Foiler Design

Discussion in 'Sailboats' started by tspeer, Nov 12, 2003.

  1. Rick Loheed
    Joined: Mar 2006
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    Rick Loheed Junior Member

    Moth Main Foil Design

    I have performed some design analysis of a hypothetical Moth main foil using Tom Speer's lifting line spreadsheet for the optimal uniform downwash plan form, applying the NACA 63-412 section- since that is common in the Moth foilers these days- for this initial study. The size is a 875mm span x 125 MAC, with a 20% flap, although this study shows the flap hingeline curved, which is obviously not practical.

    I used XFLR5, which is XFOIL re-written in C++ by Andre Deperrois, a French Aero-modeler who loves sailplanes, and quite well done at that in my opinion. You will find the polars are much wider than would normally be published- this is because the method used by the author of XFLR5 for the LLT and VLM wing analysis interpolates the polar information for each section, and you must include all points in the 'flight envelope' when generating the polars with the built in XFOIL analysis prior to the wing analysis. This must be done for all Reynolds numbers and incidence angles you expect and then some, so I did not edit the polar information, I left it extreme. It does however support a very friendly batch processing mode.

    It will not allow estimation of the strut/centerboard of the T-foil, however I can do some 3D VLM in the inviscid codes for comparison and perhaps correct the results for the viscous case if anyone is interested.

    I want to build this foil, or something like it anyway, probably with my own purpose designed section inversely designed using the XFOIL internal to XFLR5. I have a classic sailing canoe that is approximately the right weight to experiment with the foil and controls if I can figure out how to mount the rudder without destroying it...I also used Tom's spreadsheet and methods to design the wing mast you see in the Flying Canoe image!


    NACA63-412 Polars.jpg

    MothMain 6-8Kn TakeOff Condition.jpg

    MothMain 15Kn Cruise Condition.jpg

    WingPolar.jpg

    View attachment Good Moth Main Foil Images.zip

    FlyingCanoe.jpg
     
  2. Doug Lord

    Doug Lord Guest

    Flying Canoe

    Great ,Rick! I'm not sure how much research you've done on the Moth but here are some stats and notes I've found: Pounds of all up weight per sq. ft. of SA,approx. 2.58 or less to competitively foil upwind. Hull beam to length 10/1 or higher for early takeoff; virtually double-ended to allow crew pitch change to create higher foil angle of attack with least drag for early takeoff, SA per sq. ft. mainfoil area=81.7, Mainfoil loading(nominaly 80% main; 20% rear foil)=169 pounds.(based on mainfoil area of 1.04 sq.ft.) "Veal Heel" technique developed by Rohan Veal(World Moth Champion): allows excellent upwind performance at a windward heel angle of about 15°-significantly better than if sailed flat upwind.
    Can you mention some of the details of your canoe-like sail area, weight, foil areas etc.. What kind of altitude control system do you have in mind-will it be affected by pitch up as is the Moth wand? Will you use some sort of hiking aid, trapeze or sliding seat to gain RM? Will the daggerboard and rudder be retractable? One last question: will you design the daggerboard and rudder installations to allow easy changes to the foil(s) angle of incidence for testing?
    Sorry about all the questions but I'm very interested in your thinking about this stuff!
    ---------------------
    Thanks for the comment about the aeroSKIFF 16 rig- maybe it has some merit.
    ===============================
    edit: Rick, I was just looking at your drawing again and I noticed what appear to be flaps on the vertical fin and rudder. I can imagine how you would use the one on the daggerboard but would you be using the one on the rudder to replace normal rudder movement? Eric Sponberg and I have planned to test a rudder with a "stepped" flap, see:
    aeroSKIFF 14 side view
    Address:http://www.boatdesign.net/forums/attachment.php?attachmentid=5297&d=1141571544 Changed:10:12 AM on Sunday, March 5, 2006
    The idea was to have the rudder slide up and down like a daggerboard using the flap to create turning force. The step is to allow the turning force to be more or less the same on or off foils so that rudder throw would be the same.
    Your rudder stock area appears to be fixed so I was thinking that you might be using the flap for turning?
     
    Last edited by a moderator: Apr 22, 2006
  3. Rick Loheed
    Joined: Mar 2006
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    Rick Loheed Junior Member

    Flying Canoe

    Doug,

    Actually, I have had a design for a flying catamaran called the 'Longbow 22' since the mid '80's, I just never enacted the plan. For some history, while in Indiana I raced an M-16 Scow with the Lafayette Sailing Club, Lafayette Indiana, racing Portsmouth handicap with Lightnings, Lasers, Interlakes, Flying Scots, Finns, and an E-Scow or two occaisionally and of course other M-Scows on Lake Freeman. It was very competitive.

