Who dares to suggest a reason for this?

[trux]

Pretty much dead flat across the bottom at the ball of the foot. Of course the tops of the feet are on an angle and there is a gap under the arch. I get the impression outward canted footplates would force the knees apart when the legs are bent?

Will have a good look at my mono(s) tonight and see how my feet sit in them

I may be wrong, but I still have the feeling, after watching the video with the first prototype again, that the angle between the feet support and the ax actually controls the wings attack angle (at least at the first prototype). If you look at the video, on my mind it is rather apparent that the feet support angle is not constant but rather changes during the kick, reversing so the blade angle. At upward kick you can see Ted (I suppose it is himself on the video) spreading knees slightly. Am I correct, Ted, or just dreaming to be? Or is it really only the bungee that limits the wing rotation and assures reactivity? EDIT: as I am looking at the new designs, it may be indeed the second case.

 

[trux]

For one, the pitch axle has been moved forward. In the last design it was located near the toes and was also very forward on the foil itself - two problems here... the first, the axle being out at the toes and the foil even further back, there is a tremendous amount of strain on the ankles when one tries to engage one's full power into the mono... and after a few hours you find your ankles are extremely sore. ...

I agree that the strain to the feet is extreme, and the bigger, and the more back the plates are. On the other hand it is also clear you lose amplitude and efficiency moving the blades forward. It is exactly why I think the Freedom Fins (a remotely similar concept) cannot really work efficiently (better told one of the reasons).

I always wondered why no (mono)fin manufacturer though of putting the blade on a stick that would be fixed to the shins, instead of the feet, putting so the fin further back. That would have several advantages:

1. Less strain on the feet
2. No problem with blade angle like at current monofins (not Lunocet, though)
3. Having higher amplitude
4. Having longer lever at smaller angle change, hence smaller need for compensating the attack angle of the blades (also smaller dead points due to it). It would allow using a thinner hydrofoil profile, reducing the drag too
5. The attacking edge of the fin would not be so much in the turbulent "shade" of the body and feet, but rather the entire leading edge would be active (unlike at standard monofin) working so in "cleaner" water as Andy wrote
6. If necessary, you could still use the feet to control the blade angle of attack, or an additional small kick at the end of the cycle (similar as dolphins do when accelerating) - that would not cause any big strain. Alternatively, they could be used to change the tension of the bungee, changing so the reactivity, but I suspect it is actually what the feet already do at your Lunocet, and what you call the "six speeds", or not? (EDIT: Hm, after looking at the design again and closer, it looks like you manipulate the "speed tensioner" by hand. Wouldn't it be better to enable changing the gear by the feet? For example putting the gear between the heels and changing it by pressuring them more or less together? That might be relatively natural - at high effort you are tense, so pushing heels together would tense the foils, relaxing the heels would relax the foils too - on my mind much better than having to do it by hand, because by hand you cannot change the gear truly dynamically in full speed as you accelerate or decelerate)

Did you experiment with such shin fixation too, Ted? If yes, what are the arguments against it? Is the strain on the back and abdomen, or leg muscles too big?

 

[chrismar]

With a normal fin, the changing angle of the feet work to the advantage of the fin from an angle of attack point of view. With the lunocet's variable angle of attack, such an advantage would be lessened. However I suspect that the mundane mechanical issues with shin attachment would be difficult to overcome, especially comfortably fitting the fin to different people. Although Ted seems quite good at dealing with those kinds of problems...

Ted, I assume you've explored the relationship between force, velocity and angle of attack. Would you care to share some general findings, ie. optimal angle of attack for a fin blade at say 1-1.5m/s?

 

[trux]

With a normal fin, the changing angle of the feet work to the advantage of the fin from an angle of attack point of view. With the lunocet's variable angle of attack, such an advantage would be lessened.

