Too bad you can't direct it upward into the fancy cowling you made, it would still be in the flow of the prop!
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Too bad you can't direct it upward into the fancy cowling you made, it would still be in the flow of the prop!
I maintain that in calmer waters that it will be fine. I'm kinda thinking it would have been better not to have shown the vids, the fact that a hull made to practice a method actually works at all is a bonus. Consequences of the design such as the splashing are really secondary to the main aim and I'll not be dwelling on it.
Busy laminating sheet CF/GF for parts of the twins project. Following experiences with this little red one some changes are being introduced to the hull, again, but I'm nearly there and I have everything I need to get on with them.
In the mean time, etc , here's a vid of the little red one in calmer waters at last. It's still windy here and I had to go to a corner of the lake to find some shelter, but nonetheless only the occasional clip of water on the prop, proving it was unfair conditions that were causing most of the problems with splashes with this design hull:
Here's that little boat in the best conditions yet, no splash problems
I'm about 1/4 of the way through mounting a screamy engine in that one, but it'll have to wait as I'm back on the Twins at last
That is running beautifully Jeremy How`s the progress coming along on the twin`s.
By the way are you using some form of software program to assist in the designs that your developing?
I'm rebuilding the passion for the twins, it's been a bit of a break but there was a plan.
I've just deleted a bunch of diatribe, I'll give the simple version. I've worked around Marine Engineering for most of my life and for a total of some 21 years at a place that makes high speed motor yachts. I used to be a test skipper and believe you me we test them hard, you kinda pick up things regarding the properties of planing hulls when your pushing 65 tons around the bay at 35 knots, I'm in Supplier Quality Management now but I reside in the Engineering and Design department and I'm surrounded by designers, naval architects and other specialists in Laminating, Vibration, and not least hull performance.
So, up to some years ago I'd made loads of airboats that were basically flatties with hull sides like a powerboat. Now sadly almost all of my photos have been lost but this one image remains of the typical boats I was making for maybe 20 years or so:
Some of them had slight tunnels, some one, some two, and when I came back to make some more it was with the sole intention of eliminating torque roll which plagued me on all of these till the later two tunnel versions. When I made the little red boat it was to try the glass over foam thing for the first time, but to help me with that I generated some of the shapes that that I planned to encounter on the true boat. The freak of this is things like the tunnels on the red boat are that wide because I wanted the offcuts to make the cockpit, being a materials miser .
Add to that my noticing that the SI3 was such an accessible boat to make that worked so well, I figured there was stuff to learn from these two boats so held off on the twins to see what prevailed. The net result is a significant number of changes to the planned twin, I'll be changing attack angles and worrying less about weight, tunnels are to be deeper than planned, steps are to be introduced, and sponson profiles are to be quite different.
The way I derive this however is entirely in my head, I try to consider Bernoulli's theory and how that works and pull that into my scratchbuilds. I mostly visualise construction before starting, but often make little test pieces to prove one thing or another. The SI3 was the first time I had ever built a model from plans. I don't use any software or anything and usually shape things 'in the hand', with no drawings other than templates for matching sides. The key difference between my way of configuring hulls and the SI3 is that I like lift strakes and longitudinal steps to control lift and side movement, the SI3 works well through a fairly unique property of railing on the outside sponson in a turn, mine rely on lifting the outer sponson and dropping the inner to rail on a lift strake or tunnel edge.
What I learnt from the red boat is that I could go a lot narrower in wetted area than I'd imagined. It's tricky to see in these vids, but it is actually totally on the surface of the water under way, we purposefully arranged to take this photo in clam waters to show that:
With the right level of power that boat will skim much better, but it'll turn like a pig at higher speeds I reckon due to being too narrow, we'll see. With steeper AoA's it would be less demanding on power too I figure.
So right now I'm pulling all of this stuff together to reconfigure the Twin. The only firm decision is that I'm not going to be making an Electric version, I've seen too many hassles with that stuff for it to interest me. I believe I'm close to the final arrangement of the boat, but there won't be any drawings etc to see until I know what I'm making and want to make up templates, for which I use a Vector Graphics program (CorelDraw) and draw out the shapes with a sign plotter configured for pen plotting.
