Photo cycle Dynamics in three or more Spring-Piston Airguns Chap four

The particular editor wishes to apologize to the readers for the hold off in publishing this section.
The publisher takes full responsibility with this delay, in no way was this particular the Author’s fault.
So , let’s return to business:

LGU/LGV energy plant swap: How does altering power plants affect functionality and does a longer offset move port make a difference?

This journey was initiated by Yogi’s (of GTA fame) query about how transfer port (TP) geometry affects the overall performance of spring piston surroundings rifles. Most break-barrel and several underlever (HW 77-97 series) air rifles have the TP located above the center of the particular compression tube, whereas the particular newer underlevers (TX200, LGU) have a TP that is dedicated to the compression tube. John Tyler has written many articles in Airgun Planet Magazine where he varied the particular TP diameter and size in the same rifle, yet to our knowledge, no one has been doing a detailed comparison of main and non-central TPs. Hector realized that the Walther LGU and LGV were almost identical except for the TP geometry, so he recommended we compare these two guns more closely to try to solution Yogi’ s question. In this particular chapter, I swapped the particular piston, mainspring, and activate group between the LGU plus LGV. In principle, utilizing the LGU power plant within the LGV, and vice versa, should help isolate the consequence of the TP geometry. Preferably, everything except the TP geometry should remain exactly the same when the swap is made. When one takes the power vegetable from the LGU and describes in the LGV, the main difference is going to be that the LGU spring is usually pushing air through a lengthier, offset TP compared to in order to was in the original LGU compression setting tube. The same is true once the LGV power plant is positioned inside the LGU. Does the particular LGV power plant learn better when it’ s pressing air through the short, focused TP in the LGU? However, other things also change once the swap is made. For example , the particular fit of the piston close off in the compression tube is certainly slightly different. Ideally you might take the same rifle plus move the TP close to, as Mr. Tyler do with TP length plus diameter, but this would be very hard and would involve creating a highly specialized rifle.
Figure 1 discusses the accuracy of the LGU before and after swapping its energy plant with the LGV. Precision is better and velocity is all about 20 fps lower prior to the swap. The standard deviation within muzzle velocity is nearly similar, suggesting that the consistency from the power plant does not rely on which rifle uses that will power plant.  

Fig. 4. one LGU accuracy based on 10-shot groups from the bench in 20 yards before a) and after b) the exchange with LGV piston, springtime and trigger group.
Physique 2 shows the precision of the LGV before and after changing its power plant using the LGU. The LGU acquired about 20 fps using the LGV power plant however the LGV dropped by a lot more than 66 fps with the exact same batch of QYS Cupola pellets when it used the LGU power plant! This shows that the LGV was much better tuned for its power flower and is more sensitive in order to power plant changes compared to LGU. Overall, accuracy had been better before the swap, however the first three groups along with JSB Exact 4. 53 mm after the swap certain look good!

Fig. 4. 2 LGV precision based on 10-shot groups in the bench at 20 back yards before a) and after b) the swap with LGU piston, spring and cause group.
Now let’ t take a look at the efficiencies from the two rifles before and after the particular swap, as shown within Fig. 3. The effectiveness of the LGU dropped significantly with the LGV power place. Cocking work increased can be 22% but the muzzle power increased only by about 5%. The efficiency of the LGV also dropped when using the LGU power plant, but not as much. Even with the LGU strength plant, the efficiency from the LGV was still very good, especially with the JSB pellets. It’ s interesting the fact that most efficient pellet depends on the energy plant. I would have naively expected that it just depends upon what pellet friction in the weary, but it’ s very clear that with its original strength plant, the LGV has been slightly more efficient with QYS Dome pellets, but with the particular LGU power plant, the particular LGV was significantly more effective with JSB 4. 53mm pellets. The LGU’ t greater efficiency loss within using a borrowed power vegetable could be due to the TP, yet there may be other reasons. For example , this may also happen if the LGU piston seal is a bit small compared to the LGV piston close off. In that case, the LGU piston seal would slide along with very low friction in the LGV compression chamber whereas the bigger LGV piston seal might be a tighter fit in the LGU compression chamber, which would after that encounter more friction plus produce lower muzzle velocities. I didn’ t observe much of a difference in piston seal friction when placing the pistons, but if I actually were to do this experiment once again, I would have kept the particular piston seals on the authentic rifles, that is, put the LGV piston seal on the LGU piston when inserting the particular LGU piston into the LGV and put the LGU piston seal on the LGV piston when inserting the LGV piston into the LGU.  