No, it would not. Actually, with the foil type of blade you can achieve higher efficiency than with a plain flat blade. Lunocet is actually combination of both - a solid hydrofoil, and a flexible blade (similarly as a dolphin tail fin). And the feet still add to the flexible angle during the kicking cycle. The solidness of the foil, and the profile of the foil, allow reducing the dead spaces at the end of the cycles, making so the energy transfer more efficient.

 

[trux]

Looking again at the designs, photos and videos of the old and the new Lunocet, I find a pity the new Lunocet lost the concave concept - the three parts of the old fin, by changing the angle, formed a concave form, which on my mind greatly helped with the efficiency of the propulsion. Unlike at the old fin, where it was achieved with the V-shape of the arms, at the new prototype, there seem to be only a single straight axis.

I may be wrong, but although the new fin looks lovely, I like the old system somehow better - not only it was in its behavior closer to the dolphin fin approved by millions of years of evolution, but I think it really had some great advantages. I understand the reasons for the change, but think that keeping the concave shaping would be still possible even with moving the blades forward. On the other hand, from the viewpoint of manufacturing costs, the new concept is certainly much simpler and easier to mass-produce.

Looking forward to it anyway

 

[ADR]

Hi Trux,

I wonder if some flexibility between the footpockets(dreaded with a normal flexible monofin) would in the case of the new version of the lunocet create a concave bend as the previous model had?

 

[Mullins]

Wouldn't that mean a convex shape? And isn't there a whopping great axle running underneath them anyway?

 

[trux]

Hi Trux,

I wonder if some flexibility between the footpockets(dreaded with a normal flexible monofin) would in the case of the new version of the lunocet create a concave bend as the previous model had?

Having only a single small photo originally, I thought it too. But reviewing newer photos and the videos again, I have the feeling the concave shape is indeed created only by the wings flipping around the axis. Unlike I supposed, I do not think now anymore the feet platform had variable inclination angle. However, Ted still did neither deny nor confirm the theories, so we can only speculate

 

[trux]

Wouldn't that mean a convex shape? And isn't there a whopping great axle running underneath them anyway?

No, it is a concave form (see the image explaining the difference between concave and convex I posted in another thread - most people indeed confuse the terms very easily). A convex form is definitely not good at a fin, because instead of forcing water backward, it is being pushed sideways, losing so a lot of energy - that's exactly what happens some Glider monofins as we could see in the above mentioned thread.

As for the old fin, there was not a single axis, there were two of them in a V-form - look at the photo earlier in this thread

 

[Mullins]

Trux - I did mean convex. If you allowed the fin to bend in the middle, between the footpockets, wouldn't it just fold when pressure was applied? Just like our Hyperfins seem to be doing?

 

[Mullins]

I mean, you could make it concave if you rotated your feet with plenty of force to oppose the water pressure. But this would require more force than most people could generate.

Of course, if each blade on the new-style lunocet was on an independent axle that was angled backwards, THAT would create a concave form on both the up and down strokes. Although of course there would be nothing to stop water spilling through the middle, like there was in the previous model.

 

[trux]

I mean, you could make it concave if you rotated your feet with plenty of force to oppose the water pressure. But this would require more force than most people could generate.

You can achieve a concave form with no effort, if you have the right design - just have a look at the photos of fins I posted here - the attacking part of the blade definitely creates a concave form - on my mind better at the Volo fin than at the split fin, but the split is not necessarily bad - the partial leak through the split "may" be actually reducing turbulences (but maybe also not - that would require some tests in hydro tunnel)

Of course, if each blade on the new-style lunocet was on an independent axle that was angled backwards, THAT would create a concave form on both the up and down strokes. Although of course there would be nothing to stop water spilling through the middle, like there was in the previous model.

The hole in the middle is just perfect in fact, because it is in the place where you lose energy, because that part is not in the ideal attack angle and rather moving water down and up when kicking - you surely remember that it is actually what started this very thread. The hole is a quite good engineering design.

 

[Mullins]

Disagree completely re the hole in the middle. If it's ok to have a big hole in the middle of a concave design, then it's also fine to have a convex shape! There is no difference between water 'falling off' the inside of each blade, or 'falling' off the outside of each blade if they are a reasonable distance apart. A very small gap might be ok, but still not ideal.

