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Thread: Sam's Flatty


  1. #1

    Sam's Flatty

    Some pics of my son's flat bottomed project we are building. It's a SC .61 engine. The build is classic ply frames and skins, glassed over on the bottom. We are trying some new things on this one, including a water brake, but for now we want a working boat that allows such details and extras to be added later. The first pic shows a graphic of what we are heading for.

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    And a video of the engine running in the boat, whilst running it in.


  2. #2
    Nice looking rig, like the lift handle great idea! That paint job looks nice as well, is it from a rattle can? What are the dimensions of the beasty?

  3. #3
    Thanks.

    The hull is 850mm in length, LOA will be around 1020mm. Beam is 510mm, height 85mm. With all we have planned including working screen wiper, rotating radar, pilot figures and brake it's going to end up at around 16lbs.

    The paint is Automotive 2 Pack from a gun.

  4. #4
    Are we talking a functional brake?

  5. #5
    Yes mate, like the one showing here at 38 seconds:


  6. #6
    Jeremy_H I watched the video several times, kinda put a smile on you face doesn't it. I don't see how the brake works, maybe it's my glass's or a need a new prescription, how's it work?

  7. #7
    I've not found any decent information on them, they seem to be a thing that racers cobble together, unless they they are known as something else perhaps. Here's a couple of pics where what they are and how they operate is clear enough. It's basically a deflector that's dipped into the water to provide drag. The rooster tail is a consequence which does look pretty spectacular:

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    Quite small things really.

    The idea is straightforward. Fast airboats suffer from a fairly unique problem, in that at full chat the air under the boat can be enough to lift it, we all know that. But, so long as the engine is thrusting enough the bow is forced down, at high speed if you throttle off the wind wins and the boat can flip. So at the end of the course these racers deploy the brake just as they chop the engine, the drag keeps the bow down.

    Now, for a model I've no idea how much use such a thing is in practical terms, but I'm guessing it could be useful for raising a smile

  8. #8
    Rudder assy on and radio all in. It can be run like this whilst we sort out the detailing:
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    Last edited by Jeremy_H; 02-15-2014 at 05:17 PM.

  9. #9
    We managed to find a window in the 80mph winds and rain to get to the Moors today, only a couple of tanks through it as it was far too windy still with it spinning around when not wanted and unable to power it down wind at high speed etc. Lots of promise though, we've tweaked a couple of things and will try again tomorrow. Sam's dead chuffed

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    Last edited by Jeremy_H; 02-15-2014 at 04:04 PM.

  10. #10
    Much better today, winds were down and some blue skies. With weight on board to represent what's to be added yet the boat shows a need for some tweaks. For a change here's one of today's runs, from on-board.


  11. #11
    Quote Originally Posted by Jeremy_H View Post
    Much better today, winds were down and some blue skies. With weight on board to represent what's to be added yet the boat shows a need for some tweaks. For a change here's one of today's runs, from on-board.

    Looks great Jeremy, it appears from the video to pretty responsive to the air rudders and a nice lean into the turns. Was that your son in the drivers seat at the end? I'll bet he's grinning ear to ear, well done!!!

  12. #12
    My lad was running it for most of the vid, I took over in the middle to reset the rudder throw. He's enjoying it, but having second thoughts about the boat's handling.

    It's too responsive to steering at the moment, we had to reign in the movement of the rudders quite a lot by the end of the day, and ballasted the stern to get it to ride without digging-in in turns. At full throttle there was a sensation that the back end wanted to overtake the front. So, fixed ballast needed and we have now put some spray rails on, just as we did on the twin engine'd test boat. It likes drifting after setting it into a high speed turn then throttling off slightly, but he's nervous about the buoys on the club lake and wants a more rail like feel. I've re-jigged the rudder linkage to give him more scope for adjustment, We'll have to make the cockpit/superstructure as light as sensible. At least we can afford to have a robust brake system as weight is just not a problem back there. We'll probably add a cowling, but I'm thinking of inverting the engine, don't know yet. It's shaping up, but some work to do

    That vibration is bugging me, we think it's one or more of the GRP control rod tubes, as they are just under the deck and may be sounding off that. We'll try and find it .

