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Old 09-30-2013, 04:42 PM
  #76  
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.......

Last edited by *delete M i k e u p delete*; 10-01-2013 at 04:40 AM.
Old 10-04-2013, 01:22 PM
  #77  
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Very Nice - Interesting too. When you get the hydrodynamics right I think you will have a winner. As for the chine I always tend to go for a hard chine and I tend to think your a bit narrow to "Flat slide" which is making the inside edge dip.
Can't wait to see whats next.
Dave
Old 10-04-2013, 04:13 PM
  #78  
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Thanks.

It's been a brainstorming week, I fitted the spray rails and I'm waiting for pond time. So I diverted from the test rig to the final boat and opened up another can of worms

I decided to take the test boat engine mount apart to check on it, and to see how anti vibration mounts might fit within it. It's a complete re-design that's needed. I think I'm on the right path with that, I'm looking at a beam arrangement rather than the more usual radial mount, I can keep that more compact. I'll draw it before trying to describe it more, there is a possible problem with reaching the throttle lever to overcome first. The idea is to knock the corners off the vibration rather than greater isolation, so if I can make mounts from polyurethane myself I stand a better chance of keeping it small, rather than the quagmire of mount type/hardness/size/resonant frequency considerations through doing it fully.

If I'm in the mood I'll start to make another hull this weekend, one with the same hull design as the final, but just a simpler top deck. I could either transfer the gubbins from the first test boat over to that, make another twin, or a single engine version with the bits I have. My thoughts at the moment are to make with a single engine and transfer the twin over if needed. But I think the test running gear is too heavy and it may be better to simply ballast the next hull with weight to represent the twins, that way I may be able to find a target weight for the final twin rig a bit easier than coming at it from the other side. Dunno, I'll go with the flow on that one.

The SC's are mounted and ready to start running in, I hope to break the back of that this weekend. I'll see if I can rig the engines to measure the in-line thrust they give later.
Old 10-06-2013, 01:16 PM
  #79  
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Great day at a different venue today, some vid and pics here, I'll chat about it all later:



http://www.youtube.com/watch?v=Pmra7kN_kyA&feature=c4-overview&list=UUw8b4mq7g44FwvGq97q6aKw
Old 10-07-2013, 10:49 AM
  #80  
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I'd like to divert for a little and chat about the day I had above. Keen to try the spray rails I was disappointed to learn that the club pond, or lake as it's officially called, was not open due to key holders not being present. To hear the same for the normal Sunday session was a bit of a blow. So I started looking at alternatives. Living near the coast a number of estuary and seaside locations were lined up, but at the last minute a club member told me that a pond long imagined by me as no longer accessible was in fact open to public access again. And this pond was the place that I first experienced model boating in the late 1960's.

Back then, two lakes of similar size lay side by side. Both man made they are the feeder reservoirs for HP water hoses for nearby open cast China Clay quarries. But a lot has changed. Some years ago I headed there with a powerboat after a few years break from RC to find a barrier across the access road that wound across the Moors to these big ponds, and ever since I'd headed to a much smaller place within a few miles. So to hear that the big pond could be accessed again was good news, but I was told that it was now a walk from the car park. Whilst you used to be able to drive right up to the pond edge that was not the only thing that has shifted. Along with it went a plantation of Pine, and one of the lakes, now replaced by a huge hole in the ground. The quarry has edged it's way towards the lakes and eaten one of them, there's now a bank about half a mile long protecting the quarry edge, and the original road just drives right into it and disappears. To get to the lake now means a hike across boggy ground of around 500m. But it was worth it. A walk around the lakes showed no signage regarding models, just the usual 'No Swimming' and Lifebuoy stands. The lake itself was exactly as remember it, some different plumbing was in place as the old cast pipes had long gone I guess, you can see the new pipes in the vid. The rest was the same bar the view to the right, which used to be over the next lake and then open ground to the void of the quarry, it was now an imposing bank.
We were alone, the pond was dead flat, it was a slight breeze and a T shirt day in bright sun. Take it from me, not common on Dartmoor. The original launching beach was still there. It was cut into the bank by the local yacht club, who used to turn up in a removal van with these beautiful wooden yachts with what I remember as three meter masts. The yachts were self steering, using vane gear on the stern. These sometimes complex mechanical devices were works of art in themselves. This was all forty plus years ago, I wonder where they are now. I remember the last boat I ran here was an airboat, before I diverted into aeroplanes in the early seventies, it would have been mid eighties before I had another boat, and that was when I found this lake to be shut off.

