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50KJ and up...

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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Unread postAuthor: mobile chernobyl » Fri Nov 11, 2011 1:06 am

An automotive gas strut would be suitable for a similar sized pneubmatic gun (Hear that gunfreak - I made fun of myself!) - but has no place trying to dissipate recoil force from a 100KJ gun unfortunately.

Then there is also the issue of designing a linear sliding system that will work and not bind up, while still serving the purpose of holding the chamber and barrel.

Although a recoil system would be awesome, that will dramatically inflate the cost to make this...

A muzzle brake is probably a great idea for this gun finally lol. That I will definitely look into down the road.
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Unread postAuthor: myinisjap » Fri Nov 11, 2011 2:40 am

Do you have a guesstimation of how much recoil the gun will have?
If you expect it to be quite high why not use the actual shocks from a car?
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Unread postAuthor: Fnord » Mon Nov 14, 2011 11:03 pm

To figure the recoil, take the ratio of projectile mass : launcher mass, and multiply by the expected muzzle energy. Add to this the recoil from the propellant gasses, using their local speed of sound as their velocity. I think this should give ballpark figures.

D_hall wrote:Another effect that I discovered with VERA that is not accounted for in HGDT... Increased turbulence once the gases start to move.


Hmm...
It seems to me this means spark gap placement is potentially a major variable in a hybrid with sub-optimal opening pressures. How the flame front is able to interact with the now-turbulent gasses should have a considerable impact on burn times. It also seems that intentionally adding blockages to the chamber for additional turbulence may have some effect. I'm looking at the internals of a bernz-o-matic nozzle here... it seems fairly simple in construction and has the effect of 'spinning' the gasses as they exit.
It would probably be something worth replicating since it could easily be a removable chamber insert.
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Unread postAuthor: mobile chernobyl » Mon Nov 14, 2011 11:18 pm

I think that venturi nozzle is more to achieve proper air fuel mixture before the burn but I could be wrong - it sounded like you wanted this at the barrel entrance?

Good news though for this design - material cost for the tubing and all frame steel should be around $.50/lb! Makes this design seem a lot more feasible now lol.
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Unread postAuthor: D_Hall » Tue Nov 15, 2011 12:32 am

mobile chernobyl wrote:D_Hall - another question your way - How does your design cope with the [expectedly] massive recoil it generates? Is it all carefully dissipated through the trailer and into rearward movement?

I calculated maximum potential recoil force via Force = MaxPressure * BoreArea.

I designed the structure of the gun to be able to support the above mentioned force.

From there I just set the brakes on the trailer and let her slide.

In other words.... There's absolutely nothing fancy about Vera. I just built her like a brick craphouse.
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