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  1. #151
    1QwkSport2.5r's Avatar
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    Oct 2006
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    I think you're creating more work for yourself, personally. The bottom of the tub at the stern will ride on the waters surface just fine and will not have the tendency to over-lift. Hooty301's 84+ mph outrigger rides on the tub's stern without a sponson. Your rigger is a very similar style and so I would personally run the boat without anything extra bolted onto the stern besides the tub itself. If you find it doesn't have enough lift, only then add something to the stern. You need to keep the weight as low as possible or it won't get out of the water no matter how big of wedges or sponsons you use.
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  2. #152
    Quote Originally Posted by 1QwkSport2.5r View Post
    I think you're creating more work for yourself, personally. The bottom of the tub at the stern will ride on the waters surface just fine and will not have the tendency to over-lift. Hooty301's 84+ mph outrigger rides on the tub's stern without a sponson. Your rigger is a very similar style and so I would personally run the boat without anything extra bolted onto the stern besides the tub itself. If you find it doesn't have enough lift, only then add something to the stern. You need to keep the weight as low as possible or it won't get out of the water no matter how big of wedges or sponsons you use.
    If I allow the tub to run on the surface the entire tub will be at about 6-7 degrees incline which I don't think would be too good and create a teeter totter effect, all of which would be undesirable. You do have some valid points however the whole premise behind this boat is experimentation and trying different methods to see what works and what doesn't. I don't believe I have a weight issue at all and in fact may be too light that will cause it's own set of problems I'm sure. Do you know by any chance what Hooty's tub to water clearance is, that would certainly be valued knowledge to determine ride attitude.

  3. #153
    I've just been looking at Hooty's vids again, but the resolution is not enough to see what's occurring with the tub, though it would probably be difficult to see it anyway as it'll be masked by the sponson wash.

    Your point about the intended use though arcdude is important to keep in mind though, I don't know what term might be used your way but here such models are deemed as 'Sports' rather than 'Competition'. Interestingly for me I see quite a lot of furrowed brows when I explain to people that I like to design and use 'sports' models, simply because I like them to be versatile and to work for a long time. I'm a complete bore when I get competitive and I intend to stay away from seeking the very limits of performance in the future because I don't see the value for money, how many times have I spent big bucks on top flight models only to find them picky, sensitive, unreliable, costly to maintain and often quite frustrating as a result. So I support your approach to this model, it's not going to get near 84 MPH, but with the water conditions you have to overcome and a desire for a rigger style boat I think your experimentation is well founded. It would be easier to stick with convention and emerge with nothing new, odd how some folk, including some at my club kind of miss having fun at this game. Innovation is often frowned upon, and whilst directed at no one here, it's odd that often those who express disdain the most at the thought of variation and new ground seem to have no evidence of accomplishments themselves. Trying new things is often not 'safe', but it's certainly more interesting than convention to me.

    Anyway, getting back to yours, the SI3 comparison should be taken cautiously. The boat runs with the deck dead horizontal, and accurately measuring the AoA of the tub is fraught with problems because it's curved. But, as I reproduced the drawings in CAD, with accurate centre points of the various curves derived from the radii quoted in the drawings to a thousandth of an inch, I can tell you that the AoA of the tub, at full speed, is in the region of 1 degree if we assume a wetted length of 4" and a horizontal deck.

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  4. #154
    Too abbreviate ditto m8 I think the reason for the comparison to an SI3 is kind of obvious but maybe I haven't articulated the desired outcome of the boat well enough for all. The only comparison intended is that I'm trying to design this style of boat that will ride up on the sponson's trailing edge's rather than the convention of the tub riding on a cushion of air with little water clearance and as you have reflected on I will be running on somewhat unfavorable water conditions.

    I have to be honest I didn't get that technical in regards to the AoA of the tub but rather ball parked it aiming for a somewhat neutral attitude. So your anticipation is I'll be spending more time in the air than on the water? If that's the case would an airfoil on the front be adequate compensation should I encounter that situation? The intent is for the tub to be perfectly horizontal at speed and to me that necessitates a rear "whatever" in order to keep it at that plane and at this point I will have to devise whatever air foils or other mechanism's to get the desired results. I am just about done constructing a rear wedge/sponson so I'll post a pic later on. Cheers!

  5. #155
    Did a little redesign to the back end to get the desired results without an air scoop at water level and lengthening the hull. At first I thought it may not be long enough but looking at the pic's it appears to look like it may be without lengthening. On other riggers with rear sponson's they appear to total in width close to the hull width between them so that is my benchmark to start with being 2 1/5" in width at the trailing edge which should be adequate to lift the transom to the desired height. As can be seen from the back view pic it is hollow through the center so there should be little air disturbance and the wedge itself is only 5/8" in thickness and only adds 1.8 oz to the weight so in all a much better result.

