The SAGA of a DIANA 56 T/H

[Veerkracht]

Hi HM,

Now that is an very educating write up!
Ot wil take a couple of hours (weeks) to give it the right place.

Do you think it is possible that a pellet is out of the barrel before the action starts moving forwards?

Thanks!

Regards, Robert.

[HectorMedina]

Hi HM,

Now that is an very educating write up!
Ot wil take a couple of hours (weeks) to give it the right place.

Do you think it is possible that a pellet is out of the barrel before the action starts moving forwards?

Thanks!

Regards, Robert.

Hello Robert!

Thanks for your kind words.

According to all the measurements we have done, the pellet takes between 2 and 6 msecs to go from breech to muzzle.
MOST recoiling cycles take between 8 and 16 msecs. And that is without the "Twang".

So, no, I don't THINK that there is a chance of the pellet exiting the muzzle before the piston starts moving backwards, and therefore the action starts moving forwards.

But we will know much more when we have done more accelerometer plots like the one shown in the Epilogue for the ASP20.

Thanks for reading!





HM

[Veerkracht]

HM,
For me it is not possible yet to place vids, but when you type "diana 56 slomo" on youtube maybe you'll find it.
Done some testing in the past.
Otherwise I will place it myselfe when possible.
Regards Robert.

Edit: I use .22 only

[subscriber]

Deze, Robert?

[Sky]

Nice video. Clearly the sled starts moving when the Piston does, as would be expected.

[Nitrocrushr]

Good video, thanks for posting

Steve

[Veerkracht]

Thanks Subscriber!
The vid is made with simple and cheap equipment.
Each frame is +- 1/1000 sec.
You see the pellet leaving the barrel after the barrel started moving forwards again, 1 frame.
In that same frame you see the barrel dropping 0,5mm,
I think this is the area where HM's harmonick tune comes in action.

HM, Is the Original weight calculated for more power and is this a straight line compared to energy?

I also made some vids of the piston of an HW97, one can see it in the action while shooting.
Is it corect to state that the piston in a springer airgun NEVER hits the botom of the cilinder at first stroke?
Even whithout a pellet it didn't.
With a properly tuned action the piston comes at rest after the second stroke, most factory stuff takes 3 times.

Regards, Robert.

[subscriber]

I would think that if the piston did not strike the end of the cylinder when fired without a pellet, that would imply the transfer port was very restrictive.  This would amount to a serious de-tune, below the power capability of that piston mass, diameter, stroke, spring rate and preload.

If you had higher frame rate videos of a powerful springer being fired with and without a pellet, and the dry fire showed the barrel snapping forwards with higher acceleration than with a pellet, that would be evidence of collision between piston and cylinder end during dry fire.  Certainly, the air pressure in front of a dry fired piston should be much lower. Therefore not a very firm "cushion".

Now, there are lots of observations and beliefs on this board that we hold as truth because they seem logical, and no better information is available.  If you read threads about shooting pellets that are "too heavy" or "too light",  two themes emerge:

Heavy pellets cause excessive piston bounce and reduce pellet energy.  This seems to be confirmed by shooting them over chrony.   Shooting light pellets results in harshness that is attributed to the piston impacting the end of the compression cylinder.   Again, the energy of a light pellet is reduced below that of
the "right weight" pellet.   With a light pellet, some of the lost energy goes into impact between piston and cylinder end face. 

If these "facts" are true, then dry firing a similar platform must cause a direct piston collision with the end of the cylinder.    It is something that if repeated is known to break parts...

[Bladebum]

Hector, you are a wealth of knowledge! Thankyou for the good read and info!

[subscriber]

Sorry, Robert, I had not seen your videos before commenting.  Based on your HW97 videos (posted below) I would agree with you except for one caveat:  Data aliasing.

Due to the slow frame rate and obviously jerky replay, it is possible that the piston traveled further than you can see in the video on the initial stroke.  It is just that there were no frames captured to reflect that.  When your sampling rate is too slow it is very easy to get aliasing, where there is an appearance of a trend or natural frequency that is actually false.  Or to simply fail to capture something that actually happened.

The best example I can give you is this:  Watching a short barrel semi-automatic rifle being discharged, with video having too short an exposure, and too slow a frame rate:  Some shots show a large fireball from the muzzle while others show nothing.  This gives the appearance of large variations in flame, but are really just sampling errors.

So, you may be right; but I would like to see slow motion at a frame rate where the replay is smooth.

