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I try to translate for you:

My dear friend Mario this summer has given me his volcan, with the permission to make some changes and i've done some. I can tell You that now I prefer it to the mach (another great gun invented by Orvac), catching fishes over 4 mt from the tip of the shift (limit that the mach couldn't exceed). Dear Oreste (Orvac) thanks for your great idea and thanks Mario for your gift. Among all spearguns tried this is the number one for sure, try for believing. Regard to Paky, it's sure that the gun is a vela (with various configurations) but, my opinion, there's something missing, something that he doesn't speak of, that doesn't make the shaft wind, (good Oreste you've noticed it), come on Paky tell us what it is that may be I've understood it. Bye, Efisio.

 

TNX Dan

 

There are many small things, I will make some good photos of gun that all of you can see. Maybe someone will make it more powerfull than me and my friends... and evolution will continue...

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My Volcan with 3 pairs of 16 mm rubber bands (elongating rate 3.6) with a 8mm spear (130 cm long) shot the spear at the average speed of 25.1 m/s, 5 meters away from the target (no upper rubber band). Recoil is reduced and when loading the gun I still had 10 cm left to load it to its maximum capacity (it wasn't fully loaded). I have never run any tests to the gun's maximum loading capacity because I don't have the right recording equipment and because the speed I'm getting now is more than enough for my needs.

 

Oreste

That is superb for 3 rubbers 16 , is it hard to load the gun with you system. For first 10-15cm you are loading full power of bands, without paranco?

 

Tnx

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TNX Dan

 

There are many small things, I will make some good photos of gun that all of you can see. Maybe someone will make it more powerfull than me and my friends... and evolution will continue...

 

 

I agree !!! :thumbup:

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TNX Dan

 

There are many small things, I will make some good photos of gun that all of you can see. Maybe someone will make it more powerfull than me and my friends... and evolution will continue...

 

 

I agree !!! :thumbup:

 

Stefano, what do you think about this: When the gun is loaded with 2x17,5+16 on paranco and 16mm up, dyneema from paranco is hooked on shark fin in middle of spear not on end i have speed of 27ms on 4m... what is strange because rubbers are on much lower % elongation( maybe 300 %) and shaft speed different is only 3ms ?

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TNX Dan

 

There are many small things, I will make some good photos of gun that all of you can see. Maybe someone will make it more powerfull than me and my friends... and evolution will continue...

 

 

I agree !!! :thumbup:

 

Stefano, what do you think about this: When the gun is loaded with 2x17,5+16 on paranco and 16mm up, dyneema from paranco is hooked on shark fin in middle of spear not on end i have speed of 27ms on 4m... what is strange because rubbers are on much lower % elongation( maybe 300 %) and shaft speed different is only 3ms ?

 

 

I think you're focusing on the concept of speed rather than kinetic energy of the shaft.
I did a quick simulation of your speargun.
In order to have an average speed of 30.1 m / sec on 4 m and 26.8 m/sec on 5.5 m with the shaft 8x130, you must have an initial kinetic energy of about 360 joules.
To get a speed of 27 m / sec on 4 m with the same shaft, you need about 300 Joules. So 60 Joules of difference is equivalent to only 3 m/sec.
60 joules of difference between 360 and 300 joules are about 20%.
Rather than thinking in terms of speed you need to think in terms of kinetic energy in order to have a more intuitive parameter.
I hope to be able to explain the concept with .my bad english.
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TNX Dan

 

There are many small things, I will make some good photos of gun that all of you can see. Maybe someone will make it more powerfull than me and my friends... and evolution will continue...

 

 

I agree !!! :thumbup:

 

Stefano, what do you think about this: When the gun is loaded with 2x17,5+16 on paranco and 16mm up, dyneema from paranco is hooked on shark fin in middle of spear not on end i have speed of 27ms on 4m... what is strange because rubbers are on much lower % elongation( maybe 300 %) and shaft speed different is only 3ms ?

 

 

I think you're focusing on the concept of speed rather than kinetic energy of the shaft.
I did a quick simulation of your speargun.
In order to have an average speed of 30.1 m / sec on 4 m and 26.8 m/sec on 5.5 m with the shaft 8x130, you must have an initial kinetic energy of about 360 joules.
To get a speed of 27 m / sec on 4 m with the same shaft, you need about 300 Joules. So 60 Joules of difference is equivalent to only 3 m/sec.
60 joules of difference between 360 and 300 joules are about 20%.
Rather than thinking in terms of speed you need to think in terms of kinetic energy in order to have a more intuitive parameter.
I hope to be able to explain the concept with .my bad english.

