SpudFiles

Lentamentalisk wrote:If you fire harden everything but the fins, then you will get better penetration, as they don't need to pass through, and will just bend or break off.

Another solution would be to shape the dart like one of these air-dropped WWI flechettes, that way you reduce frontal areal too.

Have you fired anyof the fin stabilized projectiles yet?

sorry double post

Lentamentalisk wrote: If you fire harden everything but the fins, then you will get better penetration, as they don't need to pass through, and will just bend or break off.

You should harden the fins too in such a way that they break off brittle instead of bending and then breaking.
Every atomic dislocation is wasting your energy. A clean, brittle break costs the least energy.

I have been thinking about going with pure oxygen/propane for additional power in my normal combustion gun. What should I expect to pay for a small (perhaps the size of an HPA paintball tank) O2 tank? Can I get an HPA tank filled with pure O2? How much do fills cost?

Also, I have been thinking of using acetylene as part of an insane, remotely fired (like 100 feet, behind a barrier) 1X (normal combustion) cannon. How small do they make acetylene tanks and what should I expect to pay for one? How much do fills cost?

DYI wrote: If you plan on using oxygen instead, and want to stick with the traditional mixes numbers (which is unnecessary, and some would argue, useless when you get into varying the inert gas percentages and using a different oxidiser), add (nX * 3.09) to the propane pressure.

When you said "add nX * 3.09", if I were to make a 1X mix (14.7 PSIa) gun, would I add 3.09 or multiply 3.09 to the propane pressure?

I realize that in a 1X cannon I would not be measuring pressure in the chamber, but rather in my high pressure fuel cartridges.

Thanks again!

jackssmirkingrevenge wrote:

Lentamentalisk wrote:If you fire harden everything but the fins, then you will get better penetration, as they don't need to pass through, and will just bend or break off.

Another solution would be to shape the dart like one of these air-dropped WWI flechettes, that way you reduce frontal areal too.

This might be a completing page... http://www.ansys.com/industries/aerospace_isl.htm

can you make such a dart but with the fins in a spiral so it is rifled ?
just wodering if this will increase perpormance

sniper hero wrote:just wodering if this will increase perpormance

It increase drag fairly significantly, although you might get accuracy gains.

That said, angling the leading edge of a fin of finite thickness (i.e all of them) can induce spin - and reduce drag, in more ways than one!

sniper hero wrote:can you make such a dart but with the fins in a spiral so it is rifled ?
just wondering if this will increase performance

It will reduce penetration, as the wikipedia article on APFSDS explains:

Adding fins like the fletching of an arrow to the base gives the round stability, hence Armour-Piercing Fin-Stabilized Discarding Sabot (APFSDS). The spin from rifling decreases the effective penetration of these rounds (rifling diverts some of the linear kinetic energy to rotational kinetic energy, thus decreasing the round's velocity and impact energy) and so they are generally fired from smoothbore guns

In the same way, having the air spin the fins effectively robs the projectile of velocity at a faster rate, and hence reduces its kinetic energy.

...Thus the goal of finding a certain angle when induced kinetic energy loss is acceptable when compared with projectile performance.

When you said "add nX * 3.09", if I were to make a 1X mix (14.7 PSIa) gun, would I add 3.09 or multiply 3.09 to the propane pressure?

Well, my numbers assume that the chamber starts off full of air. If that were the case, you would simply add the stoichiometric amount of fuel, and no oxidiser. If you were to replace all the inert gases in the chamber with oxygen before fueling, simply do: 14.7/5 - that gives you 2.94, which is the pressure, in psi, of the propane you'd need to add. If pure oxygen was the oxidiser and the final chamber pressure was still atmospheric (no burst disk), you'd simply need to inject 1/6 of the chamber volume in propane (assuming that no propane escapes the chamber, that it displaces the ambient oxygen in stead).

Also, I kind of cocked up the previous numbers - it should actually say 0.62 psi/X, I was dividing the oxygen amount by six when it should have been five (there's five times as much oxygen as propane, thus a stoichiometric mix, starting with 100 parts air would be: 4.2 parts propane, 21 parts oxygen, 79 parts nitrogen, which actually equates to 0.62 psi/X, NOT 0.515).

Sorry for any problems that may have caused

Somehow i have not stumbled upon this before.....

JESUS CHRIST. i watched your videos. 995 m/s

and those darts are gorgeous.

My mind has Been blown more than the first time I heard Eruption......... that takes skill.

DYI wrote:

When you said "add nX * 3.09", if I were to make a 1X mix (14.7 PSIa) gun, would I add 3.09 or multiply 3.09 to the propane pressure?

Well, my numbers assume that the chamber starts off full of air. If that were the case, you would simply add the stoichiometric amount of fuel, and no oxidiser. If you were to replace all the inert gases in the chamber with oxygen before fueling, simply do: 14.7/5 - that gives you 2.94, which is the pressure, in psi, of the propane you'd need to add. If pure oxygen was the oxidiser and the final chamber pressure was still atmospheric (no burst disk), you'd simply need to inject 1/6 of the chamber volume in propane (assuming that no propane escapes the chamber, that it displaces the ambient oxygen in stead).

Also, I kind of cocked up the previous numbers - it should actually say 0.62 psi/X, I was dividing the oxygen amount by six when it should have been five (there's five times as much oxygen as propane, thus a stoichiometric mix, starting with 100 parts air would be: 4.2 parts propane, 21 parts oxygen, 79 parts nitrogen, which actually equates to 0.62 psi/X, NOT 0.515).

Sorry for any problems that may have caused

Ok, thanks for that.

I will be fuelling "charges" using a fuel meter. The charges are metal or PVC containers with only one opening: a schrader valve.

Each time I fuel a charge I will first connect a charge to a fuel meter of a tiny volume (just enough to put a pressure meter between a ball valve (which would be used to connect out to regulated propane first and then regulated HPA) and a female schrader valve). I will develop a means of attaching the charge firmly to the female schrader as I fuel it.

Each time I fuel my combustion tank I will release the contents of a charge into it via a female schrader (I assume these can be bought)

To fill my tank I will need the charge to contain perhaps 2 times the amount of stoichiometricly mixed molecules needed to fill the tank.

If my tank was 450 cubic inches and my canisters were 75 cubic inches (each) and it started full of a 1X stoichiometric mix of propane and air (I assume I will eventually get there by using these things over and over), I would first add roughly:

450*2 - 75 = 825 cubic inches worth of stoichiometric propane/air at a 1X mix to my charge. This would give my charge a 12x mix worth of propane and oxygen. (let us assume that this is safe, for argument).

To get this 12X mix, I would first add 12*0.62 = 7.44 PSI or 22.14 PSIa of propane to the charge (which was resting at 14.7 PSIa). I could do this by watching the pressure valve on the fuel meter.

I would then add ??? PSI of air.
Edit: I meant "??? PSI of air", NOT oxygen.

Clearly the most elegant and effective design I have ever seen. This cannon sets the standard that all future hybrids will be judged by for the forseeable future.

The Khan wrote:Clearly the most elegant and effective design I have ever seen. This cannon sets the standard that all future hybrids will be judged by for the forseeable future.

i do not share the same view, not everyone has lardas tools and machines to use you know..