Who dares to suggest a reason for this?

[Kars]

Well Ted it's great to hear you enjoy our company and passion!

Is there a need to adapt one's existing monofin technique? much?

About patents etc, it's more used to protect the big intrests, the elite, the dominent minority as they call themselves. Enterprices like Mosanto go arround pattenting existing plant gene strings farmers have used for thousands of years without any limitation. No, I don't think anymore that there is fair competition.

With the current inflation of the Dollar, Euro and other fiat currencies it's hard to give any estimate, but maybe you hint to what pricetag you're aiming at in today's currency value?
It would be nice to have also a 'cheap' version for starters. That's what I like the WaterWay's they got a line of E 130 fins which are great to start with and learn the technique.

On the Footpocket being outward canted, I think strait legs as opposed to O-legs are much better for fast and long swimming. The outward canted footplates will wear heavily on the knees like my coach explained who has also toplevel experience in the rowing sport where there are heavy loads transferred on the foot as well.

Good pressure spreading tight fitting footpockets are I think also essential for an optimal transferral of energy to the blades.

I feel it's a pitty you latest design may have lost the concave benefit.
Could you not put the wings more closer together closing the gab?
I also have some doubs about the durability and the usefullness of the bungee. As of now it seems me more like a usefull devellopment option / tool.

I'm looking forward to the first Deeper Blue article about your prototype being tested. A great way generating publicity is to have a professional finswimmer and freediver test your product in devellopment in a pool, and in Constant Weight.
Premature test(s) could also give you great and affordable feetback. One other way of getting cheap feedback is going to a freedive competition and have peolple test and try your design, and in the proces generate a lot of buzz

Love, Courage and Water!

Kars

 

[Mullins]

I don't know if you picked this up Ted, but we're quite interested in your fin rofl

 

[zerog]

Thanks!

Okay, give me a day or so to do some proper listing of terms and definitions for our "language" as well as creating some nice illustrations on the anatomy of the flapping hydrofoil... just remember, I don't intend to do this alone; and although I will call on the help of mathematicians, fluid dynamicists, aeronautical engineers, biologists, and maybe even psychiatrists, I think we should have all theories, models, formulas, etc. backed and grounded in this self-contained document. This means limiting math to simple differential equations at the extreme (I would love to keep things in algebra and trig) and defining, however exhaustive it may be, all notations ... I'm sure there will be great debates about accuracy and inclusion in this upcoming document... all the better to have faith in the final reference material. I see much more advanced discussions on the horizon when we are all on the same page with the fundamentals of lunate tail propulsion.

 

[trux]

Completly false. Have a look at that:

Lift-induced drag - Wikipedia, the free encyclopedia

Comming from the airodynamic side, ...

No, sorry Cal, it is not false. You may be expert in aerodynamics, but before jumping the gun, you should read what was actually discussed, and try understanding the problem in question.

First of all the profile of the Lunocet foil is symmetric, as well as at the profile of a dolphin tail fin. Hence, your article about asymmetric foil and the resulting induced drag does not apply here. Although there indeed exist asymmetric hydrofoils using the principle of induced drag you referred to, they are not too practical for this type of propulsion, where the foil travels through the water in both directions. They are rather used in mono-directional applications, such as a carrier for a vessel body elevated over the water surface, or at blades of a screw propeller. It is not the case at a dolphin fin or at the Lunocet (check out the symmetric profile of Lunocet foils on this picture).

Symmetric hydrofoil propulsion works on a different principle! - it is the basically the angle of attack of the entire foil + the difference of angles of its two sides that are important here. Now, it would be possible to have a technically sophisticated hydrofoil with a variable asymmetric profile, which would flip in the same way as the direction of the fin, and where the resulting induced drag would indeed help with the propulsion, but that's not the case here. Maybe at the next generation of Lunocet

In the same time, you also completely misinterpreted the problem with the opening in a fin. Nobody ever wrote here that you should make a hole in the middle of a hydrofoil to make it more efficient. The thread started with photos of monofins having opening between and along the foot-pockets. At a classical monofin, that area is indeed very little propulsive and rather just causing vertical drag, so reducing its square area as much as you can, has mostly positive effects (although as I already mentioned, you indeed have to count with some additional turbulence, which may seriously impact the positive effect of the opening).