 

great explained , tnx... i would like to try what will happend if i would hooked dyneema on shark fin in middle of spear and make pre-tension on ~ 50%

I think that shaft is bending to much on start of shoot when all power is concentrated to the last shark fin...

I would need some good high speed camera to see what is happening on begining of shoot

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Volevo solo fare un ringraziamento pubblico a google translate che aiuta tutti gli ignoranti come me e naturalmente a tutti quelli che continuano a fare ricerca su questi sistemi di arbalete e che riescono a tenere tutti incollati al forum!!

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I think that shaft is bending to much on start of shoot when all power is concentrated to the last shark fin...

You are right. Thus the closer to the center of mass you will apply the force, the smaller will be the bending of the shaft.

 

I have a question for Stefano: how can you get the initial kinetic energy from average speed? Come fai a trovare l'energia cinetica iniziale dalle velocità medie? Devi fare una stima approssimata della balistica interna.

 

M

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I think that shaft is bending to much on start of shoot when all power is concentrated to the last shark fin...

You are right. Thus the closer to the center of mass you will apply the force, the smaller will be the bending of the shaft.

 

I have a question for Stefano: how can you get the initial kinetic energy from average speed? Come fai a trovare l'energia cinetica iniziale dalle velocità medie? Devi fare una stima approssimata della balistica interna.

 

M

 

yes, sounds right but... if the pulling way is shorter will the kinetic energy be smaller ?

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It's the natural consequence at the end of the internal ballistics.

 

The bet would be to achieve a more precise shot and a reduced energy loss during the external ballistcs as a consequence of a reduced spining. Will it be enough to compensate the intial loss and take an advantage? I never did such a measurement, but I won't bet! I am still hooking at the last fins.

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[.I have a question for Stefano: how can you get the initial kinetic energy from average speed? Come fai a trovare l'energia cinetica iniziale dalle velocità medie? Devi fare una stima approssimata della balistica interna.M

Logicamente partendo dalla velocità media si può solo dedurre in modo teorico la Vmax iniziale e quindi l'energia cinetica iniziale. Sappiamo bene che per stimare con precisione l'energia cinetica iniziale bisogna effettuare misurazioni dirette della balistica interna, ma nel corso degli anni ho accumulato una serie di dati che, almeno spero,mi consentono di effettuare delle buone simulazioni per aste da 250 gr a 500 gr. Il tutto sempre partendo dai dati sperimentali sulla velocità media. In altri termini, rispondendo alla tua domanda, il metodo che uso é semplicemente quello di ricavare con un mio simulatore la curva teorica spazio/tempo (E da essa energia cinetica e velocità puntuali) di una specifica asta in modo tale da rispettare i dati di velocità media misurati direttamente col metodo della traccia audio e confrontando il tutto con altri dati accumulati nel corso degli anni (stime dei coefficienti balistici per una data asta). Logicamente se si hanno più misurazioni su distanze diverse il "reverse engineering" risulta molto più preciso ed attendibile. Con aste leggere (250-300 gr) ho molti più dati e pertanto ritengo di avere raggiunto un buon livello di precisione. Nel caso del fucile di pakystunt (Peso asta 500gr , solo 2+1 misurazioni considerate) ho precisato che si tratta di una "rapida" simulazione finalizzata non tanto ad una stima precisa dell'energia cinetica iniziale, ma a chiarire come "solo" 3 m/sec di velocità media possono in effetti corrispondere a circa il 20% dell'energia cinetica iniziale .

PS: A proposito,a breve spero di mettere sul forum un test , condotto con asta leggera e misurazioni in vasca, che potrà illustrare e validare meglio la metodica.

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Chiaro. Interessante. Con tutti i limiti del caso... che hai già evidenziato.

 

Off-topic. Ho fatto una analisi dei tuoi dati sulle pulegge che servirà a farti comprendere i miei dubbi in merito (magari ingiustificati), ma che spero ti risulterà utile come approccio metodologico ai dati. Alle prime piogge ;).

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Today I made some test with pre-load ..load 2x17,5 from paranco on first shark fin in the midlle of spear and classic rubber 16 up avarage speed is 26ms on 4 meters... here i have shortened dyneema and pre load was about 50% because I wanted that rubbers be on 100%

 

than I put preload to 20% and hooked dyneema to last shark fin and classic rubber up to last shark fin to and speed was 27ms at 4 meters

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