SpudFiles

Thanks to people that actualy understand that this IS a hybrid. I guess ill give it a shot. I was thinking about using hot glue to cast the piston but shoul I buy some epoxy instead?

psycix wrote:This is a very good idea.
Too bad some people here dont understand it.
It IS a hybrid.

Yes it is a hybrid, though it has none of the advantages of a standard hybrid.

psycix wrote:The point is that you inject fuel into a large chamber, then make that a smaller chamber, leaving you with a pressurized mix into a small chamber.

If you would have a small chamber, and then pressurizing/injecting fuel from the outside, like normal hybrids do, you would have THE SAME result.
Small chamber -- pressurized mix.

This will defenitely increase performance A LOT.
Like Ragnarok said: A pneumatic with a "small chamber -- high pressure" design is more powerful then a "large chamber -- low pressure" one.

I don't see this technique being significantly more powerfull than if the gun was simply fired without the compression step. Yes, the smaller chamber at 2x will outperform the smaller chamber at 1x but it won't significantly outperform the larger (uncompressed) chamber at 1x.

Same amount of fuel and oxygen in the gun before and after it is compressed. Total energy in the chamber is changed only a small amount by the compression.

If you compressed the mix 2x then the peak pressure in the chamber during combustion might go from 60PSIG to 75PSIG. Perhaps a significant change but probably not worth the effort.

In a typical hybrid you are using more fuel per unit volume of the chamber. A 2x gun has twice the potential energy as when it is fired at 1x. A two-fold increase in energy in the chamber is significant.

For the proposed design the amount of energy in the chamber before and after compression is increased by a fairly small amount. A 2x compression does not double the energy of the chamber relative to the uncompressed chamber at 1x.

Plus, you still need a burst disk. Might as well skip the compression step completely and operate the gun as a 1x burst disk gun. It'll perform about the same and be much simpler to build.

Based on that argument, why bother with ANY hybrids at all? Let's just make it simpler and just build double size combustions!

It clearly doesn't work that way. I personally think this is a nice way of going about the concept - it's sort of a version of DR's Gen II hybrid with a piston instead of water.

Yup that's a hybrid by any other name. For people who aren't seeing it - think chamber to barrel ratios.

A normal combustion cannon will be about 0.8:1
A hybrid will have a smaller chamber in proportion to the barrel volume, maybe 0.2:1

Now this starts as a normal combustion, and then the piston reduces the chamber size down to that of a hybrid. The end result is that you end up with a pressurised fuel/air mix inside a chamber with a c/b ratio of 0.2:1 or so.

The great thing about this is that the chamber pressure is infinitely variable without having to do any complicated calculations for your fuel air mix. It's like using pre-mixed fuel/air and then pressurising it.

One of these would be excellent as a base for your pressurisng system.



I've happily pumped a silicon sealant tube in one down to about 2/3 before realising that I'd not cut the nozzle off, so I'm sure it'd pressurise /fuel/air very happily. Possibly at higher pressures you'd want to lock the plunger in but I reckon on lower pressures you'd be fine as it is.

FeLeX wrote:Thanks to people that actualy understand that this IS a hybrid. I guess ill give it a shot. I was thinking about using hot glue to cast the piston but shoul I buy some epoxy instead?

Go for it.

But you should compare the performance of the gun with and without the compression step. I think you'll find the compression does very little. It certainly won't be any where near twice the energy of the uncompressed chamber.

Jimmy of coursee it will, other wise we might as well all go round building combustions's not hybrids.

Look at it this way, in a combustion we have our fuel air mix in a given volume at 1ATM. With this we now halve that volume, which gives us a chamber pressure prior to firing of 2ATM. Halve it again and we get a 4ATM pre-ignition chamber pressure, the equivalent of a 4x mix ina hybrid.

As long as the barrel is optimsed for this, it'll be an excellent easy build hybrid.

Ragnarok wrote:Based on that argument, why bother with ANY hybrids at all? Let's just make it simpler and just build double size combustions!

It clearly doesn't work that way. I personally think this is a nice way of going about the concept - it's sort of a version of DR's Gen II hybrid with a piston instead of water.

Can you show any data that indicates that a 2x hybrid outperforms a 1x gun that has a chamber twice as big? Both guns operating with the same burst disk.

Hybrids accomplish two things;

1. More energy in a small chamber. For the size, the hybrid will outperform a similar sized 1x gun. Since hybrid makers are typically going for kick-ass performance it makes a big difference if they can cut the chamber volume in half or in third, just in terms of making the gun a reasonable size.