And the same case (or a very similar) as with the monofins, is with the older Lunocet design. Due to the mechanical aspect of the system of the three blades, you would need either a fourth plate or a rubber sheet to cover the hole, but that space would not be propulsive anyway - it wouldn't be in the right attack angle most of the time. So better than covering it, increasing the vertical drag, letting it open helps reducing the profile, while keeping the advantage of the tri-blades concave forming.

Now, I very much agree that placing the fin (foil) backward on a narrow-profile bar ("tail"), would allow flipping the entire hydrofoil, and avoid having any opening in it. That's what I described in one of my preceding posts in this thread - if you take the time to read through it, you certainly find it. However that's not the concept we are discussing here.

So as a conclusion, I'd tell that it is always worthwhile reading carefully through the posts and trying to understand the problematics, before jumping in violently with the opening proclamation like "completely false". Not only it is not very polite, but trying to denigrate others by arguments that do not stand, may turn against you.

 

[cal]

Hi trux

First of all, I'm sorry, I didn't meant to harm you! Sorry, for taking the wrong words.

Now to the technical part (was a bit in a hurry when I wrote my last post - although having read the whole story)

No, sorry Cal, it is not false. You may be expert in aerodynamics, but before jumping the gun, you should read what was actually discussed, and try understanding the problem in question.

First of all the profile of the Lunocet foil is symmetric, as well as at the profile of a dolphin tail fin. Hence, your article about asymmetric foil and the resulting induced drag does not apply here. Although there indeed exist asymmetric hydrofoils using the principle of induced drag you referred to, they are not too practical for this type of propulsion, where the foil travels through the water in both directions. They are rather used in mono-directional applications, such as a carrier for a vessel body elevated over the water surface, or at blades of a screw propeller. It is not the case at a dolphin fin or at the Lunocet (check out the symmetric profile of Lunocet foils on this picture).

You may have missunderstof the issue of induced drag (and I admitt, the wikipedia article about it is rather bad, but I haven't found a better one up to now). Induced drag is not a feature you want to "use". It's a force which generated by a lateral flow of water induced by differences in pressure. Since it is a "breaking" force its generally unwanted.

Some very short foil/profile theory

Any foil - no atter if used on an aircraft wings, ships propellers, or fins) works by creating a difference of pressure between both sides of the wing/fin. The difference in pressure is roughly proportional to the angle of attack (AOA; angle between the undisturbed stream line and the chord of a foil). This holds true for both symetrical and asymetrcal foils. This difference of pressure creates the "lift" (or "trust", if we are talking about propelling) by "pushing on one side and "sucking" on the other.

Each profile creates a diffrenet lift at a given angle. The lift increases (to a certain point, of course) when increasing the AOA and decreases if you reduce the AOA. If you keep decreasing, It produces a negative lift.

As I mentioned the relation of AOA and lift is specific to the profile and it describes one of the main characteristics of a profile. A symetriyc foil is just a special case of an ansymetric profile which has the nature of creating zero lift at 0 degres AOA. A asymetric profile becomes neutral when the AOA is negative.


Induced drag

Figures at http://aeolus.ch/tmp/diving/induced_drag.pdf
The difference of pressure generated by a asymetric profile with a 0 or positive AOA or by a symetric profile with a positive AOA extends over the whole blade out to the tips (figure a). At the tips the wing or fin suddenly ends and there is no more "barrier" (the fin) separating the high from the low pressure region. Thus, forced by the pressure difference, the water start flowing lateral from the high pressure side over the tip to the low pressure side (figure b).

We now overlay the lateral flow with the forward motion of the fin and get the situation on figure c) for "ordinary" monos and figure d) for a symetrical foiled wing (i.e. a lunocet). The result is a long swirl which is drawn behind the diver.

This lateral flow or "swirl" adds not only nothing to the "lift" or "thrust" it also cost power to constantly create it. So neither a pilot nor a swimmer nor a formula 1 pilot wants this. It just costs to much of his precious energy.

One way to reduce this induced drag, ist to make wide, and short wings (so the proto C4 mono is quite the opposite of that). This applies to whatever airplanes (which use all sorts of tricks to avoid it, i.e. the winglet), birds, fishes and fins.

