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Rocket style fuel tank vent

Webb

Webb

Well Known Member
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I decided to vent the fuel tanks rocket style instead of re-entry into the fuselage. The one thing I didn’t want to do was to put the exit in the wing root fairing so I went thru the wing spar and exited out the bottom skin. I also added a tiny hole on top of the line just before it exits in case the exit fittings were to ice up.
 

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My understanding was reduction in fuel loss. Since I didn’t design it, perhaps Vince can provide a better explanation.
 
Webb said:
My understanding was reduction in fuel loss. Since I didn’t design it, perhaps Vince can provide a better explanation.
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The loops act as a reservoir for fuel expansion in the main tank. The internal vent line opening is at the high point of the tank, not normally submerged in fuel.
 
Webb said:
New hole In the star web.
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Hi Webb….I am honestly NOT trying to pick on you or start an argument - but for future guy’s future reference, did you run that extra hole in teh spar web by Van’s? I get ginchy about random holes in spars without designer approval….

I did use the Rocket loops for the vent in the RV-3, and we do occasionally belch a little fuel out on warm days with full tanks - just FYI. It doesn’t bother me personally, but it’s something folks should know about. We exited the vent forward of the spar, but the skin and fairings are different from on the later RV designs.

The Rocket….will probably use the Rocket loops!
 
Ironflight said:
Hi Webb….I am honestly NOT trying to pick on you or start an argument - but for future guy’s future reference, did you run that extra hole in teh spar web by Van’s? I get ginchy about random holes in spars without designer approval….
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That was my idea when asking the question. I vaguely remember another thread where someone asked about drilling a hole in a similar location for wiring purposes. If I remember correctly Vans highly discouraged that since near the root is where the spars web carries the highest shear loads.
 
Webb said:
I decided to vent the fuel tanks rocket style instead of re-entry into the fuselage. The one thing I didn’t want to do was to put the exit in the wing root fairing so I went thru the wing spar and exited out the bottom skin. I also added a tiny hole on top of the line just before it exits in case the exit fittings were to ice up.
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I recommend you re-think this.
First, over time water finds it's way into tubing low points. Offhand I'm thinking condensation or direct injection with a water hose while washing are only two means for moisture to end up in one or more of the loops. There are two or three low points the loops create that will not drain. Leading to a frozen fuel vent.

Second, the relief port to protect against ice over of the vent from airframe icing is an excellent idea. However, it should still vent outside the aircraft. As placed in the pic, every time the tank burps fuel will end up inside the wing. You are going to have fuel stains and trapped fumes. I place alternate ports on the back side of the airflow about a quarter inch or more into the slipstream. No inflight ice will collect there and burped fuel is out side the aircraft.

Cheers.
 
Paul, no offense taken. I did check a long time ago and there wasn’t a concern about a small hole in the middle of the web. Also look at the number of holes the web has in it (think Z brackets And rib rivet holes).

As far as water entering the line from a hose, it would have to travel uphill for over a foot and I don't plan to spray into the opening. As for condensation, I’m not sure there is enough air mass in a loop to provide sufficient water should it occur. Also in flight dry air will be flowing through the line and provide drying or suck the offending drop into the tank.

The vent hole is on top of the bend. Fuel exiting is usually a trickle and when making the turn, will be on the bottom side of tubing. If I see any blue staining, I’ll modify.

I may be pontificating but the jury is still out.
 
I've been hoping Bob Mills would chime in here. When we put the tapered composite wings on his -6S, we used Rocket-style vents. I think we left the original Vans vents in the fuselage, just didn't hook them up. My impression is that he gets much more burping of fuel now with the Rocket vents than we all typically get with the Vans vents. I think we have 2.5 coils for each vent. After that experience, I think I am going to stick with the standard Vans vents, even though they are more effort to install.
 
Webb said:
I’m not sure there is enough air mass in a loop to provide sufficient water should it occur. Also in flight dry air will be flowing through the line and provide drying or suck the offending drop into the tank.
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You can't suck a water drop up from a low spot like this. The water will stretch out along the tube until an air bubble can get by, and then the water will settle to the bottom of the tube again. Probably not an issue in this situation unless you get freezing, the vacuum in the tank will probably keep the air moving. The fuel burping on the next fill-up might help expel the water. :)
 
I have been using this design (the loops, not the spar hole) for 5 years with no issue and no loss of fuel. However, I live in FL and freezing isn't our big concern and I almost never fill the tanks completely. I believe, and I guess I've bet my fuel tank on it, that the suction created during flight will keep any water from blocking the line even if it does ice over. Of course, that is only true on the tank being used so if it is cold enough to freeze in 30 min or so, it might be a problem. There are many Rockets out there with this design, and probably a number of RVs, but I have never heard of ice being an issue.
 
Thank you all for the concern about the potential for water to gather in the bottom of a loop. I then have to ask if you have concern that water could gather in the lowest point of a traditional installation And cause icing problems. Esp if there is less burping to potentially push water out.
 

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I’ve been using the rocket vent since first flight 315 hours ago. The right tank vents a little when completely full. Otherwise no issues.
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Vent exit
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Often times, I will fill up from a underground storage take and the fuel in the wings will expand. When I pop the cap during preflight, the fuel spills out onto the wing. Since the top of the coil is below the vent opening inside the tank, wouldn, the fuel start siphoning out? However, With the Vans vent design, there is always a point of the vent line above the top of the vent opening in the fuel tank.
 
Webb said:
My understanding was reduction in fuel loss. Since I didn’t design it, perhaps Vince can provide a better explanation.
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What is the objective, reduction in fuel loss? The fuel that ends in the coil will :
1- trap water
2- Let air bubble by back into the tank
3- Catch a dribble instead of carmac or hanger floor
WILL THE FUEL EVER GO BACK IN THE TANK, I HOPE NOT.
I used the coil on my RV3, no problems, but what is the point ?
 
Water in the coil that freezes at altitude can cause a fuel tank to implode on descent. Yes, it has happened. It does NOT require much differential pressure!
 
Foghorn said:
I’ve been using the rocket vent since first flight 315 hours ago. The right tank vents a little when completely full. Otherwise no issues.
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Very similar setup on mine, approaching 1000 hours now, no issues other than very occasional expulsion of a bit of fuel when the tanks are full to the brim and the temps change enough to make the fuel expand. It's a very minor pain because the vent location, same as above, is *right above* my gear legs (7A), so it runs down the fairing and I have to clean off the blue dye. It comes off, and isn't permanent, as everyone knows, but if I had it to do over, I'd have figured out a different location for the vent. Other than that, they work great! And I, too, use the neat little "fairings" for both the vents and the drains (but I had them anodized in red to match my paint scheme :) ).

I'm willing to bet that there isn't anybody out there, in any RV or Rocket, who has this style vent who has had an issue with freezing moisture in the line...
 
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