    Then when I moved to Maryland, I worked for a company making computerized motion control (or ride control if you perfer) systems for high speed ships- traveling all around the globe engineering, installing and sea trialing these systems, and I 'didn't had the time' to do these fun things. Still sail, but no personal hydrofoiling. These systems included heavy involvement the design of the first 4 square meter T-foil ever produced for ride control for the 'Condor 10', a wave piercing catamaran built by Incat down in Tasmania in the early 90's. They were actually the idea of Lionel Frampton, then of Marine and General in the UK. In 2000, for a variety of reasons we started Island Engineering, Inc. and began producing our own state of the art motion control system, culminating in the first titanium 3.75m^2 T-foils mounted on the USN LSC X-Craft. We also have a hybrid hydrofoil testcraft, for which I designed and built the foils.

    So, enough of that, recently I joined this forum, where my interest in flying sailboats was rekindled, and I started working on the Longbow 22 again. Financially speaking, I have the canoe already, see the attached photo. It is my brother Phil Loheed's design, which he built in the late 70's. The weights and areas for the Moth are quite similar, so since I had the wing in XFLR5, I started scaling my design to something buildable- and there was the canoe!

    However, as you can see, the canoe is REALLY nice! But I had the canoe in Rhino already, the foils are a piece of cake because I have scripts to directly apply foil sections, I also automated Tom Speer's spreadsheet to output the chord distributions for the both foil planforms and also a ClarkY wing mast which I was also investigating originally for Longbow, so there it is!

    There are no flaps on the rudders or dagger board- they are a JPG artifact I am afraid. But I also am good freinds with Chris Hart, who has a design for a Scow type Moth on the Mothboat.com page, and have been trying to convince him to build a foiler Moth. He also works with hydrofoils and we have worked together previously. I have been talking to him about trying to come up with a Moth rig- what I should probably do is just build a Moth, but in the process maybe I can fly the canoe sine it could be the same foil. I will probably just borrow a sailboard rig, although the idea of flying the canoe with the original (very classic and pretty..) 75 Ft^2 gaff rig appeals to me too- just for fun.

    Anyhow, I can analyze wings of all sorts- I have a collection of tools for that for sure, and also have Algor and SolidWorks in addition to Rhino.

    Specs- canoe weight, about 85 Lbs. LOA- 16.5 Ft, Kaper drag predictions say 14 lbs at 6 Knots- ideal for acheiving takeoff speed, even with 2 people in it. I might need to add a smig more area on the foil.

    If you determined that the Rhino model had twice the actual required span, you win 5 points! The 850mm span is actually less than the 965mm (38 inch) beam of the canoe!

    Rick Loheed
     

    Attached Files:

  4. Rick Loheed
    Joined: Mar 2006
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    Rick Loheed Junior Member

    Control

    Sorry, forgot to talk control....

    I absolutely love the wand design of the Moth's, and have been following Dr. Sam Bradfield forever. The canoe is somewhat problematic, in that I don't want to modify it. Millions of thoughts on control have been swirling through my head, we do control systems you know... but the no-modification constraint has me thinking wand(s), off the top of the centerboard and over the side like leeboards for expedience. Maybe could add some roll control that way wth a wand both sides, sort of like SCAT but put together for ailerons..

    Because of the length, rotation to flying attitude might be tricky- the take off condition of the foil analysis previously posted is 5 degrees geometric incidence with 10 degrees of flap- this produces 250 Lbs of lift at around 6-7 Knots, correcting for immersion which XFLR5 does not do. For such cases where I can't use a biplane image foil, I use some depth correction methods from NACA report 4168.
     
  5. Rick Loheed
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    Rick Loheed Junior Member

    Just for comparison, here are some stats for boats I used to race with;

    Sail Area to Displacement Ratios for some classic racing Dinghies
    Total Main Crewed Single Crewed Single
    Sail Sail Sailing Hand SA/DISP SA/DISP
    LOA Area Area Weight, Lb Weight,Lb ratio ratio
    Kestral Feather 15.6 115 85 565 440 0.204 0.261
    Laser 13.9 76 76 300 300 0.253 0.253
    M-Scow 16 147 108 740 615 0.199 0.239
    Finn 14 115 115 500 500 0.230 0.230
    MC-Scow 16 135 135 565 595 0.239 0.227
    Interlake 18 175 120 950 825 0.184 0.212
    Lightning 19 178 120 1000 875 0.178 0.203
    Flying Scot 18 191 134 1150 1025 0.166 0.186
    E-Scow 28 323 1565 n/a 0.206 n/a

    Standard Skipper=175 Lbs, Standard Crew=125 Lbs
    Note: This data for boats sailing in the late 80's, updates are likely
     
  6. Rick Loheed
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    Rick Loheed Junior Member

    Stats

    Sorry, it didn't keep the format from Excel intact very well- it looked good in the text window editing the post......
     
  7. Rick Loheed
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    Rick Loheed Junior Member

    Sail Design

    Here is the Canoe sail analysis done in XFLR5. I want to find out if this analysis is valid- I think it should be, because for a surface you use a mirror wing, so the whole wing being there should enforce a plane of symmetry along the 'ground', as if the sail were 1/2 of the wing sticking up out of the 'ground'.

    It is not too difficult to simulate more gap by applying a mast base shape for a section at the center.

    Any comments?

    Rick Loheed
     

    Attached Files:

  8. Rick Loheed
    Joined: Mar 2006
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    Rick Loheed Junior Member

    Main Foil area

    Doug,

    Just double checking here, what are the units for the main foil area you quote? In^2?

