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Fuel-line attach to Cox prod. backplate
Page 1 of 1
Fuel-line attach to Cox prod. backplate
Hey folks, "Bob" (rsv1cox) commented recently on my methods when working with fuel-lines. Today I was installing a Cox .049 product-engine (horseshoe backplate) on one of my airplanes.. and thought I'd share how I went about it. It's difficult to install a fuel-line onto the NVA/nipple "after" the engine is mounted.. or if it happens to "pull-off" the nipple after the engine is mounted. Really small ID fuel-line will usually stay-put.. but I prefer to use fuel-line that has a slightly larger ID.
This example uses line that has a .075" ID and a .165" OD. It's categorized as "small-size" line.. although "Dubro's" small-size line has a .042" ID for comparison. If your running a high-performance engine on a suction-feed.. (as opposed to a pressure-bladder..) a little less-restriction to flow can be an advantage.
That point aside.. here's what I do to help keep the fuel-line from being inadvertently/accidentally being "pulled-off" the NVA. I use a short "sleeve" of alloy-tubing that's close to my fuel-tubing's "OD".

I then insert the fuel-tubing into the sleeve. If it's a tight-fit; I apply a little petroleum-jelly to the end of the line.. and "twist/slide" the alloy-sleeve onto the line, so that there's approximately 1/4" of fuel-line protruding. Just enough to push-onto the NVA's nipple.

This can give the fuel-line some rigidity for the ease of "initial" installation onto the nipple. Once the fuel-line is installed as far as possible.. the "sleeve" can then be pushed-forward; which compresses the line around the nipple's barb. I used blunt tweezers to push the sleeve forward; being careful not to abrade the silicone fuel-line. After the sleeve is in-place, the fuel-line isn't going to pull-off unless it's "yanked-off".

It's these little details that can save a lot of frustration at the field.
This example uses line that has a .075" ID and a .165" OD. It's categorized as "small-size" line.. although "Dubro's" small-size line has a .042" ID for comparison. If your running a high-performance engine on a suction-feed.. (as opposed to a pressure-bladder..) a little less-restriction to flow can be an advantage.
That point aside.. here's what I do to help keep the fuel-line from being inadvertently/accidentally being "pulled-off" the NVA. I use a short "sleeve" of alloy-tubing that's close to my fuel-tubing's "OD".

I then insert the fuel-tubing into the sleeve. If it's a tight-fit; I apply a little petroleum-jelly to the end of the line.. and "twist/slide" the alloy-sleeve onto the line, so that there's approximately 1/4" of fuel-line protruding. Just enough to push-onto the NVA's nipple.

This can give the fuel-line some rigidity for the ease of "initial" installation onto the nipple. Once the fuel-line is installed as far as possible.. the "sleeve" can then be pushed-forward; which compresses the line around the nipple's barb. I used blunt tweezers to push the sleeve forward; being careful not to abrade the silicone fuel-line. After the sleeve is in-place, the fuel-line isn't going to pull-off unless it's "yanked-off".

It's these little details that can save a lot of frustration at the field.
Re: Fuel-line attach to Cox prod. backplate
Thanks Roddie...gonna give this a try!
Kim- Top Poster
Posts : 8444
Join date : 2011-09-06
Location : South East Missouri
Re: Fuel-line attach to Cox prod. backplate
Kim wrote:Thanks Roddie...gonna give this a try!
I hope you do Kim! It's a simple step that can increase reliability. It can also bail you out, if you don't have any fuel-line that's small enough for the application.
I've posted this photo before.. but it's applicable to this thread. Try this; the next time you rebuild an engine with an integral fuel-tank.. (IE: Babe Bee, Golden Bee, Black Widow.. etc.)


Note also the "pick-up". A separate short piece of alloy-tubing with a notch filed in the end. The notch assures fuel-flow and keeps the pick-up located where you want it. It can really help to keep the pick-up in position when re-assembling the tank to the backplate. This example shows an OEM spring internal to the fuel-line. I'll admit; I don't always include one.. but they were originally there for a purpose. My belief is that the spring can help to disperse air-bubbles.. and possibly augment the fuel-flow through capillary-action..

Re: Fuel-line attach to Cox prod. backplate
Your theory may be right Roddie. I thought the spring was there to internally stiffen the pickup line and prevent it from buckling when bent that would restrict the fuel flow.
balogh- Top Poster
Posts : 4609
Join date : 2011-11-06
Age : 65
Location : Budapest Hungary
Re: Fuel-line attach to Cox prod. backplate
Since we're revisiting theories on fuel line ideas, here's the first video experiment I ever made. Forgive the cheesy dramatic prelude, it was my first time using WMM for editing video:
https://youtu.be/xyA6He9EX8c
https://youtu.be/xyA6He9EX8c
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while you're doing it!
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RknRusty- Rest In Peace
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Re: Fuel-line attach to Cox prod. backplate
Pretty cool vid Rusty! I know that you're partial to running bladders now.. but how'd this end up working on the Stuntman with that tank set-up? I'd like to build a Stuntman. I have one that my dad built. It's beyond practical-repair.. but I could copy it. Most of my designs are a tad large for the reed-valve engines.

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