Perhaps you could contact these guys and collaborate with them:
https://www.youtube.com/user/destinws2
https://www.youtube.com/user/theslowmoguys


One other factor that plays a role in piston bounce is the inertia of the rifle (or more exactly; the relative inertia between piston and rifle).  A third of rifle inertia is the wood stock.  When you remove that, then the compression tube can be pushed forwards and backwards more than if it were attached to the stock.  Thus, piston bounce may be exaggerated because the compression tube is pushed out of the way. 

In the videos you can see exaggerated recoil of the compression tube due to the lost inertia of the missing stock.  So, the piston velocity is reduced from what would be seen with a stock attached.  The missing energy being imparted to the compression tube instead.  If you brace or attach the compression tube to something heavy or solid, the action you capture will be different.  The stock would be idea, but you want to see the cocking slot...

Question:  Is this a "full power" HW97?

[Yogi]

Sorry, Robert, I had not seen your videos before commenting.  Based on your HW97 videos (posted below) I would agree with you except for one caveat:  Data aliasing.

Due to the slow frame rate and obviously jerky replay, it is possible that the piston traveled further than you can see in the video on the initial stroke.  It is just that there were no frames captured to reflect that.  When your sampling rate is too slow it is very easy to get aliasing, where there is an appearance of a trend or natural frequency that is actually false.  Or to simply fail to capture something that actually happened.

The best example I can give you is this:  Watching a short barrel semi-automatic rifle being discharged, with video having too short an exposure, and too slow a frame rate:  Some shots show a large fireball from the muzzle while others show nothing.  This gives the appearance of large variations in flame, but are really just sampling errors.

So, you may be right; but I would like to see slow motion at a frame rate where the replay is smooth.

Perhaps you could contact these guys and collaborate with them:
https://www.youtube.com/user/destinws2
https://www.youtube.com/user/theslowmoguys


One other factor that plays a role in piston bounce is the inertia of the rifle (or more exactly; the relative inertia between piston and rifle).  A third of rifle inertia is the wood stock.  When you remove that, then the compression tube can be pushed forwards and backwards more than if it were attached to the stock.  Thus, piston bounce may be exaggerated because the compression tube is pushed out of the way. 

In the videos you can see exaggerated recoil of the compression tube due to the lost inertia of the missing stock.  So, the piston velocity is reduced from what would be seen with a stock attached.  The missing energy being imparted to the compression tube instead.  If you brace or attach the compression tube to something heavy or solid, the action you capture will be different.  The stock would be idea, but you want to see the cocking slot...

Question:  Is this a "full power" HW97?

Seems to move more with no pellet.  Cool stuff!

-Y

[Veerkracht]

Thanks again subscriber!
It is good to know help shows up when needed.
I also understands your thoughts about the vids.
But
When in doubt, I say reproduce.
I made several vids and each one of them showing the piston not reaching the botom at first stroke.
I asumed at least one vid must have showed up when fps and shutter time was in the question.
For xample: the moving barrel vid shows the pellet leaving the barrel.
I got vids showing no pellet, is was just not there.
Then there is the energy question.
How is it possible for the piston to bounce when there is no air left to bounce on?
So
When it smells like fish, taste like fish, looks like fish, it must be something like a fish.
 

I do not want to take over HM's topic, especialy me being a brand new member.
A forum is there to exchange knowledge and there is so much of it.

Regards, Robert.

This was a 23 joule modified HW97

[HectorMedina]

@ Robert.- More than MY thread it is really Steve's. He did all the hard work, took the pictures, did the writeups. I only put some effort into planning and then presenting everything. Really the credit goes to Steve.
I am very intrigued by your videos, don't know how many videos you took before being able to capture the streak of the pellet, but it is clear it wasn't easy. On one hand, congrats on the perseverance, on the other, I have often said that repeating the same actions expecting a different outcome is either folly or faith. So, take your pick.  ;-)
In general, I do NOT trust videos. Sampling aliasing, as Peter calls it is one reason, the other is that I believe human senses to be totally inadequate for the speeds at which airguns work. If you look at the accelerometer plot in the "Epilogue" of the 56 SAGA, you will note that the smallest scale unit we can show is msecs, but this happens because we have 10 times that resolution in the sampling rate. Otherwise, it would not be metrologically acceptable.
Also I find somewhat peculiar why your 56 goes back, stops, starts moving forward, then pellet exits, then the action still moves further BACK, then another burst of air comes out (0:08 to 0:13).Yes I noticed the special powerplant you are using, and so, this would be my request to you:

The forum is what WE ALL make of it, you raise some VERY important questions and clearly have the time, ability and equipment to throw some light into the matter. SO:

¿Would you be willing to do some videos to make a Blog entry out of them?
We would not "embed" the videos in the blog post, but put links, and I would probably need Peter's help in making a frame by frame analysis. Most probably, you can coordinate among yourselves in Nederlands.
I THINK it would be an interesting collaboration.

