High Performance MPX Foil/Self-righting Trimaran-The Test Model

Discussion in 'Multihulls' started by Doug Lord, Dec 28, 2010.

  1. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Here is the video and technical analysis, followed by Problems /Solutions:

    ===================
    MPX Testing and Development------Problems and Solutions
    Here are the problems encountered in the last test sail-part of which is shown in the video
    1) Dynamic Pitch-up's: there were two dynamic pitch ups where the bow jumped up during a turn. Both those and the almost pitchpole were caused by abrupt rudder movement. In the one captured on the screen shot below, the hard rudder movement threw the boat completely clear of the water except for elements of three foils. Amazing power to do that on a 21lb scale boat. Solution is probably to enable dual rate and or exponential on the transmitter, though with practice a smooth turn could probably be learned.
    --
    2) Vang and downhaul--the gooseneck slides on a vertical rod. I tied the downhaul to the gooseneck so as the vang was tightened the gooseneck tightened the downhaul. Unfortunately, the power of the vang stretched/loosened the line dissipating the vang power-so when it was tightened to de-twist the sail it may have done that for 10 minutes but then nothing. Solution: decouple the downhaul from the gooseneck and fix the gooseneck so that it can't move down(or up for that matter). Maybe add a cunningham grommet if there is not room around the gooseneck for the downhaul to work. Increase the purchase of the downhaul to 8/1.
    --
    3) Peak Halyard and GCD-Gaff Control Device is the thing sticking up above the gaff to which the peak halyard is attached-line stretched. Solution: convert to spectra and /or increase purchase. I may change the position of the bowsie in order to make it easier to adjust when the Wing Tip is in place.
    --
    4) Sheeting system-line from the jib side of the drum jumped off because, under a lot of load, the sheet induces slack at the drum. This actually makes me happy-I was afraid I might have stripped the $380 winch! Solution: add a block with a spring to that side of the drum so slack never happens. Note to self: never subject the winch to loads outside its design range-reef, switch rigs or don't sail!
    --
    5) Rig slack. This happened because I didn't tighten the shrouds enough for those conditions which allowed the rig to go fore and aft a lot which allowed the top of the main to have undue influence on the pitch stability of the boat as well as screwing up the set of the jib. Will discuss the matter with the crew to see to it that the shrouds are always tightened.
    --
    6) Being overpowered:
    a. I dodged a bullet this time by not ruining the sail winch-it is NOT set up for the load found with a 9-11mph breeze+boat speed+ waves. Will go with the SA limits I know and use the windmeter to make sure I've got it right.
    b. Will design and build a new #2 rig instead of reefing the original main*. The reefing system I used on previous boats won't work with the rotating wing mast.
    I was mighty impressed with the way the boat handled the fact that it was overpowered and sailing in big waves(for the model) so I want a rig that will hopefully allow sailing in almost any condition. Removing the jib in those conditions wouldn't help-too much wind for the main only.
    * This will be expensive and take some time. In the meantime I have an old rig for a much smaller boat that I may use. Will at least have entertainment value when the mast snaps like a twig......

    ====================
    Next test sail will be in wind between 5 and 7 mph*. The designer(that would be me) says the foils should work in those conditions and the boat crew(that would also be me) has been warned to not repeat the joyriding in unscripted conditions!
    *I tend to use mph and not knots because the wind pressure table I have is in mph and the foil lift formula uses mph(ft/per second). If you want knots divide mph by 1.15.
    Stay Tuned........

    https://www.youtube.com/watch?v=LmXCdAlo4mk&feature=youtu.be
     

    Attached Files:

  2. Rosebud

    Rosebud Previous Member

    ....and, this instability will be complicated by the leeward angle of heel. The lift vector is not simply vertical, but has a transverse component to it as well. And, as the main hull lifts, there is a dynamic lift translation from vertical to horizontal taking place.

    Additionally, the lack of "any" buoyancy in the aft portion of the floats also appears to be creating an uncontrollable angle of attack as the boat heels, and before there is enough speed for the float foils to create the necessary lift to counterbalance the heeling force.

    This is evidenced in the video, as every time the main hull lifts, the platform takes on a significant nose-up attitude. As this nose-upup attitude increases, the float foils begin to stall, causing the boat to slow significantly to a point where the main hull returns to the water.

    Regards,

    -Rosebud
     
  3. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ======================
    1) There is a slight component to leeward as the thing takes off but this is countered by the tow in of the vertical portion of the ama foils and of the ama itself. And when the boat exceeds a certain altitude, the main foil flap goes up, creating downforce and a horizontal component of lift to weather-similar to Veel heel on a Moth.(see illustrations below)
    2) There is no lack of buoyancy in the aft portion of the floats. There is no need for any more buoyancy in the ama.
    3) Its not true that every time the main hull lifts there is a significant pitching up-there are portions of the video where there is no pitch up at all -including some of the time when the main hull is flying. However, I know now that the angle of incidence increase(2.5 to 3 degrees) I tried on the main foil for this test sail was a mistake and that probably was a factor in the two "mush-ups" . Additionally, it may be true that the wands are too long and trying to set the designed angle of heel too high. I'll know more about that tomorrow.There are three different kinds of pitch instability seen in the video:
    a.) dynamic pitch-up caused by abrupt rudder movement,
    b.) pitchpole caused by abrupt rudder movement with contributing factors including waves, loose shrouds and poor sail control and being overpowered,
    c.) mush-up-not as violent as 1 or 2 -not fully understood except that there is a high probability that the factors mentioned in 3 above are involved in addition to the fact that the boat was overpowered and had other problems-see "Problems and Solutions" above.
     

