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Trux,

I envison being able to adjust fin power while hands are locked in place over head. there would be no breaking form and I certainly wouldn't advocate putting it on the waist.

The cable is routed along the body for streamlining and the wheel is in your hand so that you can undulate your body and spin the wheel at the same time. It doesn't take that much practice to swim and do valve drills at the same time, and that's when we're playing with three different valves, so adjusting just one, albeit at a higher rate of speed, should be a piece of cake.

The tension to spin the wheel isn't as great as you might think- unless the valve hasn't been serviced in some time.

I promise to stop the Wizard of Oz comments.

Jon
 
Okay, we are focusing on a very finite area... I think what you are saying is that if there was a gradual transition from lower tension to higher tension, there there would exist the opportunity to accelerate at a slower rate, gradually ramping up input... whereas, I am saying, in sixth speed, the diver must (or should really for maximum efficiency) provide an anaerobic burst into the mono to actuate the mono to the proper pitch... sixth speed is demanding a higher input on the part of the diver to actuate the foil to the proper angles... the interesting thing, in my opinion, is that there may be a tension setting proportional to energy input... here is some backing for this... on the last lunocet design, I found that the single speed somewhat limited stop setup demanded a certain amount of exertion... if I gave the lunocet any more at the start, I would stall the foil and I was very much over pitching as I approached top speed... I really think I can resolve an action that involves an anaerobic burst of energy that creates intense acceleration and maximum speed within the sixth speed alone.
 
I envison being able to adjust fin power while hands are locked in place over head.
Perhaps for recreational freediving it may be OK, but certainly not for competitive freediving or fin-swimming - and that's what the high speed, or high efficiency / perfect hydrodynamism are for. Already keeping a knob in your hands will seriously change the ideal hydrodynamic profile. Moving it when changing the speeds, will mess with it even more. If we speak just about recreational diving, then I would certainly prefer avoiding all the hassle with the cable and rather really just adjust the bungee tension by hand directly on the fin as it is today. But of course, if someone prefers cable, why not - as you wrote it is very easy to add with no modifications, so why not having it as an option, if you find it useful.
 
I'd rather picture something more like a trigger that could be worked between thumb and palm - perhaps like a bike shifter type lever strapped to one palm and activated with the other.

More interesting is the idea of the fin self adjusting - but I can't quite picture it.
I do understand the problem, and it is interesting.

(Ted - the digitized raindrop impact pattern on the fin would look very interesting in blue and green - or shades of blue)
 
Ted, you argument with the overbursting is interesting. I think I'll have to try making some calculations to see if I am really wrong (but intuitively I cannot believe it). There is the vertical blade resistance (kick induced), the horizontal resistance or pressure (speed induced), and it has to be in balance with the resistance of the bungee. In the same time the amplitude of the kick and the pitch must diminuish with the speed, and so does the frequency of the kick - I am just not sure right now, if it is really the frequency in time that goes down, or rather just the length of the cycle in space that grows - I need to look at it closer. Maybe Cal would know better. Anyway, quite interesting stuff! :)
 
The dial on the back of the blade looks like a perfect candidate for putting a slob-winder on since it's already on the market.

Of course, since Ted has already designed high performance brakes for cycling I could envision something that slips onto the back of the hand and uses a thumb shifter, or something smaller, that wouldn't ruin the hydrodynamics of it- kind of like STI for monofins.

It sounds like there may be something in the works at a much higher level from Ted's most recent posts- where it does so automatically- kind of like performance cars that get closer to the road as they accelerate, to improve performance, without any extra input from the driver.

Jon
 
Ted

Trying to follow all this. Saved up a few questions that I'm pretty sure you've considered;

How much power are we talking about? I have some old figures that show 400 Watts aerobic (30 minutes) and 0ne KW of 'instant' power with a 7 second limit. Close?

Is there an optimum distance from the centre of rotation to the foil.

What is the thinking on frequency of oscillation.

Since your quest is different from a free diver's, are there any obvious changes that would improve efficiency at 1 meter per second. (streamline the feet, attached the foil to the shins or moved it back)

Almost 50 years ago the Aqueon was very impressive. May your Lunocet be even more so.
 
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From the work of Dr. Frank Fish, who has provided me much data on swimming morphology and kinematics of dolphins, frequency increases but the tail amplitude of swimmng dolphins actually varies little with speed... I was quite suprised by this when I first learned it... but it seems frequency and pitch angle are your major dynamics in increasing speed...
 
