Tuning Definition - Tuning To The "Knee"
- Thread starter KodiakJac
- Start date
It's a poorly used term by some tuners/enthusiasts.
en.wikipedia.org
For pcp's it means to tune to 96% +/- 1-2% of your plateau, which is not the knee of a curve, more like the thigh or femur lol.
Knee of a curve - Wikipedia
For pcp's it means to tune to 96% +/- 1-2% of your plateau, which is not the knee of a curve, more like the thigh or femur lol.
Upvote 0
The benefit is it is a state of tune least sensitive to the inevitable variations in pressure and hammer strike.
Upvote 0
It's a poorly used term by some tuners/enthusiasts.
Knee of a curve - Wikipedia
For pcp's it means to tune to 96% +/- 1-2% of your plateau, which is not the knee of a curve, more like the thigh or femur lol.
What are the X and Y axes when tuning a PCP to the knee?
Thanks!
Last edited:
Upvote 0
Also quick and short valve action. Less dwell, typically a bit more pressure. Theoretically great for harmonics, and reduction of turbulence. As well as shot cycle dynamics and overall gun behavior.
Upvote 0
IDK about axis, but ideally you crank your hammer tension up pretty good, at least to the point that the gun isn't behaving poorly. Then you crank up the pressure slowly and find where your max power output is. Log your data. There is usually a power plateu where returns (in power increase) slow and even stagnate as pressure is turned up more and more. You want to be in this zone of stagnation. Just before max power output. You can also tune to the plateu on the other side of peak power as well. Just have to test and see what works best.
Upvote 0
Y is the velocity.
X is any variable that influences the valve’s behavior (lift and dwell). Generally, it’s hammer spring tension because it is usually the easiest thing to adjust. But it could be the regulator setpoint or a valve limiter/buffer or some other variable.
Upvote 0
As compared to being up on the velocity plateau, yes. But “quick and short valve action” can also mean tuned somewhere on the downslope where dwell is shorter still. The gun becomes ever more quiet with a pleasant and sedate shot cycle. However this state of tune is more susceptible to a high extreme spread, and a slow first shot caused by regulator creep.
Upvote 0
In short it is tuning hammer spring tension right to the point that no more velocity increase is seen and then backing off the tension slightly. What I have started doing is tuning slightly past this point in my guns with a power wheel. For example, with my fx Maverick I over tune slightly on power wheel 7 (max) for my selected reg pressure. I do that for temp fluctuations which cause slight fluctuations in regulator pressure. Under normal circumstances I will shoot with the whee at 6 or 5. When the reg moves up a few bar I can move the wheel to 7 and still have a high power consistent tune.
Upvote 0
Thanks guys!
I think I understand. And I've also been reading other threads on this topic. In particular, I've found a lot of comments like this...
"...turn the hammer down until velocity starts to drop. Then you’ve reached the “knee” of that reg pressure."
That's the approx 95% of maximum velocity you're talking about, correct? Turning the reg pressure up on a set hammer spring value might also find the knee, as you could see an initial increase in velocity, but at some point that velocity would flatten out, and then potentially start to drop as the reg pressure would overpower the set hammer spring value, correct?
So, I'm looking for the relationship between the hammer spring and the reg pressure in tuning to the knee, and finding the point of max velocity, and then backing off about 5%, correct?
I think I understand. And I've also been reading other threads on this topic. In particular, I've found a lot of comments like this...
"...turn the hammer down until velocity starts to drop. Then you’ve reached the “knee” of that reg pressure."
That's the approx 95% of maximum velocity you're talking about, correct? Turning the reg pressure up on a set hammer spring value might also find the knee, as you could see an initial increase in velocity, but at some point that velocity would flatten out, and then potentially start to drop as the reg pressure would overpower the set hammer spring value, correct?
So, I'm looking for the relationship between the hammer spring and the reg pressure in tuning to the knee, and finding the point of max velocity, and then backing off about 5%, correct?
Upvote 0
D
Deleted member 58109
Guest
I've done some reading up on this finding the knee.
it seems to my understanding is that not only is it the gun, it's also the pellets along with the grain.etc
how i been tuning is to what grain pellet i use for example jsb 15.89 reg at 130 bar HS backed all the way off
I increase spring pressure and notice 3 things, velocity along with how far the spread to me that's fps 800-805-812 variance.
i also notice the sound of the gun it changes (lets you know when its happy) same reg pressure increasing HS tension 1/8 turn at a time
I notice there comes a point where the spread is only 1-2 fps apart in a 6-shot string 1-3 10 shot string go beyond that HS adj it gets inconsistent. (the knee). to me at that velocity at that HS adjustment at that reg setting is it for that pellet.
I've found this way of tuning to be pretty consistent
22gr jts reg 140 bar HS 2-3/4 from flush i get real consistent strings again.
its actually pretty Amazing.
it seems to my understanding is that not only is it the gun, it's also the pellets along with the grain.etc
how i been tuning is to what grain pellet i use for example jsb 15.89 reg at 130 bar HS backed all the way off
I increase spring pressure and notice 3 things, velocity along with how far the spread to me that's fps 800-805-812 variance.
i also notice the sound of the gun it changes (lets you know when its happy) same reg pressure increasing HS tension 1/8 turn at a time
I notice there comes a point where the spread is only 1-2 fps apart in a 6-shot string 1-3 10 shot string go beyond that HS adj it gets inconsistent. (the knee). to me at that velocity at that HS adjustment at that reg setting is it for that pellet.
I've found this way of tuning to be pretty consistent
22gr jts reg 140 bar HS 2-3/4 from flush i get real consistent strings again.
its actually pretty Amazing.