So coming back here seemed a fitting place to bottom out the test boat. I keep switching from one aspect of this project to another and it's time to get back on to a single path really, so I'd decided by the time I'd got there that this was it for this model and all the testing and I should concentrate on the final project boats. One of its main purposes was to explore air rudders, and it's done that for me admirably. I now know enough to be able to say that they are not going to work on the final model's hull's, as a fan of water rudders for those forty years coming to these now has shown me that they demand very different things from hull design, and my idea of compromising between the two was really going to leave me with reduced capability in each. So I'll be building air rudder boats down the line for sure as they are a joy of their own, but these two really need hydro'ish approaches to make them work. I was in the process of redesigning the hulls when this came to me, I was in so much doubt that I'd figured another test hull was in order. But really, I can stick with the hull design that has a history of working for me, as in the two sponson boats I've shown pics of before, and add the element of steps without trying the conflict of making it work with air rudders.
The main need for this hull though was the twin engines of course. So, it works, but the need for buoyancy is greater than normal because of the inevitable weight. This will be offset by the lift in the hull at rest, I've had to ballast to the stern a couple of times, so in between there is a need for a real light mount. I've been routing around the shop for bits of titanium (damn awful stuff to machine) and Carbon with this in mind. I'll sort that, it just needs some serious thinking .

As it's swan song the spray rails had a pronounced effect. I'd put on 8mm high rails in triangular section of about 15mm width. Right from the get go the bad news was a sense of drag as the boat didn't seem to lift so readily to start with, but it had a more distinct drop over the hump on to the plane and when it got there the wake was a lot cleaner. The control of water running up the sides is clear to see, the hull flattened a lot, too much in fact as the tightest turns had the forward quarter under water. Some increased air is getting under the boat, just a little, but the lift is the root to the flatter running as the pressure is trapped between the rails further aft rather than escaping up the sides. The turn hopping has been eliminated, but so has all of the side slide. Perhaps somewhere in between is a rail that will be just right for that, maybe short of the transom would be better. Mine went too far forward, that didn't help the nose turns as predicted as the whole boat was railing more level in the turns. Reducing the size would recover that drag problem too and effect the top end so much.
I learnt a little trick. Throttle off in a bank turn and the boat sat flat, open the throttle straightaway and it would circle flat to the water. Back off then open up again and it would circle in a bank. This was totally predictable and controllable, and quite odd to be honest. We video'd it, I might pop it up.
The twin engines though are a real joy, it's been great to date having this thing around. The mount held up and showed a serious need for vibration control, so a light suspended mount required, not too challenging then . The engines have been pulling a heavy cart and they may well end up on another twin boat, but for now the hours spent running this one need to go into building, so let's talk about that.

I'm still working on the hull drawings, and I think I know where the construction method is heading. It's pretty much going to have to be foam or balsa with a carbon/glass skin. Carbon/Glass over balsa and lite ply structures is known to me, foam is not. I'm erring towards the foam though, as longevity is an aim of these models, and no matter how well you finish something, how well you seal it, and how well you look after it, wood moving is a fact of life. So I have to look into the foam thing, at my job we have a huge 5 axis CNC milling machine, it fills a building and can machine out a 60 foot hull in foam for laying up to become a plug to make a mould, bigger hulls are made in sections. Those guys know a lot about foam and finishing it, so I'll be picking their brains first. In the mean time the drawings include structure for frame building. This will not be wasted as cutting and profile gauges can come from them for foam use.
I'm awaiting delivery of some Polyurethane bar for machining the bushes for mounting the engines. It's harder than I'd like, 93 Shore, so I'm looking for softer stuff. But I've worked with this before and whilst it's an awkward sod to machine simple shapes can be made accurately. The material on the way is intended to make suspension bushes for competition cars, I must be the only guy in the street with rally spec bushes on a van lol! But the aim is to damp the vibration rather than try and eliminate it, so they may be ok. There's ways to maximise what flexibility it has. What I will say is that it's tough stuff and should be a good material to use if I can get the right level of isolation. If it's no good the mount design will permit change to other materials without having to be remade, I'd like to stick with Polyurethane if I can though as it really lasts.

I guess things will slow down on this thread, I've a lot of stuff to sort but the pace will pick up once I have the final boats under construction.