(about the figures: Their not to scale in any way! Maybe the AOA may apperas strange for a downstroke but its roughly what will result by the overlapping foward and downward movement of the fin)

In the same time, you also completely misinterpreted the problem with the opening in a fin. Nobody ever wrote here that you should make a hole in the middle of a hydrofoil to make it more efficient. The thread started with photos of monofins having opening between and along the foot-pockets. At a classical monofin, that area is indeed very little propulsive and rather just causing vertical drag, so reducing its square area as much as you can, has mostly positive effects (although as I already mentioned, you indeed have to count with some additional turbulence, which may seriously impact the positive effect of the opening).

I agree partly. I can follow your idea. However I think that these holes are way to small to acheive the positive effect of not having to "push" water arround. Behind the body it's quite turbulent anyway. But I think, the holes have a perfect size to produce a lot of turbulence which again cost a lot of energy.

And the same case (or a very similar) as with the monofins, is with the older Lunocet design. Due to the mechanical aspect of the system of the three blades, you would need either a fourth plate or a rubber sheet to cover the hole, but that space would not be propulsive anyway - it wouldn't be in the right attack angle most of the time. So better than covering it, increasing the vertical drag, letting it open helps reducing the profile, while keeping the advantage of the tri-blades concave forming.

I'm not sure wether your talking about the old or the new lunocet design. The old 3-part wing doesn't have this problem. The reason why I think a gap has to be avoided is not the propusion, which could be achieved. It is about the induced drag which can be recuded since, with a gap in the middle, it wouldn't only occur on either outsides but also additionally in the middle of the fin. (That was the whole point of my last post.)

Now, I very much agree that placing the fin (foil) backward on a narrow-profile bar ("tail"), would allow flipping the entire hydrofoil, and avoid having any opening in it. That's what I described in one of my preceding posts in this thread - if you take the time to read through it, you certainly find it. However that's not the concept we are discussing here.

That was my first idea, too. No, its not the currect concept of lunocet. But I wouldn't say it's not the concept at all. The last design stage of lunocet was quite like this.

So as a conclusion, I'd tell that it is always worthwhile reading carefully through the posts and trying to understand the problematics, before jumping in violently with the opening proclamation like "completely false". Not only it is not very polite, but trying to denigrate others by arguments that do not stand, may turn against you.

Again, I didn' wanted to insult you and therefore I'm sory. I probaly wrote a bit too fast. And - I had read whole thread ;-)

have fun,

Michael

 

[jome]

Ted, you're my new hero (sorry Dave).

The discussion has moved well beyond my technical understanding, but I just wanted to say that I find it incredibly cool that you are doing this in the first place, but also that you are going "open source" on it. Probably cannot contribute much, but just like a zillion others, I will be following this with great interest and also spread the word. The freediving community is small, but I suppose at least at first those are the potential customers. Although I can imagine the Lunocet taking off in a more general "water activity"-crowd manner if you have some luck.

What I'd really like to see at some point is an experienced mono diver doing different kinds of dives with the Lunocet in good visibility (pool conditions). Just to get a feel of how it moves and how it compares to traditional monos.

By the way, how cool is it to have your own dive pit How deep is it?

 

[fcallagy]

Might be jumping in here out of my depth as the engineering speak is a bit beyond me at present however a though popped into my head re teds brakes. as high spec as they obviously are do you need a technique to use them or do you just pull the lever?

My point being we all swim/fin differently and while one fin may suit me and my style it my not suit another. I was wondering is there a possibility of a fin that maybe continues up the body covering ankles/knees that puts you in the correct position for the most efficent swimming or is this then becoming to much of a machine rather than a fin?
And could this cut down on the subjectivity to some extent as the style needed to power the fin would be more uniform.

 

[BennyB]

I've been trying to follow this but it's moving way out of my depth, so i'll just happily smile, nod and wait until the photos and vid come out.

Ted, an outstanding job! We need more pioneers like you about.

One question i'm not sure if it's been covered here yet - will the device be made to handle pressure at depth? ie. could a diver take it deep? By deep i'm talking anything deeper than 10m, say between 10m and 200m.

Cheers,
Ben

 

[trux]

Now to the technical part ...

