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Measuring speed of the shaft

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
Batman-alex said:
Thank you, I so-so and presented that this dependence was calculation description...
This dependence of Exp... what level does dV undertake on dt ?
Click to expand...

U = Uo*e^(-t/(R*C))

Uo is voltage of the battery. I took 2 x 9V batteries in series to have 18 V on the capacitor.

Take for C = 220 uF, for R = 100 Ohm and make calculation in excel. You can calculate U for changing t from t = 0.004 sec to t = 0.03 sec. For dL = 0.178 m you'll get for t = 0.004 sec speed about 40 m/s and for t = 0.03 sec speed about 6 m/s.
 
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I made a calculation based on measured data. This might be a speed of shaft on 32 bar and 7 mm free shaft, for Cyrano 1100. Spanish often use their guns on 32 bar (11 mm barrel) or 24 bar (13 mm barrel) with 7 mm "free shaft"

 
Coming from гафика, possible boldly use the harpoon 8 mm. This will reduce the initial velocity of the harpoon...
Will Reduce the loss on кавитацию and loss to energy on разогрев water (the thermodynamics)...
Will Enlarge toughness of the harpoon and striking pulse...
Dalinoboynosti will too increase...
 

Vlanik, that is all true what you suggest! Some of guys use 8 mm and more for big fishes. But mostly the are using 7 mm with 13 mm barrel.

What is a difference in starting speed of the shaft in air and in water according to your calculation? Have you any example for 7 mm or 8 mm shaft?

For similar diagram as above for 7 mm shaft, for 8 mm would be necessary about 41 bar for Cyrano1100. Some 13 mm pneumatic would be better choice for 8 mm shaft. That would require about 29 bar.
 
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tromic
The Advantage is beside harpoon 8 mm. Plenty of fineness to tell...
But between you and me language barrier...
You more simply to try and destroy the existing myths...
Beside you it is enough knowledges, itself all оцениш.
 
I am a sign with this with this work...
She is created on my request...
 
I had not measured it myself but I found an article on Internet that claimed, based on some measurement that if we had two shafts of same mass one longer/thiner and the other shorter/heavier than the second would have more penetration or longer effective range. The thiner/longer would have more losses due to higher friction-drag. I believe this is true for any shaft, band gun or pneumatic gun.
 
It would be interesting to know the velocity when the shaft actually strikes the target as by then the effects of line drag and other spear drag factors will have slowed the shaft to what will be the impact velocity and hence impact energy. This is why some spear shaft speed measurement devices (e.g. Niko Brummer's frequency based measurements) used a small interval marked shooting line to pass through a pulse counting device or line shadow detector that allowed the velocity at any distance out from the gun muzzle to be calculated from the increasing time gap between line pulses being generated at the line shadow detector as the shaft and hence the marked line being dragged behind it slowed. The marked line also contributed to drag itself unless it was the only "shooting line" present. The effect of different shooting line textures and diameters could only be independently measured if different types of line could be incrementally marked and I assume that this was not really practical with lines such as monofilament, hence these different line type measurement would also require the presence of the specially marked line.

In your system you change the length of your thin triggering thread to pull the second timing switch located at or near the gun muzzle at varying distances out from the gun to progressively build up a velocity graph against flight distance travelled, is that correct? The final velocity of the shaft as it approaches the target is important as it will determine the impact energy with which the shaft will strike the target and the damage that it can inflict provided that the target has not changed position sufficient for the shaft to either miss or just knock a few scales off. Up close we may have the problem of shafts passing completely through the prey and thus possibly having less control over it, but at greater distance we need to know what damage our gun is capable of delivering and hence select the characteristics of our weapon accordingly.

Shorter guns may be constructed to be very powerful for their size, but aiming problems make hits less likely using them at greater distances, so for a given gun/spear/sighting radius length there must be a "reliable range" band and it is inside that band of distances we require the gun to launch a spear that will penetrate and hopefully disable the target. Determining the far end of that "reliable range" band is where the shaft velocity measurements would be most useful in my opinion. As to what distance the "reliable range" band would end for each gun, spear length, etc. is open to debate, but it should be related to angular aiming errors for a given sighting radius as any hits become less certain. Of course with a modicum of luck you can hit anything provided the spear is still moving, but success will occur less often and the shaft may either bounce off or just slightly tip the fish over momentarily.

Repeatability of the same measurement is important in order to know when a measured difference is real rather than being within the experimental variability for the exact same gun/spear/speartip and line set-up. This requires many shots for the necessary number of measurements, so perhaps concentrating on the far end of the "reliable range" band of distances may be more productive for different length spearguns, in addition to the muzzle velocity, as everything is in a sense "downhill" from there.
 

