in front of the other, that can pivot back whilst keeping the foil AOA constant. Much more forgiving when hitting things in the water and easier to beach. It does make control linkage tricky though.
    I'll post pics of the actual beast once I have the top deck finished and ammas fitted...there are a few other little novelties!
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ===================
    ozandy, a couple of questions:
    1) is the mainfoil really shorter on one side than the other-excuse if I missed the explanation.
    2) does the boat not have a rudder foil?
    ----
    Here is the Pi28 telescoping foil and few other dry pictures of the boat and foils:
    click for a better view-
     

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  12. ozandy
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    ozandy Junior Member

    Hi Doug,

    1) No! Its just my quick rendering in Powerpoint. It is symmetrical. I didn't want the top view messing with the side view.
    2) The back-end is not shown...just the wand setup. I didn't have time for a full pic. I should make a full model in Sketchup but I prefer to work on the real thing for now.

    Thanks for the pics. That is one sexy looking boat!
    A bit too advanced for my garage though.
    The foils look like they have flaps on them...is this for trim or is it dynamically controlled somehow? (just looked harder. control rods in LE of struts!)
     
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  13. Doug Lord
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    Doug Lord Flight Ready

    ozandy, not sure its of any interest but the first Moth foiler to win a race at a major event was Brett Burvils surface piercing main foil Moth-two vertical struts and two surface piercing main foils:
     

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  14. ozandy
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    ozandy Junior Member

    Cheers Doug.
    I started with a similar concept as a power boat setup but got intrigued by the modern Moths. I used to sail Moths when they were wide, flat and concave at the bow so I have a bit of a fascination with them.
    Would that setup allow for, or work with Veel heel?
    My original intention was for 4 surface peircing foils that could all pivot back. Two at the front on ammas with dihedral (sloping under the boat), two at the back with anhedral (sloping out from centerline) as the rudder. The one thing that worries me with foiling is the collision consequences and I thought this might mitigate some danger as welll as making easy to launch and land.
    In the end I chickened out and went with something more proven...with the slip/roll twist for interest.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    ===============
    Burvills boat probably wouldn't have been able to do Veal Heel-at least with the benefit a bi-foiler can experience.
     
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