You two are very smart persons and I am sure we can achieve an interesting analysis.

Coming now to your questions:

There are THREE weights of HPM:  One for the 12 ft-lbs people, one for the 20 ft-lbs people, and one for the 56 people.
It is the COMBINATION of weight AND location what acts as a dampener of the muzzle's oscillations, thereby shifting the loci of the maximum excursions in TIME. By ensuring that the pellet leaves the muzzle more or less when the muzzle is in one of the extremes, where perpendicular movement has come to a max and now starts heading the other way, we ensure that small variations in MV (natural to EVERY airgun)  will not affect POI.

Can the piston reach the end of the travel without pellet in the chamber? Yes it can. BUT it would mean a TP that is oversized.
What is happening in the HW97? You can clearly see how the spring has "travelling waves" that raise all sorts of havoc.
When there is no pellet in the chamber it does NOT mean there is no air, and air compressed to enough pressure is just as hard as a solid. A flow of air that needs to flow faster than the speed of sound will obturate rather than allow the flow (unless the temperature is driven high enough) so, even without a pellet, the air that is inside the compression cylinder, given a small enough orifice WILL act as a wall.

What we see in your video is that AFTER the pellet is expelled there is ANOTHER jet of air exiting the barrel therefore you need to see that there IS air in the barrel and in the compression chamber, even after the pellet has exited the muzzle. You have proof of that in YOUR OWN video.

If it smells like fish, poops like a fish, looks like a fish; . . .  it could be a politician!

;-)

@ Peter.- Damage does not necessarily demonstrate physical contact between two parts, either a fluid or a supercompressed gas can transmit enough energy to damage parts.
Thanks for your help in this, your frame by frame analysis is brilliant.

See above and let me know if you would like to participate.

@Bladebum.- Thanks!

@ Yogi.- I am still considering your proposal. I just need to find some elements. ;-)

Thanks for reading!






HM

[Veerkracht]

Hector,

Thank you for your reaction!
I will take your suggestion in mind.

Also I find somewhat peculiar why your 56 goes back, stops, starts moving forward, then pellet exits, then the action still moves further BACK, then another burst of air comes out (0:08 to 0:13).

Looking at the results from the Harmonics Expert,
is your 56 is doing the same?

Regards, Robert.

[HectorMedina]

Hector,

Thank you for your reaction!
I will take your suggestion in mind.

Also I find somewhat peculiar why your 56 goes back, stops, starts moving forward, then pellet exits, then the action still moves further BACK, then another burst of air comes out (0:08 to 0:13).

Looking at the results from the Harmonics Expert,
is your 56 is doing the same?

Regards, Robert.

I'll need to send the High Speed camera to Steve and let him do the filming.

If you see the (very bad) video here:

https://www.ctcustomairguns.com/hectors-airgun-blog/a-high-speed-analysis-of-the-way-the-zr-mounts-work

And you look closely at the "fixed" portion of the scope rail in the gun, it would seem that no, the gun doesn't move back further after the first piston strike... But then the video is really bad and it is a full bore,  full power, version.

Keep well and shoot straight!






HM

[subscriber]

Hector,

I appreciate that a fluid can act solid, if a collision happens at high enough speed.  This is what people experience when they jump off a cliff into the ocean.

Rather than argue if the air pressure is high enough or applied abruptly enough to cause damage when a springer is fired without a pellet, I would just contemplate this:  When there is a pellet in the breech, the peak air pressure behind it must be higher than when the same airgun is fired without a pellet, because the pellet acts as a temporary obstruction.

Now, perhaps that peak pressure results in enough adiabatic heating, to then aid the flow through the TP as it is converted to plasma.  Perhaps the lower bulk peak air pressure when fired without a pellet reduces the heating of air, to the extent that the air does not behave as a very thin plasma, but as a much more viscous gas. That, in turn acts to restrict flow through the TP, and cushion the piston?  This would seem like very clever or very lucky engineering.

Or, it is the air near the OD of the piston seal that has to achieve much higher radial acceleration without a pellet loaded, because of the higher peak piston speed:  Just as the piston is about to reach the end of the cylinder, that air might act both as a cushion and as the source of extremely high localized pressure.   Damaging then, perhaps a bit like cavitation causes damage, despite insignificant bulk pressure further away from a pressure vessel wall. 