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  4. Gary Baigent
    Joined: Jul 2005
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    Location: auckland nz

    Gary Baigent Senior Member

    Doug, another whisper (suggestion?) in yer shell-like ear: if you're determined to keep the over balancing main foil, then reduce its area. I know you've posted endless balanced mathematical screeds about yer foil design but ... just looking tells us the boat is appallingly unstable in pitch, it is a mess, and therefore dog slow ... so if perchance, you decide to reduce lift and allow the boat to balance (maybe sweetly) more on on lee and rudder foil than the main unit, maybe, perhaps, you and we will see some decent sailing. At the moment, less than zero. And forget about negative lift on the rudder foil, you want the opposite.
     
  5. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    MPX Testing and Development

    Thanks for the effort Gary-me and my "shell like ear" appreciate it.....
     
  6. DennisRB
    Joined: Sep 2004
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    Location: Brisbane

    DennisRB Senior Member

    That was me. I actually believe it is the opposite. Setting up the radio controls to best use the RC vehicle actually shows good rc skill. Sub optimal setup shows a lack of understanding of the radio and its features.

    Like I said, some of my planes would be unflyable without these same settings. If I somehow managed to haphazardly fly them without the settings it would not make me a better RC pilot, it would just make me stubborn RCer with an almost out of control plane.

    2 minutes of reading the manual Doug + 1 minute of adjustments. Just do it FFS :D
     
  7. Madrc570
    Joined: Aug 2013
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    Location: Australia

    Madrc570 Junior Member

    My 5 Cents

    Hi Doug, here is my little analysis for the video, I have taken into account what everyone (including yourself) has said here plus my own opinion this is not necessarily the main problem but it may be helpful.

    1. Wand length: The wands seem to bee about 30% too long, once the boat is flying the main hull but not the AMA's the heel angle is far more than 17 degrees (I think). this is causing the lift from the up tip foils to be reduced a lot because the lifting portion of it is no longer close to horizontal, its closer to vertical, so that means that the lift is acting outwards not upwards, and the only force vector from this acting upwards is the pivoting force around the main hull. If the wand length was about 2/3- 1/2 of what it is now, (the boat flies about 20cm above the water not 40cm/50cm), then there should be a lot more vertical lift from the AMA foil, allowing the AMA to start planing, and then foil.

    This also means that the rig is more efficient as it is more perpendicular to the wind

    (This could be all wrong, but a few people and your self have sort of mentioned it and I think it might be a major key to the puzzle)


    2. Depth of AMA foil

    I think the only other thing that may help is to have a deeper AMA foil, as your main foil is something like 60cm deep and the AMA foils are about 25-30 roughly, the foil not only performs better the deeper it is, it also allows for it to foil in bigger waves, but this would be a mod for later on as it would take a lot of time and design work.

    I think you are definitely right about the rudder having to do with the pitch ups/ nose dives, I speak form experience when sailing pretty much any dinghy, planing or not, the lift caused by the rudder when turning can really affect the heel, not directly but through the centerboard. If you turn towards the wind, the back of the boat wants to sink down and to leeward as this happens the centreboard's angle of attack changes so that it is lifting up and to windward so there is a combined effect to make the boat heel right over to leeward and pitch right up for as long as the rudder is turned. The opposite will happen when bearing away.

    https://www.youtube.com/watch?v=r2az1xMu10g
    (go to 12:10 to see what I mean)

    I think you probably know this anyway !! :p

    I think the best thing to help this is to just keep sailing the boat and learn how to use it to your advantage.

    I hope these suggestions help a bit, If they are all completely wrong then I'll probably learn a lot from why anyway!! :p :)

    I agree with you completely on the rudder scenario.

    Congratulations on achieving a great outcome for only the SECOND SAIL. I can't wait to see more of it!!

    Kind regards
    Curtis
     
  8. 2far2drive
    Joined: Nov 2011
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    2far2drive Senior Member

    This is pretty much what I was trying to say also. And I agree, ditch the video guy, make some adjustments, fix the rc part and sail the thing FFS! :)

    I mean this in good spirit Doug. I just get so tired of talk and no action. People yammering about multihulls and this and that and they've never even sailed. Anyways, carry on.
     
    DennisRB likes this.
  9. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    MPX Testing and Development

    -------------------------
    Thanks ,Curtis! You hit on two suggestions Magnus has made and you should be damn proud that your analysis is so close to his!
    I'm checking the wands today. As for lengthening the ama foil-that's a possibility but not until a lot more testing is done. Besides being overpowered
    the vang, downhaul and "peak halyard" all failed to one degree or another. I think I've fixed them. Next test is Tuesday.
     
