Handyguy wrote:
Would converting a piston to aluminum (to reduce weight and recoil) affect performance?
And it all started with such a simple question
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| Springer piston dynamics https://www.airgunforum.ca/forums/topic66162-60.html |
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| Author: | rsterne [ Sat Jan 17, 2015 4:13 pm ] |
| Post subject: | Re: Springer piston dynamics |
Dieseling, NO.... Controlled combustion is what the Cardew's found, tested, and explained in their books.... They are a must read for anyone seriously interested in springers.... Bob |
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| Author: | Penage Guy [ Sat Jan 17, 2015 4:22 pm ] |
| Post subject: | Re: Springer piston dynamics |
Has the Cardews' experiment using a nitrogen only atmosphere been reproduced? If it has, no one has remarked on it very much. It seems that the idea that some combustion occurs and that explains the springer's degree of power has been taken as a self-evident truth that should not be questioned. |
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| Author: | rsterne [ Sat Jan 17, 2015 4:26 pm ] |
| Post subject: | Re: Springer piston dynamics |
Not as far as I know.... I'm a "combustion agnostic", but to tell you the truth I really don't care enough to do it, my interest lies in PCPs.... Bob |
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| Author: | joe hickey [ Sat Jan 17, 2015 4:56 pm ] |
| Post subject: | Re: Springer piston dynamics |
Since we're talking about heat as a probable cause as to why springers are capable of such power, I was reading yesterday Jim Macari,s findings that the transfer port of a springer is more efficient if its rough instead of polished, to introduce friction as the air moves past it, which in turn creates more heat, and thus more power and efficient use of the air.He experimented with drilling steps in the pressure side of the TP, but if turbulence is considered a benefit for producing heat then perhaps simply tapping the Tp without increasing the dia. Might work even better. |
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| Author: | Chevota [ Sat Jan 17, 2015 6:40 pm ] |
| Post subject: | Re: Springer piston dynamics |
A rough transfer port might generate a slight increase in temp, but the restriction in flow more than kills anything that might be gained. That makes as much sense as a pcp having a rough port to heat the air, which would also be a failure. You want the air to get thru the port as quickly as possible, any delay will cost you. Well, there are other factors, you don't want to sacrifice too much pressure in exchange for the flow. As for the combustion theory, I have never used an O2 free charge of air in a springer, but I did test a gun using only tungsten disulfide dry lube. The gun was cleaned using brake cleaner and hot soapy water to completely strip it of oil. As expected the velocity did not drop. Actually it did gain a few fps after I coated everything with light motor oil, which I attribute to better sealing at the main and breech seals, but if it was the oil burning it was not even close to what the Cardews claimed. I could fill one with some misc inert gas as a test, which I do have lying around, but what's the point. Unless O2 or the O2/N2 mix itself burns at those pressures/temp, and obviously it doesn't, there's no point in testing O2 free. Some people have told me they've used Krytox oil which apparently doesn't burn at all, not even a diesel on the first shot, and again no power loss... I'm not saying a typical springer using motor oil or similar won't gain some power burning oil, I'm saying it'll be nothing like some believe and you probably won't even be able to measure it since springers typically vary in velocity more than the gains from the burn. |
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| Author: | GerardSamija [ Sat Jan 17, 2015 6:46 pm ] |
| Post subject: | Re: Springer piston dynamics |
Perhaps irrelevant, but they do dimple golf balls to reduce drag. The trapped air in those tiny dimples offers less friction than a smooth surface. Of course the golf ball dimpling may also have something to do with controlled flight... no idea really as only curling bores me more deeply than golf. Just suggesting this as having some possible relation to notions of rough transfer ports improving performance; it could be the reverse of what Jim was thinking, that he was actually increasing flow rate by reducing friction when roughening up the TP instead of increasing it, attributing the velocity increase to the wrong element. |
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| Author: | EverHopeful [ Sat Jan 17, 2015 6:47 pm ] |
| Post subject: | Re: Springer piston dynamics |
Handyguy wrote: Would converting a piston to aluminum (to reduce weight and recoil) affect performance? And it all started with such a simple question
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| Author: | joe hickey [ Sat Jan 17, 2015 7:09 pm ] |
| Post subject: | Re: Springer piston dynamics |
I love it that a simple question can open such a brainstorming event. Thats one of the main reasons I'm a member. I learn from the efforts of others and add input where I may have anything that might be even remotely relevant, without fear of ridicule for being ignorant of the facts. |
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| Author: | Chevota [ Sat Jan 17, 2015 7:23 pm ] |
| Post subject: | Re: Springer piston dynamics |
Gerard; I've wondered the same thing, but rather impossible for us to do... It would be interesting to see whatever an ideal surface is, and how much better it is. I've also wondered the same about aircraft. I can see generic planes not having dimples for various reasons, like cost, but what about specialty aircraft like racing and speed or distance record attempts... A rough port is far from dimpling so he was no doubt getting more drag, and if he saw gains I'd love to see how and what the real reason was. My guess is his original smooth port was too small and the rough one he drilled out had more gains thanks to the diameter than losses from the surface. I have no doubt that if he smoothed that new port again he'd see even more gains. Smoothing the port is something I do to all my guns because most are in horrible condition. They're often so bad I wonder how they did it. All I can picture is some sweatshop worker being forced to use a dull/worn drill bit and forcing it rather than replacing it, which I'm sure many mfg's do to save a buck. I suppose if anyone is curious they could test a gun as-is, new and rough, then smooth it, then rough it again. Maybe rough it with course sandpaper, then use finer and finer paper until smooth and see how things change. I think the difference will be small, and again velocity varies a lot already so it might be a lot of work for very little info. Just taking the gun apart for each step, and the cleaning/re-lubing will have an effect, so unless it makes a dramatic change it would be hard to know for sure what caused it. And nobody it going to do this to ten or more guns to see an average. |