OK, Cal, so now we seem to agree on the principles. After your first post where you referenced an article showing the classical asymmetric foil profile, I admit not really reading through myself, and was falsely under the impression you try to suggest the propulsion power at monofins comes from the asymmetric foil profile. I also wrongly interpreted your use of the term induced drag. I apologize for those false assumptions.

I see that in fact we agree that the propulsion power at the fin comes from the angle of attack. And we also agree that the angle of attack serves not only for creating the propulsion power, but causes a drag force too. That's why I mentioned in my previous posts that the angle of attack needs to be reduced with increasing speed, and that's also why Lunocet has its "gearbox" increasing the tension of the bungee, limiting so the angle of attack for higher speeds.

Now, I hope you agree with me, that the area of a monofin near the foot-pockets that flexes only minimally, finds itself close to 90 degrees to the kick movement (vertical), hence causing maximal drag to the vertical kicking force, and in the same time being close to 0 degrees to the forward body direction, hence practically not helping with the propulsion.

So taking this part away, will not reduce the propulsion, but will seriously decrease the vertical drag. By taking that part away you do in fact exactly what you suggested in your initial post - increasing the aspect ratio of the active blade. In the same time, I agree with you that the holes on all of the fins shown in this thread are far too small. I also agree that the turbulences caused by the holes "may" overweight the advantage of the reduced vertical drag, and I mentioned it already earlier, but I do not think anyone can tell it directly without complex modeling or testing.

As for your comments about the current design of monofins - I think that you conclusion that it is for practical reasons is closer to the reality than that people do not know about the induced drag at low aspect ratio foils. Well, common users may not know all the theory involved, but there are certainly skilled experts among the manufacturers and their developers.

At bi-fins, the practical reasons are apparent - bi-fins have many practical advantages over monofins for recreational diving, or spearfishing, and you do not really have the room for increasing the width.

At monofins, using a flat flexible blade is the simplest, and easy to manufacture. Lunocet is the next step in the technical evolution, that progresses only slowly, because the developing and manufacturing costs are simply too high, considering the tiny market monofin users represent.

You also need to take in view, that the propulsion and the mechanics of a long bi-fin (or monofin) is more complex than at a solid foil. In fact the long blade moves in a sinusoid. If you look at some videos, you can sometimes see almost a full sinusoid on some longer blades (for example the new C4 monofin) - so in one moment all the descending and ascending slopes create a propulsive force. It also reduces the induced drag (you could compare it to several high ratio foils connected after each other). It is likely inefficient at higher speeds, but there may be possibly some advantages at lower speeds. Personally I do not think the concept can work well enough, but on the other hand I also do not agree that only the last part of the long blade at long fins is active. I agree it is not a good concept, but on the other hand it is not as bad as it may appear on the first look.

 

[zerog]

Sorry Trux... I never answered your question about how the pitching works on the last design...

The old design has two 10mm titanium pitch axles located at the forward extent of the foils as you probably guessed... the axles flex a bit in the actuation provided by the water pressure during the stroke; this flex happens inside the foil but does not cause the foil to flex spanwise... because of this, the foils are brought closer together, allowing them to pitch. And as you correctly observed (as did Dave), the swept back angles of the pitch axles allow the development of the concavity.

Jome... :thankyou the "test lagoon" behind my shop is 35 ft. deep. There's a video on the making of it on Subhuman Project: Biomimetic | Ocean | Exploration ... look under "now playing", then "test lagoon".

BennyB... Thanks!... the foam core is cured inside a 30 ton press and when the laminaton of the carbon is done inside the mold, the foam is compressed. This creates an internal foil pressure exerted by the foam on the inside surface of the laminate... so to answer your question, we should be fine at depths exceeding 200m ... however, we have yet to test it :hmm

 

[Jon]

I may not understand all engineering jargon being thrown around, but I know cool when I see it- and this thing rocks! I like the snowboard graphics that you can choose from as well.:friday

I really like how the feet attach to the blade- no painful footpockets. I also like how one could have one fin for winter and summer diving- since the footpocket would adjust for different socks which is unlike my current monofins.

Since there is an adjustment knob on the back of the blade, I wonder if it's possible to run a slob-winder from the blade, through the wetsuit, and up to one's wrist. That way you could keep your body position constant as you adjusted the tension on the blade with one hand. Here's a couple of pictures of a slob-winder so you know what I'm talking about.