  10. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    MPX Testing and Development

    ----------------------
    You must be kidding! There is no life w/o video. Studying the video is incredibly important in developing this boat.
     
  11. high on carbon
    Joined: Dec 2004
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    Location: Toronto

    high on carbon Wing Nut

    If video is that important, get a go-pro and simply stick it on your baseball cap. you'll be looking at the boat most of the time anyhow...
     
  12. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    MPX Testing and Development--------Stunning Results!

    Stunner #1:
    Before this sail and after the first sail ,I set the boat up as you see it below with the red straight edge parallel to the static waterline(post 1377), which in turn is supposed to be parallel to the flight waterline. I discovered the AOI was 1.5 degrees on the main foil and zero degrees on the rudder foil-the main foil should have been at least 2.5 degrees. So I reset it to 3 degrees which I now know to be a mistake.
    So I was flat out stunned to find the AOI on the main foil at 4.5 degrees with the rudder still at zero. That is way, way too much angle and is surely part of the cause of the "mush-ups". But the real mystery is how in the hell did it change? You may remember that ,because it had moved from before the first sail to after the first sail, I made a lock that was supposed to hold the wand plate(to which the mainfoil is attached) and prevent any movement. I've wracked my brain to try to figure out how it could have moved. The only answer is that it moved from when I set it up on the stand to when I took the main foil off and lowered the boat down to attach the lock. It was inconceivable that the wand plate could move during or just before installing the lock so I didn't put the damn boat back on the stand to check it after the lock was installed. I had a very difficult time with it that day but I definitely should have double checked it. Just a most frustrating thing!!!!!
    -------------------
    Stunner #2:
    Once I had the boat up on the stand and level fore and aft(parallel to the static waterline) with the foils installed and the mainfoil hooked up to the wands, I put a wedge between the aft bottom of the daggerboard and the flap to hold the flap at zero(neutral). I then measured the distance the wand tip was below the water line-and incredibly the wands were three inches too long!!!!! No idea under the sun,moon and stars how I could have made such a mistake--just blows my mind but it slipped by somehow.....
    -------------------
    Solutions:
    #1-set the AOI at 2.5 degrees, remove the foils, take the boat off the stand, reset the lock, put the boat back on the stand and re-attach both foils and remeasure! Geez......
    --
    #2- Devise an easy way to adjust the wands, then install it. At the very least cut 3" off the wands.
    ================
    There is absolutely no doubt that these two screw ups were responsible for some of the odd behavior of the boat(mush ups).
    These are the problems that have or will shortly be corrected-an amazing list:
    1) vang failure,
    2) downhaul failure,
    3) peak halyard stretching,
    4) wing tip too big,
    5) sail winch overloaded, jibsheet problem,
    6) extremely sensitive steering resulting in pitch-ups,
    7) AOI too much on main foil,
    8) wands too long.
    9) boat overpowered in 9-11mph wind
    Now that I found #1 and #2 above I'm actually pretty happy-because the boats behavior is not a mystery any more. How #1 and #2 happened is still somewhat of a mystery.
    Pictures of set-up today-Left to Right-1) wedge to hold flap at neutral to measure AOI and wand depth, 2) set up with red straight edge, 3) & 5) wand plate with lever arm and wands in neutral, lock attached to front of plate-single nut in center forward part of plate retains the daggerboard and main foil, 4) Wand and lever angle at flap neutral :
     

    Attached Files:

  13. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    MPX Testing and Development

    Did you say "go pro"??? We don't use swear words on this forum! I guess you missed the part where I unpacked my brand new go- pro that had been sitting in its original packaging for two years and.......it didn't work. Company said "warranty expired nothing to be done" and I'm out $350. Interestingly, the IgotU GPS tracker I bought at the same time and that sat just as long works perfectly-though I have questions about it's accuracy-but at least it works.
     
  14. Darth Reapius
    Joined: Mar 2014
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    Location: Australia

    Darth Reapius Junior Member

    wow... the 3 inches that you picked up on the wands... perfectly explain what i was thinking when it was taking off the way it was, just didnt know how else to explain it except hold the power increase the amas foil lift, solid find, (give it a big reach next time out ;) yew)
     

  15. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    MPX Testing and Development

    -------------------
    When you combine the wands being too long with the way excessive AOI you have a problem! This is actually really good news: I had thought that I'd have to figure out what was wrong with the design and it turns out the design may be just fine-the assembly was flawed-and really badly flawed. I just can't figure out how those wands got by me. When I get time and the inclination I'll look back in my work notes and try to figure it out. For now -no matter-it's just great that all the problems in that video may be solved.
    PS- but you know: considering all this, the thing did really well-like it was fighting to fly-that's what that big pitch-up(below) was all about- the Fire Arrow was trying to tell me something! No, I ain't losin it-I done found it.....
     

    Attached Files:

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