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@dgeesaman tomorrow I should be free. Between the Aerodynamics of Ping-Pong balls, shuttle-cocks, dimpled spheres Freezbies, Canterbury Tails, AGN, and Emily Dickinson, it has been a 6 week LSD trip.We agree on that. Tumbling pellets are an airgun issue (or grossly defective pellet) and not a ballistic behavior thing. It’s like testing the braking performance of tires on a car that’s rolling.
Troy when do your doctors release you into the wild again? The stress might be showing bud. Fun fact I downloaded those papers and a few more last night. I also aligned myself of the formal definition of drag force, which I have been guilty of violating. I have a lot of reading to do.
On the first of these references, it is unfortunate that the tests were all carried out on relatively high nose drag pellet designs, all with recognized poor BC values. This led them to make the wrong conclusion on where the majority of the drag is generated. The wind tunnel tests on pellet shapes I initiated when working also gave some spurious results from pressure measurements (though they were flare stabilized bomblets, not pellets, honest guv)Rafeie M, Teymourtash A.~ Aerodynamic and dynamic analysis of three common 4.5 mm-caliber pellets in transonic flow
Corey K. ~ Airgun pellet performance using computational fluid dynamics
I am eagerly awaiting your peer review paper proving the perceived errors in the papers I referenced are actually errors as well as one additional paper ~ Nicos Ladommatos - Influence of air pellet geometry on aerodynamic drag .On the first of these references, it is unfortunate that the tests were all carried out on relatively high nose drag pellet designs, all with recognized poor BC values. This led them to make the wrong conclusion on where the majority of the drag is generated. The wind tunnel tests on pellet shapes I initiated when working also gave some spurious results from pressure measurements (though they were flare stabilized bomblets, not pellets, honest guv)
As for using CFD for pellets, if you were to make a list of projectile characteristics which cause CFD accuracy problems, pellets have them all. It does produce pretty pictures, which look impressive, though.![]()
So you two are both basically telling us pellets suck. And we need to be shooting slugs? LolI am eagerly awaiting your peer review paper correcting the perceived errors in the papers I referenced as well as one additional paper -Nicos Ladommatos ~ Influence of air pellet geometry on aerodynamic drag .
When pushing my .177 10.3 grain long waisted pellets too fast I found that after they passed the apex of their trajectory they would drop into the target nose high and "keyhole", this was at 60 yards. At about 70 yards they would spiral.Thank you all for your replies and thoughts. I read them and considered all the possibilities offered. Peashooter described the nonrounded holes as keyholing, which is a great way to put it. Beerthief said to use thicker paper for the target, excellent advise. I make targets from posterboard/foam presentation board from dollar tree. Mounted on a DIY pellet trap made from a storage bin. I shoot from the same spot, 25 yards to the target. Spiraling has been suggested, along with deformed/defective pellets. Which makes sense, seeing as all pellets came from the same tin. Washed, lubed, and weighed, and shot at the same session. With the pellets that hit in the rings are nice round holes, as the ones off the rings are keyholes. Perhaps considered flyers. Again, Thanks to all, it was great to see so much response to my post. I am still learning, Thank you!
Well having now read aerodynamic research papers on: boat tailed bullets used for long range competition, diabolo pellets, baseballs, and Ping-Pong balls...... l would say comparing a diabolo to a slug is similar to comparing a Ping-Pong ball to a baseball.So you two are both basically telling us pellets suck. And we need to be shooting slugs? Lol
Sorry. My attempt to inject some humor![]()
I am afraid you will have to wait a very long time then. I did not suggest that the reports were wrong, just that the pellet shapes chosen led to a biased conclusion. This can be easily seen and checked in the calculated drag coefficients, which are higher than those derived from free flight measurements. The tunnel drag coefficients appear to be around 20% higher than measured free flight values.I am eagerly awaiting your peer review paper proving the perceived errors in the papers I referenced are actually errors as well as one additional paper ~ Nicos Ladommatos - Influence of air pellet geometry on aerodynamic drag .
Thanks!
Troy
That is interesting as it matches the results of modelling spiralling on heavy pellets, and appears to be due to the gyroscopic stability factor being too high, making the pellet sluggish in reacting to the changing airflow direction as the trajectory curves down.When pushing my .177 10.3 grain long waisted pellets too fast I found that after they passed the apex of their trajectory they would drop into the target nose high and "keyhole", this was at 60 yards. At about 70 yards they would spiral.