Yes, it is possible to achieve a concave form with no effort through fin design. We are all aware of that. But introducing 'flexibility between the footpockets' of this latest Lunocet, as Andy mentioned above, is not going to achieve this. If you did introduce this flexibility, you would need effort to create the concave shape. Angling the axles backwards is going to achieve it, as per my post immediately above.

 

[jome]

I'm lost with all the engineering porn...I just want to try the damn thing

 

[trux]

Disagree completely re the hole in the middle. If it's ok to have a big hole in the middle of a concave design, then it's also fine to have a convex shape! There is no difference between water 'falling off' the inside of each blade, or 'falling' off the outside of each blade if they are a reasonable distance apart. A very small gap might be ok, but still not ideal.

No, I am afraid you are not quite right. A hole at the root (before the flex) is quite different than a convex shape at the top of the flex as we see it at the monofins in the other thread:

The hole really just lets water through in the less efficient place. Water that would be otherwise moved only down and up, reducing so the drag in the vertical direction. In contrary, at the convex V as you see at the bent monofin, you lose a lot of water (energy) in the most efficient place of the blade - the one where otherwise the most efficient attack angle should be, and that normally should move the water backward. When the blade is bent, you move the water sideways instead. There is a giant difference between the two cases.

You can look at dolphin tails - they do not have holes in the fins (because the entire fin moves in the attack angle), but the tale is rather narrow just before the fin (in the part that moves with high amplitude, but does not work in attack angle). It serves the exact same purpose - reducing the vertical water resistance. You want to move the minimal possible amount of water vertically, but the maximum backward.

​

Now you are right that the size of the hole may matter - there are two main effects of the opening - first reducing the vertical drag (positive), and modified flow and turbulences causing changes in the lengthwise drag (probably negative, but in some cases it may have some positive component too), so it is necessary to find the optimal size by testing, but that's far to be simple. Both effects depend on many factors, most of all on the forward speed. At high speeds, where the kick amplitude and angle of attack should be lower, the hole should be minimized, at low speeds a bigger hole would likely help better.

Yes, it is possible to achieve a concave form with no effort through fin design. We are all aware of that. But introducing 'flexibility between the foot-pockets' of this latest Lunocet, as Andy mentioned above, is not going to achieve this. If you did introduce this flexibility, you would need effort to create the concave shape. Angling the axles backward is going to achieve it, as per my post immediately above.

Yes, you are right here, but it is also the way the old Lunocet works - on my mind, the bridge between the feet is in thick titanium and hence solid, practically non-flexible. What looks like flexing in the video on the first look, is in fact just an optical effect caused by the flipping wings, when you look at it more carefully. The concave form is being created completely passively without effort, by the water resistance and the elasticity of the three blades connected with a rubber sheet.

 

[zerog]

You guys are great! I wish we were neighbors!

Let's step back and look at what we're doing here...

We entered this forum, this discussion, as enthusiasts separated by oceans, coming to together to share insights and knowledge on a common passion... but it seems to me that something else may be happening as a result of many things converging from what's possible with the internet to what's possible with biomimetics...
We have an opportunity here to do real pioneering work. I have decided not to apply for patents on my work. I have several patents to my name from other projects and have held them for over a decade. They cost me a lot of money and I am glad that I have them on my brakes but something rubs me wrong about gleaning the secrets of a million years evolution, the dolphins' secrets, and claiming them as my own. What I'm trying to say here is that in my opinion, intellectual property rights sometimes slow progress and I am more eager to launch a human out of the water than to make a buck... don't get me wrong though, my lunocets will be expensive but only because they will be expensive to produce. I and my small team here will do all the artisan work ourselves from machining to anodizing, molding to stitching... but, I would like to and will share here and on my website, all of my findings opinions, theories, etc. with you, my aquatic brothers, without regard to trade secret or intellectual property rights... frankly, if someone takes my ideas and produces a better mono, one that gets me further out of the water, I'll have two words for him/her, "thank you!"

