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min. flow required at optimal RPM?

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Thinking min. flow required at optimal RPM?

Post  roddie Fri Nov 03, 2023 3:31 pm

Curious to know what the most aggressively-ported Cox .049/.051 engines (naturally aspirated) require for "fuel-flow". Will the venturi pull fuel through a short length of tubing with a 1/32" (.031") inside diameter without becoming fuel-starved?


Last edited by roddie on Sat Nov 04, 2023 1:18 pm; edited 1 time in total (Reason for editing : specified inside diameter)
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Thinking Re: min. flow required at optimal RPM?

Post  Ken Cook Fri Nov 03, 2023 3:36 pm

I'm pretty sure it would work but fuel viscosity and outside temperature would be a huge factor in that equation.
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Thinking Re: min. flow required at optimal RPM?

Post  balogh Fri Nov 03, 2023 3:46 pm

I use a bit larger diameter fuel tube between the tank and the carb and add a short, smaller dia section just at the carb fuel nipple, to minimize pressure drop of fuel in the feed line. The only fuel starvation I sometimes experienced was caused by the commonly known air seeping into the carb along the needle valve stem, that we all cure by pulling that short silicone tube over the NV and the threaded end of the spraybar..with some care these COX  critters will never let you down.. Very Happy RC Plane
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Thinking Re: min. flow required at optimal RPM?

Post  roddie Fri Nov 03, 2023 5:04 pm

Thanks for the replies gents.. I found a source for .031" ID X .062" OD silicone tubing.. which reduces overall weight when compared to garden-variety sm. size silicone line.. and could possibly be used in a micro clunk-tank/fuel pick-up application. Trying these things out is all part of the fun!
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Thinking sub-micro silicone tubing

Post  roddie Wed Nov 29, 2023 7:00 pm

Hi friends. I received the aforementioned sub-micro silicone tubing a few days ago (a few days ahead of Amazon's delivery forecast)

min. flow required at optimal RPM? Amazon16

This tubing is small........ but it does have a substantial wall-thickness.  

min. flow required at optimal RPM? Amazon15

I love small stuff.. probably why I love the Cox 1/2A engines... and anything else that might contribute to their longevity.

I did pose the question of whether a higher-performance Cox 1/2A engine would be able to draw enough fuel through this lines' small ID... naturally aspirated..  to sustain combustion while running at full-bore. Huh...

This tubing may well be a better suited for .010/.020 displacement glow engines. I'll note my findings here.
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Thinking Re: min. flow required at optimal RPM?

Post  roddie Wed Nov 29, 2023 9:19 pm

As Ken Cook pointed out; the fuels' viscosity and ambient air-temperature will surely affect the flow-characteristics of the tubing.

Here's a photo comparing "this" tubing with the Dubro #221 (sm.) tubing.

min. flow required at optimal RPM? Compar10

Might this tubing work for a balloon-tank set-up.. as a perforated pick-up tube? It would make the most use of the available space inside the balloon.
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Thinking Re: min. flow required at optimal RPM?

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