Backwards math to optimize energy output

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ackuric

ackuric

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Mar 10, 2017
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Colorado, United States
Time for the reveal of a few secrets. How to quickly find out how minor changes may effect your energy output in a traditional pcp. For these simple solutions, you need to know some of your rifles specs.



***Port size Increase/Decrease***

Port OD / Bore OD

.2 / .25 = .8

What is your energy output 80% of? Lets say this rifle is at 60 fpe.

60 fpe is 80% of 75. (60/80 = .75)

New port size = .225

.225/25 = .9

Your new energy output with this port size should therefore be 75*.9 = 67.5 FPE. To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 67.5/2 = 33.75 gr. No considerable changes in hammer strike should be needed. Increased air consumption to be expected.



***Plenum Increase/Decrease***

Plenum volume = 30 cc

Increasing volume to 50cc

CC use per shot = 5

Setpoint = 2000

2000*30/35 = 1714 psi

2000*50/55 = 1818 psi

1818 - 1714 = 104

104 / 2000 = 5%

30 cc energy output = 60 fpe

50 cc energy output = 60 fpe * 1.05 = 63 FPE

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 63/2 = 31.5gr. Slight increase in hammer strike will be needed. Increased air consumption to be expected.



***Pressure increase/decrease***

Regulator pressure / Set point = 2000

Increasing to 2200

2200/2000 = 1.1

Energy output at 2k = 60 fpe

Energy output at 2.2k is therefore 60*1.1 = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additional hammer strike will be needed to overcome the additional pressure holding the valve closed. Increased air consumption to be expected.




***Barrel Length increase/decrease***

Old Barrel length 20"

New barrel length 22"

Energy output at 20" = 60 fpe

60 / 20 = 3

3 * 22 = 66

New energy output potential = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additionally you will be required to create more dwell/lift and use more air to make use of the additional barrel volume.



And there you have it, some backwards, napkin math, for known pcp configurations and what energy you can expect when modifying the above parameters. Simple ain't it? These are all ballpark approximations, and the barrel calculation is by far the most unforgiving due to its dynamics, but will get ya within reason.


 
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Time for the reveal of a few secrets. How to quickly find out how minor changes may effect your energy output in a traditional pcp. For these simple solutions, you need to know some of your rifles specs.



***Port size Increase/Decrease***

Port OD / Bore OD

.2 / .25 = .8

What is your energy output 80% of? Lets say this rifle is at 60 fpe.

60 fpe is 80% of 75. (60/80 = .75)

New port size = .225

.225/25 = .9

Your new energy output with this port size should therefore be 75*.9 = 67.5 FPE. To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 67.5/2 = 33.75 gr. No considerable changes in hammer strike should be needed.



***Plenum Increase/Decrease***

Plenum volume = 30 cc

Increasing volume to 50cc

CC use per shot = 5

Setpoint = 2000

2000*30/35 = 1714 psi

2000*50/55 = 1818 psi

1818 - 1714 = 104

104 / 1714 = 6%

30 cc energy output = 60 fpe

50 cc energy output = 60 fpe * 1.06 = 63.6 FPE

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 63.6/2 = 31.8gr. Slight increase in hammer strike will be needed.



***Pressure increase/decrease***

Regulator pressure / Set point = 2000

Increasing to 2200

2200/2000 = 1.1

Energy output at 2k = 60 fpe

Energy output at 2.2k is therefore 60*1.1 = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additional hammer strike will be needed to overcome the additional pressure holding the valve closed.




***Barrel Length increase/decrease***

Old Barrel length 20"

New barrel length 22"

Energy output at 20" = 60 fpe

60 / 20 = 3

3 * 22 = 66

New energy output potential = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additionally you will be required to create more dwell/lift and use more air to make use of the additional barrel volume.



And there you have it, some backwards, napkin math, for known pcp configurations and what energy you can expect when modifying the above parameters. Simple ain't it?

Click to expand...


First question: Why isn't the increase in power proportional to the area of the port rather than the diameter of the port?

Second question: You use two constants in your pelnum math which are not obvious to me. Why 35 in the one calculation and 55 in the next calculation and what do those two constants represent?

Third question: Why do you treat the power increase as linear with pressure increase all other things being equal? Is it really linear of is this just a heuristic?

Fourth question: Actually this question is the same question as number three. Why would the increase be linear or is this another heuristic?

Nothing complicated going on here, the real question is are you sacrificing much accuracy with your heuristics?




