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Coiled tank vent question

L

Larry DeCamp

Well Known Member
I have rocket coil vents with two coils and the chamfer faces forward. The vents DONOT drip with full tanks on level ground. The vents are open when you blow in them with fill caps off. However, I am getting fuel stains on the bottom of the wings and flaps behind the vents. They only extend out of the wing about 1" with tip cut at 45degree. They are not bent forward 90 degree like a pitot tube. The fuel loss is not significant, just unsightly. Any theories or suggestions ??
 
Larry DeCamp said:
I have rocket coil vents with two coils and the chamfer faces forward. The vents DONOT drip with full tanks on level ground. The vents are open when you blow in them with fill caps off. However, I am getting fuel stains on the bottom of the wings and flaps behind the vents. They only extend out of the wing about 1" with tip cut at 45degree. They are not bent forward 90 degree like a pitot tube. The fuel loss is not significant, just unsightly. Any theories or suggestions ??
Click to expand...

The way these fuel vents work, if installed properly, is that they provide a reservoir for expanding fuel. The internal vent must run right to the highest point of the tank. If this end is not properly located and is normally immersed in fuel with the tank full, this fuel will run down into the coil and partially fill it, reducing your expansion reserve.

As the fuel in the tank expands on a warm day, fuel will continue to fill the coil until it overflows or the fuel level in the tank drops.

So... I put in a 3 coil loop in the wing roots and I've never had a fuel drip.
 
vlittle said:
The way these fuel vents work, if installed properly, is that they provide a reservoir for expanding fuel. The internal vent must run right to the highest point of the tank. If this end is not properly located and is normally immersed in fuel with the tank full, this fuel will run down into the coil and partially fill it, reducing your expansion reserve.

As the fuel in the tank expands on a warm day, fuel will continue to fill the coil until it overflows or the fuel level in the tank drops.

So... I put in a 3 coil loop in the wing roots and I've never had a fuel drip.
Click to expand...

Vern,
Do you have the 3 loop system in your 9-A or just the Rocket? On my old RV-10, the 1/4" vent tubes came straight out of the tank about 2 inches and then straight down and out the wing root. Rarely dripped unless the tanks were over filled. I am considering removing the current vent tubing from the cockpit of my RV-9A and doing the Rocket style loop if that works because of the simplicity of the design. My wings were quick build so I have no idea how careful or precise the workers do the internal tank vent line. Anyone do the loops in the 9-A with success?
 
The problem is not dripping

My problem appears to be fuel coming out in flight ( insignificant quantity) staining wings. ASSUMING the vent is pressurized in flight, it is not logical to me that any liquid in the coils or tank (if the vent were submerged ) would come out ? I would also expect the wing root/fuse intersection is a VERY positive pressure in flight :confused:
 
Climb

With fuel trapped at the bottom of the loops, as you climb the air trapped in the top part of the loops wants to expand and may push out some fuel. JMHO
 
The local guys using this vent use a 3 coil version. To my knowledge, there hasnt been any fuel stains.

Tom
 
Thanks. I'm going to rip that mess out of the cockpit and do the 3,,,,maybe even 4, loop vent. I don't think I will have an issue and I won't overfill. If it leaks and causes a mess I can always do the per plans vent afterwards.
 
I also have the 3-4 coil loop in the wing root on my -7A with no issues. A typical can of car wax is the perfect size for wrapping the tubing into the correct size loop.
 
Coiled vent tubing

Does anybody have any concerns or comments about vent icing now that the vents are not in the warmer air that exits the cowl?

Don B
 
cajunwings said:
Does anybody have any concerns or comments about vent icing now that the vents are not in the warmer air that exits the cowl?

Don B
Click to expand...

NO. This is the same location as Vans uses for the RV-10 which work perfectly.
 
Me too

I've had an issue of fuel being pushed out of my vents after leveling off at cruise with full tanks. I can smell the fuel, right after lowering the nose. I'm guessing that my QB wings have the vent tubes a little too low, and are immersed in fuel, so the lower air pressure at altitude is squeezing some out.
I manage it by: either not filling to the rims, or attempt to burn a little from both tanks before climbing too high.
I've also smelled a little fuel after acro with less than 1-G maneuvers. I guess the residual fuel that had been residing in the loop, gets worked around until it finds its way out the vent.
 
Mark Dickens said:
My understanding is that avgas freezes around -100C, so I'm not terribly worried about it.
Click to expand...

Don?t think the fuel is the concern, it?s the accumulation of enough ice on the end of the tube to block it.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
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