GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: oldpro on March 23, 2021, 07:54:17 PM
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On a typical gas ram or magnum break barrel does anyone know the heat it produced on its firing cycle and pressure?
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IIRC, Cardew said about 1500 psi and about 800*F....
Bob
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Hi Travis, If you knew what the seal material was, the manufactures specs. would list the heat range of the material.
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For a modern magnum spring piston rifle there are a lot of factors that can vary the peak pressures and temperatures. I think you will find peak pressures can spike into the 2000-4000 psi range and temperatures can spike into the 2000 degree F range. The temperature spike duration is very short (maybe 100 -200 microseconds?) and the thermal mass of that air volume is small so synthetic seals are not damaged by the brief exposure.
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For a modern magnum spring piston rifle there are a lot of factors that can vary the peak pressures and temperatures. I think you will find peak pressures can spike into the 2000-4000 psi range and temperatures can spike into the 2000 degree F range. The temperature spike duration is very short (maybe 100 -200 microseconds?) and the thermal mass of that air volume is small so synthetic seals are not damaged by the brief exposure.
"so synthetic seals are not damaged by the brief exposure."
Hummmm.....depends on the number of shots, mechanical condition and tune level of the gun, the seal material (early FWB 124 sporters were notorious for seal breakdown) and even lubing procedure..........
(https://i.imgur.com/kfIIHga.jpg) (https://i.imgur.com/pXwwwTx.jpg) (https://i.imgur.com/l5rIlGt.jpg) (https://i.imgur.com/hlHUIlH.png)
A couple early broken down FWB sporter seal pics.......
(https://i.imgur.com/JiEiK3Y.png)(https://i.imgur.com/4gjApua.png)
Anywhoo, generally you're correct with the newer HW piston seals, however I have seen a few with cracked seal faces like this.........
(https://i.imgur.com/gRq0z07.jpg)(https://i.imgur.com/R1S6sDD.jpg)
I replaced my oring sealed piston cap with a properly fitted newer design HW95 piston seal (the HW factory seals can be undersized) and didn't have any "erosion issues" during the 1200 shot test. After the test I replaced it with my "home rolled" oring sealed piston cap..........
(https://i.imgur.com/DCnUGNM.jpg) (https://i.imgur.com/JaMH7MG.jpg)
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With respect to the heavily referenced work by Cardew, I think we need to take it up a notch when discussing MODERN Magnum Springers. The air rifles TODAY (40+ years later) use polymers that didn't exist back then and magnum muzzle energy levels are now up to 34 fpe as opposed to the previous work at a much lower fpe.
If anyone is seriously interested in the Physics of spring-piston air rifles, you should read/download this...
https://www.researchgate.net/publication/274638905_Internal_Ballistics_of_Spring_Piston_Airguns (https://www.researchgate.net/publication/274638905_Internal_Ballistics_of_Spring_Piston_Airguns)
Peak temperatures and pressures occur during pellet travel in the bore and are significantly
higher than the corresponding values at bounce time. The highest chamber pressure and
temperature are 29,248 kPa and 1452 K, respectively, while the highest values for the
breech are 27,298 kPa and 1,506 K.
1452 K = 2154 F
29248 kPa = 4242 psi
If you have read that and though it was well done, this next one is an eye-opener also!
https://www.researchgate.net/publication/277953420_Spring_Buzz_and_Failure_in_Spring_Piston_Airguns (https://www.researchgate.net/publication/277953420_Spring_Buzz_and_Failure_in_Spring_Piston_Airguns)
Sweet! ;)
(Credit and thanks to Tom Tucker https://www.gatewaytoairguns.org/GTA/index.php?topic=161010.msg155792808#msg155792808 (https://www.gatewaytoairguns.org/GTA/index.php?topic=161010.msg155792808#msg155792808) for introducing me to this excellent analysis.)
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So, very close to the melting point of steel!.... and way past that of aluminum or synthetics.... or lead!.... ::)
Bob
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RE the reference you linked, a paper by Dr. Domingo Tavella, there is a diagram on page 28 (fig. 10) which shows the firing cycle for a Beeman RS2.... It gives the chamber pressure at piston bounce as 5273 kPa (765 psi) and the temperature as 1218*K (1732*F).... Your quote occurs immediately after that diagram.... Are not all the numbers given the result of calculations?.... There are many assumptions made in the model, including zero transfer of heat and energy to the parts of the gun, and the conclusions mention other possible sources of error....