 
Upvote 0
I totally get it but I thought you only gain 10-15 feet per second per every one inch of barrel length? Yo!
Click to expand...


Wrong, so, so , so wrong....please. If you go from 10 inch to 20 inch barrel at 3000 psi, you say I can only expect 100-150 fps? This is so far from correct...
Click to expand...


Well, if you only increase your barrel length by one inch, it may well be only ten or fifteen FPS increase. In particular if your barrel is very long because you are assuming the increase with barrel length is linear, which you clearly show it not to be here, right? Maybe the math isn't as trivial as you are making it?
 
Upvote 0
Time for the reveal of a few secrets. How to quickly find out how minor changes may effect your energy output in a traditional pcp. For these simple solutions, you need to know some of your rifles specs.



***Port size Increase/Decrease***

Port OD / Bore OD

.2 / .25 = .8

What is your energy output 80% of? Lets say this rifle is at 60 fpe.

60 fpe is 80% of 75. (60/80 = .75)

New port size = .225

.225/25 = .9

Your new energy output with this port size should therefore be 75*.9 = 67.5 FPE. To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 67.5/2 = 33.75 gr. No considerable changes in hammer strike should be needed. Increased air consumption to be expected.



***Plenum Increase/Decrease***

Plenum volume = 30 cc

Increasing volume to 50cc

CC use per shot = 5

Setpoint = 2000

2000*30/35 = 1714 psi

2000*50/55 = 1818 psi

1818 - 1714 = 104

104 / 2000 = 5%

30 cc energy output = 60 fpe

50 cc energy output = 60 fpe * 1.05 = 63 FPE

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 63/2 = 31.5gr. Slight increase in hammer strike will be needed. Increased air consumption to be expected.



***Pressure increase/decrease***

Regulator pressure / Set point = 2000

Increasing to 2200

2200/2000 = 1.1

Energy output at 2k = 60 fpe

Energy output at 2.2k is therefore 60*1.1 = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additional hammer strike will be needed to overcome the additional pressure holding the valve closed. Increased air consumption to be expected.




***Barrel Length increase/decrease***

Old Barrel length 20"

New barrel length 22"

Energy output at 20" = 60 fpe

60 / 20 = 3

3 * 22 = 66

New energy output potential = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additionally you will be required to create more dwell/lift and use more air to make use of the additional barrel volume.



And there you have it, some backwards, napkin math, for known pcp configurations and what energy you can expect when modifying the above parameters. Simple ain't it? These are all ballpark approximations, and the barrel calculation is by far the most unforgiving due to its dynamics, but will get ya within reason.

Click to expand...

OH YES I SHOULD... Speaking specifically in terms of the claim of 20" barrel vs 22" is what I was referring to just that extra 2 inches. Gaining an additional 6fpe??? THATS WHAT I'M QUESTIONING HERE. Yo!
 
Upvote 0
Time for the reveal of a few secrets. How to quickly find out how minor changes may effect your energy output in a traditional pcp. For these simple solutions, you need to know some of your rifles specs.



***Port size Increase/Decrease***

Port OD / Bore OD

.2 / .25 = .8

What is your energy output 80% of? Lets say this rifle is at 60 fpe.

60 fpe is 80% of 75. (60/80 = .75)

New port size = .225

.225/25 = .9

Your new energy output with this port size should therefore be 75*.9 = 67.5 FPE. To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 67.5/2 = 33.75 gr. No considerable changes in hammer strike should be needed.



***Plenum Increase/Decrease***

Plenum volume = 30 cc

Increasing volume to 50cc

CC use per shot = 5

Setpoint = 2000

2000*30/35 = 1714 psi

2000*50/55 = 1818 psi

1818 - 1714 = 104

104 / 1714 = 6%

30 cc energy output = 60 fpe

50 cc energy output = 60 fpe * 1.06 = 63.6 FPE

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 63.6/2 = 31.8gr. Slight increase in hammer strike will be needed.



***Pressure increase/decrease***

Regulator pressure / Set point = 2000

Increasing to 2200

2200/2000 = 1.1

Energy output at 2k = 60 fpe

Energy output at 2.2k is therefore 60*1.1 = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additional hammer strike will be needed to overcome the additional pressure holding the valve closed.




***Barrel Length increase/decrease***

Old Barrel length 20"

New barrel length 22"

Energy output at 20" = 60 fpe

60 / 20 = 3

3 * 22 = 66

New energy output potential = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additionally you will be required to create more dwell/lift and use more air to make use of the additional barrel volume.



