Calculating efficiency???

[Michael]

Alright airgun geeks, I need your help with something. What is the equation to figure out how efficient an airgun is?

I've been using this equation but I believe it only gives me how much energy is produced per CC.

Reservoir: 300cc
Total air used: 250b starting pressure – 150b ending pressure = 100b
Total air used x total reservoir: 100b x 300cc = 30,000

Projectile: 25.4g @ 960fps for 47 shots
Ave energy per shot: 52fpe (70.5 joules)
Total energy: 70.5j x 47 shots = 3313j

Total air used x total reservoir / Total energy = Energy per CC
30,000 / 3313 = 9 joules per CC


Take for example another airgun with a larger reservoir, a smaller usable air range, lower shot count, and lower FPE. This results in more energy per CC.

Reservoir: 480cc
Total air used: 250b starting pressure – 180b ending pressure = 70b
Total air used x total reservoir: 70b x 480cc = 33,600

Projectile: 25.4g @ 940fps for 40 shots
Ave energy per shot: 48fpe (65 joules)
Total energy: 65j x 40 shots = 2600j

Total air used x total reservoir / Total energy = Energy per CC
33600 / 2600 = 12.9j per CC


But in my mind the 2nd airgun is less efficient because I'm getting less energy, less shots, less FPE, out of a larger air reservoir.

There must be a different equation to figure out "efficiency".

 

[elh0102]

You guys are making me feel pretty stupid. I just shoot 'til the pellets are kind of dribbling out the barrel, refill, repeat. I need to work on some formulas and tables.
Seriously, I try to establish and efficient tune, but then I'm done. I guess the math would describe the efficiency, but I'm hard pressed to see why I care. But then I had trouble with basic algebra, both doing it, and understanding why I should.

 

[Stubbers]

You guys are making me feel pretty stupid. I just shoot 'til the pellets are kind of dribbling out the barrel, refill, repeat. I need to work on some formulas and tables.
Seriously, I try to establish and efficient tune, but then I'm done. I guess the math would describe the efficiency, but I'm hard pressed to see why I care. But then I had trouble with basic algebra, both doing it, and understanding why I should.

Some of us nerd out on pcp's, I historically did but have settled down a lot since, I don't shoot strings or record efficiency anymore, but it is/was good data to have especially when learning the ropes initially. You can definitely tell by ear if you're efficient but even that takes some training. One could say it used to be a 'measuring contest' back in the day, where as now most guns have so much on board air it's silly to compare and really who cares!

The formula for included regulated volume isn't too complex, my person spreadsheet does it.

Below is the formula, where d3 is ending pressure and b6 is your set point, d5 is avg fps, d6 is projectile mass, d2 is beginning pressure, d4 is shot count, b5 is plenum volume, b38 is reservoir volume. Simple IF statement looks at if you're shooting below set point. So if anyone wants to add this to their own sheet, have at it.

ROUND(IF(D3<B6,ROUND((ROUND(D5*D5*D6/450240,1)*D4) / ((B38*0.0610237 * (D2-D3) / 14.5038) + (B5*0.0610237 * (B6-D3) / 14.5038)),2),((D5*D5*D6/450240)*D4) / ((B38*0.0610237 * (D2-D3) / 14.5038))),2)

-Matt