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Old 12-16-2018, 07:41 AM   #46
DUCA2
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Re: Super Cavitation Tip Shafts

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Originally Posted by popgun pete View Post
For rollerguns it is necessary to look at this thread.
https://forums.deeperblue.com/thread...agrams.107171/

The side pulley rollerguns multiply the band contraction rate under load by a factor of two, but the band tension into the wishbone is halved, so the number of bands have to be doubled for the spear to be powered with the same level of force. Under this "block and tackle" drive system the band contraction rate is slowed, so doubling the speed is not the multiplier users hope for unless more bands are added to the "band battery" and that is where the world of diminishing returns rears its ugly head. The inertia and drag of the split pulley drive system is only redeemed by having a gun configuration where the rubber mountain is removed from the top deck of the gun. It is just simple physics explored in the rollergun diagrams. A well balanced standard gun in terms of band power matched to the shaft will shoot as well as any more elaborate gun, but must be matched to the job. To shoot further and more accurately one needs a longer gun for the longer sighting radius and improved angular estimation of the target as the barrel in-line sighting or convergent line aiming are more easily judged. Reproducibility of shots and killing range are important as is the "armour" or body structure of the target. No point in hitting a fish if the shot bounces off, equally frustrating is turning the fish into a kite full of beans and zooming around on the line. This is why when you hunt different species and locations you need a brace of guns, i.e. the right tool for the job. Unfortunately at times you discover that you did not bring the right gun, but that is spearfishing.

Popgun Pete... En principio gracias por traducir.

Gracias por el enlace al foro , no lo conocia prometo leer temas interesantes para mi...toda información es poca.

No quiero utilizar este foro para debatir sobre fusiles, sistemas etc etc
pienso que para debatir "SUPERCAVITACION" todo esos conceptos tienen que estar superados ya.


Yo insisto en este tipo de fusil, porque es el único ( que yo conozco ) capaz de propulsar un trozo de metal a mas velocidad
que el propio elastómero , piston , muelle etc para el tema de " SUPERCAVITACION "

Para pescar que cada cual utilice lo que mejor piense y configure su fusil como mejor sepa ....eso seria otro tema.

yo puse un estudio sobre la velocidad de contracción de elastómeros para mejor entendimiento.

yo puse un vídeo explicativo con dos distancias una azul y una roja en una misma unidad de tiempo que demuestra el doble de velocidad ( inicial )

es lo que me interesa para el tema que nos ocupa..

Por supuesto yo se que la energía potencial elástica acumulada se dividirá por dos ( x2 ) mas para mi, en tema de supercavitacion no me preocupa...
puedo poner mas numero de gomas o reducir la masa de la varilla...

Yo puedo reducir la longitud de la varilla y su masa , poner el numero de gomas necesario para obtener una muy alta velocidad...

También tengo claro que no es un sistema IDEAL ....Que si un elastómero estirado al 400% puede alcanzar 45m/s cuando lo monte no voy alcanzar 90m/s
pero puede que 55 o 60/s puede que si....

Lo importante sera la forma de la punta
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Old 12-16-2018, 02:11 PM   #47
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Re: Super Cavitation Tip Shafts

DUCA2
Translated from Spanish
Popgun Pete... In principle thank you for translating.

Thanks for the link to the forum, I knew I promise to read interesting topics for me... all information is little.

I don't want to use this forum to debate about rifles, systems etc etc.
I think to debate "SUPERCAVITACION " All those concepts have to be overcome already.

I insist on this type of rifle, because it is the only one (that I know) capable of propelling a piece of metal at more speed
That the elastomer itself, piston, dock etc for the theme of "SUPERCAVITACION " to fish that each use what best thinks and configure your rifle as best known.... that would be another topic.

I put a study on the speed of contraction of elastomers for better understanding.

I put an explanatory video with two distances a blue and a red one in the same time unit that shows the double speed (initial)

It is what interests me for the subject that concerns us..

Of course I know that the elastic potential energy accumulated will be divided by two (x2) more for me, on the subject of supercavitacion not worry me...
I can put more number of rubbers or reduce the mass of the rod...