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| Author: | joe hickey [ Sat Jan 17, 2015 7:25 pm ] |
| Post subject: | Re: Springer piston dynamics |
Anyway,,,back to the question at hand. A theory of mine that I recently tested on a slavia 624 was to choke the leade port. That is,, I made an insert from a piece of brake line where the tube cutter crimped the end of the tube, then with wet 1000 grit sand paper, rolled tightly and chucked in a drill, I polished the interior and the crimped end untill just the pellet head could pass through, but not the tail. Theidea came from when my grandson and I were playing with bean or pea shooters. I noticed that if I held the bean by squeezing the straw, blew into it and suddenly released the bean, it flew much faster. In fact I chronied one bean at 157 fps. A 50 fps increase over just holding my toung against the straw and letting go. The results with the slavia was a 25 fps avg increase. From 330 avg to 355 avg. I plan on trying the same test on my qb57 when I get the time. The theory is to hold the pellet longer until the buildup of pressure forces it through the restriction and then suddenly lets fly. |
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| Author: | Chevota [ Sat Jan 17, 2015 7:37 pm ] |
| Post subject: | Re: Springer piston dynamics |
The breech should already do that for you, is that gun different somehow? And what about the bore, are you making the pellet too small for the rifling? I'm guessing not, or maybe I'm not understanding what you did.You can also try pellets with thicker, harder, or larger skirts. Or bend them larger. This is one reason most people lose power by seating a pellet with a tool, it removes that cork like effect which holds the pellet until the time more ideal. |
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| Author: | Chevota [ Sat Jan 17, 2015 8:00 pm ] |
| Post subject: | Re: Springer piston dynamics |
Gerald: Almost forgot, but to make the spring sheath/piston liner dealie I typically use plastic from a 2-liter soda bottle which are ~.011-.016" thick but some guns have more space to fill so whatever works. I imagine the notebook binder would be just fine, but you can also use other bottles like vinegar, bleach or whatever. Same with making buttons, but usually buttons need to be .006" or less so you can install some made of whatever, then sand them down, or use those super thin water bottles that collapse in your hand which are as thin as .003. I assume you have them in Canada, but in the US we find them in bulk packs of 18 or so 16oz bottles at the supermarket. I have instructions w/pix on the sheath and buttons if you want, chevota at hotmail and I'll send it. |
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| Author: | GerardSamija [ Sat Jan 17, 2015 8:46 pm ] |
| Post subject: | Re: Springer piston dynamics |
Pictures might help. I'm still not getting what 'buttons' are, sorry. Looking at this page - http://springgunning.com/tune.html - it seems installing buttons involves machining recesses into the piston somehow then gluing in delrin or other plastic bearing discs. Sounds dicey, especially if the thing is case hardened. Wouldn't know how to neatly grind in a bearing recess through that kind of hardness. The breech end of the barrel of the QB57, or at least mine, is sufficient to hold the skirt of an RWS Hobby pellet flush, no tendency to drop in. But the barrel generally is slightly larger than the Crosman barrel I've used on my 2240 for example. That barrel's rifling leaves distinct, deep impressions in the skirt of recovered pellets. The QB57's barrel rifling is visible, but not deeply cut into the skirts. It's a bigger bore, if only a couple of thousandths, so it seems likely the pellets are being dumped a lot earlier than they would be from tighter bores. I wonder if I could find some ~12gr pellets with fatter skirts than Hobbys... seems unlikely though as Hobby pellets always run a bit fatter than anything else I shoot. I've got one of my wife's binder shells to try. Seems a firm enough plastic, fairly strong, about 0.020" thick. If it's too thick I'll try some bottle plastic. But the spring fairly rattles around in there, lots of room, so we'll see... Not tonight though. Picked up some neoprene and some diving wetsuit contact cement from my local outdoor fabric dealer (such a cool shop, just a block away) and am going to start gluing on pieces to the cylinder, see how that does in making the sound more tolerable. Just laying the neoprene onto the gun when shooting helps a lot. Glued may be better, or not, don't know yet. It'll be my physically comfortable on my cheek in any case. |
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| Author: | GerardSamija [ Sat Jan 17, 2015 9:00 pm ] |
| Post subject: | Re: Springer piston dynamics |
Oh, and I did a quick search regarding piezo pressure sensors for high pressure applications. Found this article discussing experiments on vastly higher pressures involved with a potent firearm cartridge and various barrel lengths, with flash hiders and suppressors in the mix along with people's hearing: http://www.sadefensejournal.com/wp/?p=1093 Some pretty cool use of tech there. Could be applied on a testbed springer if someone wanted to play around. Maybe stagger the sensors along the cylinder so they could be spaced closer together near the transfer port. Put one right inside the transfer port, on a gun where it was deep enough anyway. |
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| Author: | Penage Guy [ Sat Jan 17, 2015 9:18 pm ] |
| Post subject: | Re: Springer piston dynamics |
GerardSamija wrote: Oh, and I did a quick search regarding piezo pressure sensors for high pressure applications. Found this article discussing experiments on vastly higher pressures involved with a potent firearm cartridge and various barrel lengths, with flash hiders and suppressors in the mix along with people's hearing: http://www.sadefensejournal.com/wp/?p=1093 Some pretty cool use of tech there. Could be applied on a testbed springer if someone wanted to play around. Maybe stagger the sensors along the cylinder so they could be spaced closer together near the transfer port. Put one right inside the transfer port, on a gun where it was deep enough anyway. What kind of information would these sensors reveal? |
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