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  6. #156
    I was getting a little concerned about how things were going to sit in the water when done so I wrapped the tub and sponson's in plastic wrap and placed some wood doweling in to hold things together and chucked the gear in approx where it should go and lowered the boat into the bathtub like it was a newborn. It sits nicely with the tips of the sponson's about an inch above water level and I measured the back sponson tube which is sitting at 3/4" above the water. As I admired how pretty it sat there and no sooner did I get a few pic's I started to notice the wood change color at the back of one sponson and let me tell you that's the fastest a newborn has been ripped out of a tub by the scruff of it's neck LOL. How this translates into how well it'll come up onto plane I have no idea but I'm guessing it shouldn't be too bad.

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  7. #157
    Accounting for the rudder I'd say there's a pretty good chance it'll get up OK, but it's still marginal I think. Saying that sounds like a safe bet, but again I'm visualizing it and I can see how the SI3 deck comes into play to aid that one. I suppose my current unqualified prediction is that you might be able to get it up with a drag start. I say that because My SI3 demonstrates quite different starts between a full tank of fuel and a near empty one. When full it'll start at any speed, I can accelerate as gently as I like, with a less full tank if i'm too slow with the throttle it submarines. To over come the latter I hit the throttle hold at low idle, shift the stick to max, release the hold and it'll get enough of the noses out of the water to bring it up almost is a short of shock technique. So if yours really is marginal, then that may be a route to a solution. QED.

    At this stage we should not dismiss an engine angle change to aid any potential problem, some up thrust will have an effect, it's bound to, the issue is only whether such an angle compromises speed running. Again, QED.

    An active platform for finalising things is the way to go now I think. You have, in effect, three options right now and some running time will clarify directions to go in in an accelerated manner towards the solutions.

    Nice tub.

  8. #158
    Did a final mock up to show a more accurate running attitude, I placed dowel's in to simulate the sponson tubes and to show the position of the final assembly. The tubes for the finished setup will be much wider. The rudder currently on the boat may be inadequate to do the job, it is the tapered one from speed master so I'll have to consider an alternate that will hopefully mount in the same bracket. Time to disassemble and do the finish sanding, odds and ends, then fiber glass the tub and sponson's.

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    Last edited by arcdude; 06-14-2014 at 02:17 PM.

  9. #159
    Anyone have any idea what type of airfoil, or does it matter? In rc planes the general rule is the foil should horizontally line up with the center of the prop does the same apply for air boats? Thoughts

  10. #160
    All of my wings have used the prop thrust, rather than the air moving over the wing through the boat's movement, to assist with stability. I've no real scientific evidence for this, I started with one used to lift a rear end and they've stuck since. With a wing on yours being so much further back I'm not sure how that thrust will be, as it'll be somewhat different that far from the prop. But, I guess it's about the need, if the issue is purely speed vs stability, then maybe it needs to be more out of the propwash if the wing is to come into effect when the boat deviates, i.e. like arrow fletching, if it's about altering the attitude of the boat under way then in it would be different, as prop wash will be added too by airspeed I guess.

    I think the centreline position approach is based on the reasoning that it'll be more evenly effective for a given movement when control inputs are applied to elevators. It's not actually where most of the airflow is as that exists as a rotating 'cylinder' of air coming off the prop blades, so I reckon for a more sensible height for a horizontal stabiliser wing to be about two thirds up the height of the prop blade from the bottom.

    Within this though there is the possible advantage of a vertical stabiliser or fin. Straight line stability would be aided by one, so it's height may allow a much higher wing.

    Sorry, airfoil. I've used symmetrical and classic foil sections, sometimes upside down. It's going to have more effect with a true foil, which means it can be smaller that a simple flat thin sheet, if the aim is to use the air fore lift or down force. If it's aerodynamic stability that's required then thin sections with greater chord apply I would think.
    Last edited by Jeremy_H; 06-16-2014 at 02:05 PM.

  11. #161
    Thanks Jeremy, From my understanding I agree the centering of the stabilizer on a plane is for directional control and somewhat placed in the neutral zone of limited air flow. I really don`t want 8`` uprights at the back of the boat and was inclined to go in the neighbourhood of 5``- 6`` max in height which would be about center of the lower half of the prop blade so I`d imagine the flow would be somewhat constant at that elevation, also not to be overlooked but wouldn`t there be some reflected airflow off the water surface. With the tub so small in diameter it could have a more lifting effect whereas most boats the hull would be wider preventing the air from reflecting back up. The width I was considering is only about 5``- 6`` and around 2``- 2.5`` in depth and a full symmetrical design on the uprights and wing itself. The problem remains what to make it out of and to be light as possible. For construction I was considering sandwiching eighth inch ply inside and out to be shaped with a one sixteenth thickness of aluminum plate in between and tabs protruding out where necessary to provide fastening points, what do you think. Is there a possible lighter option.

