Energy Stored in Tank
I’ve read it a couple of other places in this forum – gas guns are addictive like crack, once you start fiddling with them you can’t stop.
Anyhow, I started fiddling with some of the physics of what, at first, seems like a simple machine. Well, not really that simple when you get into it.
Here’s a view of overall efficiency for a “Talon-like” scenario. Assuming a 40 psi per shot pressure drop and allowing tank temperature to go back up after the shot, the energy in the tank drops by about 650 ft-lb. This is interesting because the pellet kinetic energy out of the barrel is around 30 ft-lb. It’s a lot of energy expended to get that 30 ft-lb…
Have a look at the attached PDF for details. I’d really like a sanity check of this approach. Also, I’d be happy to send along the underlying spreadsheet, if anyone is interested. (Don’t know if spreadsheets attach correctly to these posts.)
I’ve gone down the same rabbit-hole that led to Hall Consulting’s Gas Gun Design Tool. I’ve ended up with a model of the tank/valve/pellet/barrel system. Hall has been pretty clear that he’s not interested in sharing the underlying algorithms in GGDT, which is his absolute right. So I’ve redeveloped some a model of the first-order effects in a big ‘ol spreadsheet. I’d be happy to send this along, if there’s interest.
-x356b
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Thanks for the kind words Doug. You’ve got it right about what’s happening in the tank system.
When a 500 cc tank loses 40 psi out of 3000 psi, that’s 642 ft-lb of energy lost from the tank. In the case of my not-well-tuned Condor, that 40 psi drop only gets me about 30 ft-lb of energy in the pellet. MAW has a much better tune and gets 100 ft-lb.
In any case, it’s interesting to note that it took 642 ft-lb of energy from the tank to get 100 ft-lb from MAW’s muzzle. So that’s about 15% efficiency, which is not unusual for gas operated machines.
By looking at tank energy lost per shot, the effect of tank volume is removed and it’s easy to make an apples to apples comparison of one gun’s operating mechanism, barrel, & pellet to another gun’s.
If anyone is interested, I’d be happy to send along the spreadsheet so you can make the calculation for your particular case.
-x356b
RStearne is the one who figured out the rws 850 hammerli airmagnum.
Good catch Maw! So easy to overlook the simple everday overall experience of just going out and doing lots of shooting.
I don’t know about that ,but when I drop 40 psi in my tank, per shot, I am shooting around a 100 ft pounds of energy ,with a 70 grn slug, out of my 24 in., 25 cal.
That is some real brainiac genius stuff, you have there! It is simply beyond my full ability to comprehend. Let’s see if I got this correctly………
So very basically you have figured that a certain volume storage tank of of air compressed to a certain pressure will equal a certain potential of energy. Now you have extrapolated the the air consumption per shot to equal the amount of expended energy removed from the total potential of the tank to arrive at the amount of energy consumed per shot vs the final energy realized by the projectile? Do I understand this correctly? So, your synopsis is that it takes a great amount of effort expended during the task of delivering any significant force downrange from the business end ofthe machine as designed for this task?
I think I understand your premise. It is just the spreadsheet, it’s terms and units and the mathematics I havent got a clue! That is some scientific advance knowledge that is beyond a mere commoner mortal such as myself! But truly fascinating non the less… I am sure there is a lot to be learned and some room for advancement by utilizing mathematical modeling and predictive engineering when designing more efficient, accurate and more powerful air/gas arms.
Please don’t be discouraged by others lack of participation, I am sure you have much to contribute to the advancement of this addictive hobby. Someone whom might be better to review your math might be RStearne over on the GTA forum, he is very heavy into egineering/scientific formulas and has a strong mathematical grasp. He is easily identified by his Avatar which is the muppet character wearing a Darth Vader mask.
But please stick around here and continue to make your contributions, there are many of us who remain fascinated none the less! Welcome aboard!
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Here’s an updated view of the tank energy spreadsheet, with some better documentation.
-x356b