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BTW, Ted, didn't you experiment with adding "[ame="http://en.wikipedia.org/wiki/Wingtip_device"]winglets[/ame]" to the wings? Cal mentioned the problematics earlier in this thread - increasing the effective aspect ratio of the foil reduces the induced drag. Winglets are used at planes to reduce drag with this principle, and it would likely work in water too, though the question is how important it is at the speed a swimmer can reach with it.

Well, then it remains only covering the fin with shark skin to reduce turbulences and we can start breaking the records :)
 
From the work of Dr. Frank Fish, who has provided me much data on swimming morphology and kinematics of dolphins, frequency increases but the tail amplitude of swimmng dolphins actually varies little with speed... I was quite suprised by this when I first learned it... but it seems frequency and pitch angle are your major dynamics in increasing speed...
Yes, indeed, it surprises me too. I wonder if it is the same case at fast swimmers like the tuna fish. It surprises me especialy because if you keep the same amplitude, you are getting much more problems at high speed (low pitch) keeping the optimal angle of attack at the extremities of the kick, when the angle of the lever (tail) is already equal or bigger than the needed pitch. I wonder if dolphins control the pitch of the tail fin variably across the kick to conpensate it and to get the optimal angle of attack.
 
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You guessed it! ... Trux, you're a pretty sharp guy!
 
Well, if someone is sharp here, then it is certainly you, Ted :king - you figured all this long before us. Additionally I really admire the professional approach you have to the testing, construction, and manufacture - it is absolutely incredible!

OK, so I went to sleep with the problems in my head, and run hundreds of laps with Lunocet and other fins on my legs during the night (what an exhausting sleep :)). And it proved useful - now I believe I understand it perfectly. I see in fact, Ted and myself, although opposing, we were both right. Let me explain it (sorry, it is long, but I tried making it comprehensive even for those not aware of all the details):

Let's simplify the propulsion model maximally - let's ignore all non-substantial factors like the turbulences, induced drag, vortices, variable speed and variable power during the kick, the asymmetry of the kick and human body anatomy, diverse knee and ankle flexes, and let's forget even the lever Lunocet works with. Let's say we have an ideal case where there is a constant kicking force in both downward and upward direction, and where the hydrofoil support moves only vertically without any lever angle, with a constant amplitude, just like a piston in a cylinder of a car engine. I also assume that the tension of the bungee is already adjusted to the available kicking force and that we neither over-power nor under-power it.

In this case, the vertical kick force against the hydrofoil acts against two reactive forces - the speed induced pressure (the bigger the faster you go) and the pitch-controlling bungee resistance (constant, more precisely growing with the angle, but considering it constant will work for this simplified model). So now, if your available kicking force is constant (you push with the maximal force from the start to the end), and if we consider the bungee resistance constant, the kicking force is directly in reaction with the speed induced resistance reducing the pitch. So here, Ted is perfectly right, that you do not need any stiffer bungee at high speeds, because the hydrofoil will always travel in the right angle of attack as a result of balance between the kicking force and the speed induced frontal pressure on the hydrofoil.

Now, the resistance force of the bungee is not constant, but rather growing with the foil angle, hence smaller at higher speeds (smaller pitch). So at higher speed, there is less resistance which you then must compensate for with lower kicking force to avoid overpowering the fin. Although it is already an argument for increasing the stiffness with growing speed, let's ignore this factor for now.

The above simplified example assumes a constant amplitude of the kick. Now that will work fine if the support of the fin is always perfectly horizontal as we assumed. As Dr. Fish (what a Nomen Omen if it is his real name!) told Ted, that's indeed the case at dolphins - not only the lever they use is quite longer than at humans, but due to the flexibility of the body and tail, and due to the muscle control of the tail fin, they are able to keep the fin in the ideal angle of attack during the entire kick.

