Air usage Efficiency Calculator for PCPs ??? (another calculator added 9/7)

[melloroadman]

Can I ask why is CI used instead of psi as the efficiency standard . Marvin

[rsterne]

Because psi is only half the number you need.... You also need the volume of the container that the pressure is contained in.... The "CI" in the standard is at 1 Bar pressure.... ie normal atmospheric pressure....

If you just used psi, then you would get a different answer for a gun tethered to a SCUBA tank than for the exact same gun on it's own.... It the tank was 10,000 cc and the gun only 100 cc, your pressure drop would be 100 times larger for the gun alone, so if you based the efficiency on that the results would indicate the gun was 100 times as efficient when tethered....

Bob

[melloroadman]

I understand what you are saying . But for a tethered rifle the solution has been addressed . So if we take the tethered out of the picture . Why is CI the bench mark ? Marvin

[lloyd-ss]

Marvin,
 The cubic inch is one cubic inch of air at 14.5 psi (standard pressure, approx 1 bar), so there is both volume and pressure needed to equalize everything.

If you always shoot out of the same gun with the same tank, it doesn't really matter.  If you have a 400 cc tank and it drops 30 psi per shot, and then you put on a 200cc tank, it will drop 60 psi per shot.  The bar-cc or cuin at std pressure are just ways to be able to compare apples to oranges.
Lloyd

[lloyd-ss]

........................
All I'm doing is trying to come up with a guideline "standard" of performance in a PCP.... that hopefully, with enough data will show relatively similar levels of efficiency across all calibers.... There will always be exceptions to the rules, of course.... and maybe someday we'll understand enough about all the factors that affect efficiency to make sense of it all....

Bob

Bob, I agree that having some standard way to compare different calibers and guns might be nice.  I just think the choice of 950 fps puts the bigger calibers at a disadvantage and none of them will show good eff at 950 fps.  It's like trying to dyno a big block chevy at the same RPM as a DOHC honda.  They BB Chevy is going to run out of breath.

Testing a big bore at 950fps puts up a couple of obstacles that the small calibers don't have:
You'll need higher air pressure.
You'll be limited to a light weight bullet.
Shooting a light weight bullet is always an eff disadvantage for a big bore.
You will be coming off the edge of the efficiency plateau so a shot at 2500 psi will give a totally different eff than a shot at 3400 psi, even though they might both achieve 950 fps.

My point is that I think you will be trying to get comparable, relevant eff numbers while operating  the big bore out of its normal eff range.

IMHO.
Lloyd

[melloroadman]

Thank you both . The apple to orange thing helped . For me the calculator will be very useful for finding out info on my individual rifles not comparing big to small so much . Marvin

[rsterne]

ahhhhhhhhhhh I see what you're saying Lloyd.... OK, so just use the FPE numbers (which come from a roundball at 950).... but you could just as easily say that the FPE = twice the weight of a roundball and leave the velocity out of the picture all together.... *grin*....

Are you OK with that?.... Looks like it should be pretty close.... "A PCP operating at an FPE equal to twice the weight of a roundball should have an efficiency of about 1.0 FPE/CI"....

Bob

[lloyd-ss]

ahhhhhhhhhhh I see what you're saying Lloyd.... OK, so just use the FPE numbers (which come from a roundball at 950).... but you could just as easily say that the FPE = twice the weight of a roundball and leave the velocity out of the picture all together.... *grin*....

Are you OK with that?.... Looks like it should be pretty close.... "A PCP operating at an FPE equal to twice the weight of a roundball should have an efficiency of about 1.0 FPE/CI"....

Bob

Ok, that sounds like a good starting point to explore from.
Lloyd

[melloroadman]

As this is set up it is a average of air usage over a shot string . Were as Lloyd gives us info on a one shot bases on his mule . Way more equipment than I have . And I am not competing here as well . But if I know that the maximum energy of my rifle is at 3000 psi . I tether it to a tank with a regulator and good gauges that are marked in 100 psi interments . Shoot say 200 shoots and use 100 psi of air . Average out my chrony reading which should all be very close . Use this calculator correctly . I should have a very accurate reading as to what this said rifle does in effency at its top power level correct . Marvin

[lloyd-ss]

Marvin,
Hmm, let me think about this.  The regulator changes things.
Lets say you set the reg to 3000 psi and hook it up to the gun so that the gun is pressurized to 3000. You check the gauge on the tethered tank and it is ... say, 3700.  Then you shoot your string.  The gun is still at 3000, but the tank has dropped to 3600.  Then into the calculator for the volume you would put the water volume of just the tethered tank.  Starting psi would be 3700, and ending psi would be 3600.

