Out of interest what size TP as the AA Pro/elite got ?.
Les..
Out of interest what size TP as the AA Pro/elite got ?.
Les..
This has the makings of an interesting thread. I'd like to try & get an understanding of how the variables interact with one another.
Noticed a comment "The flow rate calculator in the link is for fluids, not air."earlier on in the discussion but isn't air classed as a fluid? I think all gasses are regarded a fluids. They are complex in some respects as they are compressible fluids as opposed to liquid fluids which are generally regarded as incompressible.
Looking forward to learning a bit about flow rates & fluid dynamics....
My bachelor's and master's dissertation were based around fluid dynamics, simulation and modelling. One on IC cylinder head flow and one on external aerodynamics. Can be very interesting, but when it comes to transfer ports I would just stick with physical testing. Too many variables and life is too short
When writing my earlier post the idea of filling the cylinder ahead of the piston with water crossed my mind too. I thought if I suggested it someone might say'ok, you first' & I wouldn't fancy trying to dry out intrrnals of a springer, even a clunker of a springer. Still as a theoretical model it would be interesting if the weight of the fluid could somehow be factored out & the empirical perfomance evaluated with changes being introduced step by step so the effects of them could be measured. It would take out any varriability arising from the clmpressability of the air. But how it would translate into the real world is anyones guess so I think the advice that life is too short & its probably better to just roll up your sleeves & get cracking ks good advice.
It will be interesting to see any results from those that have carried them out.......standard rifle v port diameter, differant stroke v port diameter or variability with port volume etc. Its a big topic........but very interesting.
I was thinking about making a brass insert as a transfer port, my idea is to make it tapered down from compression tube, with a convex entry, so no sharp corners, highly polished [mirror]. My theory is based on - as a youth I used to polish cylinder head ports on my motor bikes & it did improve performance - better intake/exhaust flow. just an idea at the moment?
PS. in engineering terms the word fluidic covers both liquid & gas.
Last edited by cringe; 21-03-2021 at 10:50 AM.
It is possible to create a model to calculate flow rates. You need to go to modelling all the components, the forces between them and the air itself in the barrel and cylinder. This isn't easy but I did it about 10 years ago. There is no simple formula you can use.
If the transfer port gets too small, the flow between the cylinder and barrel chokes as the air can't go supersonic (based upon its properties in the cylinder). This is a bad thing as the flow levels off and the pressure in the cylinder goes up a lot. The higher pressure air in the cylinder pushes on the front face a lot harder and makes the forward recoil push horrible.
The pressure difference between the barrel and cylinder causes the choking. Smaller diameter ports have more resistance so make the pressure difference higher, which leads to choking. So do longer or rougher transfer ports.
BB
There has been a number of findings from experiments conducted shared with us over the years and, if I remember correctly, the short answer usually boils down to no fancy shapes / bell mouths etc required. Just a nice, parallel, smooth port with no sharp, jagged edges. I think one of the links that T20 posted onto the thread about HW80 transfer port size to the Pyramydairblog shows a few experiments with differing layouts and I'm sure I've seen plenty of others in the past. That old thread is now on page 1, by the way.. Jim has provided some brilliant information over the years on the subject in Airgun World.
As has been said up above, all very interesting and intriguing stuff.
THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
NEXT EVENT :- August 3/4, 2024.........BOING!!
Crikey, can't resist this. When I was knee high to Ronnie Corbett I had an air rifle ... well maybe I should say 'we had' because my friend and I both used it. No idea where it came from or what it was, maybe a Wobbly Jaguar or a Diana 15/16? I remember firing nails, cocktail sticks and potato bits and ..... don't know how, but using it as a water pistol. It wasn't very good. I can't remember how we loaded it. Maybe trickled water in as we cocked it? We did suss that it needed oiling after a few shots though...
Oh the things you do in the innocence of (very) youth.
Cheers, Phil
3.0 x 15mm, and it's too small, even when the bore is reduced down to 25mm. TOok that one out to 3.2, but the accelerometer data indicates it shoudl be opened up a little more.
I'll be doing some experiments with my FAC one next year - I don't have all the tools and equipment with me on this trip - or even a shrono. Will also bring a machined lighter piston. However I have no doubt that 3.0 will be too small for a 30mm tube... 3.4 woudl be my guess..
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.