If one were to attach accelerometers to the compression cylinder and piston, that data should indicate if the whole mass is involved in a significant collision, or just the contact surfaces.

Generally, I think that higher time resolution instruments would be helpful to ensure nothing is being missed...

[Veerkracht]

I think the second stroke is doing the damage without pellet.
It slams dead against the botom of the cilinder.
If I posted the whole vid you would see that the spring reaction after that lasts much longer.
So it is bad for the seal and the spring.
I could hear the "tick" of air going through the barrière.

Regards, Robert

[MartyMcFly]

Since the idea of high speed photography is being discussed, has anyone considered running experiments with a compression tube made out of plexiglass? It would allow filming of the piston in action rather than guesstimating it’s dynamics from recoil measurements.

I’m definitely not a material scientist, but perhaps a plexiglass compression tube could be made on a mini-lathe and matched with a regular barrel/breech in a vise.  Filming the piston and any associated flash from air combustion would be an amazing experiment. The first guy to do it first could be called (insert deep voice) - The man with the plexiglass gun! - Kind of catchy don’t you think? 

-Marty

[HectorMedina]

Hector,

I appreciate that a fluid can act solid, if a collision happens at high enough speed.  This is what people experience when they jump off a cliff into the ocean.

Rather than argue if the air pressure is high enough or applied abruptly enough to cause damage when a springer is fired without a pellet, I would just contemplate this:  When there is a pellet in the breech, the peak air pressure behind it must be higher than when the same airgun is fired without a pellet, because the pellet acts as a temporary obstruction.

Now, perhaps that peak pressure results in enough adiabatic heating, to then aid the flow through the TP as it is converted to plasma.  Perhaps the lower bulk peak air pressure when fired without a pellet reduces the heating of air, to the extent that the air does not behave as a very thin plasma, but as a much more viscous gas. That, in turn acts to restrict flow through the TP, and cushion the piston?  This would seem like very clever or very lucky engineering.

Or, it is the air near the OD of the piston seal that has to achieve much higher radial acceleration without a pellet loaded, because of the higher peak piston speed:  Just as the piston is about to reach the end of the cylinder, that air might act both as a cushion and as the source of extremely high localized pressure.   Damaging then, perhaps a bit like cavitation causes damage, despite insignificant bulk pressure further away from a pressure vessel wall. 

If one were to attach accelerometers to the compression cylinder and piston, that data should indicate if the whole mass is involved in a significant collision, or just the contact surfaces.

Generally, I think that higher time resolution instruments would be helpful to ensure nothing is being missed...

As usual, I think you are absolutely right. AND I would add that BOTH your scenarios are possible and do happen:

Consider that if you seat a pellet too far into the rifling, then MV drops. Meaning that REDUCING the opposing force created by the pellet's inertia and fit into the chamber will ALSO reduce the peak pressure. That is something that we have all experienced (or can easily test).
My experiments with synthetic piston faces led me to believe that the temperature AND the pressure at the compression chamber walls are MUCH higher than at the center. We learned that from the "soot spots" left on the piston's face when I was trying to establish the peak temperature in the compression chamber. So we have reasonable proof of that. IDEALLY, this would mean that the most efficient piston face would have a truncated "aerospike"  in the center. Alas this is not industrially possible, though it would have another positive effect: it would reduce the length of the transfer port.

Now, I don't think it was neither lucky, nor clever engineering.

It is simply the result of over 150 YEARS of EVOLUTION of a basic design. We lost the "fuel" when we went from leather seals to synthetic, but we gained pressure and temperature, and UNDERSTANDING of what is happening.

A simple way of testing if one scenario prevails over the other would be to compare the HW97 to the HW95. Virtually the same powerplant, but the 95 is INCAPABLE of transferring plasma through the TP, whereas the 97 is. So, seeing if there is a difference between the pellet/no pellet relation in both powerplants would teach us something.

¿Are you listening Robert? LOL!

Thanks again for your brilliant explanation.

Keep well and shoot straight!






HM

[HectorMedina]

I think the second stroke is doing the damage without pellet.
It slams dead against the botom of the cilinder.
If I posted the whole vid you would see that the spring reaction after that lasts much longer.
So it is bad for the seal and the spring.
I could hear the "tick" of air going through the barrière.

Regards, Robert

At least in break barrels, we can prove that. Again, see the accelerometer curve of the ASP-20 in the "Epilogue" and you will see that the second piston slam is HIGHER than the first one (the pellet driving one).

Pretty scary,  . . . LOL!

Keep well and shoot straight!





HM