Last edited by Jeremy_H; 10-07-2013 at 10:52 AM. Reason: typos
Old 10-10-2013, 09:25 AM
  #81  
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Mock up of a single flexible mount:



The Polyurethane has turned out to be pretty good for flexibility on such a small bush. They have top hat steel bushes inside the Poly ones, they meet in the middle to allow the bolt to be fully tightened. By adjusting the length of the steel bushes the degree of compression of the coned top of the Poly bushes can be controlled, the Poly bushes themselves can be adjusted for length so they vary in how much they swell sideways into the hole in the mount as well. So between the two there's a sensible ideal to be found for the degree of stiffness the mount has.
Old 10-11-2013, 09:12 AM
  #82  
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Here's the vid of the turns I referred to:

http://youtu.be/jxKsckSlqps
Old 10-11-2013, 11:23 AM
  #83  
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Induced flat turns were slow speed and close radius while bigger turns were no change at all from video. Correct!
Old 10-12-2013, 07:53 AM
  #84  
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Flexible mounts for the final boat under way. The Polyurethane bushes give a sensible degree of flexibility in the hand, and I've built in room to adjust these if I need to tighten them up. There seems to be no ill effects from fuel on the mounts. Heavy though I must say, 1 5/8 oz in the bushes and steel spacers alone, but I've a plan to relieve the engines of most the weight of the silencers, which gives me a lot to trade with.



Learning about foam at the moment. I've used it to make GRP mould plugs before but only by hand shaping, but only sub parts, never a whole model. I've not used templates and hot wire which I think is what this project needs. The PVC Foam board I used for the test boat is viable, but it's surface is too soft, needing a GRP skin to toughen it up, and if you're going to do that then you'd might as well use a lighter former in the first place. So it's a good material for some things, but maybe not for my aim of long lasting models.

I'm close to having the wire cutter and I've some foam to play with, so that's the plan for next couple of weeks whilst the mount is progressing, know where I'm heading with it to buy in foam for the boats in a fortnight or so. I have the glass and carbon laminating mats ready, and I'm looking into resins to suit the foam.

Drawings are progressing, but there's a few challenges I've got if I want to achieve the desired arrangement, not least is the way the engine pylon fixes into the hull. I may need some help there .
Old 10-12-2013, 02:04 PM
  #85  
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This makes the setup a bit clearer (this is the .40 rear engine [test boat had a .25]), aluminium beams will be anodised black or grey. From here two 'Z' shaped beams will run to the front engine

Old 10-13-2013, 04:56 AM
  #86  
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Forward engine mount now done too. This prop up shows how they will sit. I need to leave enough room between them for the throttle links. I'm looking at running independent throttle linkages, with suspended engines the throttle control is a transmitter of vibration, links between the two engines into a common control like the test boat may therefore be asking for trouble, it depends if my fuel tubing 'springs' on the throttle rods can stop vibes getting through too much. Only one way to find out by running the mount independently soon, the pic shows a rough idea of one of the beams that will join the motors :


Last edited by Jeremy_H; 10-13-2013 at 05:10 AM.
Old 10-13-2013, 06:18 AM
  #87  
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So your going to run one upside down
Old 10-13-2013, 01:02 PM
  #88  
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No Mate, as you see it in the picture, same arrangement as the test boat. Maybe I'm giving you updates at too short an interval so things are not as clear as they should be. I should show you a drawing really, but I don't use them much for machining such parts, just do it in my head. The time it takes to draw it is better spent making it lol!

Here's the Z beams in place. These are going to be very much lightened. A vertical bulkhead between the engines holds the Z beams apart, it may help to show what the arrangement is like.


Last edited by Jeremy_H; 10-13-2013 at 01:08 PM.
Old 10-14-2013, 06:15 AM
  #89  
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Nice work Jeremy, that is looking robust and compact - a few holes here and there to lighten it and that looks like it will work well. Are you going to use a single mast to hold the motors - I am trying to picture how that will connect. Very cool - Likin the inline twins
Old 10-14-2013, 09:31 AM
  #90  
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Thanks.

I'm toying with two ways to arrange the pylon I've used OK before. One is a pair of side by side 6mm plates, they'll be about 25mm apart, which are lightened. But the one I'd like to use again is a pair of thin walled 25mm dia aluminium tubes. With accurately cut ends, located on spigots top and bottom, and held in compression via an HT through-stud they are neat, light, services can go up them, and by machining flats to form a rebate up to half way across each side a flush panel can be fitted to close the sides off. They can be angled, so long as the internal fixing stud is vertical with enough landing top and bottom they stay firm. This is what was in my head in the original post drawing of the final boats. Of course I've not put the forces of two engines through them, but they've been fine with a single .61 before, sure I still have one buried somewhere.

The pylon will mate with the lower engine beam via a simple plate running underneath the bottom Z beam on the centerline, of around 30mm width. I plan to make brackets which link to the plate which close off the very ends of the Z beams providing good load spread.

