Who dares to suggest a reason for this?

[Bill]

Trux
Great diagrams. I learned two things about the Aqueon design. One has bothered me for decades and the other I missed. More respect for the designer/engineer all the time. Can't wait to see what an 80 meter monofin diver does with his, when it arrives in Kona.

[ADR]

Originally Posted by Bill

... One has bothered me for decades and the other I missed.....

Hi Bill,

You can't leave us guessing, please spill the beans on both of those.

[Bill]

Hi Andy
Nothing new for you, just has to do with the way the foil works and why the bungee was so effective. In my mind I always wanted to move the pivot of the foil to the front and make it more like a fin. The bungee seemed out of place compared to the quality of the rest of the machine. Trux' diagrams let me get the visualization right. It's fun to put something new in this old RAM. Sort of like the new word I learned a few weeks ago, whinge.
Soon we'll get to see if the memory from 1971 matches the reality of '08.

[ADR]

Hi Bill,

We need to get you or make you another Aqueon, as you speak of it as you would a long lost brother. It doesn't seem right that you no longer have one. If I make one at some point I think I'll make one for you too.

If the angle of attack on the Aqueon was maintained by the bungee then I'm stumped a little by the Lunocet. From the pic and movement in the video I can't work out if it is a simple forward pivot with a stop point or if there is some internal spring system on the shaft of the pivot.

[trux]

Originally Posted by ADR

If the angle of attack on the Aqueon was maintained by the bungee then I'm stumped a little by the Lunocet. From the pic and movement in the video I can't work out if it is a simple forward pivot with a stop point of if there is some internal spring system on the shaft of the pivot.

I am curious about it too, but assuming from the photos available, I do not think there is any such mechanism. To me it looks more like you control the blades by the sideway inclination of your feet. I may be wrong though.

[Bill]

The way it works IMHO. It uses the flat plate in the centre (with lots of leverage) to change the angle of the foils. Like a boost tab on an an aileron or elevator.

[Bill]

By the way Andy, I think your holes are a good idea to eliminate the part of the fin that produces thrust in the opposite direction. Not needed on the 'up' stroke because the ankles can easily adjust, so just have a one-way panel that opens on the down stroke. Even better have it partially open so that it acts like a slot on a wing or a jib on a sailboat.
Very limited improvement though, that part operates in 'dirty' water.

[HJ]

Originally Posted by trux

Nobody told the angle is 90 degrees. The angle is more like 45 degrees, but may be different - that also depends on the speed and the profile of the hydrofoil (if profiled hydrofoil is used), and some other factors.

Sorry, trux. I thought you said right angle (90degrees).

However, I have to repeat again, with plain feet, or with a short non-flexible blade fixed to the feet, you will simply not manage to set the blade/hydrofoil/feet into the right angle during the entire cycle (minus the dead points), while you do manage keeping good attack angle for considerable parts of the cycle with a flexible blade, or with a hydrofoil with a variable angle, like at the Aqueon.

A flat or non-flexible blade or foot will deliver thrust through the arc of movement as it approaches the 0 angle, just like your first diagram shows. FYI: I just came back from the pool. I timed a barefoot 25m with dolphin kick. I then put on a pair of very short, very stiff fins (the kind used for swimming training). I reduced my time by 15%. Then I put my foot against the fin and I observed that the fin increased my surface area by about 15%! (just guessing)

So, of course, you can propulse even with the non-flexible fin, but you need to exercise full force in the moment the blade is in the best attack angle, and then relax for the rest of the cycle.

One has thrust force throughout the arc moving toward 0 angle, but it diminishes as your approach 0 angle, as you show. I'm not sure about the resting part. Maybe mono kickers can do this because the kick tempo is slower than for swimmers. When I dolphin kick with fins I believe I am doing constant motion, although I am not positive about that.

Unlike that, at flexible fins, or the Aqueon, you transform the kicking energy into the forward motion for much longer parts of the cycle.

Yes, I think you're right about this.

To make it more clear I designed the following (very) simplified diagrams. They both represent only one half of the cycle (the downward kick). The real-life situation is little bit more complex (beside others, to certain limited degree, you improve the angle of attack with your feet and knee bends), but for understanding the principle the diagram is more comprehensible in this way.

I like it.

The first one if for a fix blade/hydrofoil - the blade is in the right attack angle only in one part of the top half of the kick. Only there it transforms the kick energy into some thrust, but the transformation is the lower, the further down you kick. At the bottom you actually brake. I designed only the more interesting vertical and horizontal resulting forces, but correctly the force has both vertical and horizontal elements at each point. There could be a second diagram for the upward kick that would look practically identical, just the smaller green part (thrusts) would be at the bottom.

Yes. This makes sense. The only thing I would add is that the upward kick is much weaker (and forces generated) because of the anatomy of the human body.

Good job!

[ADR]

Originally Posted by Bill

The way it works IMHO. It uses the flat plate in the centre (with lots of leverage) to change the angle of the foils. Like a boost tab on an an aileron or elevator.

I think you are right as the fin also does the impossible and flexes in a concave fashion when the load comes on. This would support what you are saying.

What did you think of my theory for v-bend in the other monofin thread?

[trux]

Originally Posted by ADR

What did you think of my theory for v-bend in the other monofin thread?

Not sure if you ask me or Bill, and not sure if you mean this thread: http://forums.deeperblue.net/monofin...in-review.html, but if so, then unlike at Lunocet, that monofin bends into the V in the wrong way, oppositely (unless I interpret the Glide photo incorrectly).

Lunocet creates a concave V, the Glide monofin a convex V. While the active concave profile of Lunocet prevents the water from escaping sideways, and pushing it backward instead (using so more energy for the propulsion), the passive convex profile of Glide does the exact opposite and pushes even more water sideways than a standard monofin (which is already quite bad from this point of view too) and wastes a lot of energy unnecessarily.

There is another passive way creating a concave V profile at a blade that I would love to see at a monofin. It is used at many modern scuba bi-fins (for example Mares Volo) - they have reinforced sides and a soft central part (or even a slit at split fins). It then creates the concave V passively while you are kicking and helping the propulsion considerably. It just needs to be put into the right dimensions and stiffness for a monofin, but I am persuaded it would work at the monofin as well as at bi-fins. I already created a thread about it - the thread http://forums.deeperblue.net/monofin...it+fin+monofin from 2005 was actually my very first post at DB

[Mullins]

Yes, the V-bend Andy is referring to is definitely a bad thing. The question is what causes it. His theory is that it is caused by the shape of the blade - specifically, the cut-away 'shoulder' on the newer hyper style designs.

[trux]

Originally Posted by Mullins

Trux - the V-bend Andy is referring to is definitely a bad thing...

Yes, I agree, that's exactly what I wrote. I hope it did not sound oppositely Is there any other thread about it, or do you both refer to the one I linked in my previous post?

[ADR]

Sorry for the confusion, its the last bunch of posts in this thread and I posted a bunch of fin pics with an explanation

http://forums.deeperblue.net/monofin...s-hyper-3.html

and yes i think the centre split idea might be worth trying and that fin with the holes in it in the thread above is a good candidate

[Bill]

I think it might be easier to run two stringers of uni-directional glass at about 20% each side of centre from the leading edge to 60-70% back. Fences on the wing tips (like C4 rails) work great on airplanes. No reason they wouldn't reduce drag on a fin, all else being equal. Wish I could get excited about building a mono Andy, but every time I kick one my TI hip says "don't ever do that again".

[ADR]

lets build you a new hip then