1) Any general thoughts or concerns to the overall design? Probably charge it to 100psi max. Always remember that PVC is prone to cracking if mistreated. In other words, while a PVC barrel can be done, the larger it is the more cognizant you have to be about its treatment. Be nice to it lest it gren...

Well, the biggest issue is "How do you STOP the piston in the pump stage?" If you're soft stopping it, that implies your piston velocities aren't very high which in turn implies that your pressures aren't very high which in turn means your velocities won't be very high which in turn begs the questio...

Very interesting. At those velocities, does the sabot shatter on exit? I would be lying if I said I haven't been thinking of ways to pack a 2 stage gun into a rifle-esque design. Well, they're multi-piece designs that are literally held together by the bore of the gun. The moment they're clear of t...

Hint: Side 7 has the title "Typical FI Laboratory Gun Sabot" and photographs of 2 different sabot designs.

Yes, H and O are great. That's why you see 'em used in rockets. For bonus points, run it just a bit fuel rich and you get even lower molecular weight without much loss in temperature. And yes, that's why rockets run such. The same physics apply! That said, running H/O in a gun at anything that resem...

What are methods of passing beyond the local SOS? The previously mentioned exploitation of Maxwell-Boltzmann distributions. Highly inefficient and has it's own limitations. Not useful for much more than braggin' rights. I imagine things like raising temperature beyond that of standard combustion or...

A few thoughts in no particular order.... 1 - Post-combustion chemistry absolutely matters. It can drastically alter the local sonic velocity. 2 - Traditional powder-based guns can go much faster than OP's listed 5200 ft/s. I've personal experience with a gun that runs at 8,900 ft/s. 3 - I'm a bit b...

Jack got it right.

I didn't keep anything, but if you've a specific question I'm likely to be able to answer it.

I don't remember where it's stashed, but it's actually on this site somewhere....

And as a minor brag, I set a new personal best last weekend....



...Still not going to win any championships, but I felt really good about that run.

As hinted at in the previous post.... The most likely cause is incorrect fuel/air ratio. Unfortunately, this is not an easy thing to measure with a "spray and pray" potato gun. First things first? Ditch the hair spray (that is an affront to the potato gun gods!), and find a way to MEASURE how much b...

jackssmirkingrevenge wrote: ↑

Wed Nov 29, 2023 3:29 pm

I believe a stoichiometric mix ratio is assumed depending on the chosen fuel.

Correct. I am NOT going to loop in PEP or any similar combustion codes!

That's enough experimentation for this session but I would also like to try cutting down the baffle to make the "second chamber" smaller to see if that makes a difference, I wonder if it will increase or reduce peak pressure at the disk. If my gut is right, making the baffle shorter (increasing vol...

A mesh screen would kick up turbulence but also suck up a lot of heat. We have discussed before if running the chamber fan during firing might increase the burn speed. Way back when I measured burn speed in a closed chamber at 1x with/without the fan running and with one or three sparks gaps. There...