While I have tremendous respect for Dr. Tavella (whom I communicated with regarding his paper on PCPs during his brief stay on the GTA), I believe that thermodynamics, while a useful tool towards understanding the internal workings of an airgun, may be on the opposite side of the spectrum (Theoretical vs Experimental) to using simple assumptions such as Lloyd and I do now on PCPs.... and that the truth lies somewhere in the (very complicated) middle.... There can be no doubt that what happens during firing of an airgun DOES affect the temperature (and indeed condition) of the parts, as shown by the melted and eroded seals in the posts above.... so cannot be a completely Adiabatic process....
Bob
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I read and understood the simplifications made. The good agreement of the model and chronographed pellets implies the simplifications aren't generating any gross errors. I apparently have more trust in the theoretical thermodynamics as presented.
Simplified calculations/estimates can be VERY useful tools. When quick estimates provide good-enough results I'll use them every time. No point in solving multiple simultaneous coupled differential equations with a computer unless you are writing a thesis or a research paper. That said, my THANKS to Dr. Tavella for making the effort so that we don't have too ;)
My springer practice routine is usually 5-15 groups of 10 shots each. I have on occasion seen a small but measurable (chronograph data) difference from the first couple "cold" bore shots to a more stable and consistent "warm" bore string. IMO that means adiabatic heating is not 100% because some heat is being added to and retained by the internal parts. This is confirmed in his paper.
I set up a simplified "springer" computer simulation prior to reading Dr. Tavella's paper and thought I was getting simulation errors because peak pressures were around 150 bar with no heating (my over-simplification). With heating my pressures would spike over 250 bar which I "thought" was too high (a simulation error).
I was further confused when I examined some pellets I fired from a 200 bar unregulated PCP and a magnum springer (Hatsan Mod125). The skirt deformation on the PCP pellet was barely visible while the skirt deformation on the springer pellet was MUCH larger. In this one specific case my conclusion is the peak springer pressure was higher than the PCP pressure of 200 bar. After seeing those bloated springer pellets and then reading Dr. Tavella's paper I'm thinking the higher than expected peak pressures from my simulation and the peak temperatures from his paper are not far from what is really happening inside these air rifles.
Regarding seal damage... for the brief exposure to a single shot of a normal functioning springer there is effectively no seal damage. I stand by that statement and we can agree to disagree on the minutiea. Is there cumulative wear, impact, and thermal damage over 1000 to 5000 to 10000+ shots? Of course there is.
Images of...
crumbling 40+ year old polymer seals
transfer port melt-erosion
blackened seal surfaces with little penetration
erosion channel down the side of a seal from superheated air
seal in near new condition after 1200 shots
I've seen (and repaired) many similar seals so all these images are familiar.
Some of the conditions are given, but many are not. What I'd like to know regarding these images:
How old? (polymers can degrade over time regardless of use)
How many shots? (cumulative impact, wear, and thermal damage is a certainty)
How many dry-fires? (depends on the rifle, but this minimal resistance piston impact can be physically brutal)
How much and what kind of oil & grease were used? (especially in the carbon black images, the increased pressure and thermal damage from excessive dieseling can greatly shorten seal life)
Uncertain why Travis asked for the numbers. All this may just be noise instead of an answer to his real question. Hopefully he'll explain in more detail?
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Looking deeper into this and running some simulations this weekend. I should have some good data that will define the possibilities.
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Getting test data for the temperature spike is not easy. Looks like Lloyd did some testing with a fine wire TC back in 2019 https://www.gatewaytoairguns.org/GTA/index.php?topic=163928.msg155828828#msg155828828 (https://www.gatewaytoairguns.org/GTA/index.php?topic=163928.msg155828828#msg155828828). He didn't post a transient response but commented on the difficulty of catching the spike. The Omega TC page shows a 3ms time constant for a .001" wire TC which is too slow for this measurement, probably need less than a tenth of that. There are some papers on sub-ms sensors, but applying them to a high temperature may be tough.
