My hybrid (piston version)

[wyz2285]

Well, I really really wanted a Flak 88 gun
I found my self the stuffs I thing I'd need, like pneumatic cylinders etc.
Most importantly, I want to get rid of the burst discs, also I want on-board fuel supply and metering system.
So I made my own propane tank, manometric fueling, 5 way 2 position valve for charge/fueling. Already finished the piston/valve this afternoon as well so as the spark plug (so small should let me light it up mix20), just have to put the chamber and the suspension (the difficult part).

[POLAND_SPUD]

wow wyz
do keep us updated

[MrCrowley]

Welcome to the club

What is that plastic fitting rated for by the way? I'd be worried about the pilot pressure rising significantly during firing and not being able to vent fast enough. Your design is a bit smaller (assuming the largest brass fitting in your photo is no bigger than 1" n.b.) than what I was working with but I had constant problems with piston bounce until I increased the flow of my pilot spool valve. So even if there is an open exhaust port for the pilot air, it may be highly compressed for a split second before venting completely.

[wyz2285]

Well I got a huge problem, the venting port it's larger than the valve output, witch means I need more pressure in the pilot chamber than the actual chamber. I will to dramatically reduce the venting port to 8mm dia instead of 15 mm dia. Still so I'll need 20 bar in it for the valve open at +50 bar (for mix < 10).
That plastic piece is rated to at least 15 bar (the tubes I use with it are 15 bar rated but I used it up to 30 bar with no problem.). So according to my math the pilot pressure has no way to get up to 30 bar without the venting port open, not worried about it.

[MrCrowley]

So according to my math the pilot pressure has no way to get up to 30 bar without the venting port open

As I said before, things might be different because you're working on a much smaller scale than my cannon but I buggered a 300PSI gauge on my pilot because, even though the vent opens immediately, the pressure built up in the pilot because it couldn't escape fast enough out the port. The gauge face blew off and the dial wound all the way around to the wrong side of the pin that marks '0' on the pressure gauge (you can even see it in one of my vids)

I also don't think it's likely that this part will fail but I thought I better mention it anyway.

[wyz2285]

Make sense, after I reduced the venting port, the flow is poor (a 7mm id tube with a 6mm bolt pass through). But I'm still confident

[Labtecpower]

flak 88 FTW

I would replace the plastic part with something sturdier, I don't have good experiences with hybrids and plastic parts..

[jackssmirkingrevenge]

Well, I really really wanted a Flak 88 gun :lol

Sooo... is it going to be put of a cruciform mount and have a recoiling system and everything?

Shame it won't dump cartridges like the original...

[wyz2285]

Well, I really really wanted a Flak 88 gun :lol

Sooo... is it going to be put of a cruciform mount and have a recoiling system and everything?

Shame it won't dump cartridges like the original...

Of course
BTW Jack I'm working on a combustion version as well... using cartridges !:D