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Hybrid RPG Launcher

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Hybrid RPG Launcher

Unread postAuthor: Hotwired » Mon Mar 05, 2007 11:15 am

I decided to knock up a demonstration diagram of a less than conventional hybrid design.

Its RPG shaped because it looks better than a square ended tube. (click to enlarge)

Image

Essentially it's a pipe sealed at one end and inside it is another pipe sealed at the opposite end.

The internal pipe is a reuseable hybrid chamber and projectile. The forward end is sealed and the rear end is semi-sealed with a burst disk. It is charged before use with valves in the nose under the "rpg" tip.

To fire it there are two metal bands around the inner tube, these make contact with two low voltage power supply sprung contacts in the outer tube walls. When the contacts are made, a circuit is made and a bulb lights up to confirm electrical contact.

Actual firing is made by pressing two switches. The first disconnects the low voltage power supply and the bulb. It also connects up a high voltage circuit to the metal bands.

The second switch switches on the high voltage circuit which electrifies the metal bands and two metal electrodes which go from the bands into the chamber and arc to ignite the mix.

The burst disk at the rear of the inner pipe ruptures and with all the trapped gas behind it, the inner tube is blasted out.


Bonuses of this design are:

Quickfire ammo. You just slide a charged shell into the launcher and pull the trigger.

A really impressive looking design that betrays nothing of how it works externally if constructed properly.

A VERY big projectile that needs less stabilising from a barrel because it is in fact quite like a rocket - all the gas is being released from inside it even after exiting the launch tube.

It won't really be for destructive messing about because each projectile will be rather more expensive than usual. They are however reuseable after resealing with a new burst disk and recharging with gas and air.

I might or might not make it but I felt like sharing it anyway.
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Last edited by Hotwired on Mon Mar 05, 2007 11:27 am, edited 1 time in total.
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Unread postAuthor: th3p0p0 » Mon Mar 05, 2007 11:25 am

sounds rely nice but what is it made out of and what mix will you be using this at :lol: thats if you make it rite. any way looks perty sweet on paper.
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Unread postAuthor: Hotwired » Mon Mar 05, 2007 11:32 am

Its just a demo design to show how it could be done really.

If I actually went ahead with it I'd try to use a PVC construction to keep down weight and for ease of construction. The mix could be anything but to be handheld its likely to be kept down to 3x or so.

If it wasn't handheld and to a budget it would be a steel launcher and a mix that was short of liquification.
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Unread postAuthor: th3p0p0 » Mon Mar 05, 2007 11:38 am

still its ingenues. 3x isn't that a little high?
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Unread postAuthor: Hotwired » Mon Mar 05, 2007 11:52 am

I've never built a hybrid :P

3x could possibly be too much, I'd start with a 1x mix and work my way up. Probably finding new materials for the burst disk along the way.
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Unread postAuthor: WOW!! » Mon Mar 05, 2007 1:53 pm

But it is on your shoulder + its a Hybrid= not good.
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Unread postAuthor: th3p0p0 » Mon Mar 05, 2007 2:13 pm

not if he makes it rite. I mean rely if its guna blow up its not guna mater ware it is :lol: it cold be on your head or in your arms if it gos so are you :violent3:
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Unread postAuthor: boilingleadbath » Mon Mar 05, 2007 4:11 pm

...PVC?!

Hell, maybe you'd reuse the PVC for the pressure chamber of a hybrid after that type of abuse, but I sure as hell wouldn't!

...maybe thinwall steel/aluminum/copper pipe, though.
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Unread postAuthor: Hotwired » Mon Mar 05, 2007 5:07 pm

The gas ignition would be happening behind a double layer of pressure rated pvc.

The backblast could be an issue as it isn't too far off a rocket and the hot gases will be being forced out behind it as it exits the launcher. A blast shield is likely to be needed, if not, then a helmet with a solid plastic visor and appropriate clothing.

Before everyone starts screaming about it being too close, it will not at first be a hybrid. The cartridge/shell/rocket things will be filled with just a normal combustion mix and if it seems safe enough to continue with hybrid mixes then that'll happen next.

I can't see reusing pvc as an issue. There are pvc hybrid cannons and althrough the chamber isn't usually hurled through the air these projectiles will have a soft foam nose cone (as the grenade bit) and are not intended to be used for demolishing objects.
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Unread postAuthor: iknowmy3tables » Mon Mar 05, 2007 5:33 pm

wheres the barrel if theirs no decent sized barrel then the energy in is used less for launching the projectile and more for making ears bleed
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Unread postAuthor: Hotwired » Mon Mar 05, 2007 5:39 pm

I did say it was less than conventional.

It telescopes out to almost twice the launchers length before letting go and flying off, as far as a barrel goes you could say the launcher is a barrel but the projectile will keep on accelerating after its out because of all the hot gases escaping from inside it.
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Unread postAuthor: Pete Zaria » Mon Mar 05, 2007 5:47 pm

Just construct a small scale model and try it. It won't be very expensive.

Use all sch80 NSF-PW; half inch for the "rocket" with a half inch union, and whatever it will fit in for the "launch tube" (also using sch80 nsf-pw). Put an end cap on the other side of the "rocket" with a schrader in it. After filling the "rocket" with gas/air, put some sort of protective cap over this schrader to protect it on impact - this cap should be weighted to make the rocket front-heavy, I'd think...

Build a simple propane meter with a tire gun tip to fuel with, via the schrader. You could use a 12v compressor or bike pump (either must have a gauge of course) for pressurizing the "rockets" with air. I'd use a 1.5x mix at first (just enough to be considered "hybrid"). I would not personally shoulder-fire anything more than a 2x mix in PVC. Use metal if you want to go higher than that. In fact, to be safe, remote-fire it the first few times...

Your idea for an ignition system sounds fine. At my local hardware store, they have a roll of thin steel - it looks like electrical tape but it's thin sheet metal. That stuff would work well for making the "contacts".
Instead of screws or something for a spark gap inside the "rockets", I'd consider building a mini spark strip. It would be less likely to get fouled up / misaligned on impact than screws, I'd think.

Let us know how it goes.

Peace,
Pete Zaria.
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Unread postAuthor: deusXmachina » Thu Mar 15, 2007 8:49 pm

Meh....large projectiles, while logic would say have more stability, aren't so great in practice.

Here's what I would do if you want to have cartridges for a hybrid. Have a typical barrel and chamber cannon, say a 4" chamber. I'd personally use metal but at a minimum sch80, Inside of that you slide in cartridges with a "pringles can" design, i.e. encapped at one end and burst disk on the other. To fire, you would load the charged chamber (the only real slow part of the process but I suppose you could figure a way to incorporate the ammo in the cartridge) into the larger chamber, close the cleanout, and fire. Take out the spent casing, put in a new chamber.

_________________________
||| ____________________ \____________________
||| | ] 0
||| |___________________] ____________________
|||_______________________/

||| - Cleanout/endcap
| - Smaller endcap
] - Burst disk
0 - Disproportionate ammo (hey not bad for ASCII)

Perhaps you could find a way to stick the ammo on the end of the cartridge chamber.
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Unread postAuthor: spudkilla » Thu Mar 15, 2007 11:07 pm

WOW! Could this be the NEW hybrid.....hmmmmm.
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Unread postAuthor: mopherman » Tue Jun 05, 2007 5:41 pm

Do you guys think it would be easy to ake a hybrid rocket like this by using a wireless detonator and a launch pad? that would be so sweet
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