Jon

 

[trux]

Since there is an adjustment knob on the back of the blade, I wonder if it's possible to run a slob-winder from the blade, through the wetsuit, and up to one's wrist. That way you could keep your body position constant as you adjusted the tension on the blade with one hand. Here's a couple of pictures of a slob-winder so you know what I'm talking about.

As I already wrote in one of my previous posts, I'd find much cooler if you could change the gear (tension of the bungee) simply by pushing heels more or less together. In fact it is rather natural - when you start forcing at high speed, you muscles naturally tense, and the heels get easier together than when relaxed. So in this way you would gradually increase the bungee tension as you accelerate, and decrease as you slow down - changing so the foil angle of attack almost automatically. If it worked, it would be a real bomb and would allow much better dynamic efficiency over a range of speeds. The question if whether the force of the heels is sufficient to change the gear, but I imagine there is a mechanical way to amplify the heel movements, if one really wants to implement it.

 

[zerog]

I think it's a good idea Trux... the only thing that flags me as a potential problem is the limited travel of the heels vs. the tension change in the bungee. There is a 50lb. difference in tension from speed 1 to speed 6. However, as I stated earlier, with the pitch axle located further aft, the pressure on the foil is more balanced about the pitch axle which translates into less tension required to manipulate the foil so this difference doesn't have to be so high if the axle was balanced even further... definitely worth looking into! ... you know, I haven't tested this guy yet and I wanted to leave myself plenty of room for dialing it in.

 

[Jon]

Since there's already a dial on the back I think a slob-winder could snap right in place without much re-design- as in none.

The cable is thin enough that it could run right up the inside of the suit and come out by the wrist- where it would fit neatly into the palm of your left hand- because I am left-handed and all things should be designed around my limitations to start with.

I worry about adding too much complexity into a Wizard of Oz type device- where you need to click your heels to go home. rofl

Jon

 

[trux]

... you know, I haven't tested this guy yet and I wanted to leave myself plenty of room for dialing it in.

Yes, I am aware the travel of heels is rather limited, and that it may be a problem to translate it into sufficient tension of the bungee. And Jon is also right that adding some complicated hi-tech device may not be the best way. On the other hand swimming with the cable would not be a good option either. Additionally you could not modify the tension in full speed with it either. It means you could change the tension practically in full stop only. It is already quite a progress against the standard monofin, which has a constant stiffness, but does not help with reaching the highest possible speeds.

It's like having a bike or a car without any gearbox - either you set it up for high speed and then you won't manage to start without external help (or will get too tired before reaching the traveling speed to be able accelerating more); or you set it up for low speed and then you only keep crawling around slowly. So only having the possibility to control the angle of attack on-the-fly without leaving your hydrodynamic position with the hands over the head will allow for efficient accelerating from zero to the maximal speed.

Fortunately it is not as bad as I describe above in the example with a bike, because a freediver can still control the angle of attack to some extend with flexing the knees more when accelerating. Although it is not ideal, it is what freedivers do with standard monofins anyway. Still, I believe the heel-controlled gearbox would be marvelous.

 

[Jon]

The cable is no big deal. It would come out of the back of the blade and go in your wetsuit by the ankle. From there it runs up your leg to your arm and out your wrist. The handle pops out the wrist cuff and ends up in the palm of your hand. There is no external cable flopping around as it all runs through the inside of your suit. I've swum with cables inside my wetsuit before without any issues- I had a battery operated wetsuit heater that ran the cable though the suit into a heating pad in the suit.

I don't understand why you wouldn't be able to switch power settings on the fly? You can do so on a bicycle- while climbing a hill, at slow speed, caked in mud, and sucking in bugs. Maybe he needs to invent Hyperglide for the fins- just as he reinvented bicycle brakes.

I know that with a momentary stop I can switch out the power setting on my scooter, and the fancier ones can switch on the fly- just ask Longfins. Mine is mechanical and his is electronic, but both of them can be done many times on a dive to maximize power.

If it would only take a short hesitation to switch gears that would be quite alright- like when turning around at the bottom plate. Still, as I stated before, I see no reason why it couldn't be changed under pressure.

Now, tell me again why clicking the heels is a better option Dorthy.

Jon

 

[zerog]

Very insightful Trux!...

