SpudFiles

So y'all
I read ur posts all the time and im blown away by the knowledge. I've been building for a few years now and I've built some really nice combustion guns. I've done a lot of research on hybrids but i need a little help on the fueling. If i have a 55 cubic inch chamber and a2.2 meter pipe, and i wanna make a 3x mix. How do i do the math. Please help
Thanks guys

It depends on how you're fuelling. There have been several different approaches.

However, the maths for two common approaches is already addressed here: http://www.spudfiles.com/hybrid-cannons/topic13602.html

Im using a 13 inch half inch meter pipe with 100psi gauge

Sorry, I can't actually do the maths for you.

I'll check your answer if you post one, but it's important that you understand how to do the maths yourself.

Fuel Charge Pressure (In PSI)
1x 0 (normal combustion firing)
2x 14.7
3x 29.4
4x 44.1
5x 58.8
6x 73.5
7x 88.2
8x 102.9

This is the air pressure in the chamber used with different charges. I don't really want to guide someone on how to do meters as it is a topic in and of itself, plus if you are even thinking of venturing into hybrids, one really should have a solid grasp on how the other things work and know how dangerous they can be.

Thank u but i could have just gone to advanced spud guns site and copied the same chart.... i think there was a miscommunication here. What I'm trying to figure out is.... let's say i wanna use a 3x Mic. My meter pipe is 2.3ci in vol. My chamber vol is 56ci. At a 3x mix i think i should be injecting 44 psi of propane. I'm frustrated!!!! @ a 3x mix multiply the amount of fuel in chamber normally by 3 or not.
Then for the air do i just use 14.7 x my mix number?????

whoops, sorry for the misunderstanding. There is a fueling hybrid 101 in the stickies at the top. It is more accurate, but on a basic combustion spudgun it works like this:

http://www.burntlatke.com/lp.html

To use on hybrids, simply put the mix in 3 times for a 3X mix, etc. The Fueling 101 would be much more accurate as the fuel adds some pressure in a closed chamber like on a hybrid. It's close and will work up to about 6x mixes, after that I don't know as I have only went 6X at the highest. I couldn't get 7X to fire and TBH it was probably due to the problem with the fuel throwing off the chamber pressure measurement.

I used to have a calculator thing, many computers ago, I no longer have it but that site is one of the best for explaining it and giving you formulas to use. I forget the brand of regulator I used to use but it went from 0-60psi and was made for BBQ grills.

sw5amped wrote:I'm frustrated!!!!

Getting worked up over it is not a good thing - hybrids and getting yourself into a frame of mind where you act irrationally are not a great combination.

My meter pipe is 2.3ci in vol. My chamber vol is 56ci. At a 3x mix i think i should be injecting 44 psi of propane.

In all seriousness, the thread link I posted earlier has all the necessary maths for that (other than a reminder that atmospheres are 14.7 psia, but you seem to know that) and it's not difficult.

But you are close.

Then for the air do i just use 14.7 x my mix number?????

If you're measuring by absolute pressure, yes. However, gauges don't do that, so you need to remember that the 14.7 psi of the first mix number is provided by normal atmospheric pressure.

Awsome!!!! Thanks bro!!! I think i just needed to hear it from someone els. I appreciate all ur help. I tend to act like a prick when i get confused. Esp when it comes to building launchers!!!! Ill run my numbers and hit u back later. Thanks again

hi i have built over 20 combustion launchers now im venturing in two hybrids now i have a sch 40 steel pipe as my combustion chamber and it holds 38.6 ml i was wondering if you could provide me with the math equations so i could work out my fuel to air mix please i have read just about everything there is to no and im still lost

burstmewideopen wrote:i was wondering if you could provide me with the math equations so i could work out my fuel to air mix please i have read just about everything there is to no and im still lost

Have you had a read through this?