Unfortunately though, humans with a Lunocet fin are close but still not entirely like dolphins. The lever is quite short (especially if you have a bad style and bend your knees while kicking), and we are not able to keep the hydrofoil support in a horizontal position, but rather moving it on a lever under a variable angle. Let's say it is +-20 degrees. Now let's look at the serious consequences it has:

At the start (speed zero), the ideal angle of attack is roughly 45 degrees. You adjust the tension of the bungee so that with your kicking force the hydrofoil moves to the angle 45 degrees at zero speed induced frontal drag. So far so good. The pitch is 45, the lever angle is 0, and the angle of attack is 45 too. Now the kick continues upwards, the lever angle grows until the max of 20 degrees. Lets assume the pitch angle is constant at given speed - 45 degrees. In fact the kicking force is not entirely constant, and we would also need to use trigonometric functions to calculate for the change of the forces and change of the pitch, but those changes, at the small angles are relatively unimportant for our calculation. So (still standing) we have a constant pitch of 45 degrees, but a lever of 20 degrees - the resulting angle of attack is no more 45 degrees, but just 25. Well, that's not too bad. Especially assuming there are many other factors affecting the efficiency, the relatively small reduction of propulsion due to less than ideal angle of attack in the extremity would not make a big difference. We can still tell - so far so good.

Now we start gaining speed and the necessary angle of attack falls down and the blade indeed sets in position automatically due to the speed induced pressure. In the moment we reach the speed when the needed angle of attack is 20 degrees, we are getting into real troubles - it will be 20 in the middle, but at extremities it will be zero - so far still not too bad: with angle of attack equal zero you are simply gliding when in the extreme positions (up and down). But when you get even higher speed, and the pitch lower than 20 degrees, in the extremity the angle of attack will be negative, meaning that you start braking and won't be able to get over this critical speed.

You have two basic ways for solving this problem - either a technically challenging system keeping the hydrofoil support horizontally all the time, or voluntarily reducing the kicking amplitude with growing speed. Already here, I believe that the possibility to adjust the bungee tension on the fly would help with reducing the amplitude - the growing stiffness would help you naturally reducing the amplitude. But even if you think you do not need that and that you can learn the right style without it, let's look what happens:

The angle of attack falls from 45 (minus the angle of the leading foil side to the chord) at zero speed to zero at high speed. Yes, at high speed you can have a immobile solid hydrofoil and still propel with it, thanks to the angle the opposing sides have. The great advantage of the solid hydrofoil is that it has dead space close to zero. Hydrofoil with an angle of attack needs to flip to the opposite direction, hence losing the propelling power in the dead points of the kicking cycle. The bigger the angle is, the bigger the dead space.

When you go faster, the pitch falls down, and consequently the dead spaces too, but since you also need to limit the amplitude to avoid kicking out of the zone of efficient angle of attack, you need to reduce the dead spaces as much as possible. And that's exactly what you achieve by increasing the bungee tension. Although by making the foil stiffer, you under-power it slightly (kicking with a less than ideal angle of attack), it allows you greatly reducing the amplitude (staying so in the most efficient zone) while minimizing the loss during the foil reversion.

So my conclusion is that indeed the possibility to control the bungee tension on the fly, making the fin stiffer at higher speeds (while reducing the kick amplitude in the same time) would help the efficiency and reaching higher speeds better than without it. On the other hand, with the progressively stiffer fin, you really need to decrease the kick amplitude at high speed, otherwise you get easier into the negative efficiency zone at extremities of the kick.
 
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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.

That's true. I called that the "Afahrtsproblem" wich could be translated as "slow start problem". At the start you have 0 Forward speed and therefore need to have a fairly big deflection of the wing to produce an efficient angle of attack. Which increasing speed you start to have not only a downward speed (due to the downward movement movement of your legs) but also a forward speed component due to the forward movement of the whoel diver with its wing. This this reduces the angle which the wing has to form against the direction of the movement of the whole fish/diver. So far I agree with you.

Lets asume, that the force we can apply with our legs is constant for any speed. The area of the wing doesn't change obvously. Mets simplyfy the whole thing a forget about many other things for a moment. The difference in pressure we produce could therefore be calculated as Force per Area. Which with the before met assumptions would be constant. If we further assume that the neutral Point of the foil doesen't move pedending of the angle of attack (In fact it does as one of the other main characteristics of a profile.), the torque (trosional moment, ist that the correct translation') would be constant as well.

We would produce a constant lift over all speeds. Aince the lift is roughly proportinal to both the angle of attack and the speed, The AOA would allway adjust to the current speed.

Of course not all above met assumptions are "true enough" and we let asside, that the ension of the "spring" grows proportional to the length its drawn. But with a wisely chosen axle and lever position one could achieve a quite good "power curve".



