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building a serafinocet

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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serafino

New Member
Jun 18, 2008
65
3
0
Hey guys,
I love the idea of the lunocet. I'm only 16 so I don't have 1,300 to spend on the fin. I love the idea of the fin so much I'm building my own. I'm a fabricator I love making things. I have built many things such as a recumbent bicycle. I see this as a new opportunity to learn even more. All I have built so far on this project is the foot plates and its just the plates without any mounts or laces for my feet. This is the very beginning of my project I'm going to use this thread to show what I've done the problems I encounter and how I have done it so far. Also I'm sure I'll have problems with the design at first every prototype does, so when I encounter my first problem I'll post up and ask for advice. I'll post pictures of the plates in a few minutes when I get the chance to upload them.
Serafino
 
Here is a picture.
Its just 1/4 inch aluminum. It took me an hour tonight to just cut out and file the pieces. I used a piranha hydraulic cutting machine to cut it out and the files to make it smooth. I then bead blasted it (similar to sand blasting except glass beads are used). I haven't drilled any holes yet I need to come up with a better design to see where to place a pipe for the fin blade to rotate on. I may add some holes to add grip for booties and to lose a little weight. I got this metal for free from the scrap bin so some cosmetic defects are present (with the price of aluminum these days I don't mind at all).
 
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The lunocet may be patented. You got to check, otherwise you may be sued, I think. Americans, that's what they love isn't it? Sueing people? I once read that a burglar sued the house owner when he fell through the roof of the house he was robbing. Apparently he won the suit. That's madness.
 
No, Lunocet is not patented (yet), and I do not think anyone could sue you if you make a personal copy. And also ethically there nothing wrong with it, as long as you do not present it as your own invention (which is not the case here).

To Serafino: good job, but unfortunately I see only the first picture. From it I would tell the wings are simply cut from a plate of aluminum. Did you worked them then to give them the hydrofoil profile? That's rather fundamental and without it, they won't really work properly. At Lunocet the hydrofoil profile is rather thick (the wings are molded into a form - you can see it on the photos in the threads about Lunocet).
 
I only posted one picture. I have only made the plates. Ya I haven't even started thinking about the wings yet.
In this picture (not mine) it looks as though they are made out of a thin sheet of aluminum that is bent. I doubt I'll be able to afford carbon fiber. I know I could do it out of a sheet of aluminum fairly easily. I'm not sure how far swept back the wings should be I'm just gonna guess that. Also anyone know whats a good angle for the wings to be off to the foot plate?
 
My advice to you: try copying the 2.0 version. I don't think the version above is that good, simply from a fluid mechanics POV. Call it a "hunch..."

Pete
 
Wow, very skilled you are I'm sure! Good luck sir, I hope it's rewarding.
 
I think the version on the main page is different than what you have above. But I could be wrong.
 
I see now. Those look completely different than the ones I saw on their last. I think I'll try to get it more like those except for the carbon fiber since that takes a lot of effort and money.
 
Hi Serafino

I would not copy the version 1 nor 2. Version two has serious lacks in hydrodynamics (in my humble opinion - see other threads). Version one has rather difficult to implement flexing machanism and is too little adjustable for an experimental fin (again in my humble opinion and from what I can see in the few pictures).

I haven't yet brought my idea of a wing-fin to a usable paper/CAD drawing. But if you invest a little thinking effort you will be able to find a relatively simple solution which sould work as well as the lunocet prototypes.

For a wing type fin it absolutetly not necessary to use carbon fibre since the mechanical stability comes from the build-up of the whole compound (which is not just layerd fibre but rather has a core). I would use ordinary glass fibre (about 10 times cheaper) on a styro foam core. Of course the foam core would not be usable for deep dives and would have to be replaced by something more pressure resistant such as rohacell. But for a study of the mechanical and fluid dynamic details it would surely be sufficient.

How to cut a foam core for your wing? (Sorry, german only. I have to transalante it some day. The pictures probably help a bit): Technik - modellflug.aeolus.ch

Then layer it with some glass cloth and slowly hardening epoxy (at least 24 hours). I would estimate that 3 to 5 layers of 160g/sqm and a top layer of 80g/sqm glass cloth would be sufficient for testing a prototype up (down?) to some 5 to 10m. You write you are a handcraftsman so i think you will be able to learn an figure out the details of moulding the wings yourself

(Tip: If you dissolve the foam core (aceton) after the epoxy/glass shell of the wing has hardened, you can make it resistant to pressure by allowing the watter to freely enter the (now hollow) wing - And of course there are a lot more elaborate layering techniques available ;-)

Have fun and let us know of your progress!