This is a great observation as to when it is happening and what it is doing to effect the impact on target. Pellets can and do get "blown around" by an exssive amount of air leaving the bore directly after the pellet leaves. Commonly referred to as waisting air because the extra air isn't being used to propel the pellet at that point. As an experiment, try turning down rhe power just a little to see if the gun is a bit quieter and no more tumbling flier's or using heavier lead projectile's if you can't adjust power.Thank you all for your replies and thoughts. I read them and considered all the possibilities offered. Peashooter described the nonrounded holes as keyholing, which is a great way to put it. Beerthief said to use thicker paper for the target, excellent advise. I make targets from posterboard/foam presentation board from dollar tree. Mounted on a DIY pellet trap made from a storage bin. I shoot from the same spot, 25 yards to the target. Spiraling has been suggested, along with deformed/defective pellets. Which makes sense, seeing as all pellets came from the same tin. Washed, lubed, and weighed, and shot at the same session. With the pellets that hit in the rings are nice round holes, as the ones off the rings are keyholes. Perhaps considered flyers. Again, Thanks to all, it was great to see so much response to my post. I am still learning, Thank you!
Thank you for your advice. I have a break barrel .177 so the power is not adjustable. I contacted the manufacture for the recommended pellet weight, which they said 7.9 gr. However, I got a tin of Crossman domed 10.3 gr. Which when weighed out they are all over the place. The 10.6gr seem to shoot the best, from this batch. I am going to try a different brand but not sure what weight to try.This is a great observation as to when it is happening and what it is doing to effect the impact on target. Pellets can and do get "blown around" by an exssive amount of air leaving the bore directly after the pellet leaves. Commonly referred to as waisting air because the extra air isn't being used to propel the pellet at that point. As an experiment, try turning down rhe power just a little to see if the gun is a bit quieter and no more tumbling flier's or using heavier lead projectile's if you can't adjust power.
Hard to say which, but bigger or tighter in the bore seem to be working better. Maybe try some medium/heavy weight slugs for accuracy too.Thank you for your advice. I have a break barrel .177 so the power is not adjustable. I contacted the manufacture for the recommended pellet weight, which they said 7.9 gr. However, I got a tin of Crossman domed 10.3 gr. Which when weighed out they are all over the place. The 10.6gr seem to shoot the best, from this batch. I am going to try a different brand but not sure what weight to try.
I would like to try slugs, seem like the longer slug would run truer. Like a boat tail in a powder burner.Hard to say which, but bigger or tighter in the bore seem to be working better. Maybe try some medium/heavy weight slugs for accuracy too.
The lack of tumbling has nothing to do with drag as pellets are not, never have been and hopefully never will be drag stabilized. I explained pellet aerodynamic stability in a thread some time ago, but unfortunately drag stabilization keeps appearing in posts, and videos, as in the above-mentioned video series.
All types of stability, including aerodynamic and gyroscopic stability, are dependent on moments, not forces. The drag force has practically zero moment about the CG, whereas the normal forces produced by the flare when at an angle of yaw produce correcting moments about the CG. Drag has little or no contribution to the centre of pressure position, which is dominated by normal forces produced by the pellet shape. For your information, the flat based slug also has much higher drag at the base than it does at the front, yet it is not aerodynamically stable.Well, I do not fully agree with you when you say pellets are "not drag stabilized". Yes, drag is not the only form of stabilization on a pellets but a large percentage of the stability, and the ability to "self correct//stabilize", on a pellet comes from the fact that the center of gravity (GoC) of a pellet in flight is in front of the center of drag (CoD), change that by giving a pellet less drag at the back by giving it more of a boat tail and you will see the stability disappearing VERY quickly.
You will have to watch your barrel twist rate with slugs. The twist rate will dictate a maximum length for the slugs which can be stabilized. Boat tails make slugs less stable and require a faster twist rate to be stable than the equivalent cylindrical based slug of the same length.I would like to try slugs, seem like the longer slug would run truer. Like a boat tail in a powder burner.
The drag produced by the flare is there all the time, but it becomes more pronounced, and is directional when the pellet is disturbed (in yaw) and that is what causes the pellet to try and auto correct. That is the beauty of a traditional pellet and why it will even work to some extend from a smooth-bore barrel. The same "drag cone" principal was used to stabilize and auto correct other larger projectiles fired from barrels and dropped from aircraft though these days other "active" correction methods are preferred. It is a field I was involved in on large calibers (mostly 150mm and air to ground weapons) in the mid 1980's.All types of stability, including aerodynamic and gyroscopic stability, are dependent on moments, not forces. The drag force has practically zero moment about the CG, whereas the normal forces produced by the flare when at an angle of yaw produce correcting moments about the CG. Drag has little or no contribution to the centre of pressure position, which is dominated by normal forces produced by the pellet shape. For your information, the flat based slug also has much higher drag at the base than it does at the front, yet it is not aerodynamically stable.
The true aerodynamic stability of pellets was explained in this thread. https://www.airgunnation.com/threads/aerodynamic-stability-of-pellets.1276895/