  13. #13
    Quote Originally Posted by Jeremy_H View Post
    My lad was running it for most of the vid, I took over in the middle to reset the rudder throw. He's enjoying it, but having second thoughts about the boat's handling.

    It's too responsive to steering at the moment, we had to reign in the movement of the rudders quite a lot by the end of the day, and ballasted the stern to get it to ride without digging-in in turns. At full throttle there was a sensation that the back end wanted to overtake the front. So, fixed ballast needed and we have now put some spray rails on, just as we did on the twin engine'd test boat. It likes drifting after setting it into a high speed turn then throttling off slightly, but he's nervous about the buoys on the club lake and wants a more rail like feel. I've re-jigged the rudder linkage to give him more scope for adjustment, We'll have to make the cockpit/superstructure as light as sensible. At least we can afford to have a robust brake system as weight is just not a problem back there. We'll probably add a cowling, but I'm thinking of inverting the engine, don't know yet. It's shaping up, but some work to do

    That vibration is bugging me, we think it's one or more of the GRP control rod tubes, as they are just under the deck and may be sounding off that. We'll try and find it .
    Hey Jeremy Just wondering if the engine angle is set to zero degrees, if so maybe setting it down a degree or two may bring the nose up. You could set up some form of governor on the throttle linkage until he gets use to it if it makes him nervous. As for inverting the engine, that's my preference and it may help stablize or at least lessen your lean on the turns. Great looking boat, the young lad has certainly got something to brag about to his friends.

  14. #14
    Yes agree on the thrust angle, I've got some wedges somewhere that'll fix that.

  15. #15
    Fitted a first go at a water brake:

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    Operating:


  16. #16
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    So it works, some mods to improve it needed, but we'll get those done today for another go tomorrow, where we'll try to get some vid that's not shaky like today's

  17. #17
    Nice rooster tail there Jeremy, you have an internal jet drive we don't know about? So how quickly does the brake slow the boat? way to go!

  18. #18
    Hehe

    Tricky to make a judgement to be honest, it's obviously arresting the movement, it's bound to, but by what degree I'm not sure. I've added some spray rails too and I don't know what effect that's having on speed as the winds today just make such assessments a little pointless. It was so bad that turning down wind when going crosswind was impossible on anything other than full throttle, so a couple of resounding clunks with the stony edging to the lake ensued with some gnarly damage. We've patched it up for now and modded the brake by adding a plate to increase the effective area. All being well we'll try some throttle off to stop followed by braked throttle off to stop trials tomorrow, and get it on video.

    One other thing is the standard Hitec servos this boat has are painfully slow, the delay between flicking the switch and the brake kicking in is not good, Sam would like faster steering too so a couple of better servos to get.

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  19. #19
    No chance

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  20. #20
    Squeezed out today for a quick run. The bigger plate is working well, I'll get some vid as soon as able:
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  21. #21
    Hello Jeremy.
    We see that you also test different kinds of hulls.
    Grettings From Poland
    Marek&Wojtek

    Our Blog
    http://marekwojtek-models.blogspot.com/

  22. #22
    Hi Marek, yes trying some different things :-)

    Video of the brake:


  23. #23
    Fitted the wedged engine mounts today, so we will see if that improves things

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  24. #24
    The engine angle change helped a bit, changing rudders helped a bit in turns, but the phenomenon of it nosing in when at speed continued, just higher up the speed range.

    So next stage was to add some different spray rails, or lift strakes really. Simple 7x6mm section acrylic was stuck on with double sided foam tape for trials. The results were very pleasing.

    In this vid young Sam is trying to induce the nose-in followed by pole vault thing that was bugging us, it was a windy day again and weather-cocking was the order of the day, so on occasions with very aggressive turns and the wind's help it cocked over a few times, but generally it was much more solid on the water surface, turning flat, and tracking reasonably well:



    I've going to increase the length of a couple of the strakes and make them all permanent, we can then get on with finishing the rest of the model.
    Last edited by Jeremy_H; 03-30-2014 at 05:00 PM.

  25. #25
    And some pics from today:

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