With that said, I propose that we start a new thread with the first post creating a glossary of terms... a vocabulary for our language. If you guys think it's a good idea I will create the thread with the first post being a list of my own terms and definitions regarding the mechanics of lunate tail propulsion... as you and I add and create more, I will edit this original post... we may create a very valuable reference piece for this pioneering work in pursuit of the perfect human breach!

What do you think?

 

[trux]

Yes, defnitely, Ted! Please, go ahead with it and create the thread.

EDIT: and I applaud your decision not to block the further development by patents, though I am afraid others may attempt it (on the other hand they may have hard time doing so, if your fins already exist)

 

[trux]

BTW, in the article analyzing foil propulsion, I linked earlier in this thread, there is a complex mathematical calculation showing that a human with maximal power of 300 W, and using a foil of 8 dm2 (width 80cm and average length across the blade 10 cm, decreasing in the outside direction) should be able to breach 30cm above the surface.

 

[cal]

The hole really just lets water through in the less efficient place. Water that would be otherwise moved only down and up, reducing so the drag in the vertical direction.

Completly false. Have a look at that:

[ame="http://en.wikipedia.org/wiki/Induced_drag"]Lift-induced drag - Wikipedia, the free encyclopedia[/ame]

Comming from the airodynamic side, I allways wondered why the mono fins are so narrow and long. This creates a lot of induced Drag. Bi fins are even more extreme but you cannot make the wide and short for practical reasons.

The only explanation for this antilogy I could reason was that:

* people are not aware of this (unlikely)
* there must be some other practical reason.

The practical reason seems to be the angel of attack Problem. A long and narrow fin bends along its longitudinal axis creating a reasonable angle of attack which , with a short and broad fin could not be achieved without mechanis (as the lunocet does).

Now about about the hole in the middle: We should desperately be seeking to reduce the induced drag produced by any wing. Since this drag is iverted proportinal with the aspect ratio of the wing, you want the aspect ration as big as possible.

The simple Version: Having a gap in the middle makes your aspect ration (less) than halfe the one it could be. I allows to circulate water where it shouldn't be circulating thus creating energy consuming swirls which add no lift (="thrust") at all.

(Why do you think have gliders an extreme aspect ration ans no gap/hole between the wing and the fuslage? In contrary: the wing is beeing taped to the fuselage before every fligt to not allow just a little air streaming between the wing an the fuse! See: http://www.aliante4g.it/Immagini/thumb/AliantiVari/images/ash25.jpg)

 

[cal]

Hi Zerog

I have decided not to apply for patents on my work. I have several patents to my name from other projects and have held them for over a decade. They cost me a lot of money and I am glad that I have them on my brakes but something rubs me wrong about gleaning the secrets of a million years evolution, the dolphins' secrets, and claiming them as my own. What I'm trying to say here is that in my opinion, intellectual property rights sometimes slow progress and I am more eager to launch a human out of the water than to make a buck...

First I have to thank you for this! It's extremely seldom to see such an insight in today ages of copy protection and protectionism in general! Thank you once more for your decision!

About having someone else patenting it (as somebody has mentioned here): This wouldn't work since it was easy to prove "prior art". It would probably cost a lot of money to argue it on a court (One of the major problems with patenting. It's always beeing said, that patent protects the "small" inventor. I consider this rather false. Just see what happens: Big companies don't need to pay attention. I case of a case just tear the "smal" invetor to court and have him spend all his money on anttorneys and he will be quiet very fast...)

I was thinking about high aspect ration fins myself and then came accross your lunocet. Though I would not have taken such a technicaly complex approach. But - not having spent years thinking on it - yours may be a very good solution. I'm just a bit concerned about is the problem of induced drag explained in my previous post. The earlyer Version didn't had this problem (but probaly and most likely others).

Thank you for sharing your thoughts and idea!

Michael