I wonder if a testbed gun that has a small port for a probe with the tip holding whiskers of different materials could narrow down the temperature by what survives.
For the departure from adiabatic, I have seen some papers that try to establish the heat transfer coefficient in an air compression cylinder. That applied to a particular temperature trace could provide a ballpark estimate of the energy lost.
I think from the various testing threads (e.g. George's Titan hacking thread) we have methods and results for a lot of the shot cycle....except for the temperature curve.
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Seems to me this is one of the situations where measuring the temperature will alter the results.... eg. using a wire that melts, or a temperature probe that heats up, etc.etc.... Anything that works will by definition be altering (lowering) the actual temperature spike.... The result would have to be worded " the temperature exceeded XXXX *F "....
It sound like Travis might be trying to utilize Adiabatic compression to increase power output in some way.... I'm sure he must realize that Adiabatic compression works both ways, and if you use that energy spike to heat a larger volume of air, or turn it into Kinetic energy, you will lower the spike temperature and pressure.... Perhaps he is thinking of using a PCP to accelerate a piston, which will then fire the pellet from the compressed air.... hoping for boost in power?.... My gut tells me that inserting another step in the process will reduce efficiency, rather than increase it.... but I could be way off on what he might be working on.... ::)
Bob
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Seems to me this is one of the situations where measuring the temperature will alter the results.... eg. using a wire that melts, or a temperature probe that heats up, etc.etc.... Anything that works will by definition be altering (lowering) the actual temperature spike.... The result would have to be worded " the temperature exceeded XXXX *F "....
It sound like Travis might be trying to utilize Adiabatic compression to increase power output in some way.... I'm sure he must realize that Adiabatic compression works both ways, and if you use that energy spike to heat a larger volume of air, or turn it into Kinetic energy, you will lower the spike temperature and pressure.... Perhaps he is thinking of using a PCP to accelerate a piston, which will then fire the pellet from the compressed air.... hoping for boost in power?.... My gut tells me that inserting another step in the process will reduce efficiency, rather than increase it.... but I could be way off on what he might be working on.... ::)
Bob
None of those things but your getting warmer!!!
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Perhaps he is thinking of using a PCP to accelerate a piston, which will then fire the pellet from the compressed air
Bob
That of course is the way hypersonic launchers and gun tunnels work.
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On a typical gas ram or magnum break barrel does anyone know the heat it produced on its firing cycle and pressure?
To reverse engineer the question, I suppose the answer to that questions can be solved by looking at the oils which cause dieseling effect.
For example, flash point of many petroleum based oils is 60 degrees Celsius. Then, see what pressure generates the heat needed for the oil to flash. That will be the minimum pressure in the chamber, but I suspect it is much higher.
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Miles.... Yes, but don't they use a light gas to drive the projectile?.... and a burning propellant to drive the piston to compress said gas?.... I was not aware of any using compressed air to drive the piston (ie a PCP)....
Phillip.... I would suggest that is then no longer an airgun.... at least not by your Federal definition of one....
Bob
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Miles.... Yes, but don't they use a light gas to drive the projectile?.... and a burning propellant to drive the piston to compress said gas?.... I was not aware of any using compressed air to drive the piston (ie a PCP)....
Phillip.... I would suggest that is then no longer an airgun.... at least not by your Federal definition of one....
Bob
I dunno, Bob. Black powder guns aren't considered firearms by the U.S. federal definition. Couldn't see an airgun taking lead on that.
Now, we do have some localities here that have rules akin to Canadian laws on airguns.
You must be in Canada, eh?
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Yep.... Airguns are firearms here, and long guns if over 500 fps fall in the "Non-restricted" catagory.... Licensing used to be required, but other than in Quebec, currently isn't.... Handguns over 500 fps are "Restricted" however, with severe restrictions on their use and transportation, and they must be licensed by a person with a "Restricted P.A.L."....