One of the bigger other problems is see, is that the foot mounted part wich holds the whole find and its mechanics changes its angle when moving your legs up and down. This decreases the angle of attack at the maximum elongation in the upper and increases it in the lower positions.

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.

Agreed.

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.

A modelling of such things is extremly difficlut and inacurate. I trust my "gut feeling" that the holes shown are not very effective. The easiest this would be to test it...

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.

Of course. Its very difficult to understand what happens along a long flexible blade of a bi or monofin. You have not only different angles at different dephts but also different directions and speeds of movement.

Now, I unfortunately have to stop at this point. There would be a many other things to say and think about. But unfortunatley I have to leave for military service the next three weeks. No water (except frozen as snow) :-( but probably a bit of climbing at least :)

I Hope I have a lot to read when I return!

Good luck and have fun,

Michael
 
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I've been traveling and just came back to several more pages of FASCINATING discussion here, including Ted's jumping in. I applaud Ted for opening up as he has (very rare for a manufacturer), and I look forward to the first draft of the Glossary!

As you can tell, I was quickly in over my head (!) on this thread, but I am a "curious enthusiast", and I will follow this with interest.

A quick anecdote: About 15 years ago, I took that mono prototype [photo on page 1 of this thread] with me to the Bahamas to swim in an "open pen" situation (dolphins are free to come and go as they please). There was only one dolphin in the area when I strapped the mono on and jumped in. I swam around with the dolphin interacting with me. Afterward, the trainer/spotter commented that he had never seen the dolphin react like that to a human at this place. I have no idea if it was the fin shape, the size (one meter in span), or my peculiar kicking style! In any case, it was fun to try this design out "on location", and I'm looking forward to doing more in my upcoming Bahamas trip in mid-April (all free dolphin interactions). The boat captain says he'll have some traditional monos on board (I'm bringing bi-fins).

One last point: you guys keep talking about "heel-out"... you might want to switch to "toe in". This is a common way of describing non-parallel orientation. Even with automobile tires. Just a thought.
 
Ciao Trux!

I dreamt of this as well but my dreams were about proper technique when breaching... what part of the stroke would be best to be in as mid body travels out of the water to enable the rest to come while reaching still for that last morsel of bite into the water that sends you maximally and completely airborne!

... okay, regarding your last post... I feel like I've gone back in time and am having a conversation with myself and what I believed two years ago. Your logic is correct... ( I would first like to alter one point... starting pitch angle can be as high as 60 degrees, this creates a 30 degree angle of attack because there is no forward component yet only the transverse, and as I stated earlier, Frank and I are finding a 30 degree angle of attack does not fully stall on flapping foils... (this statement actually has to be qualified by saying, "with reasonable amplitudes and transverse velocities") So, I've said that your logic is correct but you are assuming that the frequency is staying the same and that the transverse velocity is relatively constant but in fact the frequency must increase as does with the dolphin... this results in a higher transverse velocity... in fact, if you could keep the transverse velocity rising at just the right rate (increased frequency) with that of the rising forward speed, you could create situation where the pitch angle and the angle of attack remain constant, for example if your transverse velocity remained equal to forward velocity and they rise together then you could have a pitch angle of 30 degrees and your angle of attack would always be 15 degrees (because if transverse velocity = forward velocity then resultant velocity is at 45 degrees to forward velocity)... this is so hard to get across without diagrams so will continue working on our reference piece...

Here is a nice work done by Dr. Fish
http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA369158&Location=U2&doc=GetTRDoc.pdf
 
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Yes, I see that the situation is much more complex. However, I doubt you can increase the frequency without either reducing the amplitude, or increasing the power. And since we assumed you are working with the maximal possible (and constant) force from the beginning to the end, decreasing the amplitude is necessary. And as I wrote, by decreasing the amplitude, the ratio between the inefficient dead spaces and the high efficient middle part grows, you need to decrease the dead spaces by trimming down the pitch.

Well, let's stop with this speculative theory, and wait for your diagrams.

As for the breaching - I am afraid it gets so complex (change of direction, body flexing, change of drag in water and air, breaching the water surface tension, variable gravitational force as you lift your body from above the surface, etc, ...), that it is barely possible to solve it theoretically. Studying videos of dolphins and other aquatic animals breaching the surface is probably the best you can do. And I am pretty sure you do it relentlessly.
 
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Hello people, keep it comming, it's a great study we're having here, I love it!