The reason the volume of the gun tank doesn't matter is because it stays at 3000 psi from beginning to end, and doesn't really loose any pressure.  The tethered tank looses all the pressure.

But if you were NOT using a regulator then the water volume of the entire set-up would have to be used (tethered tank, gun tank, and hoses).

I think your method will give pretty good results.  You could give it a try by putting some guesstimated numbers into the calculator, and then repeat it but change the psi 5 pounds higher or 5 pound lower to simulate a bad reading, and see how much difference it makes in the efficiency number.

Sounds good. 

.....................
I had to chuckle a little about your comment about not competing.  I tell you what, my test mule is apart on my bench right now.  I was shooting max power and getting really crappy air usage.  Like .5 FPE/cuin.  I think I found the problem... I hope.
But I can usually cut back to 80% power and use half as much air.

Good luck.  (If you don't know the water vol of the tethered tank, I think we can calculate that.)
Lloyd

P.S.  Bob, Please check my logic if you would be so kind.  I appreciate having someone to catch my mistakes. 

[melloroadman]

Bob gave me the water values of my tanks and I have recorded it . Might give me something to do this winter . I have a .308, .357 corsair , JH 32, 909- 32 that I can compair .  Marvin

[rsterne]

Your logic on a regulated setup is correct.... My Hayabusa has a 22CI 3000 psi tank with the output regulated to 2000 psi feeding the tube on the gun which is 110 cc.... Since the reservoir on the gun never changes pressure, you only use the (water) volume of the tank before the regulator in the efficiency calculations....

Bob

[lloyd-ss]

Bob,
Thanks.
Lloyd

[sumbud]

can you guys draw a piture or two to help us laymen understand?

[lloyd-ss]

can you guys draw a piture or two to help us laymen understand?

Is there some particular part you are stuck on?  The tethered tank setup with a regulator we were describing is kind of unusual and used mainly by the hardcore folks like Marvin who go through bullets by the truck load.  Most folks will just be shooting the gun with no external tank hooked up.
Does that help any?
Lloyd

[lloyd-ss]

I added a new fill calculator to this.  Gene put a link at the top of the page in the GTA Library, or you can find it at     calc.sikes.us
The new fill calc has a feature where if your big tank is only partially full, it can still calculate how many more fills you will get out of it.  There is also a table listing cubic foot conversions for paintball tanks and air pack tanks that are rated in minutes. 

I'm having fun doing the calculators, so if there is something else you might find handy, let me know.  There is a little "envelope" icon on the calculator page you can use to email me if you want.

Lloyd

[Bent]

Found this, searching for PCP effiency.. Really good calculator.
I had calculated it in ccm of air pr. Joule... being a "metric man" but wanting to find out whether my numbers where good or bad.

Printouts from the calculator.

[rsterne]

Not sure what you are asking.... and the printouts are hard to read (especially the 2nd one).... but it looks like the first one has very good efficiency, and the second one rather poor.... I'm guessing the second one has too hard a hammer strike for the pressure.... The HW100 is regulated, isn't it....

Bob

[lloyd-ss]

Bent,
Yes, it looks like the gun is performing very well (air efficiency-wise) at 880 fps, but turning the power up to 958 fps, the efficiency takes a tumble. The calculator can be a handy analytical tool.
lloyd-ss

[Bent]

Not sure what you are asking.... and the printouts are hard to read (especially the 2nd one).... but it looks like the first one has very good efficiency, and the second one rather poor.... I'm guessing the second one has too hard a hammer strike for the pressure.... The HW100 is regulated, isn't it....

Bob

50% showoff, and 50% asking if its correct....  . Yeah, I can see the second one is hard to read... Just have the habit of resizing below 100kb from a danish forum. And its not my HW!
I recently got a brand new Cometa LYNX V10 MkII, and after tuning and breaking in the trigger I'm liking this gun more and more.. 
I had a spare 600mm HW100 barrel thats now fitted on the Cometa, originally it only had 470mm barrel.
The Cometa is regulated to 110 bar, with this rather low reg setting I assume its good getting 44 Joules and an effiency of 0,69. But turning the screw more gives very little velocitygain.
Low: 268m/s     150 shots @ 37 Joule
1 turn: 275
2 turns: 283
3 turns: 289
4 turns: 292       50 shots @ 44 Joule
8 turns: Max... 308m/s

Bent,
Yes, it looks like the gun is performing very well (air efficiency-wise) at 880 fps, but turning the power up to 958 fps, the efficiency takes a tumble. The calculator can be a handy analytical tool.
lloyd-ss

Yes Lloyd, as you stated. The lowest power gives the best effiency.