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Thread: turn fin tuning

  1. #1
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    Default turn fin tuning

    Hello,
    I bought my first boat, a UL-1, and am going to race it at the local club. I have changed the prop to the aquacraft recommended L38X55. I am using Zippy flightmax 30C 5000 lipos. Everything else is stock.
    On the test and tune day, I flipped it one time. Now I see a couple of hairline cracks at the seams. I would include a picture, but I don't think you would be able to see the cracks in it. The cracks don't seem big and they don't appear to be deep. However, when I finished running for the day (4 runs), i pulled the plug out of the back and dumped out about 1/8 cup of water. Is this normal?
    What is the best way to seal the cracks? I bought some marine epoxy. I thought I would mix it up and then spread a LIGHT coat along all the seams of the boat.

    Now for my other question.
    I bought a replacement aluminum turnfin that is thicker than the stock one, but is straight. I did this on the recommendation of a fast guy at the club. He said the stock prop can bend under the forces of use.
    Can somebody explain to me how to tune the turn fin?

    thank you,
    tim

  2. #2
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    On page 7 and 8 of the manual there is some info on tunning the strut, rudder, and turn fin. I would suggest starting there to establish the basics. Once you've done that, test test test. While testing keep notes on what you changed and how it affected the performance and handling of the boat. Only change one thing at a time. If you make more than one you won't know which change had the most affect on the performace.

    http://manuals.hobbico.com/aqu/aqub20-manual.pdf

    Most important, HAVE Fun!!!

    Later
    Mike

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    Quote Originally Posted by rc_speed View Post
    Hello,
    I bought my first boat, a UL-1, and am going to race it at the local club. I have changed the prop to the aquacraft recommended L38X55. I am using Zippy flightmax 30C 5000 lipos. Everything else is stock.
    On the test and tune day, I flipped it one time. Now I see a couple of hairline cracks at the seams. I would include a picture, but I don't think you would be able to see the cracks in it. The cracks don't seem big and they don't appear to be deep. However, when I finished running for the day (4 runs), i pulled the plug out of the back and dumped out about 1/8 cup of water. Is this normal?

    No...you should have NO water in the hull at the end of the day. If it's not leaking in those cracks, it could be leaking around the stuffing tube where it enters the hull....mine did.

    What is the best way to seal the cracks? I bought some marine epoxy. I thought I would mix it up and then spread a LIGHT coat along all the seams of the boat.

    I have great luck running thin CA glue into those hairline cracks.

    Now for my other question.
    I bought a replacement aluminum turnfin that is thicker than the stock one, but is straight. I did this on the recommendation of a fast guy at the club.

    I tried the straight fin and didn't like it, went back to the stock one.

    He said the stock prop can bend under the forces of use.

    This should not be a problem unless you thin it down too much.

    Can somebody explain to me how to tune the turn fin?

    That is down by adjusting it up or down per the instructions in the manual. I just leave mine all the way down.

    thank you,
    tim
    Hope this helps some

    Crash

  4. #4
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    I lost my original plug and the replacement I got was much harder. I now have had water in the hull too. Took that out and covered with tape. Now my hull is again watertight.

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    ok, thanks. I spread some super glue in the tiny cracks that I got. I smeared it along some of the seams. I also spread a bead of epoxy around the joint where the prop tube enters the bottom of the hull. If it still gets water in it, I will try taping over the plug hole
    I have my first race on sunday, so I will find out how it does then.

  6. #6
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    It's also possible that it's leaking around the bolt holes on the transom or turn fin sponson. I always pull my bolts and dab some clear RTV sealer around the holes and under the brackets then retighten the bolts.

    Crash

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    Quote Originally Posted by rc_speed View Post
    .
    . He said the stock prop can bend under the forces of use.
    I think you meant the turn fin.

    and yes the stock plastic prop can and does flex.

  8. #8
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    oops, I meant turn fin. thanks for the correction.

    I saw somewhere that the boat can face 3-4 g's of force during a turn in a race. This can equate to a force on the fin of 3-4 times the weight of the boat on that fin.

    I tried to order better fins from kintecracing, but they are out of stock and the replacement production is going slowly. In fact, they refunded my money and told me to re-order them when the web site says they are in stock.

    Is there somebody else that makes a replacement turn fin for a UL-1 that is better than the stock one? I know I can make my own, but I would rather buy one.

    thanks,
    tim

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    Quote Originally Posted by rc_speed View Post
    oops, I meant turn fin. thanks for the correction.

    I saw somewhere that the boat can face 3-4 g's of force during a turn in a race. This can equate to a force on the fin of 3-4 times the weight of the boat on that fin.

    I tried to order better fins from kintecracing, but they are out of stock and the replacement production is going slowly. In fact, they refunded my money and told me to re-order them when the web site says they are in stock.