I've also been making a scetch of a design based on the aquafoil idea. The idea being creating some simple and cheap plywood wing (1), 1,5m wide. I don't know but what's the exact point of the bungy cord? In my view it's stretchyness is to create a gradual transition between the up and down stroke. Secondly I would limit the roll or pitching angle of the blade of my design by having two screws. One can thus adjust the blade on the waterside for high or low speed swimming by altering the range of movement of the wing. For CW, one would expect some low speed settings, as 1-1,5 m/s is slow. For Dynamic it can be set for higher speeds.

I was thinking for controlling and stabalising the roll of the wings on would something like a shockabsorber. The caracteristics I would be looking for would be to be soft when gradually pressured, and (very) hard being shocked - by strong explosive strokes.

For my design I'm searching for some basic data.

I already found through observing pitch wings on submarines, that the aspect ration of width (front to back) and hight (thickness) of the wing is about 5:1
From this thread I got the Angle of Attack in relation to the swimdirection, pitch, being between 15 and 30 degrees.

Furthermore the on-the-swim speed adjustments would be cool if it would be automated. But for now I would be very happy with adjusting it's properties while still in water. It's like having more than one fin, fit for all disciplines :)
If I were to swim fast, I would not mind having to overcome some inefficient initial strokes caused by a limited roll of the wing(s).

I've made some loose caculations based on the effective surface area of the monofin and landed on something like a 300% efficiency increase. I have no idea what it is to be in actual speed, but it is faster ;)

Herbelow is my hasty very basic wood design:

Translation of the terms:
Zwemrichting = swimmingdirection
Voethoek = angle of the foot
Voetlengte = Foot length
Draaipuntsafstand = Rotationpoint distance
Draaihoek = Angle of [wing]rotation
Vleugeldikte = Thickness of the wing
Vleugelbreedte = Width of the wing

Vleugelmonovin01.jpg
 
The idea being creating some simple and cheap plywood wing (1), 1,5m wide. I don't know but what's the exact point of the bungy cord? ...
You can even have a self-sustained hydrofoil without any bungee, though having the bungee has some advantages (besides others you can adjust the tension for different modes of use). Look for details about the self-sustained hydrofoil in this article - look at the last section called "nageoir ou hydrofoil auto-incident". Use Google translator if you do not understand French. Or google it up - you will certainly find English or even Dutch documents about it.

As for your idea with a simple one-piece foil - it has the advantage mentioned earlier by Cal - no gap in the middle, hence less turbulences and less induced drag. To further decrease the induced drag, you should make the hydrofoil narrower at the ends (similarly as wings at planes). 1.5m may be too much - such foil will certainly flex already quite a bit. According to the calculation in the above linked article, ideal would be a foil 80 cm long and with average width of 10 cm (bigger in the middle, smaller at the tips).

Also do not forget that you need a rather serious room around the foil under your feet to allow for the flipping, so you will need to move it little bit further.
 
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Thanks Trux, I've pulled the article through an online translator, and the auto-incident design is indeed what I'm looking for.

As for dimensions, I was thinking how much power a person could exert. I landed on the idea of going from a classic fin, and it's power consumption. I figured If oun could handle the surface area of a WW classic MD1 (biggest fin) than a similar surface area for the wing would be ok. So I took a very rough calculation of 70x60cm x 2/3 = 2800 CM2 = surface area. Starting from what's availeble in plywhood, I go from 2x18mm= 36mm for the thickness op the fin. Resulting in a wing width of 5x 3,6cm = 18cm With a total surface area of 2800cm2 I'll divide that by the 18cm and end up with 155cm. It's much but adjusting will be just as simple as sawing off :D What I'm more worried about is weight as I'm aiming for something weighing about 3KG.
As for bending I think 3,6cm will be sufficient to counter excessive bending.
As for the rotation joint I just plan on having a simple stainless steel rod through teflon rings inside the wood hinch.

to counter the enormous width maybe it's better to go with a thicker and broader wing.
5cm thickness would result in a much more practical aquafoil length of 112cm.

And like Ted, I too want to embrace the open source of idea's. The only conditions I have for using my idea's are that one should not use it to the detriment of humanity and give credit where it is due.

- Thanks Ted again for your great idea and wonderfull exemple of an emphatic, generous human being you are.

Love, Courage and Water!

Kars
 
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