Fig. four. 3 Cocking work plus efficiency of LGU plus LGV with original plus swapped internal parts.
An additional possibly important factor in the exchange is that the LGV uses a good anti-bounce piston (ABP), which usually we expect to increase snout energy by about 10% (see Chapter 2). Maybe the particular ABP is working much better in its original home, the particular LGV, than in its brand new host, the LGU? To obtain a better idea of how the weapons are recoiling, which furthermore could give some hints about how the ABP can be working, I measured the particular recoil traces of each rifles before and after the power grow swap, as shown within Fig. 4. The recoil of the LGU gets considerably stronger with the more powerful LGV spring, as can be seen with the position, velocity and speed plots in Fig. 4a). The second dip in the speeding is clearly deeper with all the LGV spring. On the other hand, the very first positive peak in the speeding is a little bit smaller with all the LGV spring. Maybe the particular ABP is moderating the particular abrupt slowdown of the piston before it starts going backward? These strong adjustments in recoil result in a little increase in the muzzle speed. Unlike the LGU, the particular LGV shows very small modifications in recoil (Fig. 4b) that are accompanied by a much larger reduction in muzzle velocity. There is extremely little difference between the original plus swapped power plants within the first few oscillations from the LGV’ s acceleration even though the muzzle velocity falls by 66 fps once the power plant is changed.

Fig. four. 4 Recoil traces displaying the position, velocity, and speed of the sled-mounted rifles more than 250 ms for the a) LGU (AADF) and b) LGV (JSB Exact) along with original (blue traces) plus swapped (red traces) piston, mainspring, and trigger team.
Figure 5 zooms within on the early parts of the particular recoil traces for the LGU (Fig. 5a) and the LGV (Fig. 5b). Also proven in the velocity vs period plots are the light door traces, which show once the pellet exits the snout. The timescale for the recoil plots was shifted in order to align the pellet get out of times for the original plus swapped components. It’ h surprising how little the particular recoil changes when energy plants are swapped, recommending that the dominant factor in recoil is not the power plant, however the rest of the rifle!? It wants me like the LGU recoil remains distinct from the LGV recoil regardless of which strength plant it uses. This is specifically puzzling since the LGV strength plant uses an ABP and the LGU power seed doesn’ t. For example , the particular shoulder just before the first top in the LGU velocity (see black arrow in Fig. 5a) occurs with both strength plants. Also, the distinct flattening at the top of the first speed peak for the LGV (see black arrow in Fig. 5b) occurs with both energy plants. The LGU strength plant does appear to improve this flattening, so probably this is where the ABP is important? Furthermore, the LGU springtime is nearly dry with a really light coating of Superlube whereas the LGV mainspring has a heavy coating associated with tar. This doesn’ big t show up very strongly within the recoil traces. Part of this particular apparent insensitivity in recoil to the power plant is a result of the far greater total bodyweight of the LGU rifle, which usually simply rescales the up and down axes in the recoil and building plots; it’ s harder to obtain a heavier rifle moving. The particular LGU will always be heavier compared to LGV, regardless of power flower! However , the qualitative form of the recoil traces appears to not depend much for the power plant and this is probably where we’ re viewing the TP geometry producing its biggest impact?   Naturally , all this analysis has to be used with a grain of sodium since the rifle is continuing to move forward in the sled given the particular huge forces pulling to the Velcro strap at the piston bounce, as Steve within NC pointed out in the Airgun Warriors thread.

Fig. 4. 5 Recoil traces showing the positioning, velocity, and acceleration of the sled-mounted rifle over 50 ms for the a) LGU (AADF) and b) LGV (JSB Exact) with original (blue traces) and swapped (red traces) piston, mainspring, and trigger group. Pellet exit times are marked by vertical black lines. Black arrows show distinctive features in the velocity traces.
In the final two figures we look at the recoil energy for the LGU (Fig 4. 6) and LGV (Fig. 4. 7). Since we know how the entire rifle moves during recoil, we can determine its kinetic energy as a function of time or position. This is important and interesting since the movement of the rifle can affect the POI. There are three ways to determine recoil kinetic energy of the moving rifle and sled. The easiest way is to use the formula E=½ mv^2, where E is the kinetic energy (the energy of motion), m is the mass of the rifle and sled added (since they’ re moving together) and v may be the velocity of the rifle and sled. Figure 4. 6a) shows the kinetic energy of the rifle and sled system as a function of time. Note that this energy is definitely positive; whenever you square a genuine (positive or negative) amount like velocity you get a beneficial answer. The kinetic power oscillates just like the velocity. Since the rifle recoils backward, the particular peak energy absorbed by rifle occurs at close to 0. 007 s, which usually corresponds to a sled placement of -3. 6mm in accordance position vs time story at the top of Fig. 4. 5a). This peak energy is certainly 2 . 4 J (1. 8 ft lbs) for that original innards and 3 or more. 0 J (2. two ft lbs) for the changed LGV innards. I positioned red and blue dots to mark these placements. The second way to determine the particular recoil energy is to use the particular instantaneous power at period t, P(t), which is only the product of the force plus velocity at that time. One can after that just integrate the power in the starting time to time t to find the energy expended in recoil during that time window. Even though I don’ t storyline the result, it looks just like the plot in Fig. 4. 6a). The third method to get the recoil energy would be to plot the force Farreneheit as a function of placement x, F(x), and then incorporate that force from the beginning position to some position by to get the energy expended to get at x. The integral together x is bit more difficult since the dx intervals differ (remember that we record having a constant time interval among points, but the distance involving the positions of neighboring factors will vary as v varies). I used this method to figure out recoil energy vs place by plotting the pressure as a function of placement x (not time! ), as shown in Fig. 4. 6 b) plus d) integrating the pressure over position, as demonstrated in Fig. 4. six c) and e). Within Fig. 4. 6 b) and d), the story retraces itself as the gun moves back and forth in position. By using this technique we see that the particular peak recoil energy takes place when the sled position about -3. 6 mm, just like be seen in Fig. four. 6 c) and e).   I placed red-colored and blue dots in order to mark these positions. Now i am very relieved to see the positions and times of such peaks, as well as the peak beliefs agree pretty well using the 3 methods. Newton was correct! The further oscillations within energy appear to be pretty constant when comparing E(t) and E(x). The recoil energy highs about 0. 003s prior to the pellet leaves the barrel or clip. So this peak recoil power could have a big impact on precision, as the rifle reaches the maximum kinetic energy before the pellet leaves the particular barrel.   The more the particular rifle moves before the pellet leaves the barrel, the particular harder it will be to collection pellets on top of each other! Within Fig. 4. 6 you can see that the peak recoil energy increases by about 25% when the LGV spring is utilized in the LGU. Unfortunately, this particular strong (25%) increase in maximum recoil energy is with a very weak (5%) embrace muzzle energy.