I can reduce the length of the rod and its mass, put the number of rubbers needed to get a very high speed...

I also have clear that it is not an IDEAL system.... That if an elastomer stretched to 400% can reach 45mm/s when I mount it I will not reach 90mm/s
But maybe 55 or 60/s might if....

The important thing will be the shape of the tip
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Old 12-16-2018, 03:09 PM   #48
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Re: Super Cavitation Tip Shafts

You really need to read the rollergun diagrams thread, but the summary diagram encapsulates most of it, although like many things the summary makes more sense once you read a book or magazine article;

Many years ago, in fact decades ago, a cable gun was created which stowed the rubber band battery inside the gun to hide the energy storage unit. The cable system was unreliable for jams and cables jumping off rollers, but lacked the modern materials we have today, particularly the cables such as dyneema, kevlar and spectra. Rubber quality has also improved so the energy storage can be greater.

Band contraction rate is not a constant and spear mass and drive system friction slow the rate down. Bands bending around rollers lose energy that was supplied by you during gun cocking, but has to be supplied from the gun's energy store when shooting, so more losses are involved. If the cables do the bending at rollers then less energy is consumed, particularly important when there are many changes of direction. The band battery needs stretch room on the gun body and one way to maximise that is to use as much gun length as possible, including the cocking stock.

Another way to gain stretch length accommodation is to use a “wiggler” storage system for the band batteries, but this is a very inefficient storage system as energy is lost with bands snaking around many rollers.

Finally the whole point of the exercise it to launch a fast moving and unavoidable projectile that will harpoon and kill or disable the fish. If we really want to kill then we use explosive or shock inducing heads which carry another energy source into the body of the target. Taken to extremes the sport of spearfishing then disappears and is replaced by something else, but I do not know what to call it.
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Old 12-16-2018, 10:34 PM   #49
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Re: Super Cavitation Tip Shafts

As an engineer, I see this idea as very difficult to achieve. Linear control is not that hard, e.g. a rocket propelled bullet thru the water that has nearly constant velocity. Trying to control a non-linear open control system(velocity varying) is extremely difficult. One can only hope for the desired effect over a short somewhat linear velocity range of the shaft's travel. Good luck. Standing by...still enjoying the conversation.
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Last edited by Marcus; 12-16-2018 at 11:32 PM.
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Old 12-16-2018, 11:48 PM   #50
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Re: Super Cavitation Tip Shafts

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As an engineer, I see this idea as very difficult to achieve. Linear control is not that hard, e.g. a rocket propelled bullet thru the water that has nearly constant velocity. Trying to control a non-linear open control system(velocity varying) is extremely difficult in the absence of feedback. One can only hope for the desired effect over a short linear velocity of the shaft. Good luck. Standing by...still enjoying the conversation.
If it was easy then it would be done already, however remember at most we are talking 30 feet maximum flight distance and usually only half that. The curiosity of fish brings about their undoing as well as their desire to eat, if we were shooting ducks on the wing then it would be an entirely different story. Super powerful guns such as the Alcedo “Sprint 62” can shoot 30 feet no problems, but are heavy to swim with and slow to load. Today even a second hand “Sprint 62” will cost $2.5K, thus we are looking for an edge in maybe the first 18 feet for a moderately powerful bandgun. A spear shaft being long is a stable projectile provided it leaves the gun without bending or wobbling. The Alcedo "Sprint 62" being dismantled is my own gun, so I know what they weigh and how bulky they are.

Used Alcedo "Sprint 62" for sale here
https://www.ebay.ie/itm/233045587604...m=233045587604
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Old Yesterday, 01:40 PM   #51
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Re: Super Cavitation Tip Shafts

If it's not too long, has no tail, has no sharkfins, and can spin, then it's not soooo hard.
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Old Yesterday, 02:35 PM   #52
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Re: Super Cavitation Tip Shafts

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If it's not too long, has no tail, has no sharkfins, and can spin, then it's not soooo hard.
Well the hardest part is probably getting someone to try it, but in my correspondence with Russian speargun makers everyone has had the same idea, but are bogged down in theory and naysayers. The tips needs square cut grooves as I have illustrated and near the end of the tip. A reverse cone hollow tip would provide a vortex generator, but we need a point to shear through the meat, unlike a bullet where a “dum dum” round can kill as velocity there is orders of magnitude greater than with a spear. Bullets tumble in fluid and the cavitation bubble is to stabilize their flight, with spears we don't have to worry about that.