One other thing I'm changing is getting back into my fun thing of having novelties and fiddly bits that may not contribute much to perfomance but can be a grin to have. Gyros are on board and with a new radio combo I've just bought I've a world of ways to include active features, like weight compensating trim tabs to balance fuel weight loss etc, active rear wing, maybe split to enable roll resistance, all just for the hell of it cuz I likes making models
And that was the non diatribe version
Last edited by Jeremy_H; 05-31-2014 at 04:09 AM. Reason: typos
That is certainly quite a list of accomplishments and valued knowledge from your professional career to aide in your passions outside of the work environment. The yellow boat pictured above is a sleek looking model, I really like the single engine pod which is what I'd like on my outrigger, at least that was the initial vision. I can certainly relate to the ability to design in one's head, I've never had a plan for any of my boats and like you visualize what the outcome should be. I'm not dissimilar to yourself in not being afraid to experiment with different ideas such as my current outrigger build, it's all an experiment with little proven foundation. I too have a kit which is a Cracker box style boat with a gas engine but chose the experimental route first, guess some of us just need to bang our heads against the wall a little harder. I was curious about the software usage because I'm trying to come up with an idea for a single rear sponson for my outrigger which to my knowledge hasn't been tried, but that's another thread! I will be watching certain aspects of this build such as the active rear wing for sure. I'm glad that was the non diatribe version Cheers!!!
This is pretty much where I am:
The engine pod has moved forward
I'm using a dummy Turbine inlet a'la H1 to cover the fuel tank/s
Stepped ride surfaces on the outer ride points (at the moment, may do all three)
Active wings (Gyro)
Pivoting turn fins
There's a few other things in there I'm still working on, but this is pretty much the outline...
Anything could change, but wood and foam is being cut
Colour in this boat pic is for clarity only. Size is an enormous 1260 LOA
That seems simple enough The pivoting turn fins, are they similar to the ones I found on the German website I directed you to a while ago? Want to see lots of pics of the hull build there m8
Can't remember details about the German fins, but there was something that mine have that they didn't , the adjustable stop I think.
I'll put up photos as usual.
What size are you going to build this overall and what size was giving you the challenge?
By looking at the size of the new boat it doesn't appear to be much wider and if I'm not mistaken the SI3 does sit quite low in the water with the one engine so I can see where additional buoyancy may be needed for sure. That is a sharp design though Are the gyro's similar to what is used in an rc heli or are they specific to watercraft, I'm not familiar with them? What will the base hull construction be out of, something light?
Like yours I want a full range of use, similar to Miss FivePoint I want it to float true and be able to troll comfortably. As such, with it not being dedicated to speed like the SI3 is, from current calculations I need about another pound of lift on the rear end, which equates to around a 50% increase in displacement back there. That's easy enough to put in at this stage.
The gyro type I'm using is a 'Headlock' type for a Heli. Too soon for a full understanding of that, but in essence these devices can operate in full heading lock mode so that it reacts fully to any detectable off axis movement. It can be installed standalone and its sensitivity dialed in via a pot on the gyro, meaning much faffing around to set it and the controls it operates up, or it can be done the way I am which has sensitivity, centering, speed, throw, exponential movement etc. all programmable via the transmitter. I can also override the gyro and manually operate the wing which may be useful for starting to give the front some lift in the water. I've proven enough on the desk to know how it works and how it can be employed, I will need to fit a fast servo though as we are talking split second reactions to make it worthwhile as a stabiliser.
The gyro's output is a command to a servo, it would normally be the one controlling the pitch of a tail rotor on a chopper, but of course any control surface that obeys the gyros requirements can be used, it just needs to see reaction to counteract the off axis movement it's detecting.
The sensitivity is used to arrange for the most efficient response it can give without over correcting and setting up an oscillation.
The primary aim is to control the front end, as the hull is purposefully lifty. But, a second gyro could control a split rear wing, which with the use of two servos would permit mixing like an Elevon on a delta wing aeroplane to allow a third gyro to go in. I'm heading into the area of ground effect with all this stuff though and whilst I welcome experimenting, I want a working model, so if I can do this additional gyros thing at low cost I will, even if it just ends up locked up for use. The main thing holding me back though is vulnerability to damage, active wings could be trashed if they are not pretty substantial or otherwise able to absorb shock.
The construction method is to be Carbon/Glass over foam, with a single ply layer in the centre, mainly to act as a load spreader for the engine pylon. In essence the same as the little red boat further back in this thread, the point of making it which became such a diversion as I'd not used the method before. Following my experiences with the SI3 and the test hull I'm not so concerned about weight as I have been, I'm more concerned about where it is.
I think a lot of people are stuck on the whole speed thing and missing out on the basic fun aspect by design of their boats, the speed thing has been done and next to impossible to beat, shame really I like the full range use idea
Well that's my crash course in gyro function I've given some thought to active wings and lightening fast reflex's would likely be required to avert a flip I would think especially when the boat is at distance and a little hard to see. A fixed setting after some experimentation may be the way to go, otherwise let the gyro's do there thing. Hat's off to you for giving it a go, thumbs up!