  12. #162
    When I had the boat mocked up for the water test I did a balance check on it and currently it is about 2`` behind the trailing edge of the sponson`s so at least I`m in the ballpark should adjustments be required later on.

  13. #163
    Started to build the airfoil for the back, I chose to make it 5`` high which will put me in the center of the lower half of the prop, I really didn`t want it too high after making several templates and standing back and looking at it this seemed to be the most pleasing. The center is one sixteenth aluminum and the outer layers are one eighth lite ply, the edges are beveled to start out before I glue them together so I don`t distort the shape of the aluminum and to clamp them it`ll be a lot easier with them flat and will be sanded to a symmetrical shape when done. I`ll also be cutting out the center of the aluminum and basically leaving a frame to lighten it a little. The tab on the top is for the wing bracket and the tab part way down is for a control rod to adjust the wing and the flange at the bottom will be bent a little to give the uprights an outward angle.

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  14. #164
    Are you planning to hole up the fins to give a key. or going for abrasion only?

    I'm wondering about strength, I can imagine the tabs suffering in a vault. I'm an expert vaulter now , some of those impacts sure make your cringe through the inevitable grin

  15. #165
    Quote Originally Posted by Jeremy_H View Post
    Are you planning to hole up the fins to give a key. or going for abrasion only?

    I'm wondering about strength, I can imagine the tabs suffering in a vault. I'm an expert vaulter now , some of those impacts sure make your cringe through the inevitable grin
    Appreciate the cautionary not there Jeremy and yes I`ve considered that, so in anticipation what I`m going to do is put guide lines or wires or something from the top of each fin down to the center of the tub to help prevent them from being bent too much. I`ve already glued one and it`s surprisingly strong and has a little flex to it without bending and very light, both sides adding up to 1.2 oz so the whole wing will only end up weighing 2 oz, more than acceptable. Because the height is an unknown at this point and may require a redesign after testing I saw no other light weight solution and they aren`t hard to make. The fins have been drilled (swiss cheesed) to accept the polyurethane glue and the aluminum was well scuffed as well just prior to gluing to prevent re-oxidization which to my understanding happens within an hour. I understand you have used a wing before have you used supports to the fins, what were they made of. I am quite eagerly looking forward to the inevitable cringe, grin phase Cheers

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  16. #166
    My wings have all had a similar mount, off the rear of the pylon. Some have been fixed to a neutral position in relation to the prop's airflow and are blended into the cowling, others like the little red boat are aluminium brackets that can be bent to a desired angle. I've never mounted an airboat wing on uprights or fins. But, to be honest they have mostly been there because I like the look of them, in your case it may possibly have a more real need. I've only once inverted the red boat and that was through hitting a buoy, and it's not fast enough to cause any impact problems, pretty much like the rest on my airboats which have been built without a diversion of all out speed as a target. The SI3 has been the eye opener in this area. According to a GPS mine is doing 44mph, so think of it as getting a good grip on your model stood on the lake bank and throwing it at the water surface at 44mph. Would it survive?

  17. #167
    I'm not to sure how this will all turn out and until I can come up with an alternative to make them a little stronger or permanent these will suffice, at least enough to find out what will be needed after some trial runs. I would have to agree that they'll in all likelihood be needed to keep the rear down. Also in designing models in the past I have learned the hard way that if an add on is built too strong you could be jeopardizing the whole model, so my thought is where do you want it to break if it's going to. As for speed well I may end up having the coolest looking water plow Lol!
    Last edited by arcdude; 06-22-2014 at 02:17 PM.

  18. #168
    Yes, I did think of the rubber band approach to some airplanes. With a lanyard attached it may not go amiss.

  19. #169
    Thought I'd share a few tips for the people that find fiber glassing to be a difficult and messy process. I'm no expert but quite comfortable doing fiber glass so what I do on tough parts with sharp corners as we all know how difficult it can be to keep the cloth tight and end up with a near perfect corner is cut the cloth over size to begin with and pick a side to apply the gel to first, the only caution here is to keep the gel a pinch away from the actual corners. What I've done in the pic is the top side of a sponson and now that it's dry I'm free to continue with another side and the cloth can be weighted a little at the bottom to hold it snug while the gel is setting up leaving you with a nice tight finish. It requires a little patience doing one side at a time but the end result is well worth it for a good finish. By doing this it eliminates the the difficult chore and stress of trying to get it all just right from the get go, a more relaxing way to go for sure.