As I see it the spear can be its usual length and the tip needs to be slightly larger in diameter than the shaft body as I have also shown in the drawings. The speed cones used to place floppers in the flow shadow of those cones would also be used or the tip head could provide that function. It will be important that the tip head screw on straight with respect to the shaft, but that is the case with removable tips anyway.

Russian spearfisherman DracoZur has proposed a variable reverse cone shape for discussion, it is show below in a sketch.
http://garpun.spb.ru/forum/viewtopic...er=asc&start=0

http://www.cneat.ru/bullet.htm
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Old Yesterday, 03:01 PM   #53
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Re: Super Cavitation Tip Shafts

I think one would have a better chance at creating the cavitation much like the bullet with air coming out of the tip. Use a pneumatic that charges the spear thru a port on the rear when seated. There would be an actuator that opens/closes a small ball valve for the front port upon firing/loading.
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Old Yesterday, 03:20 PM   #54
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Re: Super Cavitation Tip Shafts

Another of the US Navy's patents for this topic is a telescoping cavitator shown below. The common theme is a discontinuous edge that acts as a vortex generator, the exact opposite of curved contours that match streamline flow for laminar flow of the fluid against the surface of a projectile moving through that fluid at velocity.
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Old Yesterday, 03:28 PM   #55
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Re: Super Cavitation Tip Shafts

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I think one would have a better chance at creating the cavitation much like the bullet with air coming out of the tip. Use a pneumatic that charges the spear thru a port on the rear when seated. There would be an actuator that opens/closes a small ball valve for the front port upon firing/loading.
Actually some years ago there was a Croatian patent for a tubular spear that was charged up with carbon dioxide gas via a supply in the band gun that it was to be used in, the concept being that after being launched by the band the spear would be rocket propelled by the escaping gas at the rear end after that initial launch. Nothing more was heard of it!

We need to keep it simple, any nose mounted port will be jammed with tissue or sand, grit, etc, if we miss. Unlike military projectiles spears get used again and again, so the equipment needs to be rugged. Tips can be expendable, but I would want more than one shot out of them. If I wanted one shot tips then I would be using the .222 tips that I have used in the past.

New version with cone added to provide flow "shadow" for flopper on the shaft. Also non pencil tip version with flutes on tip or a tri or quad cut.
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Old Yesterday, 04:00 PM   #56
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Re: Super Cavitation Tip Shafts

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We need to keep it simple, any nose mounted valve will be jammed with tissue or sand, grit, etc, if we miss. Unlike military projectiles spears get used again and again, so the equipment needs to be rugged. Tips can be expendable, but I would want more than one shot out of them. If I wanted one shot tips then I would be using the .222 tips that I have used in the past.
Nay sayer.
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Old Yesterday, 05:37 PM   #57
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Re: Super Cavitation Tip Shafts

The idea here is to keep it simple, standard spear shaft with an integral flopper and a replaceable ring grooved tip which can have different case hardened points. If you smash the tip into a rock then you replace it with another tip, the benefit expected is improved flight time in the critical first section of spear travel. As shots rarely go beyond 30 feet underwater, and are often around 15 feet off the tip, then any gain would be worthwhile and you don't whittle down your integral tip shafts through repeated re-pointing on the workshop bench grinder.
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Old Yesterday, 05:46 PM   #58
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Re: Super Cavitation Tip Shafts

I note that the "CAV-X" ammo article was interested in the round being used in one of these, something for under the Christmas tree this year! MICOR Defense Leader 50 Ultra-Compact, Lightweight Bullpup Semi-Auto .50 BMG (12.7x99mm NATO) Sniper/Anti-Materiel Rifle.
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