Definition of a Firearm according to the ATF:
18 U.S.C., § 921(a)(3)
The term “Firearm” means:
1. Any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive;
Reference.... https://www.atf.gov/firearms/firearms-guides-importation-verification-firearms-ammunition-gun-control-act-definitions (https://www.atf.gov/firearms/firearms-guides-importation-verification-firearms-ammunition-gun-control-act-definitions)
In numerous place, in U.S. Federal Law, airguns are NOT considered firearms, because they use a compressed gas, not an explosive.... There may be many exemptions regarding the USE of blackpowder guns from licensing, etc., but my understanding is that they are still firearms.... If you have a statute to the contrary, please present it....
Bob
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Well, yes. In the formal and technical sense black powder are indeed firearms. Though, by the GCA they are not. Specific classification as "antique" regardless of their production year.
As far as licensing, in general there is no licensing required in the U.S. for ownership, under federal statute, for any firearm that is not an NFA item. When an NFA item (AOW, SBR, Silencers, machine guns...) It's a tax - not so much a license.
Only a form 4473 transfer is required from point of sale when the seller is an FFL with firearms; not required for "cash and carry sales" i.e. from one private party to another. FFL provisions still apply, just not documented via 4473 or verified by background. That is, one cannot, legally, knowingly sell to a person prohibited from otherwise owning the firearm.
So, by our standards here is the U.S., in the modern sense of our ways, we do not consider black powder to be firearms since there are no 4473 forms required and convicted felons otherwise barred from owning firearms can own them and their sale does not require an FFL, etc.
I have an FFL and employed as a federal agent that investigates this very thing from time to time. If we were to raid a felon's abode and found BP weapons, we cannot charge them for the possession unlike with cartridge firing weapons.
With that being said, crimes committed with BP are treated no differently than their counterpart. Same for airguns, too. Same for a bar of soap carved to look like a firearm, as well.
Still, yes. Yes they are firearms, but in a manner of semantics ownership wise.
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Thanks for the clarity, nice to know.... 8)
Bob
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Miles.... Yes, but don't they use a light gas to drive the projectile?.... and a burning propellant to drive the piston to compress said gas?.... I was not aware of any using compressed air to drive the piston (ie a PCP)....
Phillip.... I would suggest that is then no longer an airgun.... at least not by your Federal definition of one....
Bob
The working gasses were nitrogen or air. The maximum Mach number was 12.9. The piston was driven by compressed gas from two high pressure chambers separated by a bursting copper diaphram. The first chamber had two diaphrams, one at each end, and each diaphram was rated at a certain psi. So the first chamber was pumped up to the rated psi, but the second chamber could be pumped up to twice the rated psi without overloading the diaphram separating the two chambers. When the first diaphram was burst then the second in between the chambers would be heavily overloaded and would also burst.
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https://www.nasa.gov/centers/wstf/site_tour/remote_hypervelocity_test_laboratory/two_stage_light_gas_guns.html (https://www.nasa.gov/centers/wstf/site_tour/remote_hypervelocity_test_laboratory/two_stage_light_gas_guns.html)
It even comes in .17 caliber
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Miles, thanks for that history.... I was not aware of a PCP version, only the "light gas guns" used for hypersonic research (eg. micrometeorite collisions, etc.).... as per the example in Stan's post above this one.... With the maximum velocity possible being Mach 5 for the gas used, at the temperature reached, it is obvious why they use Hydrogen or Helium as the gas which is compressed by the (powder driven) piston to fire the projectile.... Did the pressurized chambers you describe drive the projectile directly, or did they in turn drive a piston to perform Adiabatic compression on yet a third volume of air?.... or was the final chamber filled with a light gas?....
Bob
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A large plastic piston was used which compressed the gas, air or nitrogen, which then went through a nozzle to produce the gas flow speed wanted for either the shock tunnel or the launcher depending on what it was being used for. I think the lowest speed nozzle (Mach 8.4) was used when it was being used as a launcher and I vagely remember speeds of around Mach 6 for the projectile though of course it depended on the size and weight of the projectile, which only went a very short distance before hitting a target block or being caught depending on the experiment.
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So a two stage device, the compressed air which is released by the burst discs drove a piston, which provided the (adiabatically) compressed air for the shot....
Bob
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Basically yes. The gas compressed by the piston went through a condi nozzle to produce the required velocities. The air flow only lasted for a fraction of a second but was enough to obtain the measurements when used as a hypersonic wind tunnel.