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  20. #170
    Could use a little help in mounting servo's in the radio box if anyone can offer assistance that would be great. Do you just glue blocks of wood across? is there additional bracing? Thanks,

  21. #171
    Glued wooden block would be fine, cut out trays are popular in aircraft, that would be fine too. I've been using epoxied PVC Foam board as beams, that seems to work well. Whatever you do check for enough clearance to get the servo in, easy to forget the cable entry and it's stress reliever.

  22. #172
    Quote Originally Posted by Jeremy_H View Post
    Glued wooden block would be fine, cut out trays are popular in aircraft, that would be fine too. I've been using epoxied PVC Foam board as beams, that seems to work well. Whatever you do check for enough clearance to get the servo in, easy to forget the cable entry and it's stress reliever.
    Thanks Jeremy, thought you were out for a long summer's nap Lol. I thought of using poplar beams and making a lite ply frame around the ends of the beams to epoxy to the sides. That's what I did in my airplane days but I think the boats take a lot more vibration so I was a little hesitant. Another issue I'm kind of stuck on is the cable for the throttle, I was going to go pretty much straight up as you did if I recall correctly however there is no internal lip at the top inside the radio box and really don't want it to go through the lid itself, stumped for now. I've never heard of PVC foam board. How's your progress coming along, back at your own creations?

  23. #173
    I'm 90% through a mission of some brush clearance for the garden, and eating into the paint jobs that are queuing up. I've delivered the key one:

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    So tied up at the moment, but the passion for the Twins is growing and I'll be back on to it soon enough, enjoying the weather and running the boats we have more right now.

    For throttle, what about a waterproof servo on the mount? I'm using two Hitec HS-5086WP's on the twin, they are quite light, certainly no heavier than a tuned pipe folk would just accept readily, so worth a look if it's int eh budget. To be honest they are priced around the range of a decent quality servo anyway, so not some silly figure. I'm hard-wiring mine into a shielded cable, as this is round in section making it easier to feed through watertight glands or bellows and get a good seal. The soldered joins also mean longevity over exposed extension cable plugs, with some heatshrink around them they are watertight, but it needs a dab of silicone sealer over the ribbon cable from the servo side before shrinking down, as water can track up the grooves.

    I think the control rod through the hatch is still viable though. Access to the hatch is only needed for maintenance every now and then, if you get the seals right (in fact I've found they can be 'too' sealed, I've been caught out by the SI3 being left in the sun for a while to have the hatch up off the deck with the air pressure, stretching the self adhesive seal. I'm quick to vent it now after each run, when it hisses as the air is sucked in through the radio box being cooled when afloat), then a nice smooth surface on the control rod, and a touch of synthetic lube, would allow the hatch to be lifted up by sliding bellows up it. Screw in linkages mean that total removal could be done easily enough if needed, it's not like it's after every run. Switch, charger lead access and venting could be the bottle top thing I use too.

    Other than that, if you don't have a lip or overhang for the rod to pass through, make one. In fact why not have a hatch that splits, one bit with the rod through it, and a bigger bit for your main access. It's only one line of sealing tape extra after all assuming it's tape you're using.

  24. #174
    Thanks Jeremy, hope you get back at your twin soon. I had no idea there was a water proof servo, I checked out the hitec models at $49.00 Canadian and they look like a good possibility if nothing else works out. I'm not opposed to a rubber boot through the lid to accommodate a solid wire for the throttle and that is what I may end up doing. The idea you have for access to unplug the battery with a screw on lid is also an option I may use for the same reason, the radio box is in quite tight quarters. One idea I came up with is why not use something like lithium grease of vaseline around the lid of the box, they come in nice little squeeze tubes and would be easy enough to apply. If the wood is properly sealed there shouldn't be any ill effects to the use of a lube to seal the box, it would certainly be easier to use and should guarantee a water tight seal, thoughts? Here is a couple of pics to show the relatively straight line from the box to the throttle arm.

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  25. #175
    With the need for an angle on the control rod, I'm thinking a bell crank might help. With one just behind the engine it would allow a vertical exit for the rod from the box, but cool if you have an angle solution. However, the more I think about it the more an up top servo suits to me.

    I know a few folk who use grease seals effectively, but it's not a way for me. For them to work there has to be a set of spacers under the lid so that the grease is squeezed out to a certain thickness, say 2mm. Without that the layer can become very thin indeed, which means any hatch movement could create a leak path. With the thickness the grease can ebb and flow whilst keeping in contact with both sides. But, I think it's messy, and in that position it'll be streaked down the tub deck from the propwash. I'm sticking with hatch tape as the best option at the moment.

    The bottle necks I use are around with all manner of drinks contents in them, they seem a common type, they have a lip or flange just under the lid which provides a nice surface for bonding. I leave about 4-5mm of the neck under the flange and fit that through the hatch hole, so the contact patch for epoxy or silicone sealant is large. I've never had one fail.

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