And there you have it, some backwards, napkin math, for known pcp configurations and what energy you can expect when modifying the above parameters. Simple ain't it?

Click to expand...


First question: Why isn't the increase in power proportional to the area of the port rather than the diameter of the port?

Second question: You use two constants in your pelnum math which are not obvious to me. Why 35 in the one calculation and 55 in the next calculation and what do those two constants represent?

Third question: Why do you treat the power increase as linear with pressure increase all other things being equal? Is it really linear of is this just a heuristic?

Fourth question: Actually this question is the same question as number three. Why would the increase be linear or is this another heuristic?

Nothing complicated going on here, the real question is are you sacrificing much accuracy with your heuristics?



Click to expand...



1) Whoa buddy... how about you use area instead of diameter and try to see if it works out for you prior to asking why I don't? Because it doesn't work...

2) I don't use 2 constants, I use 1, that is the volume used (5 cc) and the two variables 30 cc plenum and 50 cc plenum...are you following?

3) Yes. Pressure works in a linear fashion, you know that right? Even my calculator that spits out these calculations within 99% accuracy states so.

4) You really should study up a bit before asking these kind of questions, pressure scales linearly, 2000 psi is 2x the force of 1000 psi, much like 3000 psi is 3x the force of 1000...
 
Upvote 0
I totally get it but I thought you only gain 10-15 feet per second per every one inch of barrel length? Yo!
Click to expand...


Wrong, so, so , so wrong....please. If you go from 10 inch to 20 inch barrel at 3000 psi, you say I can only expect 100-150 fps? This is so far from correct...
Click to expand...


Well, if you only increase your barrel length by one inch, it may well be only ten or fifteen FPS increase. In particular if your barrel is very long because you are assuming the increase with barrel length is linear, which you clearly show it not to be here, right? Maybe the math isn't as trivial as you are making it?
Click to expand...


Wrong, wrong, not here to debate, please take it to pm's and don't fill this thread with misinformation. That depends on way too many variables to concretely state 1 inch of barrel is worth 10-15 fps. What if your barrel is 8" to begin with? What if its 30 inch to begin with? You really can't apply a 10-15 fps per inch of barrel rule to those...maybe the math isn't in your favor at all with 10-15 per inch of barrel and my calculation is actually a better representation...maybe you should be more open minded to learning. Then again, I am not here to force you to be mindful with your approach to this.
 
Upvote 0
Please don't keep quoting the OP...its a quick way to clutter a thread...



To YO regards to the 20" to 22" barrel, yes that increase of 6~ fpe should be obtainable and expected, and as I clearly stated in the foot notes, that calculation is the LEAST forgiving of all, and ALL of them are approximations...don't get your panties in a wad over this and skip over my footnotes that answer your concerns



Pressure and more importantly volume CAN work in near linear fashion, provided you do exactly as I stated (increase air consumption / hammer strike / dwell)...and FWIW, I cannot stress enough, these are approximations one can quickly calculate on their own and be within reason of. If you don't like it, don't use it. Simple. Debating it without a better solution is pretty much hitting your head against a wall though...have fun with that.
 
Upvote 0
Time for the reveal of a few secrets. How to quickly find out how minor changes may effect your energy output in a traditional pcp. For these simple solutions, you need to know some of your rifles specs.



***Port size Increase/Decrease***

Port OD / Bore OD

.2 / .25 = .8

What is your energy output 80% of? Lets say this rifle is at 60 fpe.

60 fpe is 80% of 75. (60/80 = .75)

New port size = .225

.225/25 = .9

Your new energy output with this port size should therefore be 75*.9 = 67.5 FPE. To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 67.5/2 = 33.75 gr. No considerable changes in hammer strike should be needed.



***Plenum Increase/Decrease***

Plenum volume = 30 cc

Increasing volume to 50cc

CC use per shot = 5

Setpoint = 2000

2000*30/35 = 1714 psi

2000*50/55 = 1818 psi

1818 - 1714 = 104

104 / 1714 = 6%

30 cc energy output = 60 fpe

50 cc energy output = 60 fpe * 1.06 = 63.6 FPE

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 63.6/2 = 31.8gr. Slight increase in hammer strike will be needed.



***Pressure increase/decrease***

Regulator pressure / Set point = 2000

Increasing to 2200

2200/2000 = 1.1

Energy output at 2k = 60 fpe

Energy output at 2.2k is therefore 60*1.1 = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additional hammer strike will be needed to overcome the additional pressure holding the valve closed.




