Search found 3197 matches

by jimmy101
Thu Feb 25, 2021 12:28 am
Forum: SpudFiles Discussion
Topic: Adding Multiple Sparks In Combustion Chamber
Replies: 4
Views: 8166

Re: Adding Multiple Sparks In Combustion Chamber

What Jack said.

Plus, more than one spark increases the spark gap, that means the gaps need to be smaller if you are going to use the BBQ piezo.

BTW, multiple sparks must be wired in series, not in parallel.
http://www.advancedspuds.com/multiple.htm
by jimmy101
Fri Feb 19, 2021 4:35 pm
Forum: Hybrid Cannons
Topic: Need help
Replies: 15
Views: 15194

Re: Need help

hectmarr wrote:
Fri Feb 12, 2021 6:45 pm
Look at this, it can illustrate for you how to work with rupture disc.
LOL, looks like the fittings salesman's wet dream.
by jimmy101
Fri Feb 12, 2021 5:10 pm
Forum: Hybrid Cannons
Topic: Need help
Replies: 15
Views: 15194

Re: Need help

"best ratio" is not a well defined concept. Do you mean "most efficient" at extracting the energy in the explosion, or "fastest projectile" but that requires knowledge of projectile and barrel ... Long story short for 1X mixtures CB ratios between 0.6 and 1.2 are all about the same. Let other factor...
by jimmy101
Wed Feb 10, 2021 11:32 pm
Forum: Hybrid Cannons
Topic: Breech System For historical Pak 36
Replies: 26
Views: 15937

Re: Breech System For historical Pak 36

Looks like you will have to use more than 1x mixture, otherwise your chamber to barrel ratio will be too small. Do you know what your designs' chamber and barrels volumes are?
by jimmy101
Wed Feb 10, 2021 11:23 pm
Forum: Hybrid Cannons
Topic: Need help
Replies: 15
Views: 15194

Re: Need help

Will the fueling method of syringe work for up to 6x or maybe 8x? The biggest syringe that is easy to get is 70ml. If you fuel into a vented chamber you are probably limited to putting in no more than about 20% of the chamber volume. After that you'll be losing an unknown amount of fuel as it leaks...
by jimmy101
Wed Jul 15, 2020 6:40 pm
Forum: Pneumatic Cannons
Topic: Calculations related to pneumatic cannon.
Replies: 9
Views: 14545

Re: Calculations related to pneumatic cannon.

The ideal gas law is not usable in the situation of a pneumatic spud gun. Three state variables (pressure, volume and temperature)n al change. You need to do more complex stuff, like take in to account the heat capacity of the air. There are very nice tools for both pneumatics and combustion guns de...
by jimmy101
Mon Jun 15, 2020 4:58 pm
Forum: Combustion Cannons
Topic: I was hoping for some feedback on my oxy-propane combustion cannon.
Replies: 7
Views: 7998

Re: I was hoping for some feedback on my oxy-propane combustion cannon.

The biggest I usually see is 150 ml. That's big enough for 1x in a 3.75 liter (229 in^3) chamber, which is a pretty big chamber. https://www.amazon.com/Syringes-Scientific-Measuring-Watering-Refilling/dp/B07C71C1LH/ref=sxin_7_ac_d_rm?ac_md=2-2-bGFyZ2Ugc3lyaW5nZQ%3D%3D-ac_d_rm&cv_ct_cx=syringe&dchild...
by jimmy101
Mon Jun 15, 2020 4:53 pm
Forum: Hybrid Cannons
Topic: I bring you some cannon performance data
Replies: 5
Views: 7322

Re: I bring you some cannon performance data

Moonbogg wrote:
Sat Jun 06, 2020 2:07 pm
jackssmirkingrevenge wrote:
Sat Jun 06, 2020 6:05 am
jimmy101 wrote:
Thu Jun 04, 2020 10:31 pm
Caliper in the fruit isle? Just take a little length of barrel!
"Security? Yeah it's that weirdo putting limes through a pipe again..."

Yeah, that wouldn't look good.
Meh. Put a cut in the 1/2" long piece of pipe and wear it into the store as an ear ring.
by jimmy101
Mon Jun 15, 2020 4:50 pm
Forum: Combustion Cannons
Topic: Propane failing to ignite reliably.
Replies: 9
Views: 11269

Re: Propane failing to ignite reliably.

Easiest way to understand C:B ratio is that if the barrel is too short, the projectile is still accelerating when it leaves the barrel (sub optimal), and if the barrel is too long, NEGATIVE pressure behind the projectile will slow it down before it exits the barrel ( if your barrel is very long, an...
by jimmy101
Thu Jun 04, 2020 11:04 pm
Forum: Combustion Cannons
Topic: Potato Howitzer
Replies: 9
Views: 14520

Re: Potato Howitzer

Looks outstanding. But the coax design is killing the performance. I would expect a gun that size to be firing something like a spud at about 150-200 MPH. From the video I would guesstimate about 50 MPH or less. Any idea what the chamber and barrel volumes are?

But it does looks sweet.
by jimmy101
Thu Jun 04, 2020 10:56 pm
Forum: Combustion Cannons
Topic: Propane failing to ignite reliably.
Replies: 9
Views: 11269

Re: Propane failing to ignite reliably.

The importance of the C:B ration is kind of over rated. If you look at the data, the velocity goes up as the chamber goes up for a fixed size barrel. Eventually the chamber get too big but that is up near C:B ratios of >5:1 or something. So bigger is generally better. The 0.8 value is actually more ...
by jimmy101
Thu Jun 04, 2020 10:46 pm
Forum: Combustion Cannons
Topic: New member... my baby, Big Red
Replies: 15
Views: 18385

Re: New member... my baby, Big Red

"Burnt Latke", ah, those were the Days... Don't need a vacuum pump to run pure O2. Just flush the chamber with the O2 before adding fuel, not all that hard really, but might get expensive. But pure O2 is up around 5x the power of propane+air. None the less, it looks like you know what you are doing ...
by jimmy101
Thu Jun 04, 2020 10:38 pm
Forum: Combustion Cannons
Topic: I was hoping for some feedback on my oxy-propane combustion cannon.
Replies: 7
Views: 7998

Re: I was hoping for some feedback on my oxy-propane combustion cannon.

What Jack said, but with a chamber that big a syringe is going to have to be huge. Is that a meter pipe system? if it is and you think the performance is lacking I would look at 2 things. (1) Is you mixture correct? Your fuel volume using air at 1 ATM is 4% of the chamber volume. (2) Big long chambe...
by jimmy101
Thu Jun 04, 2020 10:31 pm
Forum: Hybrid Cannons
Topic: I bring you some cannon performance data
Replies: 5
Views: 7322

Re: I bring you some cannon performance data

Caliper in the fruit isle? Just take a little length of barrel!
by jimmy101
Thu Jun 04, 2020 10:29 pm
Forum: Pneumatic Cannons
Topic: Calculations related to pneumatic cannon.
Replies: 9
Views: 14545

Re: Calculations related to pneumatic cannon.

The teacher isn't a "professor", it is a high school teacher so expertise in this area is probably limited. :) Mark.f gave a reasonable answer. Don't need much of a "computer", you can do it an Excel spread sheet. Wont be super accurate but were talking a high school project, not a DARPA project. Ju...