Fig. 4. 6 Recoil energy of LGU along with original (blue) and changed (red) internals: a) recoil energy vs time plus pellet exit traces, b) and d) force versus position, and c) plus e) recoil energy versus position. The peak recoil energies are indicated red-colored and blue solid sectors and are the same whether one particular uses kinetic energy within a) or integrates power in c) and e).
In Figure 4. seven I do the same recoil power analysis for the LGV using its original and LGU innards. In this case, “ original” indicates the ABP piston, which usually certainly is not a standard piston in the LGV, but it’ s what the LGV experienced when I got it. Again, three techniques for obtaining recoil power produce the same results. Time (Fig. 4. 7a) plus position (Fig. 4. seven c and e) from the recoil energy peak are usually 0. 006s and -4. 0 mm, respectively. They are very similar to the values attained for the LGU and are in line with the position of the sled during those times (Fig. 4. 5b). In this instance however , the original and changed innards produced almost the exact same peak recoil energy associated with around 3. 5 M (2. 6 ft lbs).   This is surprising because the original ABP in the LGV produces about 19% a lot more muzzle energy compared to the LGU piston and spring within the LGV. So for the same top recoil energy, the ABP in the LGV produces regarding 19% more muzzle power. Unfortunately, the ABP doesn’ t produce a similar improvement in the LGU, but this particular isn’ t surprising because the ABP needs to be specially fine-tined for each rifle. The maximum recoil energy is increased in the LGV (2. six ft-lbs) compared to the LGU (2. 2 and 1 . 6 ft-lbs), which is due to the lighter in weight mass of the LGV. There’ s another very fascinating and possibly important difference between LGU and LGV recoil energy traces. In the LGV, the pellet exits a little later and the recoil power peak occurs a bit previously, so at the time of the pellet exit the LGV is certainly moving less than the LGU. If the pellet were to keep another millisecond or so later on, the LGV would really be at rest at the moment the pellet leaves the barrel or clip. Unfortunately, all the motion prior to the pellet leaves the barrel or clip could disrupt the aim, therefore there may not be much of an edge in having the rifle fixed at the moment the pellet simply leaves the barrel. You really will need the rifle to not shift at all from the trigger draw to the pellet exit, not merely during the pellet exit.

Fig. 4. seven Recoil energy of LGV with original (blue) plus swapped (red) internals: a) recoil energy vs period and pellet exit remnants, b) and d) drive vs position, and c) and e) recoil power vs position. The top recoil energies are pointed out red and blue strong circles and are the same whether or not one uses kinetic power in a) or combines force in c) plus e).
The main conclusion of the first swap test is it may be too soon to make any kind of strong conclusions. It is obvious that the LGV is just as effective as the LGU, so any kind of arguments about the inefficiency associated with long, non-central TPs doesn’ t apply here. Right now there also was a strong asymmetry in the muzzle energy obtain and loss when strength plants were switched. The particular LGU gained much less compared to LGV lost when the strength plants were switched. Probably the ABP was enhanced for the LGV and didn’ t produce the same level of improvement in the LGU? Additionally, it is clear that the distinctive recoil traces of the two weapons was maintained even after the strength plants were switched, which implies that the rifle itself (maybe the TP geometry) much more important than the actual strength plant in determining the way the rifle recoils. It’ ersus also interesting that the maximum recoil energy significantly improved in the LGU when using the more efficient LGV spring and ABP, but that the increase in snout energy was very fragile.
​ On the other hand, the ABP within the LGV produced the almost the same peak recoil power as the LGU piston plus spring, but with a much increased muzzle velocity.
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