***Barrel Length increase/decrease***

Old Barrel length 20"

New barrel length 22"

Energy output at 20" = 60 fpe

60 / 20 = 3

3 * 22 = 66

New energy output potential = 66 fpe

To obtain this you will need your projectile to be roughly 1/2 grain per fpe, ie: 66/2 = 33gr. Additionally you will be required to create more dwell/lift and use more air to make use of the additional barrel volume.



And there you have it, some backwards, napkin math, for known pcp configurations and what energy you can expect when modifying the above parameters. Simple ain't it?

Click to expand...


First question: Why isn't the increase in power proportional to the area of the port rather than the diameter of the port?

Second question: You use two constants in your pelnum math which are not obvious to me. Why 35 in the one calculation and 55 in the next calculation and what do those two constants represent?

Third question: Why do you treat the power increase as linear with pressure increase all other things being equal? Is it really linear of is this just a heuristic?

Fourth question: Actually this question is the same question as number three. Why would the increase be linear or is this another heuristic?

Nothing complicated going on here, the real question is are you sacrificing much accuracy with your heuristics?



Click to expand...



1) Whoa buddy... how about you use area instead of diameter and try to see if it works out for you prior to asking why I don't? Because it doesn't work...

2) I don't use 2 constants, I use 1, that is the volume used (5 cc) and the two variables 30 cc plenum and 50 cc plenum...are you following?

3) Yes. Pressure works in a linear fashion, you know that right? Even my calculator that spits out these calculations within 99% accuracy states so.

4) You really should study up a bit before asking these kind of questions, pressure scales linearly, 2000 psi is 2x the force of 1000 psi, much like 3000 psi is 3x the force of 1000...
Click to expand...


1) Because I thought you were giving the class here. But it will work an it will be more accurate so, since you are giving the class, and I don't understand rather than just discount the question, maybe consider answering it?

2) No, not following. The numbers I am asking about are the number 35 and the number 55, where did they come from? So ignorance is a gift I have.

3) No I do not know that pressure works in a linear fashion. Sorry. Maybe it does, maybe it doesn't. I don't have your calculator. Do you really need to talk down to me or am I imagining this?

4) Should study up a bit ...

Hmmm

Don't make me get out my fluid dynamics text books and look through them. Just help me try to understand your thinking without suggesting you are the smartest guy in the closet, ok?
 
Upvote 0
Please stop quoting the OP...and take it to pm.
Click to expand...


Do what? You started this thread. I asked you questions. Now you are referring to yourself in the third person and talking to me like I was an idiot? Why in the world would I want to go to PM with you? I might need a witness.

That said, the questions were asked in good faith. I'd be more than happy to address each one in a separate post publicly, not privately.
 
Upvote 0
1) You use diameter of port rather than area because you're not calculating the force being applied over the ports area, thats not how this calculation works, its approximating the max flow for your bore. So if you're ported to 75% of your bores diameter, you're essentially making 75% of your bores potential power output in fpe for your current configuration (pressure/barrel length/plenum volume)...

2) 5cc = constant (volume used per shot), 30 and 50 are the variables of plenum volume, 35 and 55 are the volumes all added together to calculate your pressure. This is how volume and pressure works...its pressure 2 = volume 1 * pressure 1 / volume 2. Its boyles law...a gas law...

3) Much like mass, force is linear. 2 lbs is twice that of 1 lb, while 4 lbs is twice that of 2 lbs and 4 times that of 1 lb, force works equally.

4) Yes.

5) I'd love a healthy discussion on gas/fluid dynamics :)
 
Upvote 0
I almost didn’t open this tread, but I did, and sure enough, just like all others that the OP starts up and numbers are involved, it ends up like this. It starts off with this and that, then naturally questions arise, then the OP always acts annoyed that he is getting questioned, and talks down to the ones questioning. 

Im retired from the sheet metal industry, and finished my career as a trades instructor. Sheet metal trade math was one of my favorite subjects. I loved teaching it, and there’s a way to be a teacher to a bunch of grown men, especially when it comes to math. 

I’ll tell you this though, OP, if I came across to the hundreds of students I taught like you do here when you’re questioned, well, I wouldn’t have had such a successful career. I probably would have been fired. 

You have knowledge that’s awesome, I get that, and I can safely say others see that also. It’s the style and demeanor you put out, that gets people annoyed. Just trying to offer you honest feedback on your teaching skills, or your approach to when someone questions you.

Theres only so many Airgun forums left......


 
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