75SD 3/4" hybrid with integral suppressor

[ilovefire]

not sure if that is the best thing to post right after telling someone that a hybrid is nothing to really worry about

[Labtecpower]

you should be happy it even hit the back stop wouldn't be the first hole in your wall.

Talking about glow plugs... I was thinking about this one.
Do you think it will get hot enough?

That syringe feuling looks reasonally simple. Good thing I have a infinite source of syringes ranging from 1 to 50 CC.

When I build something like this, I will machine a steel chamber I think.
I dont like the idea of pressurized plastics right next to my face
(if I make a gun, it will look like a musket)

[jackssmirkingrevenge]

Talking about glow plugs... I was thinking about this one.
Do you think it will get hot enough?

I've tried to use nichrome wire several times without success, as Fnord had pointed out here what works for an atmospheric mix will not necessarily work for a pressurised mix. On the other hand, daccel successfully used hot wire ignition for his cartridge hybrid, but using very fine steel wool which likely needs to be replaced after every shot.

As to my latest fail, I found the projectile and the level of deformation after hitting a 1/2" thick sheet of chipboard backed up by a granite slab is substantial especially compared to a relatively unused CO₂ capsule.

Closer examination of the breech also illustrates the construction defects which allowed it to happen. First of all, the cross section of the barrel is discoloured in a similar manner to the inside, meaning it was exposed to the hot gasses on firing, giving them a surface to push on and ultimately crack the epoxy. Secondly, the 40mm o/d tube which I used to sleeve the barrel was not roughened on the inside, therefore not contributing any significant strength to the join and when the fail occured, allowed the barrel to pop clean out while the sleeve itself remained attached to the threaded fitting.

[Labtecpower]

I practiced fueling on a small pill bottle (70 ml)
the amount of gas needed was 2.5 ml. Luckily I had exactly the right syringe lying around

I got it to fire a few times, with quite an impressive "pop". after that, my piëzo broke down stupid pieces of plastic...

Maybe I will buy an ignition coil or something like that. I think it's more reliable.

[Fnord]

was not roughened on the inside

tsk tsk...

Hey JSR, why don't you get out that clear acrylic tube you used for high-speed combustion tesing and try running some nichrome wire in it for an ignitor?

It would be a good way to test the feasibility of glow plugs and a good way to actually judge the temperature needed to ignite a propane/air mix. IIRC it's quite high at somewhere over 1200 F, so you'll probably need to up the voltage till it gets nice and orange.

[Labtecpower]

I freaked on my piëzo, so I tried ignition with a piece of steel wool.
It didn't work however.
I used exactly the same fuel - air mixture, so that isn't the problem.
Isn't it hot enough?

So far, I don't understand hybrids enough to make one

[jackssmirkingrevenge]

was not roughened on the inside

tsk tsk...

I doubt that would have helped anyway, the fundamental defect was allowing an exposed area where gas could attempt to force the barrel and threaded fitting apart.

Hey JSR, why don't you get out that clear acrylic tube you used for high-speed combustion testing and try running some nichrome wire in it for an ignitor?

Filmed a couple of shots, to be posted in the clear launcher thread as soon as youtube decides to process my video 0_o

I freaked on my piëzo, so I tried ignition with a piece of steel wool.
It didn't work however.
I used exactly the same fuel - air mixture, so that isn't the problem.
Isn't it hot enough?

Did the steel wool glow red/white hot? What power supply were you using?

[ramses]

I freaked on my piëzo, so I tried ignition with a piece of steel wool.
It didn't work however.
I used exactly the same fuel - air mixture, so that isn't the problem.
Isn't it hot enough?

So far, I don't understand hybrids enough to make one

Burning steel consumes oxygen. Perhaps the steel wool consumed too much oxygen and left you with a mix that was too rich to fire. Then again, the fuel should have ignited from the heat of burning steel.

[Labtecpower]

The steel wool jjust burned away.Could be that it uses too much oxygen.

[spoeft]

how exactly do u get the fuel from the syringe in your chamber , through the schrader valve with a connector of some sort ? or just through the union when its open ? cause with a 12 mix , the pressure from fueling is gonna rise in your chamber ?
or am i wrong about that ? :p

lol lots op questions ^^

[jackssmirkingrevenge]

I'm using a mixture of propane and butane, so I calculated a 3.5% fuel concentration per mix number. Basically add your chamber volume to the dead volume of the pump (in the case of my Beto shock pump it's 1.75mL), multiply by 0.035 then by the mix number. Fill the syringe to the calculated volume, inject in chamber, close burst disk and pressurise.

You might also want to have a look at this thread.

[RamboNucke]

Is it really that quiet that most of the noise is from the impact? I've been dreaming of super silent spudgun for years. Do you use iron wool and water? My latest attempt is a 2l bottle-extension to the barrel with some iron wool and holes. With hdrogen/air 1l chamber it sounds like two small books slapping or dropping a beer bottle. I think I don't have a chance of silencer for large volume combustion.

[jackssmirkingrevenge]

I wouldn't say it was "super silent", but it was very kind to my ears compared to my other hybrids, which considering it's the most powerful one I've ever made is significant. The trick in this case was a long barrel and an extremely high volume suppressor. It's also a two chamber design which helps efficiency. I used some steel mesh (you can see it wrapped around the barrel in the last video on this thread) but a fairly limited amount.

Don't forget that in a hybrid, you still have a volume of compressed nitrogen that contributes to the noise, something which a combustion doesn't.

[jackssmirkingrevenge]

As I didn't have an operational 3/4" hybrid, I took the barrel from this and made a connection for my current test chamber together with a new slimmer 50mm diameter suppressor body.

Just gave it a spin, here it is at 420 frames per second:

[youtube][/youtube]

Definitely not as quiet as the "drainpipe", even though the chamber is less than half the size.

[King_TaTer]

Aww, you should have went for the head! But impressive nonetheless. Pic of the new suppressor?