    This would mean it is only 0.567 Ft^2 or 0.0527M^2?
     
  9. Doug Lord

    Doug Lord Guest

    mainfoil area

    Rick,I made a mistake in the foil loading; it is not 176 but 169 lb.'s per sq.ft. and I corrected it on the previous post. That is based on a Moth of 220lb.'s all up with a 160lb. crew , 85 sq. ft. SA and a 1.04 sq.ft. mainfoil area.The world champion is in the 140's but as best as I can determine from various reports competitive upwind foiling is possible up to around 160 pounds crew weight. That's one reason why there is such a need, in my opinion, for a Peoples Foiler that will allow crew weight as a singlehander up to around 220 -250lb.'s and also for a two person boat-both capable of excellent low wind takeoff and relatively light air upwind foiling.
     
  10. Rick Loheed
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    Rick Loheed Junior Member

    Loading

    Wow- definately a light man's deal with competitive Moth racing then-

    I weigh 185, not bad for 52 yrs....but my brother weighs well over that, he's taller and older.

    If I continue the canoe project then, and assuming it will be sensible at an 80/20 percent split and say 270 Lbs total, I would need a min of 1.08 Ft^2 fwd and 0.27 Ft^2 aft, and at this level XFLR5 corrected via NACA-4168 for 0.85 Ft. immersion predicts it requires an incidence angle of 9.5 degrees with ten degrees of flap at 7 knots to take off. I have'nt actually finished a whole balance on the idea yet- it was only a spark of an idea when I created that JPG of the canoe.

    I might like to include my brother, so this probably will be too small- I'm not planning to race the canoe, so maybe 1.61 Ft^2 Fwd and 0.4ft^2 aft for 2.02Ft^2 total.... (I need to go back and add induced drag for flapped case, I forgot to add a Cd/Degree of flap when I calculated the flap effectiveness ratio, so I do not have a correct model for the drag in my spreadsheet plus I need to add the T junction, spray drag, windage of hull and people, etc..) However, for my 270 Lb total This results in 134 Lbs or so per sq ft., and take off at 7 Knots with a 4.5 deg incidence and 8 deg of flap. These foil sizes might limit top end perhaps- won't know until I complete a good force model. As for lift though, it looks right now as though at 25 Knots it needs -4 degrees of flap to limit the lift to 270 Lbs at zero incidence.
     
  11. Doug Lord

    Doug Lord Guest

    Foil Areas

    Rick, from a "practical"(what we know works) standpoint you might want to reconsider the aft foil area though I certainly defer to your far greater technical foil design knowledge. On Dr. Sam's Rave the rear foil is 50% of the total mainfoil area and on a Moth the rudder area is approximately 60% of the mainfoil area.The Rave sails with 80% of the load on the mainfoil and 20 on the rear foil.The Rave mainfoils are 1.77sq. ft. each(3.54 sq.ft. forward) and are loaded higher than the Moth foiler from takeoff on up. Approximate mainfoil loading at earliest takeoff for the Rave is 184lb. per sq.ft. but because the foils also develop RM the loading goes much higher.
    I think I remember a discussion with John Ilett(builder of World Champion Moth foilers) where he said that they had originally tried 50% for the rudder foil related to the mainfoil but went a bit larger(60%) to
    aid in early takeoff with the boat pitched up. We either discussed it or I read it somewhere....
    Best of luck with your boat!
     
  12. Rick Loheed
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    Rick Loheed Junior Member

    Loading

    Thanks for all the feedback, Doug. I certainly agree with the 'people's foiler' concept.

    So far, I have really only been hypothetically speaking of the canoe design- I really need to do all the lift, drag and moment balances to find out what will work for an area split between the foils. It seems so easy though , starting from the Moth concept foil design I originally had in mind here. I would like to take my wife and a cooler with me too....

    Just for interest sake, Our 1/4 scale model for a 56 meter ferry (~45 Ft.), aluminum 15,000 Lb hydrofoil testcraft has a 60/40 split. It flies very well and is fabulous at seakeeping. It sports a radar altimeter for height control.
     
  13. Doug Lord

    Doug Lord Guest

    Foil Split

    That's interesting stuff you've done ,Rick. For what it's worth: from just observation of the Moth it appears to me that the loading between the foils changes from the early takeoff pitch up( 60/40 to 55/45?) to "cruising" at speed( 80/20) .
     
  14. casavecchia
    Joined: Jan 2004
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    Location: Italy

    casavecchia Senior Member

    Moth meeting yesterday on Lake Orta, Italy.
    Two foilers were present, a Mistress and Glen Oldfield's one off Moth. Glen's boat has a much smaller elliptical aft foil, about half the surface of the Mistress, and foils beautifully.
    Marco.
     

  15. Doug Lord

    Doug Lord Guest

    Oldfield Moth

    Very interesting Marco! Are there any pix any place that you could provide a link to? I'm curious about the conditions the two boats sailed in -can you fill me in? How about the mainfoils on both boats: about the same size and aspect ratio or different?
     
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