Michael
 
Thanks for that post. I think I'll make it out of fiberglass now pour in some acetone to dissolve the foam and drill a small hole to have pressure equalization. I can't do anything today since I popped the bursa in my ankle. I should be able to go to the store and pick up some supplies. I'll make a jig for using a hot wire to cut out the foam. I'll also make a metal cut out to get the hydrofoils foam cut outs to be symmetrical.
Thanks for the help so far,
Serafino
 
This sounds like a stupid question but my mind is blank right now. For the actual fin part of it that will be made out of fiberglass( the hydrofoil) do I want both sides of it curved or more like a wing with only one side curved?
 
Hello mate

I just read about this design its nice and i never knew about Lunocet... But technical wise i would recommend for you to check a real lunocet and see the angle by yourself...
I am saying this because i am mechanical engineer and we have studied one course called flow measurement and if you can believe that every case in fluid life is unique and there is no common formula to be found for all cases and so that to calculate and angle for an equipment... The only way was to solve our question were to take each case and derive its formula!!! believe it it was one of most complicated courses, and of course after calculations there should be time for testing and finalizing with bunch of readings to get the best values and shapes... this design is aerodynamics related as well... Same difficulty here aerodynamics is unique case study where there is machine to fix prototype to be tested there...

This what i can help with if someone knows about the angle would help better
 
Both sides are cantilevered to produce "lift" in each direction. Like an aerobatic airplane wing. Based on looking at their design. Functionality wise I don't know how it all works. Salethefish's explanation shows the complexity...
 
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I wish I could see one in person. I don't think anyone here in CA has a lunocet. If you do speak up and tell me. So now that I know it needs to have a curve on both sides I can start the shaping of the foam I bought today. Oh here is a model made from paper, cardboard and the aluminum plates I made earlier.

 
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Hi serafino

I would strongly advise curve both sides. A profile that is only curved on one side produces a quite good lift (=thrust) in the case of a limited range of positive angle of attack with a moderate drag. However, when exposed to a negatve angle of attack, such foils work very very bad. You don't want to do it! I would suggest to start with a symetrical foil (ignoring the fact, that you don't apply the same force on up- and down-stroke). Choose a simple, non laminar NACA foil ([ame="http://en.wikipedia.org/wiki/NACA_airfoil"]NACA airfoil - Wikipedia, the free encyclopedia[/ame], for instance something between NACA 009 and 0015, depending on your construction requirements) which works at your Reynold numbers ([ame="http://en.wikipedia.org/wiki/Reynold_number"]Reynolds number - Wikipedia, the free encyclopedia[/ame]).

About calculation (as it has been mentioned here): With a little understanding of hydro/aerodynamics you can calculate some very rough corner points but don't expect the results to be more acurate than +/-25%. Caculation of your fin is by far not required. I don't know what hydrodynamic construction detail I would probably calculate except the rough position of the axle of the wing and the corresponding lever forces.

About simulation of the water flow (before somebody mentions it): forget about that. Way too complex and with too many unknown parameters. Lots of measuring forces, angles etc. would be necessary just to get some feedback about the accuracy.

The best way - in my opinion - is: Think a bit, make a guess, experiment. Keep your desingn simple and clean and expect to make several different variants to compare and learn about the effects of your variations. Chose a simple design with some room for asjustments of lever lengths, position of axles and returning forces.

have fun

Michael
 
Really because I "placed an order" to get some info and I actually had someone call me about the order. They seemed eager to sell it to me. So then whats the big deal about the lunocet its like the chevy volt all this hype about a prototype that isn't being produced. Maybe if mine works well I'll start producing hydrofoil monofins . Well in 2 hours I get to go into the shop and cut out a few guides to help cut out the foam. I spent 28 dollars on foam and 30 on aluminum its ridiculous. I have a 300 dollar budget for this I'm hoping I'll get alot of freebies.
 
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