I was not going to go into this until I had put up the reference piece I am working on but here is something I think you'll appreciate and will shed some light on why I'm so excited about this six-speed design...

Your comparison of starting in sixth speed to that of starting a bike in high gear shows great logic but get this... the angle of attack is manipulated by roughly two factors with this design -(lets leave out what can be augmented by the knees, ankles, etc.) they are the forward speed of the diver and the tranverse input of the diver. This is a slippery thing to grasp but basically the speeds are set to the input of the diver... you see if you really punch it in speed 1 from a dead stop you will over pitch the foil because there will be too much pressure... however, the tension provided in speed six allows you to give it everything you've got... you've got to or you will under pitch... now once you get going, the pressure reduces and the pitch angle falls (this is one of those terms I wanted to sort out with the reference glossary) but the angle of attack to the resultant flow remains pretty constant.


I am still working on the reference piece, but one thing I'd like you to digest is that there are two angles we will be discussing...

1. Angle of Attack - the angle the foil makes with the resultant water flow (that being attributed to the relative proportions of transverse motion to forward velocity).
note: the angle of attack should be between 15 and 30 degrees and should remain relatively constant regardless of forward velocity. 30 degrees is definitely in the realm of stall for air foils and hydrofoils that are not flapping but in our work we have found that reversal and shedding of vortices occurs before full laminar flow separation on flapping foils which is hugely to the advantage of bumble bees, geese, dolphins, and lunocet divers

2. Pitch angle - the angle between the chordline of the foil and the direction of forward velocity of the diver when the foil is at mid amplitude.
note: this angle is maximum when diver is static (just starting) and minimum and top speed.

 

[Fondueset]

Wow!
It so happens I have been obsessed with monofins lately. Winter these past few weeks has been brutal so I am only getting into the bay on the weekends. Its good but not when the air and wind are so cold that exposed flesh freezes in minutes! Today I finally resorted to a pool and was not allowed in despite pleas from lap swimmers who know me!!! Too dangerous - the lifeguard thought I would collide with someone and the pool would get sued!!!! He was intensely neurotic and started speed rapping when I tried to reason with him - so I waited a slipped away. He looked maybe a little asbergery so best not to push.

sorry - only an explanation of compulsive monofin thinking. I have been trying to image a fin the flexes convex - based on how the fins on rayed fin fishes work - But now I find this amazing thread! I am not up on the edge like many who are posting here - But the new lunocet is beautiful!

Zerog - I greatly appreciate the spirit and precision of your posts - and your passion for the work. Your sentiment re- patents is beyond the pale. Its awesome to see you posting here!

I'll step back and read now.

 

[trux]

Now, tell me again why clicking the heels is a better option Dorthy.

Well, quite simple, Jon. If you want to change the speed with your cable in full speed, you need doing it with the hands perfectly stretched above your head. Now, excuse me, even if I accept carrying a 2m long cable (which I would prefer avoiding), I really do not see myself manipulating the knob with both hands without seriously losing the ideal hydrodynamic position and without losing speed. If you have the knob just at your belt, then it is even much worse - manipulating it there will slow you down even much more. Unlike that, when changing the tension with your heels, you would not need to move a mm from the ideal shape.

 

[trux]

Your comparison of starting in sixth speed to that of starting a bike in high gear shows great logic but get this...

Thanks, Ted, for the technical details and explanation of some terms. Yes, I understand the difference and importance of both the angle of attack and the pitch. And yes, I see what you mean that the pitch angle falls as the pressure reduces with increasing speed. However, excuse me, but I am still persuaded you could get from the fin much more if you could increase the tension of the bungee with increasing speed. It is not to change the pitch or angle of attack - the ideal ones are given as you tell. It is to allow you pushing stronger with lower frequency (and amplitude) - similarly like when you change speeds when riding a bike.

So yes, you are right, the blade will change the angle with increasing the speed, but if it was stiffer (stronger kept by the bungee), you could push stronger at keeping the same angle, hence also propusling more. This is the exact reason why sprinters use very stiff blades, while freedivers or distance swimmers quite soft ones (and yes, I am aware of the differences between the flat flexible blade and a flipping hydrofoil). So if I may permit expressing my opinion, I still believe that the possibility to change the stiffness on-the-fly (and without leaving the hydrodynamic position) would be a real revolution in monofin swimming.