    Is there somebody else that makes a replacement turn fin for a UL-1 that is better than the stock one? I know I can make my own, but I would rather buy one.

    thanks,
    tim
    Scroll to the bottom, 3 to choice from. http://www.offshoreelectrics.com/products.php?cat=67 stock one is their as well other two have similar dimension except stock is .01" thicker & .15" shorter.
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  10. #10
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    Quote Originally Posted by rc_speed View Post
    oops, I meant turn fin. thanks for the correction.

    I saw somewhere that the boat can face 3-4 g's of force during a turn in a race. This can equate to a force on the fin of 3-4 times the weight of the boat on that fin.

    I tried to order better fins from kintecracing, but they are out of stock and the replacement production is going slowly. In fact, they refunded my money and told me to re-order them when the web site says they are in stock.

    Is there somebody else that makes a replacement turn fin for a UL-1 that is better than the stock one? I know I can make my own, but I would rather buy one.

    thanks,
    tim
    3-4 g's maybe more, (I don't know) I read someone data logged 7g in a UL1 powered rigger.

    I don't know of anyone else that makes a replacement fin, make your own, I use stainless but it is a pain in the A$$ to cut and work.

  11. #11
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    Quote Originally Posted by Jeepers View Post
    3-4 g's maybe more, (I don't know) I read someone data logged 7g in a UL1 powered rigger.

    I don't know of anyone else that makes a replacement fin, make your own, I use stainless but it is a pain in the A$$ to cut and work.
    7gs, really? that's nuts. I wouldn't have ever thought a rc boat could pull that. 3-4 is a good bit, but 7 WOW you figure a military jet pulls around 10 in high g turns. Impressive
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    Quote Originally Posted by Diesel6401 View Post
    Scroll to the bottom, 3 to choice from. http://www.offshoreelectrics.com/products.php?cat=67 stock one is their as well other two have similar dimension except stock is .01" thicker & .15" shorter.
    yep and they all bend under hard cornering. in my opinion they flex to much to give precise cornering.

    Tim you could add some bracing like in this pic, and attach it to the side of the hull.
    Attached Images Attached Images

  13. #13
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    Quote Originally Posted by Diesel6401 View Post
    7gs, really? that's nuts. I wouldn't have ever thought a rc boat could pull that. 3-4 is a good bit, but 7 WOW you figure a military jet pulls around 10 in high g turns. Impressive
    Diesel here is the post I saw on the rigger, the data was logged by Eagle tree system



    http://www.rumrunnerracing.com/fefor...&highlight=JAE

  14. #14
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    Quote Originally Posted by rc_speed View Post
    I would rather buy one.

    thanks,
    tim
    Tim,

    I have one of the kintec straight fins I can sell. It's brand new, never used. Let me know if your interested.

    Later
    Mike

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    Quote Originally Posted by longballlumber View Post
    Tim,

    I have one of the kintec straight fins I can sell. It's brand new, never used. Let me know if your interested.

    Later
    Mike
    If he doesnt take it I will. I want to try it on my 7xl setup.
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  16. #16
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    Quote Originally Posted by Jeepers View Post
    Diesel here is the post I saw on the rigger, the data was logged by Eagle tree system



    http://www.rumrunnerracing.com/fefor...&highlight=JAE
    Sweet, cool info
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  17. #17
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    Quote Originally Posted by Jeepers View Post
    yep and they all bend under hard cornering. in my opinion they flex to much to give precise cornering.

    Tim you could add some bracing like in this pic, and attach it to the side of the hull.
    I dont hit the turns that hard. Don't race, normally runs fast straights and soft turns, I'm sure even though I'm letting off the throttle a lot in the turns theirs some flexing going on.
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  18. #18
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    I did some research (google is a wonderful thing).

    let's assume the boat is going 40mph around the corner.
    The Namba nationals shows the radius of the corner to be 35 ft.
    So we will assume we are all expert drivers and take the inside line at a constant radius.

    40mph = 58.666 ft/sec
    A (lateral acceleration) = v(velocity)^2/r(radius) = (58.666^2)/35 = 98.333ft/sec

    g-forces = A/gravity = 98.333/32 = 3.07 g's

    a boat going 45mph around this same corner will generate 3.89g's
    a boat going 50mph will be at 4.8g's

    now this is all based on running a smooth line. If a boat turns sharper around one of the corners, the g forces will go up. For instance, the boat has to make a sudden turn to avoid another boat. If you are going 40mph and turn a corner that has a 15ft radius, you would generate 7 g's.
    what if you are running a boat with a hotter motor than the stock UL-1 and are going 50mph and need to make the sudden jog to avoid that idiot that flipped in front of you? (NOTE: it is always the other guy who is the idiot. Me/you the driver never makes any mistakes. LOL) You will generate 11.2 g's of force on the boat.


    I hope this makes sense. It sounds about right. It has been a LONG time since I have had to deal with this type of physics.

    tim

  19. #19
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    I don't see the issue here?

