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A heavy 75x hybrid

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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Re: A heavy 75x hybrid

Unread postAuthor: Alex345 » Fri Feb 12, 2016 10:52 am

Jesus christ, this thing is gonna be awesome! You thinking of putting a muzzle brake on her? Unless you're gonna shoot APFSDS like rounds.
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Re: A heavy 75x hybrid

Unread postAuthor: Futterama » Fri Feb 12, 2016 2:48 pm

Frozen wrote:Image

Were you going with this design after all?
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Re: A heavy 75x hybrid

Unread postAuthor: Frozen » Sun Feb 14, 2016 6:16 am

I am not sure about a muzzle brake, I will see if I have enough shop hours available to make one.

I did go with that design with some modifications, the complete cross section of the cannon looks like this:

assembly.png (13.44 KiB) Viewed 926 times

The bolt holes are not in the right places in the section picture because I would have needed to take the section at different angles for each part but you get the idea. In the picture you can also see the new barrel locking mechanism that I designed yesterday, I will turn a groove on the barrel 3,5mm deep and 20mm wide and the put a ring on it that is split in two which locks the ring in the axial direction. Then a flange with bolt holes is slid over it preventing the two ring pieces from coming apart and allowing me to attach the barrel to the part on the left. This way I will have a possibility to change the barrel in the future in case it gets damaged without the need to machine a new part to weld it into. I did the simulations for barrel groove depth and I could have done a 5mm groove at which point the pressure of 700 bar would have ripped it apart. With a 3,5mm groove that pressure is somewhere in the 1000 bar range which is way above the maximum pressure of the cannon.
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Re: A heavy 75x hybrid

Unread postAuthor: Daltonultra » Tue Mar 27, 2018 3:49 pm

Frozen wrote:
matti wrote:You can make threaded bolt hole circle in the chamber pipe ends if the wall thickness is sufficient. It's more compact and cleaner look then tie rod type.

I know I could and the wall thickness would allow it, but it would require me to make the chamber volume smaller to keep the same theoretical burst pressure for the chamber. HGDT simulations suggest that at 75x mix the reduced chamber volume would decrease the kinetic energy by about 10% and at low mixes like 10x the kinetic energy decrease would be about 20%. The bolt holes in the chamber walls weaken that part of the chamber, so to keep the wall strength I would have to do it like this:
If the pressure area would go all the way to the end of the chamber, there would be lots of local stresses in the walls of the bolt holes even larger than those in the inside walls of the chamber. That would make the bolt holes the weakest part of the chamber if not made like the diagram above. For M16 bolts class 8.8 the minimum thread engagement length would be around 25mm so I would have to drill atleast 30mm deep holes in the chamber. That would make the decreased chamber length about 40mm on each end and thus making my effective chamber length about 190mm long compared to the original 270mm. To me the cleaner look is not worth the decreased power. If however I am unable to find a large enough piece of round steel then I would be forced to do it this way.

Would it make more sense to use a threaded end plug than to use bolts? Then you' wouldn't have bolt holes compromising wall thickness, and you'd have many times the thread engagement area.
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Re: A heavy 75x hybrid

Unread postAuthor: D_Hall » Sat Mar 31, 2018 6:29 pm

Yes, but often that's not required and it results in a much more difficult to manufacture part.
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