In the past I've done glass cloth over foam and it req's at least two 6 oz layers of cloth to give it any resilience to damage. One consideration I had in the past is to glass strong enough to keep things solid and come up with a running surface to adhere to the bottom for strength. Is the carbon in it's use a similar process to that of glass, never given it much thought really. I applaud the centre layer of ply in between the foam, plenty of strength there. The SI3 performs extremely well at least from what I can tell by the video's considering it's weight, I would have been seriously concerned in an end weight of 9 lbs but as you state if properly applied it could be an asset.
2 x 6oz cloth, is that right? That's a huge layup. I'll be using something like 1 1/2oz Chopped strand mat, woven cloth is only stiff in two axis (assuming it's bi-axial mat), and it's overused in modelling imho. CSM is stronger with its omni-directional stiffness. Areas needing additional stiffening will have CF down, and stressed areas additional CSM.
Generally Epoxy is needed for Carbon, there are some specialist Polyester resins out there that can be used, but it's not as good as even a basic epoxy.
The application is the same, unless it's expected to be seen, where one has to be careful not to disturb the weave. Thankfully on this boat the CF will not be visible so no worries there. I use spreaders and rollers to consolidate the mat, brushes are only used to wick off excess resin.
The double layer of 6oz was for the bottom of a snow machine I built out of foam in the styling of a hydro with an air rudder and an experimental spring loaded rudder blade, it was fun. The snow and ice crust can be quite brutal on the bottom of a machine blazing by at lightening speed lol. How flexible is the CF and does it come in varying thickness like fiber glass?
CF's flexibility depends on the mat construction. Like any fibres they resist bending longitudinally, so where we want stiffness on one plane we might use single axis mat, fibres all arranged in one way with light 'weft' threads to keep it in shape for laminating, I'll take a photo of some tomorrow. We however, usually in pursuance of the visual aspects of CF rather than practical, use biaxial mat. This can be in various weaves, most common being 'plain' and 'twill'. The weave actually compromises stiffness in any laminating mat, but if we were to compare like for like weights of CF to Glass I'd say that the CF results in a structure around twice the stiffness of glass parallel to the weave. Torsionally, e.g. twisting a square panel across opposite corners, it's not much better. This is why CSM is better than woven when it comes to omnidirectional stiffness. A woven mat gives added strength through grouping fibres, I often see a misunserstanding when it comes to CF in respect to stiffness vs Strength, folk seem to think CF is both, it's not. In fact it's quite brittle.
CF is available then in different weaves, and varying weights, but this is limited as 'cold' or 'hand' layup is not how CF is used in the real world. It's normally a mat pre-soaked, or impregnated, with resin which is ready to cure, commonly called 'Prepreg' mat, only storing it in refrigerators stops it from curing. This sticky product is laid into moulds, vacuum bagged, then put into a Autoclave to heat and compress it through a vacuum being raised.
Yay! I made a part for the Twins today , a servo mount for the front engine milled from Delrin (third pic is the original servo):
I need to dismantle the mount to drill a fixing hole, then I'll rig the linkages properly for each engine, and maybe rig the radio gear up and run the motors with the control means I've mentioned, single stick throttle, but engine balancing done via a separate rotary control on the transmitter. This will also give me a chance to run in the engines more as experiences with our two other SC's point towards a long run in period. It would be nice to bottom them out and set up the servo throws, limits, throttle curves, transit idles and engine cuts on the bench as it were. It'll give me a chance to get closer to the finding out which of the numerous props configs I can have will be best.
Last edited by Jeremy_H; 08-21-2014 at 06:32 PM.
I'm sure your cranking away like a mad scientist there Jeremy, how's the hull coming along?
Stalled again for a while whilst I fiddle with something else
Got back to this today, cut out a new ply profile, and started building up the foam sections.
The idea here is to shape a few things in stages, adding to the build-up once the bulk of the shaping is done in each stage. I'm hoping this will help to keep things even, and reduce work.
Before starting this I was staring at the paper profile again and reconsidered the bits I wasn't sure about, but I've gone with it as it is, as certain parts were becoming fat. In particular the cockpit, which I thought was to narrow, but I'm going for F1 tall and thin look and increasing the whole height of the lumpy bit in the centre of the boat.
Parts are arriving, in particular telemetry gear which will give me engine rpm and engine temperatures back at the transmitter, some Hytec waterproof servos for steering, front wing, water brake and possibly hatches, and materials for various controls, the rudder, and engine pylon footings. In essence have most parts to sort it, but fuel tanks remain an unknown, right now I think making them is the only option.