    I run the stock, old, thinner fin, hammer all the way down, through the turns and one of the turns is a hairpin 180. I have never had a bent fin or even flipped my boat in a turn. This is entering the corners at 50mph never letting off. It hugs the water like an ole time slot car. It's the same with all the UL-1's I've seen at my pond. The only issue is after a turtle strike and having to reset the fin and resharpen the leading edge if it gets messed up.

    Why the need for another fin? I'm I missing something?

  20. #20
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    I don't like the thought that the turn fin is flexing while I am cornering. It is a personal thing for me. The boat runs fine in stock form, though.

    The other thing for me is that I am thinking of using a hotter motor to run in the P-mono class. This would make the boat faster and thus more g's on the turn fin. I don't want to lose a race because the turn fin bends and changes the handling. I am trying to prevent a problem before it actually becomes a problem.

  21. #21
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    I just want to try the straight fin out and compare to the stock in my 7xl set-up, I am having a hard time keeping the front in the water. I think the straight may also help with chine walk in my set-up. Just testing and seeing whats better. So far my best luck has been strut 1" l40x57 prop and strut neutral. Still wants to get airborne. If straight fin doesnt work Ill try a airdam. I like testing new things, but if I dont make in progress with this boat I will dump the 7xl set-up and attempt a ammo 2300.
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    Quote Originally Posted by Diesel6401 View Post
    If he doesnt take it I will. I want to try it on my 7xl setup.
    Sorry, rc_speed got it.

    Thanks
    Mike

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    Quote Originally Posted by longballlumber View Post
    Sorry, rc_speed got it.

    Thanks
    Mike
    Cool no prob, good pick up RC_Speed.
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    Quote Originally Posted by Diesel6401 View Post
    Just testing and seeing whats better. So far my best luck has been strut 1" l40x57 prop and strut neutral.
    Lowering your strut to 1 1/8" or 1 3/16" will help your UL-1 run tighter. Neutral is not the way to go. Strut needs to be tilted downward in the back roughly 2 degrees. Simply lowering strut will achieve that angle because of the stiff 1/4" stuffing tube. Grimracer turnfin is a verygood fin and if tilted correctly will reduce chine walk. Please read your UL-1 manual.

    PS...adding a little more weight to bow will also help.


    ...

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    Quote Originally Posted by detox View Post
    Lowering your strut to 1 1/8" or 1 3/16" will help your UL-1 run tighter. Neutral is not the way to go. Strut needs to be tilted downward in the back roughly 2 degrees. Simply lowering strut will achieve that angle because of the stiff 1/4" stuffing tube. Grimracer turnfin is a verygood fin and if tilted correctly will reduce chine walk. Please read your UL-1 manual.

    PS...adding a little more weight to bow will also help.


    ...
    Yea I have played with different turnfin adjustemnt (straight up & down, swepted), I didnt like how it ran swept and up & down seem like too much lift. I will add a little down tilt on the strut, that will prob bring the front end down enough to stop the occasional blow over. Splayed battery config I like, chine walk is a lot better that way, I could do your aoa mod detox but for now I'm going to keep playing around with the spayed batts. I'll keep testing away, all part of the fun (manual is in my bathroom, so it gets read A LOT )
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    Quote Originally Posted by detox View Post
    Lowering your strut to 1 1/8" or 1 3/16" will help your UL-1 run tighter. Neutral is not the way to go. Strut needs to be tilted downward in the back roughly 2 degrees. Simply lowering strut will achieve that angle because of the stiff 1/4" stuffing tube. Grimracer turnfin is a verygood fin and if tilted correctly will reduce chine walk. Please read your UL-1 manual.

    PS...adding a little more weight to bow will also help.


    ...
    Don't forget he is using a much hotter motor than the stock UL1 (7XL).
    Last edited by Jeepers; 05-01-2010 at 02:13 AM.

  27. #27
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    Quote Originally Posted by detox View Post
    Grimracer turnfin is a verygood fin,
    ...
    it is a good design just to soft,

    I bent one going hard into a corner, hammer down hard right rudder, bent the fin 90 degrees to the hull, couldn't even get the boat back in it would just go in circles. I am not the only one in our club that has done this. most of us now make our own.

  28. #28
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    I run the Kintec straight fin on the UL, swept all the way up....Runs like a charm, got less lift than the stock one....Diesel, got 57mph on my 7XL this week (M445), looking to move up to the M447, and will really push the limits to a M645.....Lots of power, finally got it trimmed in nice.....strut is at 7/8".....Norm

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    Quote Originally Posted by ncornacchi View Post
    I run the Kintec straight fin on the UL, swept all the way up....Runs like a charm, got less lift than the stock one....Diesel, got 57mph on my 7XL this week (M445), looking to move up to the M447, and will really push the limits to a M645.....Lots of power, finally got it trimmed in nice.....strut is at 7/8".....Norm
    cool, good info buddy
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    I have never folded my UL1 turnfin. Maybe some batches were made using softer aluminum.

    With L40 x 57 prop do not be afraid to go deeper on the strut. I went deep using my Nue1515 1y combo. Larger props may need shallower strut setting


    ...

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