I actually have a fixed length thin triggering thread which I can bind on a mono line on different distances from the shaft end. On the beginning of a thread is one switch actuator and on the end is another switch actuator. Distance between them is fixed and is about 20 cm. It is similar to "marked shooting line" but instead of marks I use a switches. Instead of counting pulses between two marks to determine the time interval I generate a voltage corresponding to time interval and measure it with digital voltmeter. The first method ("marked shooting line") is more accurate but is more difficult to set up for measurement in sea.

Here is one method more:
http://apox.ru/info/teoriya/1157-izmerenie-skorosti-garpuna-pri-pomoshhi-ballisticheskogo-mayatnika
 
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This apox.ru article mentions the various parameters that need to be measured and the equations being used, but there is little here about the results or the degree of agreement between any experimental observations and theoretical calculations. Results from mathematical calculations are only as good as the assumptions used. Any influencing factor not accounted for in the calculation or which is imprecise in its measurement or estimation will affect the final result, the question will be by how much? If the effects are very minor then these factors can be ignored, but underwater ballistics for spears seems to require a lot more experimental work to resolve these issues. The real question is it worth it when most users soon find out what works from practical experience, however a scientific approach could dispel some misconceptions, if any exist, as then they could be specifically tested for in purpose designed experiments.


While physical dimensions of the spear are easy to measure e.g. diameter, weight, length; the "form factor" that determines the spear's hydrodynamic drag appears to be not so straightforward to determine. I think that I will have to read the original articles which are probably in Italian.

The effects of different types of shooting line that cause varying degrees of drag will influence the velocity of the shaft, so a line equipped shaft will be flying slower at the same distance out from the muzzle compared to a freeshaft, hence the presence of the line affects the speed and hence the drag effect on the spear itself at that travel distance from the gun. There is consequently some interaction between the operating variables.
 
I recall seeing some spear velocity versus distance graphs showing that a thicker diameter shaft will initially travel at a slower velocity than a smaller diameter shaft, but at a certain distance out from the gun the heavier shaft possessed more velocity than the lighter shaft which had slowed more rapidly due I assume to its reduced mass. Hence the velocity graphs for the two spears crossed over at that travel distance, but I have not retained any copy of it. Niko Brummer produced such a graph (unfortunately his web-site seems to no longer exist) and Sergiy Kravchenko found a similar result during his own tests. The same hydropneumatic gun could fire a restricted range of shaft diameters, so the gun's stored energy for shooting these shafts was a constant. I remember Sergiy saying that his experimental results did not agree with a calculated prediction from a formulae based method, which I suspect was the Fusili.xls spreadsheet.

I downloaded that spreadsheet some years ago after Sergiy alerted me to it and tried to unravel it, I remember some constants in formulae incorporated on subsidiary pages with many figures to a number of decimal points and was unsure of their exact derivation, so I did not pursue it. The Fusili.xls spreadsheet is on my old computer, I spent some time turning the gun page labels into English.
 

The ballistic pendulum will be affected by water opposing its movement and may not really be applicable for spears, which unlike bullets and air rifle pellets are both long and heavy projectiles. The pendulum is more likely to be rotated in the horizontal plane with an off centre hit as the spear shaft sticks a long way out from the centre of the target mass and will cause the measurement apparatus to twist. Considering the size of the guns that propel them and the energy available spears are probably the heaviest and longest projectiles used in portable weapons, so just as well that curious fish come within their range or we can close the shooting distance through stealth or treachery.
 
I made some calculations using formulas from Filippo Anglani article. I used results from my measurement data for 7 mm shaft and Cyrano 850 on 25 bar to calculate "k" and "Cb" in formula for energy. Graph for 7 mm shaft should be reliable - accurate. For 6,5 mm and 8 mm I am not sure, maybe they are good, if the formula is good. You can see that the 8 mm shaft would have longer range than 7 mm shaft. From energy I calculated the speed of the shaft.





http://imageshack.us/photo/my-images/69/formulagraf.jpg/
 
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Reactions: Don Paul
The Pneumatic handguns have more high KPD than арбалеты...
So they are capable to disperse толстые and more heavy harpoons before necessary velocities...
Herewith, quite not it is necessary to disperse the harpoons before velocities above 30 m/sec.
The Harpoons 8 mm. прочнее than harpoons 7 mms...
They less are bent when charging...
This particularly it is important under long stem, where ed fine harpoon concerns the stem and scratches him(it)...
The more heavy harpoon, стособен pull for itself more thick and strong линь...That advantageously at hunt on large fish...
The more thick harpoon has a more low amplitude of the own fluctuations at shot and more radio frequency of these fluctuations...This in turn, reduces his(its) energy losses...
 

That is all right, but 8 mm is more difficult to load than 7 mm or 6,5 mm.
No problem if you use Easy Loader: http://forums.deeperblue.com/pneumatic-spearguns/74889-air-gun-easy-loader-5.html#post854102
 
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