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Post  aspeed Fri Mar 19, 2021 9:53 pm

batjac wrote:
aspeed wrote:I don't see why the 80 TPI needles can't work.

They can work for hard tanks or balloon tanks.  But for bladders they are too coarse.  With a fine needle valve on bladder, you have adjustability.  I did bladder on an 80TPI needle once, and it was less than a 1/4 of a turn from too rich to run, to too lean to run.  You've gotta be quick and precise using a coarse needle on start, and tweaking it in to the sweet spot is almost impossible.  

The Rough Mark
 I was thinking of the Rossi needles that are stiffer to turn, and have the end bent.  Then maybe 1/4 turn would be OK.  Yes I do hate bladders, but have to use them sometimes. On one of my 'Bees, the needle would pull right out because the thread was so loose.  I put release wax on the needle and put half a drop of red loctite on the needle and it stiffened up and holds the setting well.  No need for a seal.  That may possibly work with a finer adjustment like a bent end on the needle or solder on a bigger diameter knurled knob?  Just thinking out loud.
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Post  batjac Sat Mar 20, 2021 3:14 am

aspeed wrote:That may possibly work with a finer adjustment like a bent end on the needle or solder on a bigger diameter knurled knob?  Just thinking out loud.

You could surely give it a try. Experimenting is half the fun. If I were to try a coarse needle on bladder again, I'd try something I read somewhere, maybe here, a long time ago. Between the bladder and the NVA, use a small piece of tubing as a limiting orifice. Either find a way to make a small hole to reduce the pressure, or what I would do is just take some pliers and crimp the tube to limit the flow. Make up a bladder and fill it with air, and crimp down on the tube until the flow is very low. If I didn't have a dozen other projects going on now, I'd try it. Maybe I'll try it in a couple of months.

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Post  Ken Cook Sat Mar 20, 2021 5:40 am

While the 128TPI works on bladder, it's still not the best solution. It has it's problems  and the black friction sleeve is a POS which fails quickly. The barb design is poor  and the tubing can pop off very easily. I've had to forfeit combat matches due to this problem. I've used the 128 in a remote application by making a banjo fitting and running the fuel through the needle backwards so to speak which improves it ability to resist pressure and not leak so much through the threads. A F2D needle is far superior to the Cox setup.The best needle assemblies I've used which are no longer available is the combat VA .049 needle.

Using a restrictor such as a bead or tubing with a small hole in it to reduce the flow on bladder isn't recommended. When filled the pressure is far greater when the bladder is expanded. The problem occurs when it begins to deplete and the pressure change is so great the fuel mixture goes too lean.  I've mentioned this many many times in regards to bladders. Bladders don't prefer a load, this means smaller lighter pitch props. In addition, higher nitro and not 35%, nitro levels in the 50% - 70% levels. When you run nitro in these percentages, your running them rich which not only cools the engine, your not trying to hold back as much pressure via the needle valve. The smaller diameter lighter pitch also decreases needle sensitivity.

            Whenever I see bladders posted on this site, most have purchased from Texas Timers which is all latex. These bladders work but they have a short lifespan and even shorter when exposed to hot fuel aka fuel can sitting in the sun or sun exposure in general. Those bladder are low pressure bladders and are used for 30 second free flight operations. Therefore filling them for 3-4 minute fuel runs are essentially destroying them from stretching them out. You want reinforced surgical tubing which maintains it's elasticity almost all the way to the end and not changing the pressure.
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