What I have no idea about yet, and this is holding up progress of the hull design, is how the pylon is to fix to a foam hull. Also, because I want discrete services, i.e. no external cables or fuel lines etc, I want to run everything up the pylon, which means they'll enter the pylon under deck level. Thinking sideways right now I'm figuring an access panel in the bottom of the boat is in order. With a decent fit and stuck down with Sign vinyl it'll provide access to loads of connections right up to the servos, which will be mounted upside down under the cockpit. The panel would be out of the wetted area when on the plane, he said .

Last edited by Jeremy_H; 10-15-2013 at 10:03 AM.
Old 10-15-2013, 03:26 PM
  #91  
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I've buttoned off the Z beams and the spacer bulkhead doobries are under way. In between I've been skipping sideways to see if pylon tubes can be the silencers . It's possible with water cooling, but a little sideline to think about for a while, at least till I have to commit in some way.

A range of 10 and 11 inch props are in the post, and I'll see if I can get these running on the mount on the weekend, albeit with the standard silencers.

Old 10-16-2013, 06:06 AM
  #92  
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Jeremy, you are the mini machining master! Hats off.
Old 10-16-2013, 03:03 PM
  #93  
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You're very kind sir, thank you.

Some goodies arrived already!! Great service from Leeds Models who seem to be the only people on this part of the planet who when asked about pusher props don't act as if you'd requested a lightly grilled Prairie Dog with French Fries and a side salad. They had everything I wanted, 10" and 11" options, though one's turned out to be an electric which I will chat with them about. I've gone back to APC's as the advantages are clear to me, but I must say I think their QC is slipping with more mould flashings and variation than when they first came out. Come on APC pick up the TPM program!
I've sacrificed my much loved CNC aluminium spinner type for lightweight Irvine ones, in black, which is becoming a theme . It's one way to lose weight right there but I will miss the benefits of well balanced and trued aluminium ones with their mild flywheel benefits and far superior resistance to electric starter damage .

Old 10-18-2013, 12:47 AM
  #94  
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how about a prop nut jeremy?
Old 10-18-2013, 04:20 PM
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Originally Posted by Altered1
how about a prop nut jeremy?
Yeah that's an option, easy to make too. But I don't find them as ideal as spinners with backplates, where the starting load is transferred to the prop driver, and less pressure is needed to get a good drive off the starter cup with the bigger diameter. You often see videos of guys jabbing the cone with the starter to get a decent enough drive. Not a method for me. Make a prop nut a bigger diameter for better drive and they just undo so readliy, needing unreasonable tightness to keep them in place.

If the boat works well enough I'll go back to the Aluminium ones, but even then the need for black ones means the anodising is going to be vulnerable.
Old 10-19-2013, 05:20 AM
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Some bolts to find and tanks to be temporarily rigged somewhere and the mount is ready to try:



Getting heavy though. I reckoned a 9 1/2 lb boat for the engines used in the test (test boat ended up around 13 1/2 lb), with these engines the boat has had to grow a bit, So I've given myself an 11 lb target. Right now then I've to make the rest of the boat under around 9 lb.
Old 10-22-2013, 01:45 PM
  #97  
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Should be EASY to make a 9 pound boat out of foam - use lighter weight glass cloth and epoxy.
Old 10-24-2013, 02:30 PM
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Yeah I reckon, just the weight distribution to pay attention to. I'm waiting for more foam at the moment after poor hot wire cutting results from the thick stuff I have, so I've diverted to playing with water pickups for the exhaust cooling. I've made up a 3 way flush scoop rigged to some vertical tubes to see what sort of lift I can get. This is a biggish bore to start with, 4.5mm as it's easier to go from big to small as the trial progresses, transom mounted for ease.

Talk of a hooley this weekend though, so low probability of it being calm enough to try it.

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Last edited by Jeremy_H; 10-25-2013 at 11:31 AM. Reason: typos
Old 10-25-2013, 05:19 AM
  #99  
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That is super cool...Literally. Hopefully.
Old 10-25-2013, 11:36 AM
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Yeah you never know, the principle is common, but there does not seem to have been the need for such height that I can find, and the biggest available commercially in the UK is 4.5mm, I'll make them bigger if that's a route to a solution.

Ran the SC's for the first time today, the .40 is silky but the .32 is a noisy crackling little bugger. Only one tank each so far but whilst the .32 is exhibiting typical tight engine properties the .40 is throttling well and picking up from idle smoothly from the get go. The mount is firm and the damping is clearly taking the edge off vibration. But, it's the two running together that's the real test and I've not done that yet, hopefully tomorrow, I'll take a vid if weather permits it to happen, the weather is turning ugly here as storm 'St Jude's comes over the Atlantic, threats of the worst winds for decades.

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