Upvote 0
A good tune will definitely tend to have a lower ES especially if the gun really likes the pellets you are shooting. In other words, I find the ES is both the tune and the pellet dependent.
I turn the hammer spring up until velocity stops increasing and then I shoot groups at slightly lower hammer spring settings. Sometimes I try going past the velocity peak. On my Avenger, about 1/4 turn past the peak seems to be more accurate (even if it is less efficient). But usually I set the velocity 3-5% under the peak. But then I check velocity a day later to see if the first shot velocity is significantly lower. If it is, I turn the HS up a little and try again.
I turn the hammer spring up until velocity stops increasing and then I shoot groups at slightly lower hammer spring settings. Sometimes I try going past the velocity peak. On my Avenger, about 1/4 turn past the peak seems to be more accurate (even if it is less efficient). But usually I set the velocity 3-5% under the peak. But then I check velocity a day later to see if the first shot velocity is significantly lower. If it is, I turn the HS up a little and try again.
Upvote 0
Here's what I've learned about tuning:
Tuning to the 'knee' means finding the right balance of hammer spring tension for a given regulator setting (right?). This setting is optimal for air usage and minimizing extreme spread in pellet speed. BUT this may not lead to the ideal pellet speed for a given pellet, and it may not be the most accurate tune in terms of accuracy for a given gun (these are complex systems). Hence the never-ending search for the right combo, and the existence of extreme benchrest competitions.
Does anyone disagree? Anything to add? I've only recently acquired a regulated air rifle and chrony. I can't wait to dive into this.
If anyone in the Greater Boston area wants to shoot some stuff and talk shop, hit me up.
...It's a Taipan Vet 2 standard in .25. I know you were about to ask.
Tuning to the 'knee' means finding the right balance of hammer spring tension for a given regulator setting (right?). This setting is optimal for air usage and minimizing extreme spread in pellet speed. BUT this may not lead to the ideal pellet speed for a given pellet, and it may not be the most accurate tune in terms of accuracy for a given gun (these are complex systems). Hence the never-ending search for the right combo, and the existence of extreme benchrest competitions.
Does anyone disagree? Anything to add? I've only recently acquired a regulated air rifle and chrony. I can't wait to dive into this.
If anyone in the Greater Boston area wants to shoot some stuff and talk shop, hit me up.
...It's a Taipan Vet 2 standard in .25. I know you were about to ask.
Upvote 0
I think you have it Plinky. The other point that doesn't seem to be mentioned is that velocity is lower with too little but also too much hammer spring. If you are too high, velocity increases as you turn down the hammer spring tension. It seemed odd to me first time it happened. In this sense the peak is sort of a knee.
Upvote 0
Here are the intial tests I did to determine the plateaus on a .22 700 cm FX Panthera.
The "knee" is approximately 97% of each plateau.
I tested the rifle to find the muzzle velocity plateau for several regulator settings and a range of hammer settings for each reg setting. Testing was done from the bench with the rifle tethered at 230 BAR. For each reg setting, the hammer setting started at 2.5 on the Micro which was then increased in 5-click increments until max mv was achieved. The first tests were all done with Patriot .218 34 grain slugs.
138 BAR max mv was 965 fps at 3+5 hammer
145 BAR max mv was 969 fps at 3+10 hammer
150 BAR max mv was 988 fps at 3+15 hammer
155 BAR max mv was 1001 fps at 3+30 hammer
160 BAR was mv was 1011 fps at 3+35 hammer
The second test used H&N .218 33 grain slugs at 160 BAR. Max mv was 1010 fps at 3+20 hammer.
The third test used ZAN .218 33 grain slugs at 160 BAR. Max mv was 1024 fps at 3+30 hammer.
JackHughs
The "knee" is approximately 97% of each plateau.
I tested the rifle to find the muzzle velocity plateau for several regulator settings and a range of hammer settings for each reg setting. Testing was done from the bench with the rifle tethered at 230 BAR. For each reg setting, the hammer setting started at 2.5 on the Micro which was then increased in 5-click increments until max mv was achieved. The first tests were all done with Patriot .218 34 grain slugs.
138 BAR max mv was 965 fps at 3+5 hammer
145 BAR max mv was 969 fps at 3+10 hammer
150 BAR max mv was 988 fps at 3+15 hammer
155 BAR max mv was 1001 fps at 3+30 hammer
160 BAR was mv was 1011 fps at 3+35 hammer
The second test used H&N .218 33 grain slugs at 160 BAR. Max mv was 1010 fps at 3+20 hammer.
The third test used ZAN .218 33 grain slugs at 160 BAR. Max mv was 1024 fps at 3+30 hammer.
JackHughs
Last edited:
Upvote 0
I'm a little more confused now. You talk about HS 3+5, 3+10, 3+15. etc. Please explain that . My Avenge X has only one HS adjuster.
Upvote 0
I tend to work backwards. I typically set the hammer spring to something I know is much more than maximum for the reg pressure I've set. It saves me doing shot after shot not knowing when it will max out. By immediately knowing the max velocity, I can start backing down to a certain percentage (usually I do 2% to 3% less)
Of course, this will only work when down tuning a gun. All of the guns I've gotten so far are all tuned much higher than what I want. I have to down tune all of them. In this case, I know my desired tunes are all within the gun's capabilities. If you're up tuning, there will sometimes be a situation when a plateau is not achievable for a given reg pressure with the stock hammer spring.
Of course, this will only work when down tuning a gun. All of the guns I've gotten so far are all tuned much higher than what I want. I have to down tune all of them. In this case, I know my desired tunes are all within the gun's capabilities. If you're up tuning, there will sometimes be a situation when a plateau is not achievable for a given reg pressure with the stock hammer spring.
Upvote 0