2. They are burst disk guns which allow the chamber pressure to rise more before the projectile starts to move. This reduces the chances of the projectile leaving the barrel before the fuel is completely burned.

In the proposed design the energy in the chamber changes very little when it is compressed to 2x. 15 PSI additional pressure will boost performance only minimally since the burst disk is mostly what controls the peak pressure in the chamber. The total energy in the chamber is increased only slightly by the compression.

Can you show any data that indicates that a 2x hybrid outperforms a 1x gun that has a chamber twice as big? Both guns operating with the same burst disk.

I would have though the fact that the hybrid is already pressurised gave it an advantage over a conventiona lcombustion.

jimmy101 wrote: Can you show any data that indicates that a 2x hybrid outperforms a 1x gun that has a chamber twice as big? Both guns operating with the same burst disk.

Hybrids accomplish two things;

1. More energy in a small chamber. For the size, the hybrid will outperform a similar sized 1x gun. Since hybrid makers are typically going for kick-ass performance it makes a big difference if they can cut the chamber volume in half or in third, just in terms of making the gun a reasonable size.

2. They are burst disk guns which allow the chamber pressure to rise more before the projectile starts to move. This reduces the chances of the projectile leaving the barrel before the fuel is completely burned.

In the proposed design the energy in the chamber changes very little when it is compressed to 2x. 15 PSI additional pressure will boost performance only minimally since the burst disk is mostly what controls the peak pressure in the chamber. The total energy in the chamber is increased only slightly by the compression.

But that's the point here isn't it? That we're getting a lot of power out of a little gun, and we're seeing a very quick and easy way to meter fuel and pressurise said gun, no fiddling with compressors, no complicated and precise pressure/volume calculations, instantly variable chamber pressures.

Go for it, it looks like a simple thing to make, and could be great fun, and using a cartdidge gun even gives you something that looks quite cool.

The burst disc has little control over the peak pressure. The pressure can still rise after the disc has been blown.

A 2x hybrid will produce roughly twice the pressure of a 1x combustion, regardless of burst disc. That double pressure is a very significant change.

If I were to take one of my pneumatics and halve the chamber size, but double the chamber pressure, performance would rise significantly because the integral of the pressure over the whole barrel will be higher.

I am 100% certain that in a competition between a 1x combustion with a 2 litre chamber and 2x hybrid with a 1 litre chamber, the hybrid would show very significant performance increases.

^ spudblaster15's research has proved that the burst disk does have an effect over peak pressure, from my tests, 5x mix with 2layers of coke can burst disk is alot more powerfull than 1layer...

Jimmy really I dont want your dirty claws on my post. You argue just for the sake of arguement. If you STILL dont unferstand how it works look up ICE. This gun is supposed to be a mini so if I make a chamber twice as big just to get the same performance (which it highly doubt I will) that would defeat the purpose of a mini. And since when coming up with something new is such a bad thing? Really Id like it if you wouldnt reply here anymore. You replied to my other posts and all it led to was a meaningless argument.

SPG thanks for a REALLY good idea. That way I could also compress it more than just by pushing it.

I was messing arround yesterday and I JB welded the top of a coke bottle (the part that has threads on it) to a 3/4 pipe. Not to sure if that will be a good burst disk holder. o.O
I will cast a hot glue piston later on tonight. Pictures coming soon =)
My plan is to first test if the dang thing will even be as easy to fire as I expect it to and if yes then I will work on the design more and creat a nicer and cleaner version.

Edit: By the way Jimmy what ARE the advantages of standard hybrid?

Here's a thought: What if the piston was forced through combustion? Essentially, the launcher has "two chambers" and a piston separates the two. When the rear chamber is ignited, it forces the piston forward. The chamber closest to the barrel (primary chamber) is ignited. The piston will compress the burning gases in the primary chamber and...well, the rest can be figured out.

FeLeX thanks, hope it helps, they're cheap as chips those guns, so should be easier to make up.

Compression by pre-combustion? Well tis a bit complicated isn't it? and it's need a twin chamber system, which would incease size of the gun, which isn't the aim of this simple mini-self-pressurising-hybrid.

Hubb good idea but the hard part would be timing the ignition, and would use more fuel, if he has a lathe he could make the chamber fit on a caulking gun, the psiton attached to the "metal circle that puches the caulking". And just fuel it, pump the caulking gun till the desired pressure, and ignite.